Delocalization Drives Free Charge Generation in Conjugated Polymer Films

DOE PAGES

Pace, Natalie A.; Reid, Obadiah G.; Rumbles, Garry

2018-02-19

We demonstrate that the product of photoinduced electron transfer between a conjugated polymer host and a dilute molecular sensitizer is controlled by the structural state of the polymer. Ordered semicrystalline solids exhibit free charge generation, while disordered polymers in the melt phase do not. We use photoluminescence (PL) and time-resolved microwave conductivity (TRMC) measurements to sweep through polymer melt transitions in situ. Free charge generation measured by TRMC turns off upon melting, whereas PL quenching of the molecular sensitizers remains constant, implying unchanged electron transfer efficiency. The key difference is the intermolecular order of the polymer host in the solidmore » state compared to the melt. We propose that this order-disorder transition modulates the localization length of the initial charge-transfer state, which controls the probability of free charge formation.« less

Battery-Charge-State Model

NASA Technical Reports Server (NTRS)

Vivian, H. C.

1985-01-01

Charge-state model for lead/acid batteries proposed as part of effort to make equivalent of fuel gage for battery-powered vehicles. Models based on equations that approximate observable characteristics of battery electrochemistry. Uses linear equations, easier to simulate on computer, and gives smooth transitions between charge, discharge, and recuperation.

Highly tunable charge and spin transport in silicene junctions: phase transitions and half-metallic states.

PubMed

Mahdavifar, Maryam; Khoeini, Farhad

2018-08-10

We report peculiar charge and spin transport properties in S-shaped silicene junctions with the Kane-Mele tight-binding model. In this work, we investigate the effects of electric and exchange fields on the charge and spin transport properties. Our results show that by applying a perpendicular electric field, metal-semiconductor and also semimetal-semiconductor phase transitions occur in our systems. Furthermore, full spin current can be obtained in the structures, so the half-metallic states are observable. Our results enable us to control charge and spin currents and provide new opportunities and applications in silicene-based electronics, optoelectronics, and spintronics.

Closed-form expressions for state-to-state charge-transfer differential cross sections in a modified Faddeev three-body approach

NASA Astrophysics Data System (ADS)

Adivi, E. Ghanbari; Brunger, M. J.; Bolorizadeh, M. A.; Campbell, L.

2007-02-01

The second-order Faddeev-Watson-Lovelace approximation in a modified form is applied to charge transfer from hydrogenlike target atoms by a fully stripped energetic projectile ion. The state-to-state, nlm→n'l'm' , partial transition amplitudes are calculated analytically. The method is specifically applied to the collision of protons with hydrogen atoms, where differential cross sections of different transitions are calculated for incident energies of 2.8 and 5.0MeV . It is shown that the Thomas peak is present in all transition cross sections. The partial cross sections are then summed and compared with the available forward-angle experimental data, showing good agreement.

The Variable Transition State in Polar Additions to Pi Bonds

ERIC Educational Resources Information Center

Weiss, Hilton M.

2010-01-01

A vast majority of polar additions of Bronsted acids to alkynes involve a termolecular transition state. With strong acids, considerable positive charge is developed on carbon and Markovnikov addition predominates. In less acidic solutions, however, the reaction is much slower and the transition state more closely resembles the olefinic product.…

Local entanglement entropy of fermions as a marker of quantum phase transition in the one-dimensional Hubbard model

NASA Astrophysics Data System (ADS)

Cha, Min-Chul; Chung, Myung-Hoon

2018-05-01

We study quantum phase transition of interacting fermions by measuring the local entanglement entropy in the one-dimensional Hubbard model. The reduced density matrices for blocks of a few sites are constructed from the ground state wave function in infinite systems by adopting the matrix product state representation where time-evolving block decimations are performed to obtain the lowest energy states. The local entanglement entropy, constructed from the reduced density matrices, as a function of the chemical potential shows clear signatures of the Mott transition. The value of the central charge, numerically determined from the universal properties of the local entanglement entropy, confirms that the transition is caused by the suppression of the charge degrees of freedom.

Possible mechanism to enhance spin-fluctuation-mediated superconductivity in two-dimensional organic conductor

NASA Astrophysics Data System (ADS)

Nonoyama, Yoshito; Maekawa, Yukiko; Kobayashi, Akito; Suzumura, Yoshikazu; Yamada, Jun-ichi

2008-10-01

Mechanisms of superconductivity in quasi-two-dimensional organic conductors have been investigated using an extended Hubbard model by using the transfer energies between BDA-TTP molecules for β-(BDA-TTP)2I3 based on the X-ray experiment data and the extended Hückel calculation. We obtain several mean-field solutions with charge orderings which may represent short-range orderings or low-energy fluctuations in the low-dimensional electronic system. In the pressure-temperature phase diagram, a charge ordered metal state almost degenerates with a normal metal state between an insulating phase with charge ordering and the normal metal phase. Using the random phase approximation (RPA) and the linearized gap equation, the transition temperature of the superconducting state is estimated for the charge-ordered metal state and the normal metal state. It is found that transition temperature of the superconductivity induced by spin fluctuations in the charge-ordered metal state is much higher than that of the normal metal state and that the superconductivity in the charge-ordered metal state is the gapless d-wave. This suggests that the short range charge ordering may also contribute to an enhancement of spin-fluctuation-mediated superconductivity. The difference in the superconducting states between β-(BDA-TTP)2I3 and β-(BDA-TTP)2SbF6 are briefly discussed.

Pairing Symmetry Transitions in the Even-Denominator FQHE System

NASA Astrophysics Data System (ADS)

Nomura, Kentaro; Yoshioka, Daijiro

2001-12-01

Transitions from a paired quantum Hall state to another quantum Hall state in bilayer systems are discussed in the framework of the edge theory. Starting from the edge theory for the Haldane Rezayi state, it is shown that the charging effect of a bilayer system which breaks the SU(2) symmetry of the pseudospin shifts the central charge and the conformal dimensions of the fermionic fields which describe the pseudospin sector in the edge theory. This corresponds to the transition from the Haldane Rezayi state to Halperin's 331 state, or from a singlet d-wave to a triplet p-wave ABM type paired state in the composite fermion picture. Considering interlayer tunneling, the tunneling rate-capacitance phase diagram for the ν=5/2 paired bilayer system is discussed.

Correlating melting and collapse of charge ordering with magnetic transitions in La{sub 0.5-x}Pr{sub x}Ca{sub 0.5}MnO{sub 3}

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nadeem, M., E-mail: mnadeemsb@gmail.com; Iqbal, M. Javid; Farhan, M. Arshad

2016-08-15

Highlights: • Concept of normalized magnetization is introduced to explain relative magnetic transitions. • Coexistence of two magnetic modes is correlated with the magnetic transitions and MIT. • Field induced melting and collapse of charge ordered antiferromagnetic (CO-AFM) state into ferromagnetic (FM) state is conferred. - Abstract: The magnetic properties of polycrystalline La{sub 0.5-x}Pr{sub x}Ca{sub 0.5}MnO{sub 3} material are investigated at different temperatures. The existence of magnetically diverse phases associated with various relaxation modes and their modulation with temperature and doping is analyzed. La{sub 0.5}Ca{sub 0.5}MnO{sub 3} exhibited field induced melting and collapse of charge ordered antiferromagnetic (CO-AFM) phase intomore » ferromagnetic (FM) state. This phenomenon results in lowering of Neel’s temperature (T{sub N}) along with changes in the slope of magnetic moment with temperature. Using normalized M(T) curves, the variation and interplay of charge ordered temperature (T{sub CO}), Curie temperature (T{sub C}) and T{sub N} is conferred. The coexistence of two magnetic modes is explained as major ingredient for the magnetic transitions as well as metal to insulator transition (MIT); where melting and collapse of charge ordering is conversed as basic feature in these Praseodymium (Pr) doped La{sub 0.5}Ca{sub 0.5}MnO{sub 3} materials.« less

Phase separation and second-order phase transition in the phenomenological model for a Coulomb-frustrated two-dimensional system

NASA Astrophysics Data System (ADS)

Mamin, R. F.; Shaposhnikova, T. S.; Kabanov, V. V.

2018-03-01

We have considered the model of the phase transition of the second order for the Coulomb frustrated 2D charged system. The coupling of the order parameter with the charge was considered as the local temperature. We have found that in such a system, an appearance of the phase-separated state is possible. By numerical simulation, we have obtained different types ("stripes," "rings," "snakes") of phase-separated states and determined the parameter ranges for these states. Thus the system undergoes a series of phase transitions when the temperature decreases. First, the system moves from the homogeneous state with a zero order parameter to the phase-separated state with two phases in one of which the order parameter is zero and, in the other, it is nonzero (τ >0 ). Then a first-order transition occurs to another phase-separated state, in which both phases have different and nonzero values of the order parameter (for τ <0 ). Only a further decrease of temperature leads to a transition to a homogeneous ordered state.

Enhanced coherent oscillations in the superconducting state of underdoped YB a 2 C u 3 O 6 + x induced via ultrafast terahertz excitation

DOE PAGES

Dakovski, Georgi L.; Lee, Wei -Sheng; Hawthorn, David G.; ...

2015-06-24

We utilize intense, single-cycle terahertz pulses to induce collective excitations in the charge-density-wave-ordered underdoped cuprate YBa 2Cu 3O 6+x. These excitations manifest themselves as pronounced coherent oscillations of the optical reflectivity in the transient state, accompanied by minimal incoherent quasiparticle relaxation dynamics. The oscillations occur at frequencies consistent with soft phonon energies associated with the charge-density-wave, but vanish above the superconducting transition temperature rather than that at the charge-density-wave transition. These results indicate an intimate relationship of the terahertz excitation with the underlying charge-density-wave and the superconducting condensate itself.

Pseudo-direct bandgap transitions in silicon nanocrystals: effects on optoelectronics and thermoelectrics.

PubMed

Singh, Vivek; Yu, Yixuan; Sun, Qi-C; Korgel, Brian; Nagpal, Prashant

2014-12-21

While silicon nanostructures are extensively used in electronics, the indirect bandgap of silicon poses challenges for optoelectronic applications like photovoltaics and light emitting diodes (LEDs). Here, we show that size-dependent pseudo-direct bandgap transitions in silicon nanocrystals dominate the interactions between (photoexcited) charge carriers and phonons, and hence the optoelectronic properties of silicon nanocrystals. Direct measurements of the electronic density of states (DOS) for different sized silicon nanocrystals reveal that these pseudo-direct transitions, likely arising from the nanocrystal surface, can couple with the quantum-confined silicon states. Moreover, we demonstrate that since these transitions determine the interactions of charge carriers with phonons, they change the light emission, absorption, charge carrier diffusion and phonon drag (Seebeck coefficient) in nanoscaled silicon semiconductors. Therefore, these results can have important implications for the design of optoelectronics and thermoelectric devices based on nanostructured silicon.

Detonation propagation in annular arcs of condensed phase explosives

NASA Astrophysics Data System (ADS)

Ioannou, Eleftherios; Schoch, Stefan; Nikiforakis, Nikolaos; Michael, Louisa

2017-11-01

We present a numerical study of detonation propagation in unconfined explosive charges shaped as an annular arc (rib). Steady detonation in a straight charge propagates at constant speed, but when it enters an annular section, it goes through a transition phase and eventually reaches a new steady state of constant angular velocity. This study examines the speed of the detonation wave along the annular charge during the transition phase and at steady state, as well as its dependence on the dimensions of the annulus. The system is modeled using a recently proposed diffuse-interface formulation which allows for the representation of a two-phase explosive and of an additional inert material. The explosive considered is the polymer-bonded TATB-based LX-17 and is modeled using two Jones-Wilkins-Lee (JWL) equations of state and the ignition and growth reaction rate law. Results show that steady state speeds are in good agreement with experiment. In the transition phase, the evolution of outer detonation speed deviates from the exponential bounded growth function suggested by previous studies. We propose a new description of the transition phase which consists of two regimes. The first regime is caused by local effects at the outer edge of the annulus and leads to a dependence of the outer detonation speed on the angular position along the arc. The second regime is induced by effects originating from the inner edge of the annular charge and leads to the deceleration of the outer detonation until steady state is reached. The study concludes with a parametric study where the dependence of the steady state and the transition phase on the dimensions of the annulus is investigated.

Charge state manipulation of qubits in diamond

PubMed Central

Grotz, Bernhard; Hauf, Moritz V.; Dankerl, Markus; Naydenov, Boris; Pezzagna, Sébastien; Meijer, Jan; Jelezko, Fedor; Wrachtrup, Jörg; Stutzmann, Martin; Reinhard, Friedemann; Garrido, Jose A.

2012-01-01

The nitrogen-vacancy (NV) centre in diamond is a promising candidate for a solid-state qubit. However, its charge state is known to be unstable, discharging from the qubit state NV− into the neutral state NV0 under various circumstances. Here we demonstrate that the charge state can be controlled by an electrolytic gate electrode. This way, single centres can be switched from an unknown non-fluorescent state into the neutral charge state NV0, and the population of an ensemble of centres can be shifted from NV0 to NV−. Numerical simulations confirm the manipulation of the charge state to be induced by the gate-controlled shift of the Fermi level at the diamond surface. This result opens the way to a dynamic control of transitions between charge states and to explore hitherto inaccessible states, such as NV+. PMID:22395620

Electronic structure of negative charge transfer CaFeO3 across the metal-insulator transition

NASA Astrophysics Data System (ADS)

Rogge, Paul C.; Chandrasena, Ravini U.; Cammarata, Antonio; Green, Robert J.; Shafer, Padraic; Lefler, Benjamin M.; Huon, Amanda; Arab, Arian; Arenholz, Elke; Lee, Ho Nyung; Lee, Tien-Lin; Nemšák, Slavomír; Rondinelli, James M.; Gray, Alexander X.; May, Steven J.

2018-01-01

We investigated the metal-insulator transition for epitaxial thin films of the perovskite CaFeO3, a material with a significant oxygen ligand hole contribution to its electronic structure. We find that biaxial tensile and compressive strain suppress the metal-insulator transition temperature. By combining hard x-ray photoelectron spectroscopy, soft x-ray absorption spectroscopy, and density functional calculations, we resolve the element-specific changes to the electronic structure across the metal-insulator transition. We demonstrate that the Fe sites undergo no observable spectroscopic change between the metallic and insulating states, whereas the O electronic configuration undergoes significant changes. This strongly supports the bond-disproportionation model of the metal-insulator transition for CaFeO3 and highlights the importance of ligand holes in its electronic structure. By sensitively measuring the ligand hole density, however, we find that it increases by ˜5 -10 % in the insulating state, which we ascribe to a further localization of electron charge on the Fe sites. These results provide detailed insight into the metal-insulator transition of negative charge transfer compounds and should prove instructive for understanding metal-insulator transitions in other late transition metal compounds such as the nickelates.

Development of a ferromagnetic component in the superconducting state of Fe-excess Fe1.12Te1-xSex by electronic charge redistribution

NASA Astrophysics Data System (ADS)

Li, Wen-Hsien; Karna, Sunil K.; Hsu, Han; Li, Chi-Yen; Lee, Chi-Hung; Sankar, Raman; Cheng Chou, Fang

2015-06-01

The general picture established so far for the links between superconductivity and magnetic ordering in iron chalcogenide Fe1+y(Te1-xSex) is that the substitution of Se for Te directly drives the system from the antiferromagnetic end into the superconducting regime. Here, we report on the observation of a ferromagnetic component that developed together with the superconducting transition in Fe-excess Fe1.12Te1-xSex crystals using neutron and x-ray diffractions, resistivity, magnetic susceptibility and magnetization measurements. The superconducting transition is accompanied by a negative thermal expansion of the crystalline unit cell and an electronic charge redistribution, where a small portion of the electronic charge flows from around the Fe sites toward the Te/Se sites. First-principles calculations show consistent results, revealing that the excess Fe ions play a more significant role in affecting the magnetic property in the superconducting state than in the normal state and the occurrence of an electronic charge redistribution through the superconducting transition.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mironov, Alexey Yu.; Silevitch, Daniel M.; Proslier, Thomas

Three decades after the prediction of charge-vortex duality in the critical vicinity of the two-dimensional superconductor-insulator transition (SIT), one of the fundamental implications of this duality-the charge Berezinskii-Kosterlitz-Thouless (BKT) transition that should occur on the insulating side of the SIT-has remained unobserved. The dual picture of the process points to the existence of a superinsulating state endowed with zero conductance at finite temperature. Here, we report the observation of the charge BKT transition on the insulating side of the SIT in 10 nm thick NbTiN films, identified by the BKT critical behavior of the temperature and magnetic field dependent resistance,more » and map out the magnetic-field dependence of the critical temperature of the charge BKT transition. Finally, we ascertain the effects of the finite electrostatic screening length and its divergence at the magnetic field-tuned approach to the superconductor-insulator transition.« less

Enhancement of Catalytic Activity of Reduced Graphene Oxide Via Transition Metal Doping Strategy

NASA Astrophysics Data System (ADS)

Lee, Hangil; Hong, Jung A.

2017-06-01

To compare the catalytic oxidation activities of reduced graphene oxide (rGO) and rGO samples doped with five different transition metals (TM-rGO), we determine their effects on the oxidation of L-cysteine (Cys) in aqueous solution by performing electrochemistry (EC) measurements and on the photocatalytic oxidation of Cys by using high-resolution photoemission spectroscopy (HRPES) under UV illumination. Our results show that Cr-, Fe-, and Co-doped rGO with 3+ charge states (stable oxide forms: Cr3+, Fe3+, and Co3+) exhibit enhanced catalytic activities that are due to the charge states of the doped metal ions as we compare them with Cr-, Fe-, and Co-doped rGO with 2+ charge states.

Transition metal ions in ZnO: Effects of intrashell coulomb repulsion on electronic properties

NASA Astrophysics Data System (ADS)

Ciechan, A.; Bogusławski, P.

2018-05-01

Electronic structure of the transition metal (TM) dopants in ZnO is calculated by first principles approach. Analysis of the results is focused on the properties determined by the intrashell Coulomb coupling. The role of both direct and exchange interaction channel is analyzed. The coupling is manifested in the strong charge state dependence of the TM gap levels, which leads to the metastability of photoexcited Mn, and determines the accessible equilibrium charge states of TM ions. The varying magnitude of the exchange coupling is reflected in the dependence of the spin splitting energy on the chemical identity across the 3d series, as well as the charge state dependence of spin-up spin-down exchange splitting.

Surface charge sensing by altering the phase transition in VO2

NASA Astrophysics Data System (ADS)

Kumar, S.; Esfandyarpour, R.; Davis, R.; Nishi, Y.

2014-08-01

Detection of surface charges has various applications in medicine, electronics, biotechnology, etc. The source of surface charge induction may range from simple charge-polarized molecules like water to complicated proteins. It was recently discovered that surface charge accumulation can alter the temperature at which VO2 undergoes a Mott transition. Here, we deposited polar molecules onto the surface of two-terminal thin-film VO2 lateral devices and monitored the joule-heating-driven Mott transition, or conductance switching. We observed that the power required to induce the conductance switching reduced upon treatment with polar molecules and, using in-situ blackbody-emission direct measurement of local temperature, we show that this reduction in power was accompanied by reduction in the Mott transition temperature. Further evidence suggested that this effect has specificity to the nature of the species used to induce surface charges. Using x-ray absorption spectroscopy, we also show that there is no detectable change in oxidation state of vanadium or structural phase in the bulk of the 40 nm VO2 thin-film even as the phase transition temperature is reduced by up to 20 K by the polar molecules. The ability to alter the phase transition parameters by depositing polar molecules suggests a potential application in sensing surface charges of different origins and this set of results also highlights interesting aspects of the phase transition in VO2.

Topological phase transition and the effect of Hubbard interactions on the one-dimensional topological Kondo insulator

NASA Astrophysics Data System (ADS)

Pillay, Jason C.; McCulloch, Ian P.

2018-05-01

The effect of a local Kondo coupling and Hubbard interaction on the topological phase of the one-dimensional topological Kondo insulator (TKI) is numerically investigated using the infinite matrix-product state density-matrix renormalization group algorithm. The ground state of the TKI is a symmetry-protected topological (SPT) phase protected by inversion symmetry. It is found that on its own, the Hubbard interaction that tends to force fermions into a one-charge per site order is insufficient to destroy the SPT phase. However, when the local Kondo Hamiltonian term that favors a topologically trivial ground state with a one-charge per site order is introduced, the Hubbard interaction assists in the destruction of the SPT phase. This topological phase transition occurs in the charge sector where the correlation length of the charge excitation diverges while the correlation length of the spin excitation remains finite. The critical exponents, central charge, and the phase diagram separating the SPT phase from the topologically trivial phase are presented.

Large impact of reorganization energy on photovoltaic conversion due to interfacial charge-transfer transitions.

PubMed

Fujisawa, Jun-ichi

2015-05-14

Interfacial charge-transfer (ICT) transitions are expected to be a novel charge-separation mechanism for efficient photovoltaic conversion featuring one-step charge separation without energy loss. Photovoltaic conversion due to ICT transitions has been investigated using several TiO2-organic hybrid materials that show organic-to-inorganic ICT transitions in the visible region. In applications of ICT transitions to photovoltaic conversion, there is a significant problem that rapid carrier recombination is caused by organic-inorganic electronic coupling that is necessary for the ICT transitions. In order to solve this problem, in this work, I have theoretically studied light-to-current conversions due to the ICT transitions on the basis of the Marcus theory with density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations. An apparent correlation between the reported incident photon-to-current conversion efficiencies (IPCE) and calculated reorganization energies was clearly found, in which the IPCE increases with decreasing the reorganization energy consistent with the Marcus theory in the inverted region. This activation-energy dependence was systematically explained by the equation formulated by the Marcus theory based on a simple excited-state kinetic scheme. This result indicates that the reduction of the reorganization energy can suppress the carrier recombination and enhance the IPCE. The reorganization energy is predominantly governed by the structural change in the chemical-adsorption moiety between the ground and ICT excited states. This work provides crucial knowledge for efficient photovoltaic conversion due to ICT transitions.

Transition from direct to inverted charge transport Marcus regions in molecular junctions via molecular orbital gating

NASA Astrophysics Data System (ADS)

Yuan, Li; Wang, Lejia; Garrigues, Alvar R.; Jiang, Li; Annadata, Harshini Venkata; Anguera Antonana, Marta; Barco, Enrique; Nijhuis, Christian A.

2018-04-01

Solid-state molecular tunnel junctions are often assumed to operate in the Landauer regime, which describes essentially activationless coherent tunnelling processes. In solution, on the other hand, charge transfer is described by Marcus theory, which accounts for thermally activated processes. In practice, however, thermally activated transport phenomena are frequently observed also in solid-state molecular junctions but remain poorly understood. Here, we show experimentally the transition from the Marcus to the inverted Marcus region in a solid-state molecular tunnel junction by means of intra-molecular orbital gating that can be tuned via the chemical structure of the molecule and applied bias. In the inverted Marcus region, charge transport is incoherent, yet virtually independent of temperature. Our experimental results fit well to a theoretical model that combines Landauer and Marcus theories and may have implications for the interpretation of temperature-dependent charge transport measurements in molecular junctions.

Recoil ions from the β decay of 134Sb confined in a Paul trap

NASA Astrophysics Data System (ADS)

Siegl, K.; Scielzo, N. D.; Czeszumska, A.; Clark, J. A.; Savard, G.; Aprahamian, A.; Caldwell, S. A.; Alan, B. S.; Burkey, M. T.; Chiara, C. J.; Greene, J. P.; Harker, J.; Marley, S. T.; Morgan, G. E.; Munson, J. M.; Norman, E. B.; Orford, R.; Padgett, S.; Galván, A. Perez; Sharma, K. S.; Strauss, S. Y.

2018-03-01

The low-energy recoiling ions from the β decay of 134Sb were studied by using the Beta-decay Paul Trap. Using this apparatus, singly charged ions were suspended in vacuum at the center of a detector array used to detect emitted β particles, γ rays, and recoil ions in coincidence. The recoil ions emerge from the trap with negligible scattering, allowing β -decay properties and the charge-state distribution of the daughter ions to be determined from the β -ion coincidences. First-forbidden β -decay theory predicts a β -ν correlation coefficient of nearly unity for the 0- to 0+ transition from the ground state of 134Sb to the ground state of 134Te. Although this transition was expected to have a nearly 100% branching ratio, an additional 17.2(52)% of the β -decay strength must populate high-lying excited states to obtain an angular correlation consistent with unity. The extracted charge-state distribution of the recoiling ions was compared with existing β -decay results and the average charge state was found to be consistent with the results from lighter nuclei.

Nuclear structure properties of the double-charge-exchange transition amplitudes

NASA Astrophysics Data System (ADS)

Auerbach, N.; Zheng, D. C.

1992-03-01

Nuclear structure aspects of the double-charge-exchange (DCX) reaction on nuclei are studied. Using a variety of DCX-type two-body transition operators, we explore the influence of two-body correlations among valence nucleons on the DCX transition amplitudes to the isobaric analog state and to other nonanalog J π=0+ states. In particular, the question of the spin dependence and of the range of the DCX transition operators is explored and the behavior of the transition amplitudes as a function of the valence nucleon number is studied. It is shown that the two-amplitude DCX formula derived by Auerbach, Gibbs, and Piasetzky for a single j n configuration holds also in some cases when configuration mixing is strong. DCX-type transitions from the Ca and Ni isotopes to the Ti and Zn isotopes and from 56Fe to 56Ni are the subject of this study.

Interface and phase transition between Moore-Read and Halperin 331 fractional quantum Hall states: Realization of chiral Majorana fermion

NASA Astrophysics Data System (ADS)

Yang, Kun

2017-12-01

We consider an interface separating the Moore-Read state and Halperin 331 state in a half-filled Landau level, which can be realized in a double quantum well system with varying interwell tunneling and/or interaction strengths. In the presence of electron tunneling and strong Coulomb interactions across the interface, we find that all charge modes localize and the only propagating mode left is a chiral Majorana fermion mode. Methods to probe this neutral mode are proposed. A quantum phase transition between the Moore-Read and Halperin 331 states is described by a network of such Majorana fermion modes. In addition to a direct transition, they may also be separated by a phase in which the Majorana fermions are delocalized, realizing an incompressible state which exhibits quantum Hall charge transport and bulk heat conduction.

Unusual Thermoelectric Behavior Indicating a Hopping to Bandlike Transport Transition in Pentacene

NASA Astrophysics Data System (ADS)

Germs, W. Chr.; Guo, K.; Janssen, R. A. J.; Kemerink, M.

2012-07-01

An unusual increase in the Seebeck coefficient with increasing charge carrier density is observed in pentacene thin film transistors. This behavior is interpreted as being due to a transition from hopping transport in static localized states to bandlike transport, occurring at temperatures below ˜250K. Such a transition can be expected for organic materials in which both static energetic disorder and dynamic positional disorder are important. While clearly visible in the temperature and density dependent Seebeck coefficient, the transition hardly shows up in the charge carrier mobility.

Consequences of acid strength for isomerization and elimination catalysis on solid acids.

PubMed

Macht, Josef; Carr, Robert T; Iglesia, Enrique

2009-05-13

We address here the manner in which acid catalysis senses the strength of solid acids. Acid strengths for Keggin polyoxometalate (POM) clusters and zeolites, chosen because of their accurately known structures, are described rigorously by their deprotonation energies (DPE). Mechanistic interpretations of the measured dynamics of alkane isomerization and alkanol dehydration are used to obtain rate and equilibrium constants and energies for intermediates and transition states and to relate them to acid strength. n-Hexane isomerization rates were limited by isomerization of alkoxide intermediates on bifunctional metal-acid mixtures designed to maintain alkane-alkene equilibrium. Isomerization rate constants were normalized by the number of accessible protons, measured by titration with 2,6-di-tert-butylpyridine during catalysis. Equilibrium constants for alkoxides formed by protonation of n-hexene increased slightly with deprotonation energies (DPE), while isomerization rate constants decreased and activation barriers increased with increasing DPE, as also shown for alkanol dehydration reactions. These trends are consistent with thermochemical analyses of the transition states involved in isomerization and elimination steps. For all reactions, barriers increased by less than the concomitant increase in DPE upon changes in composition, because electrostatic stabilization of ion-pairs at the relevant transition states becomes more effective for weaker acids, as a result of their higher charge density at the anionic conjugate base. Alkoxide isomerization barriers were more sensitive to DPE than for elimination from H-bonded alkanols, the step that limits 2-butanol and 1-butanol dehydration rates; the latter two reactions showed similar DPE sensitivities, despite significant differences in their rates and activation barriers, indicating that slower reactions are not necessarily more sensitive to acid strength, but instead reflect the involvement of more unstable organic cations at their transition states. These compensating effects from electrostatic stabilization depend on how similar the charge density in these organic cations is to that in the proton removed. Cations with more localized charge favor strong electrostatic interactions with anions and form more stable ionic structures than do cations with more diffuse charges. Ion-pairs at elimination transition states contain cations with higher local charge density at the sp(2) carbon than for isomerization transition states; as a result, these ion-pairs recover a larger fraction of the deprotonation energy, and, consequently, their reactions become less sensitive to acid strength. These concepts lead us to conclude that the energetic difficulty of a catalytic reaction, imposed by gas-phase reactant proton affinities in transition state analogues, does not determine its sensitivity to the acid strength of solid catalysts.

Influence of image charge effect on impurity-related optical absorption coefficients and refractive index changes in a spherical quantum dot

NASA Astrophysics Data System (ADS)

Vartanian, A. L.; Asatryan, A. L.; Vardanyan, L. A.

2017-03-01

We have investigated the influence of an image charge effect (ICE) on the energies of the ground and first few excited states of a hydrogen-like impurity in a spherical quantum dot (QD) in the presence of an external electric field. The oscillator strengths of transitions from the 1 s -like state to excited states of 2px and 2pz symmetries are calculated as the functions of the strengths of the confinement potential and the electric field. Also, we have studied the effect of image charges on linear and third-order nonlinear optical absorption coefficients and refractive index changes (RICs). The results show that image charges lead to the decrease of energies for all the hydrogen-like states, to the significant enhancement of the oscillator strengths of transitions between the impurity states, and to comparatively large blue shifts in linear, nonlinear, and total absorption coefficients and refractive index changes. Our results indicate that the total optical characteristics can be controlled by the strength of the confinement and the electric field.

Influence of oxygen vacancy on the electronic structure of CaCu3Ti4O12 and its deep-level vacancy trap states by first-principle calculation

NASA Astrophysics Data System (ADS)

Xiao, H. B.; Yang, C. P.; Huang, C.; Xu, L. F.; Shi, D. W.; Marchenkov, V. V.; Medvedeva, I. V.; Bärner, K.

2012-03-01

The electronic structure, formation energy, and transition energy levels of intrinsic defects have been studied using the density-functional method within the generalized gradient approximation for neutral and charged oxygen vacancy in CaCu3Ti4O12 (CCTO). It is found that oxygen vacancies with different charge states can be formed in CCTO under both oxygen-rich and poor conditions for nonequilibrium and higher-energy sintering processes; especially, a lower formation energy is obtained for poor oxygen environment. The charge transition level (0/1+) of the oxygen vacancy in CCTO is located at 0.53 eV below the conduction-band edge. The (1+/2+) transition occurs at 1.06 eV below the conduction-band edge. Oxygen vacancies of Vo1+ and Vo2+ are positive stable charge states in most gap regions and can act as a moderately deep donor for Vo1+ and a borderline deep for Vo2+, respectively. The polarization and dielectric constant are considerably enhanced by oxygen vacancy dipoles, due to the off-center Ti and Cu ions in CCTO.

Internal transitions of neutral (X) and negatively charged (X(-)) magneto-excitons investigated by optically detected resonance (ODR) spectroscopy

NASA Astrophysics Data System (ADS)

Nickel, Hans Andreas

Optically detected resonance (ODR) spectroscopy, an experimental technique combining spectroscopy in the far-infrared and visible regimes of the spectrum, has been applied to non-intentionally- and modulation-doped, quasi-2D GaAs/AlGaAs heterostructures at low temperatures and high magnetic fields to study internal transitions of neutral (X) and negatively charged (X--) magneto-excitons. In quasi-2D GaAs/AlGaAs heterostructures with a low density of free carriers, such as undoped multiple-quantum-wells, the ground state of optical excitations is the neutral exciton. This hydrogenic system was studied by far-infrared ODR spectroscopy, and internal excitonic transitions (IETs) 1s → np+/- from the ground state (1s) to excited states (np+/-) were found. Three samples of different well widths were studied systematically, and the behavior of the observed transitions as a function of the sample well-width was as expected. A predicted consequence of an inherent symmetry to the system was verified experimentally for the first time by the simultaneous observation of IETs and electron and hole cyclotron resonance in one sample in one experiment. In addition, it was also found, that the observability of IETs is destroyed as soon as there is a sign of X---recombination in the photoluminescence spectrum. In quantum wells with a small number of excess electrons the ground state of the system under optical excitation is the negatively charged exciton, X--. This mobile system of a hole binding two electrons differs significantly in certain aspects from its immobile impurity analogue, the negatively charged donor ion D-- . The mobility of the charged complex is tied to a hidden symmetry of magnetic translations, which leads to a new selection rule, that forbids X-- bound-to-bound transitions, in contrast to the D -- system, in which these transitions are dominant. In this dissertation, several samples that show X-- recombination in photoluminescence measurements were studied with ODR spectroscopy, and internal singlet and triplet bound-to-continuum transitions were observed for the first time. The experimental results were found to agree well with theoretical numerical calculations. Furthermore, the theoretical predictions were verified: no bound-to-bound X-- internal transition was observed.

Ising tricriticality in the extended Hubbard model with bond dimerization

NASA Astrophysics Data System (ADS)

Fehske, Holger; Ejima, Satoshi; Lange, Florian; Essler, Fabian H. L.

We explore the quantum phase transition between Peierls and charge-density-wave insulating states in the one-dimensional, half-filled, extended Hubbard model with explicit bond dimerization. We show that the critical line of the continuous Ising transition terminates at a tricritical point, belonging to the universality class of the tricritical Ising model with central charge c=7/10. Above this point, the quantum phase transition becomes first order. Employing a numerical matrix-product-state based (infinite) density-matrix renormalization group method we determine the ground-state phase diagram, the spin and two-particle charge excitations gaps, and the entanglement properties of the model with high precision. Performing a bosonization analysis we can derive a field description of the transition region in terms of a triple sine-Gordon model. This allows us to derive field theory predictions for the power-law (exponential) decay of the density-density (spin-spin) and bond-order-wave correlation functions, which are found to be in excellent agreement with our numerical results. This work was supported by Deutsche Forschungsgemeinschaft (Germany), SFB 652, project B5, and by the EPSRC under Grant No. EP/N01930X/1 (FHLE).

Gravity dual of spin and charge density waves

NASA Astrophysics Data System (ADS)

Jokela, Niko; Järvinen, Matti; Lippert, Matthew

2014-12-01

At high enough charge density, the homogeneous state of the D3-D7' model is unstable to fluctuations at nonzero momentum. We investigate the end point of this instability, finding a spatially modulated ground state, which is a charge and spin density wave. We analyze the phase structure of the model as a function of chemical potential and magnetic field and find the phase transition from the homogeneous state to be first order, with a second-order critical point at zero magnetic field.

Substituent and Solvent Effects on Excited State Charge Transfer Behavior of Highly Fluorescent Dyes Containing Thiophenylimidazole-Based Aldehydes

NASA Technical Reports Server (NTRS)

Santos, Javier; Bu, Xiu R.; Mintz, Eric A.

2001-01-01

The excited state charge transfer for a series of highly fluorescent dyes containing thiophenylimidazole moiety was investigated. These systems follow the Twisted Intramolecular Charge Transfer (TICT) model. Dual fluorescence was observed for each substituted dye. X-ray structures analysis reveals a twisted ground state geometry for the donor substituted aryl on the 4 and 5 position at the imidazole ring. The excited state charge transfer was modeled by a linear solvation energy relationship using Taft's pi and Dimroth's E(sub T)(30) as solvent parameters. There is linear relation between the energy of the fluorescence transition and solvent polarity. The degree of stabilization of the excited state charge transfer was found to be consistent with the intramolecular molecular charge transfer. Excited dipole moment was studied by utilizing the solvatochromic shift method.

Soft x-ray emission from solar wind charge exchange in the laboratory

NASA Astrophysics Data System (ADS)

Shimaya, H.; Ishida, T.; Ishikawa, S.; Suda, S.; Tanuma, H.; Akamatsu, H.; Ohashi, H.; Ijima, N.; Inoue, M.; Ezoe, Y.; Ishisaki, Y.; Ohashi, T.; Shinozaki, K.; Mitsuda, K.; Liu, L.; Wang, J.

2013-09-01

We have observed the emission spectra in collisions of bare oxygen ions with a helium gas target in the soft x-ray region with a window-less silicon drift detector at the collision energy range of 48-80 keV. The dominant soft x-ray emission corresponds to the 1s-2p transition of hydrogen-like oxygen O7+ produced by the single-electron charge exchange reaction. Other emission lines are the 1s-3p, 1s-4p and 1s-5p transitions of O7+, and also the 1s2-1s2p transition of O6+ produced by the true double-electron capture. The cascades from the upper states result in a large population of the 2p state, even though the direct capture into the 2p state is extremely scarcer than those into the 3p, 4p and 5p states.

Cyclotron transitions of bound ions

NASA Astrophysics Data System (ADS)

Bezchastnov, Victor G.; Pavlov, George G.

2017-06-01

A charged particle in a magnetic field possesses discrete energy levels associated with particle rotation around the field lines. The radiative transitions between these levels are the well-known cyclotron transitions. We show that a bound complex of particles with a nonzero net charge displays analogous transitions between the states of confined motion of the entire complex in the field. The latter bound-ion cyclotron transitions are affected by a coupling between the collective and internal motions of the complex and, as a result, differ from the transitions of a "reference" bare ion with the same mass and charge. We analyze the cyclotron transitions for complex ions by including the coupling within a rigorous quantum approach. Particular attention is paid to comparison of the transition energies and oscillator strengths to those of the bare ion. Selection rules based on integrals of collective motion are derived for the bound-ion cyclotron transitions analytically, and the perturbation and coupled-channel approaches are developed to study the transitions quantitatively. Representative examples are considered and discussed for positive and negative atomic and cluster ions.

The low-energy, charge-transfer excited states of 4-amino-4-prime-nitrodiphenyl sulfide

NASA Technical Reports Server (NTRS)

O'Connor, Donald B.; Scott, Gary W.; Tran, Kim; Coulter, Daniel R.; Miskowski, Vincent M.; Stiegman, Albert E.; Wnek, Gary E.

1992-01-01

Absorption and emission spectra of 4-amino-4-prime-nitrodiphenyl sulfide in polar and nonpolar solvents were used to characterize and assign the low-energy excited states of the molecule. Fluorescence-excitation anisotropy spectra and fluorescence quantum yields were also used to characterize the photophysics of these states. The lowest-energy fluorescent singlet state was determined to be an intramolecular charge transfer (ICT) state involving transfer of a full electron charge from the amino to the nitro group yielding a dipole moment of about 50 D. A low-energy, intense absorption band is assigned as a transition to a different ICT state involving a partial electron charge transfer from sulfur to the nitro group.

Electron Scattering from MERCURY-198 and Mercury -204.

NASA Astrophysics Data System (ADS)

Laksanaboonsong, Jarungsaeng

This experiment is the first electron scattering study on mercury isotopes. Electron scattering from ^{198}Hg and ^{204 }Hg has been performed at the NIKHEF-K Medium Energy Accelerator. Measured cross sections cover an effective momentum transfer range from 0.4 to 2.9 fm^ {-1}. Elastic cross sections were determined for scattering from both isotopes. Cross section for inelastic excitations in ^{198}Hg below 3 MeV were also determined. Measured cross sections were fit using DWBA phase shift codes to determine coefficients for Fourier-Bessel expansions of ground state and transition charge densities. Differences between the ground state charge densities of the two isotopes reveal the effect of the polarization of the proton core in response to the addition of neutrons. Spin and parity of several excited states of ^{198}Hg were determined. Extracted transition densities of these states show their predominantly collective nature. Charge densities for members of the ground state rotational band were compared with axially symmetric Hartree-Fock and geometrical model predictions.

Photoinduced transition to charge-ordered phases from dynamical localization in the metallic phase of α -(BEDT-TTF)2I3

NASA Astrophysics Data System (ADS)

Oya, Koudai; Takahashi, Akira

2018-03-01

From theory, we investigate charge localization induced by higher-frequency off-resonance light-pulse excitation in the metallic phase of α -(BEDT-TTF) 2I3 by numerically solving the time-dependent Schrödinger equation in the quarter-filled extended Hubbard model for the material. Around e a A(max )=1 , where e a A(max ) is the maximum amplitude of the dimensionless vector potential of the pump pulse, the charge distribution is significantly changed by photoexcitation, and the light-pulse-induced collective charge oscillations continue after photoexcitation. Furthermore, the charge dynamics depend strongly on the polarization direction of the pump pulse. These results are consistent with experiment. The magnitudes of the effective transfer integrals are reduced by strong photoexcitation, and this precursory phenomenon for dynamical localization is mainly driven by a photoinduced change in the ratio of the effective transfer integrals between the two strongest bonds. For e a A(max )≳2 , the photoinduced transition to the charge-ordered state, which can be regarded as a light-dressed state, occurs because of dynamical localization. Furthermore, the type of photogenerated charge-ordered state can be controlled by choosing e a A(max ) and the polarization direction.

Analyzing the equilibrium states of a quasi-neutral spatially inhomogeneous system of charges above a liquid dielectric film based on the first principles of quantum statistics

NASA Astrophysics Data System (ADS)

Lytvynenko, D. M.; Slyusarenko, Yu V.

2017-08-01

A theory of quasi-neutral equilibrium states of charges above a liquid dielectric surface is developed. This theory is based on the first principles of quantum statistics for systems comprising many identical particles. The proposed approach involves applying the variational principle, modified for the considered systems, and the Thomas-Fermi model. In the terms of the developed theory self-consistency equations are obtained. These equations provide the relation between the main parameters describing the system: the potential of the static electric field, the distribution function of charges and the surface profile of the liquid dielectric. The equations are used to study the phase transition in the system to a spatially periodic state. The proposed method can be applied in analyzing the properties of the phase transition in the system in relation to the spatially periodic states of wave type. Using the analytical and numerical methods, we perform a detailed study of the dependence of the critical parameters of such a phase transition on the thickness of the liquid dielectric film. Some stability criteria for the new asymmetric phase of the studied system are discussed.

Spin polarized and density modulated phases in symmetric electron-electron and electron-hole bilayers.

PubMed

Kumar, Krishan; Moudgil, R K

2012-10-17

We have studied symmetric electron-electron and electron-hole bilayers to explore the stable homogeneous spin phase and the feasibility of inhomogeneous charge-/spin-density ground states. The former is resolved by comparing the ground-state energies in states of different spin polarizations, while the latter is resolved by searching for a divergence in the wavevector-dependent static charge/spin susceptibility. For this endeavour, we have used the dielectric approach within the self-consistent mean-field theory of Singwi et al. We find that the inter-layer interactions tend to change an abrupt spin-polarization transition of an isolated layer into a nearly gradual one, even though the partially spin-polarized phases are not clearly stable within the accuracy of our calculation. The transition density is seen to decrease with a reduction in layer spacing, implying a suppression of spin polarization by inter-layer interactions. Indeed, the suppression shows up distinctly in the spin susceptibility computed from the spin-polarization dependence of the ground-state energy. However, below a critical layer spacing, the unpolarized liquid becomes unstable against a charge-density-wave (CDW) ground state at a density preceding full spin polarization, with the transition density for the CDW state increasing on further reduction in the layer spacing. Due to attractive e-h correlations, the CDW state is found to be more pronounced in the e-h bilayer. On the other hand, the static spin susceptibility diverges only in the long-wavelength limit, which simply represents a transition to the homogeneous spin-polarized phase.

Pressure-Induced Charge-Order Melting and Reentrant Charge Carrier Localization in the Mixed-Valent Pb 3Rh 7O 15

DOE PAGES

Li, Yan; Sun, Zhao; Cai, Jia -Wei; ...

2017-07-01

Here, the mixed-valent Pbmore » $${}_{3}$$Rh $${}_{7}$$O$${}_{15}$$ undergoes a Verwey-type transition at $${T}_{{\\rm{v}}}\\approx 180$$ K, below which the development of Rh$${}^{3+}$$ /Rh$${}^{4+}$$ charge order induces an abrupt conductor-to-insulator transition in resistivity. Here we investigate the effect of pressure on the Verwey-type transition of Pb$${}_{3}$$Rh$${}_{7}$$O$${}_{15}$$ by measuring its electrical resistivity under hydrostatic pressures up to 8 GPa with a cubic anvil cell apparatus. We find that the application of high pressure can suppress the Verwey-type transition around 3 GPa, above which a metallic state is realized at temperatures below ~70 K, suggesting the melting of charge order by pressure. Interestingly, the low-temperature metallic region shrinks gradually upon further increasing pressure and disappears completely at P > 7 GPa, which indicates that the charge carriers in Pb$${}_{3}$$Rh$${}_{7}$$O$${}_{15}$$ undergo a reentrant localization under higher pressures. We have constructed a temperature-pressure phase diagram for Pb$${}_{3}$$Rh$${}_{7}$$O$${}_{15}$$ and compared to that of Fe$${}_{3}$$O$${}_{4}$$, showing an archetype Verwey transition.« less

Effect of Allylic Groups on SN2 Reactivity

PubMed Central

2015-01-01

The activating effects of the benzyl and allyl groups on SN2 reactivity are well-known. 6-Chloromethyl-6-methylfulvene, also a primary, allylic halide, reacts 30 times faster with KI/acetone than does benzyl chloride at room temperature. The latter result, as well as new experimental observations, suggests that the fulvenyl group is a particularly activating allylic group in SN2 reactions. Computational work on identity SN2 reactions, e.g., chloride– displacing chloride– and ammonia displacing ammonia, shows that negatively charged SN2 transition states (tss) are activated by allylic groups according to the Galabov–Allen–Wu electrostatic model but with the fulvenyl group especially effective at helping to delocalize negative charge due to some cyclopentadienide character in the transition state (ts). In contrast, the triafulvenyl group is deactivating. However, the positively charged SN2 transition states of the ammonia reactions are dramatically stabilized by the triafulvenyl group, which directly conjugates with a reaction center having SN1 character in the ts. Experiments and calculations on the acidities of a variety of allylic alcohols and carboxylic acids support the special nature of the fulvenyl group in stabilizing nearby negative charge and highlight the ability of fulvene species to dramatically alter the energetics of processes even in the absence of direct conjugation. PMID:24977317

Optical backbone-sidechain charge transfer transitions in proteins sensitive to secondary structure and modifications.

PubMed

Mandal, I; Paul, S; Venkatramani, R

2018-04-17

The absorption of light by proteins can induce charge transfer (CT) transitions in the UV-visible range of the electromagnetic spectrum. Metal-ligand complexes or active site prosthetic groups which absorb in the visible region exhibit prominent CT transitions. Furthermore, the protein backbone also exhibits CT transitions in the far UV range. In this manuscript, we present a detailed computational study of new near UV-visible CT transitions that involve amino acids with charged side chains. Specifically, using time dependent density functional theory calculations, we examine the absorption spectra of naturally charged amino acids (Lys, Glu, Arg, Asp and His), extracted from solution phase protein structures generated by classical molecular dynamics simulations, and phosphorylated amino acids (Tyr, Thr and Ser) from experimentally determined protein structures. We show that amino acids with charged sidechains present a directed electronic donor-bridge-acceptor paradigm, with the lowest energy optical excitations demonstrating peptide backbone-sidechain charge separations. The UV-visible spectral range of the backbone-sidechain CT transitions is determined by the chemical nature of the donor, bridge and acceptor groups within each amino acid, amino acid conformation and the protein secondary structure where the amino acids are located. Photoinduced CT occurs in opposite directions for the anionic and cationic amino acids along the ground state dipole moment vector for the chromophores. We find that photoinduced charge separation is more facile for the anionic amino acids (Asp, Glu, pSer, pThr and pTyr) relative to that for the cationic amino acids (Lys, Arg and Hsp). Our results provide a foundation for the development of spectroscopic markers based on the recently proposed Protein Charge Transfer Spectra (ProCharTS) which are relevant for the study of DNA-binding or intrinsically disordered proteins that are rich in charged amino acids.

Traversing the folding pathway of proteins using temperature-aided cascade molecular dynamics with conformation-dependent charges.

PubMed

Jani, Vinod; Sonavane, Uddhavesh; Joshi, Rajendra

2016-07-01

Protein folding is a multi-micro second time scale event and involves many conformational transitions. Crucial conformational transitions responsible for biological functions of biomolecules are difficult to capture using current state-of-the-art molecular dynamics (MD) simulations. Protein folding, being a stochastic process, witnesses these transitions as rare events. Many new methodologies have been proposed for observing these rare events. In this work, a temperature-aided cascade MD is proposed as a technique for studying the conformational transitions. Folding studies for Engrailed homeodomain and Immunoglobulin domain B of protein A have been carried out. Using this methodology, the unfolded structures with RMSD of 20 Å were folded to a structure with RMSD of 2 Å. Three sets of cascade MD runs were carried out using implicit solvation, explicit solvation, and charge updation scheme. In the charge updation scheme, charges based on the conformation obtained are calculated and are updated in the topology file. In all the simulations, the structure of 2 Å was reached within a few nanoseconds using these methods. Umbrella sampling has been performed using snapshots from the temperature-aided cascade MD simulation trajectory to build an entire conformational transition pathway. The advantage of the method is that the possible pathways for a particular reaction can be explored within a short duration of simulation time and the disadvantage is that the knowledge of the start and end state is required. The charge updation scheme adds the polarization effects in the force fields. This improves the electrostatic interaction among the atoms, which may help the protein to fold faster.

Method of preparing an electrochemical cell in uncharged state

DOEpatents

Shimotake, Hiroshi; Bartholme, Louis G.; Arntzen, John D.

1977-02-01

A secondary electrochemical cell is assembled in an uncharged state for the preparation of a lithium alloy-transition metal sulfide cell. The negative electrode includes a material such as aluminum or silicon for alloying with lithium as the cell is charged. The positive electrode is prepared by blending particulate lithium sulfide, transition metal powder and electrolytic salt in solid phase. The mixture is simultaneously heated to a temperature in excess of the melting point of the electrolyte and pressed onto an electrically conductive substrate to form a plaque. The plaque is assembled as a positive electrode within the cell. During the first charge cycle lithium alloy is formed within the negative electrode and transition metal sulfide such as iron sulfide is produced within the positive electrode.

Matter antimatter domains: A possible solution to the CP domain wall problem in the early universe

NASA Technical Reports Server (NTRS)

Mohanty, A. K.; Stecker, F. W.

1984-01-01

An SU(5) grand unified theory model is used to show how the degeneracy between vacua with different spontaneously broken charge parity can be dynamically lifted by a condensate of heavy fermion pairs. This drives a phase transition to a unique vacuum state with definite charge parity. The transition eliminates the domain walls in a matter antimatter symmetric domain cosmology.

Kinetic mechanism for reversible structural transition in MoTe2 induced by excess charge carriers

NASA Astrophysics Data System (ADS)

Rubel, O.

2018-06-01

Kinetic of a reversible structural transition between insulating (2H) and metallic (1T ') phases in a monolayer MoTe2 due to an electrostatic doping is studied using first-principle calculations. The driving force for the structural transition is the energy gained by transferring excess electrons from the bottom of the conduction band to lower energy gapless states in the metallic phase as have been noticed in earlier studies. The corresponding structural transformation involves dissociation of Mo-Te bonds (one per formula unit), which results in a kinetic energy barrier of 0.83 eV. The transformation involves a consecutive movement of atoms similar to a domain wall motion. The presence of excess charge carriers modifies not only the total energy of the initial and final states, but also lowers an energy of the transition state. An experimentally observed hysteresis in the switching process can be attributed to changes in the kinetic energy barrier due to its dependence on the excess carrier density.

High magnetic field studies of the charge density wave state of the quasi-two-dimensional conductor KMO 6O 17

NASA Astrophysics Data System (ADS)

Dumas, Jean; Guyot, Hervé; Balaska, Hafid; Marcus, Jacques; Vignolles, David; Sheikin, Ilya; Audouard, Alain; Brossard, Luc; Schlenker, Claire

2004-04-01

Magnetic torque and magnetoresistance measurements have been performed in high magnetic field on the quasi-two-dimensional charge density wave (CDW) oxide bronze KMo 6O 17 . Several anomalies have been found below 28 T either on the torque or on the magnetoresistance data. They can be attributed predominantly to orbital effects. Magnetoresistance data obtained up to 55 T show that a transition takes place above 30 T. This transition may be due to the Pauli coupling. The new field-induced density wave state exhibits Shubnikov-de Haas (SdH) oscillations.

Phase transitions and spatially ordered counterion association in ionic-lipid membranes: a statistical model.

PubMed

Tamashiro, M N; Barbetta, C; Germano, R; Henriques, V B

2011-09-01

We propose a statistical model to account for the gel-fluid anomalous phase transitions in charged bilayer- or lamellae-forming ionic lipids. The model Hamiltonian comprises effective attractive interactions to describe neutral-lipid membranes as well as the effect of electrostatic repulsions of the discrete ionic charges on the lipid headgroups. The latter can be counterion dissociated (charged) or counterion associated (neutral), while the lipid acyl chains may be in gel (low-temperature or high-lateral-pressure) or fluid (high-temperature or low-lateral-pressure) states. The system is modeled as a lattice gas with two distinct particle types--each one associated, respectively, with the polar-headgroup and the acyl-chain states--which can be mapped onto an Ashkin-Teller model with the inclusion of cubic terms. The model displays a rich thermodynamic behavior in terms of the chemical potential of counterions (related to added salt concentration) and lateral pressure. In particular, we show the existence of semidissociated thermodynamic phases related to the onset of charge order in the system. This type of order stems from spatially ordered counterion association to the lipid headgroups, in which charged and neutral lipids alternate in a checkerboard-like order. Within the mean-field approximation, we predict that the acyl-chain order-disorder transition is discontinuous, with the first-order line ending at a critical point, as in the neutral case. Moreover, the charge order gives rise to continuous transitions, with the associated second-order lines joining the aforementioned first-order line at critical end points. We explore the thermodynamic behavior of some physical quantities, like the specific heat at constant lateral pressure and the degree of ionization, associated with the fraction of charged lipid headgroups.

Ground-state oxygen holes and the metal–insulator transition in the negative charge-transfer rare-earth nickelates

PubMed Central

Bisogni, Valentina; Catalano, Sara; Green, Robert J.; Gibert, Marta; Scherwitzl, Raoul; Huang, Yaobo; Strocov, Vladimir N.; Zubko, Pavlo; Balandeh, Shadi; Triscone, Jean-Marc; Sawatzky, George; Schmitt, Thorsten

2016-01-01

The metal–insulator transition and the intriguing physical properties of rare-earth perovskite nickelates have attracted considerable attention in recent years. Nonetheless, a complete understanding of these materials remains elusive. Here we combine X-ray absorption and resonant inelastic X-ray scattering (RIXS) spectroscopies to resolve important aspects of the complex electronic structure of rare-earth nickelates, taking NdNiO3 thin film as representative example. The unusual coexistence of bound and continuum excitations observed in the RIXS spectra provides strong evidence for abundant oxygen holes in the ground state of these materials. Using cluster calculations and Anderson impurity model interpretation, we show that distinct spectral signatures arise from a Ni 3d8 configuration along with holes in the oxygen 2p valence band, confirming suggestions that these materials do not obey a conventional positive charge-transfer picture, but instead exhibit a negative charge-transfer energy in line with recent models interpreting the metal–insulator transition in terms of bond disproportionation. PMID:27725665

Spectroscopy of Highly Charged Tin Ions for AN Extreme Ultraviolet Light Source for Lithography

NASA Astrophysics Data System (ADS)

Torretti, Francesco; Windberger, Alexander; Ubachs, Wim; Hoekstra, Ronnie; Versolato, Oscar; Ryabtsev, Alexander; Borschevsky, Anastasia; Berengut, Julian; Crespo Lopez-Urrutia, Jose

2017-06-01

Laser-produced tin plasmas are the prime candidates for the generation of extreme ultraviolet (EUV) light around 13.5 nm in nanolithographic applications. This light is generated primarily by atomic transitions in highly charged tin ions: Sn^{8+}-Sn^{14+}. Due to the electronic configurations of these charge states, thousands of atomic lines emit around 13.5 nm, clustered in a so-called unresolved transition array. As a result, accurate line identification becomes difficult in this regime. Nevertheless, this issue can be circumvented if one turns to the optical: with far fewer atomic states, only tens of transitions take place and the spectra can be resolved with far more ease. We have investigated optical emission lines in an electron-beam-ion-trap (EBIT), where we managed to charge-state resolve the spectra. Based on this technique and on a number of different ab initio techniques for calculating the level structure, the optical spectra could be assigned [1,2]. As a conclusion the assignments of EUV transitions in the literature require corrections. The EUV and optical spectra are measured simultaneously in the controlled conditions of the EBIT as well as in a droplet-based laser-produced plasma source providing information on the contribution of Sn^{q+} charge states to the EUV emission. [1] A. Windberger, F. Torretti, A. Borschevsky, A. Ryabtsev, S. Dobrodey, H. Bekker, E. Eliav, U. Kaldor, W. Ubachs, R. Hoekstra, J.R. Crespo Lopez-Urrutia, O.O. Versolato, Analysis of the fine structure of Sn^{11+} - Sn^{14+} ions by optical spectroscopy in an electron beam ion trap, Phys. Rev. A 94, 012506 (2016). [2] F. Torretti, A. Windberger, A. Ryabtsev, S. Dobrodey, H. Bekker, W. Ubachs, R. Hoekstra, E.V. Kahl, J.C. Berengut, J.R. Crespo Lopez-Urrutia, O.O. Versolato, Optical spectroscopy of complex open 4d-shell ions Sn^{7+} - Sn^{10+}, arXiv:1612.00747

Decoupling of the antiferromagnetic and insulating states in Tb-doped Sr 2IrO 4

DOE PAGES

Wang, J. C.; Aswartham, S.; Ye, Feng; ...

2015-12-08

Sr 2IrO 4 is a spin-orbit coupled insulator with an antiferromagnetic (AFM) transition at T N = 240 K. We report results of a comprehensive study of single-crystal Sr 2Ir 1-xTb xO 4 (0≤x≤0.03). This study found that mere 3% (x=0.03) tetravalent Tb 4+(4f 7) substituting for Ir 4+ (rather than Sr 2+) completely suppresses the long-range collinear AFM transition but retains the insulating state, leading to a phase diagram featuring a decoupling of magnetic interactions and charge gap. The insulating state at x = 0.03 is characterized by an unusually large specific heat at low temperatures and an incommensuratemore » magnetic state having magnetic peaks at (0.95, 0, 0) and (0, 0.95, 0) in the neutron diffraction, suggesting a spiral or spin density wave order. It is apparent that Tb doping effectively changes the relative strength of the SOI and the tetragonal CEF and enhances the Hund’s rule coupling that competes with the SOI, and destabilizes the AFM state. However, the disappearance of the AFM accompanies no metallic state chiefly because an energy level mismatch for the Ir and Tb sites weakens charge carrier hopping and renders a persistent insulating state. Furthermore, this work highlights an unconventional correlation between the AFM and insulating states in which the magnetic transition plays no critical role in the formation of the charge gap in the iridate.« less

Observation of excited state absorption in the V-Cr Prussian blue analogue

NASA Astrophysics Data System (ADS)

Hedley, Luke; Horbury, Michael D.; Liedy, Florian; Johansson, J. Olof

2017-11-01

We present femtosecond transient transmission measurements of thin films of the VII/III-CrIII Prussian blue analogue (V-Cr PBA) in the spectral range 330-675 nm after exciting the ligand-to-metal charge-transfer transition (LMCT) at 400 nm. A global analysis including three decay-times of τ1 = 230 fs, τ2 = 1.38 ps and τ3 ≫ 2 ns could satisfactory describe the data. We observed an excited state absorption (ESA) at 345 nm, which was attributed to a charge-transfer transition from the 2E state on the Cr ions after fast intersystem crossing from the quartet manifold. An additional weak and short-lived ESA at 455 nm was also observed and was tentatively attributed to the initially populated 4LMCT state.

Asymptotic dynamics in perturbative quantum gravity and BMS supertranslations

NASA Astrophysics Data System (ADS)

Choi, Sangmin; Kol, Uri; Akhoury, Ratindranath

2018-01-01

Recently it has been shown that infrared divergences in the conventional S-matrix elements of gauge and gravitational theories arise from a violation of the conservation laws associated with large gauge symmetries. These infrared divergences can be cured by using the Faddeev-Kulish (FK) asymptotic states as the basis for S-matrix elements. Motivated by this connection, we study the action of BMS supertranslations on the FK asymptotic states of perturbative quantum gravity. We compute the BMS charge of the FK states and show that it characterizes the superselection sector to which the state belongs. Conservation of the BMS charge then implies that there is no transition between different superselection sectors, hence showing that the FK graviton clouds implement the necessary transition induced by the scattering process.

Melting of Domain Wall in Charge Ordered Dirac Electron of Organic Conductor α-(BEDT-TTF)2I3

NASA Astrophysics Data System (ADS)

Ohki, Daigo; Matsuno, Genki; Omori, Yukiko; Kobayashi, Akito

2018-05-01

The origin of charge order melting is identified by using the real space dependent mean-field theory in the extended Hubbard model describing an organic Dirac electron system α-(BEDT-TTF)2I3. In this model, the width of a domain wall which arises between different types of the charge ordered phase exhibits a divergent increase with decreasing the strength of electron-electron correlations. By analyzing the finite-size effect carefully, it is shown that the divergence coincides with a topological transition where a pair of Dirac cones merges in keeping with a finite gap. It is also clarified that the gap opening point and the topological transition point are different, which leads to the existence of an exotic massive Dirac electron phase with melted-type domain wall and gapless edge states. The present result also indicated that multiple metastable states are emerged in massive Dirac Electron phase. In the trivial charge ordered phase, the gapless domain-wall bound state takes place instead of the gapless edge states, accompanying with a form change of the domain wall from melted-type into hyperbolic-tangent-type.

Free-energy landscape of ion-channel voltage-sensor–domain activation

PubMed Central

Delemotte, Lucie; Kasimova, Marina A.; Klein, Michael L.; Tarek, Mounir; Carnevale, Vincenzo

2015-01-01

Voltage sensor domains (VSDs) are membrane-bound protein modules that confer voltage sensitivity to membrane proteins. VSDs sense changes in the transmembrane voltage and convert the electrical signal into a conformational change called activation. Activation involves a reorganization of the membrane protein charges that is detected experimentally as transient currents. These so-called gating currents have been investigated extensively within the theoretical framework of so-called discrete-state Markov models (DMMs), whereby activation is conceptualized as a series of transitions across a discrete set of states. Historically, the interpretation of DMM transition rates in terms of transition state theory has been instrumental in shaping our view of the activation process, whose free-energy profile is currently envisioned as composed of a few local minima separated by steep barriers. Here we use atomistic level modeling and well-tempered metadynamics to calculate the configurational free energy along a single transition from first principles. We show that this transition is intrinsically multidimensional and described by a rough free-energy landscape. Remarkably, a coarse-grained description of the system, based on the use of the gating charge as reaction coordinate, reveals a smooth profile with a single barrier, consistent with phenomenological models. Our results bridge the gap between microscopic and macroscopic descriptions of activation dynamics and show that choosing the gating charge as reaction coordinate masks the topological complexity of the network of microstates participating in the transition. Importantly, full characterization of the latter is a prerequisite to rationalize modulation of this process by lipids, toxins, drugs, and genetic mutations. PMID:25535341

Free-energy landscape of ion-channel voltage-sensor-domain activation.

PubMed

Delemotte, Lucie; Kasimova, Marina A; Klein, Michael L; Tarek, Mounir; Carnevale, Vincenzo

2015-01-06

Voltage sensor domains (VSDs) are membrane-bound protein modules that confer voltage sensitivity to membrane proteins. VSDs sense changes in the transmembrane voltage and convert the electrical signal into a conformational change called activation. Activation involves a reorganization of the membrane protein charges that is detected experimentally as transient currents. These so-called gating currents have been investigated extensively within the theoretical framework of so-called discrete-state Markov models (DMMs), whereby activation is conceptualized as a series of transitions across a discrete set of states. Historically, the interpretation of DMM transition rates in terms of transition state theory has been instrumental in shaping our view of the activation process, whose free-energy profile is currently envisioned as composed of a few local minima separated by steep barriers. Here we use atomistic level modeling and well-tempered metadynamics to calculate the configurational free energy along a single transition from first principles. We show that this transition is intrinsically multidimensional and described by a rough free-energy landscape. Remarkably, a coarse-grained description of the system, based on the use of the gating charge as reaction coordinate, reveals a smooth profile with a single barrier, consistent with phenomenological models. Our results bridge the gap between microscopic and macroscopic descriptions of activation dynamics and show that choosing the gating charge as reaction coordinate masks the topological complexity of the network of microstates participating in the transition. Importantly, full characterization of the latter is a prerequisite to rationalize modulation of this process by lipids, toxins, drugs, and genetic mutations.

Status in calculating electronic excited states in transition metal oxides from first principles.

PubMed

Bendavid, Leah Isseroff; Carter, Emily Ann

2014-01-01

Characterization of excitations in transition metal oxides is a crucial step in the development of these materials for photonic and optoelectronic applications. However, many transition metal oxides are considered to be strongly correlated materials, and their complex electronic structure is challenging to model with many established quantum mechanical techniques. We review state-of-the-art first-principles methods to calculate charged and neutral excited states in extended materials, and discuss their application to transition metal oxides. We briefly discuss developments in density functional theory (DFT) to calculate fundamental band gaps, and introduce time-dependent DFT, which can model neutral excitations. Charged excitations can be described within the framework of many-body perturbation theory based on Green's functions techniques, which predominantly employs the GW approximation to the self-energy to facilitate a feasible solution to the quasiparticle equations. We review the various implementations of the GW approximation and evaluate each approach in its calculation of fundamental band gaps of many transition metal oxides. We also briefly review the related Bethe-Salpeter equation (BSE), which introduces an electron-hole interaction between GW-derived quasiparticles to describe accurately neutral excitations. Embedded correlated wavefunction theory is another framework used to model localized neutral or charged excitations in extended materials. Here, the electronic structure of a small cluster is modeled within correlated wavefunction theory, while its coupling to its environment is represented by an embedding potential. We review a number of techniques to represent this background potential, including electrostatic representations and electron density-based methods, and evaluate their application to transition metal oxides.

Experimental exploration of the Mulliken-Hush relationship for intramolecular electron transfer reactions.

PubMed

Mukherjee, Tamal; Ito, Naoki; Gould, Ian R

2011-03-17

The Mulliken-Hush (M-H) relationship provides the critical link between optical and thermal electron transfer processes, and yet very little direct experimental support for its applicability has been provided. Dicyanovinylazaadamantane (DCVA) represents a simple two-state (neutral/charge-transfer) intramolecular electron transfer system that exhibits charge-transfer absorption and emission spectra that are readily measurable in solvents with a wide range of polarities. In this regard it represents an ideal model system for studying the factors that control both optical charge separation (absorption) and recombination (emission) processes in solution. Here we explore the applicability of the M-H relation to quantitative descriptions of the optical charge-transfer processes in DCVA. For DCVA, the measured radiative rate constants exhibit a linear dependence on transition energy, and transition dipole moments exhibit an inverse dependence on transition energy, consistent with the M-H relationship.

Magnetic field enhancement of organic photovoltaic cells performance.

PubMed

Oviedo-Casado, S; Urbina, A; Prior, J

2017-06-27

Charge separation is a critical process for achieving high efficiencies in organic photovoltaic cells. The initial tightly bound excitonic electron-hole pair has to dissociate fast enough in order to avoid photocurrent generation and thus power conversion efficiency loss via geminate recombination. Such process takes place assisted by transitional states that lie between the initial exciton and the free charge state. Due to spin conservation rules these intermediate charge transfer states typically have singlet character. Here we propose a donor-acceptor model for a generic organic photovoltaic cell in which the process of charge separation is modulated by a magnetic field which tunes the energy levels. The impact of a magnetic field is to intensify the generation of charge transfer states with triplet character via inter-system crossing. As the ground state of the system has singlet character, triplet states are recombination-protected, thus leading to a higher probability of successful charge separation. Using the open quantum systems formalism we demonstrate that the population of triplet charge transfer states grows in the presence of a magnetic field, and discuss the impact on carrier population and hence photocurrent, highlighting its potential as a tool for research on charge transfer kinetics in this complex systems.

Magnetic circular dichroism of UCl 6– in the ligand-to-metal charge-transfer spectral region

DOE PAGES

Gendron, Frederic; Fleischauer, Valerie R.; Duignan, Thomas J.; ...

2017-06-23

Here, we present a combined ab initio theoretical and experimental study of the magnetic circular dichroism (MCD) spectrum of the octahedral UCl 6- complex ion in the UV-Vis spectral region. The ground state is an orbitally non-degenerate doublet E 5/2u and the MCD is a $C$-term spectrum caused by spin–orbit coupling. Calculations of the electronic spectrum at various levels of theory indicate that differential dynamic electron correlation has a strong influence on the energies of the dipole-allowed transitions and the envelope of the MCD spectrum. The experimentally observed bands are assigned to dipole-allowed ligand-to-metal charge transfer into the 5f shell,more » and 5f to 6d transitions. Charge transfer excitations into the U 6d shell appear at much higher energies. The MCD-allowed transitions can be assigned via their signs of the $C$-terms: Under O h double group symmetry, E 5/2u → E 5/2g transitions have negative $C$-terms whereas E 5/2u → F 3/2g transitions have positive $C$-terms if the ground state g-factor is negative, as it is the case for UCl 6-.« less

Microscopic interpretation of inelastic electron scattering from even Ni isotopes

NASA Astrophysics Data System (ADS)

Yokoyama, Atsushi; Ogawa, Kengo

1990-10-01

Transition charge densities of inelastic electron scattering for the excitation of 2+ and 4+ states in even-mass Ni isotopes are investigated in terms of the standard shell model of the (p3/2,p1/2,f5/2)n configurations. Effective transition operators pertinent to the model space are derived by considering particle-hole excitations up to 12ħω for C2 and 14ħω for C4 transitions within the framework of a first-order perturbation theory. It is shown that surface-peaked transition charge densities can be obtained for the first excited 2+ and 4+ states, being in agreement with experiment. Particle-hole excitations up to λħω, e.g., λ=2 for C2 transition, are most responsible for that feature. Higher ħω excitations appear relatively significant in the interior region of the nucleus: They enhance the peak around the surface, improving further agreement with experiment, but for C2 transition they tend to generate another peak inside the nucleus and thus seem to deteriorate agreement with experiment. Transition densities for the 0+g.s.-->2+2,3 and 0+g.s.-->4+2 transitions are also discussed.

Phase transition detection by surface photo charge effect in liquid crystals

NASA Astrophysics Data System (ADS)

Ivanov, O.; Petrov, M.; Naradikian, H.; Perez-Diaz, J. L.

2018-05-01

The surface photo charge effect (SPCE) was applied for the first time at structure and phase transitions study of hydrogen bonded in dimer liquid crystals (HBDLCs). Due to the high sensitivity of this method, besides first-order phase transitions, characteristic for the p,n-octyloxibenzoic acids (8OBA), an order transition was definitely detected within the nematic range. We state that the SPCE, arising at the solid-HBDLCs interface due to the double electrical layer, is invariably concomitant with solid surface-liquid interfaces, and indicates that the changes of the characteristics of this layer, under incident optical irradiation, induce surface charge rearrangement and alternating potential difference. A mechanism of induction of the SPCE at the interface of solid surface-anisotropic liquids is proposed. We also indicate that this mechanism can be adapted for solid surface-isotropic liquid interface, including colloids (milk) and fog (aerosols)-condensed medium.

Quantum mechanical/molecular mechanical/continuum style solvation model: time-dependent density functional theory.

PubMed

Thellamurege, Nandun M; Cui, Fengchao; Li, Hui

2013-08-28

A combined quantum mechanical/molecular mechanical/continuum (QM/MMpol/C) style method is developed for time-dependent density functional theory (TDDFT, including long-range corrected TDDFT) method, induced dipole polarizable force field, and induced surface charge continuum model. Induced dipoles and induced charges are included in the TDDFT equations to solve for the transition energies, relaxed density, and transition density. Analytic gradient is derived and implemented for geometry optimization and molecular dynamics simulation. QM/MMpol/C style DFT and TDDFT methods are used to study the hydrogen bonding of the photoactive yellow protein chromopore in ground state and excited state.

Convergence of Ground and Excited State Properties of Divacancy Defects in 4H-SiC with Computational Cell Size

DTIC Science & Technology

2018-03-01

computational parameters needs to be established. We used density functional theory to compute defect formation energies of the neutral and charged hh... energies for the 3A to 3E transition (absorption, zero phonon lines, and emission), which is essential for optical initialization and read-out. We...PBE, defect formation energy , charge transition levels, absorption, zero phonon lines, emission 16. SECURITY CLASSIFICATION OF: 17. LIMITATION

Energy Landscape and Transition State of Protein-Protein Association

NASA Astrophysics Data System (ADS)

Alsallaq, Ramzi; Zhou, Huan-Xiang

2006-11-01

Formation of a stereospecific protein complex is favored by specific interactions between two proteins but disfavored by the loss of translational and rotational freedom. Echoing the protein folding process, we have previously proposed a transition state for protein-protein association. Here we clarify the specification of the transition state by working with two toy models for protein association. The models demonstrate that a sharp transition between the bound state with numerous short-range interactions but restricted translation and rotational freedom and the unbound state with at most a small number of interactions but expanded configurational freedom. This transition sets the outer boundary of the bound state as well as the transition state for association. The energy landscape is funnel-like, with the deep well of the bound state surrounded by a broad shallow basin. This formalism of protein-protein association is applied to four protein-protein complexes, and is found to give accurate predictions for the effects of charge mutations and ionic strength on the association rates.

Charge-patterning phase transition on a surface lattice of titratable sites adjacent to an electrolyte solution

NASA Astrophysics Data System (ADS)

Shore, Joel; Thurston, George

We discuss a model for a charge-patterning phase transition on a two-dimensional square lattice of titratable sites, here regarded as protonation sites, placed on a square lattice in a dielectric medium just below the planar interface between this medium and an aqueous salt solution. Within Debye-Huckel theory, the analytical form of the electrostatic repulsion between protonated sites exhibits an approximate inverse cubic power-law decrease beyond short distances. The problem can thus be mapped onto the two-dimensional antiferromagnetic Ising model with this longer-range interaction, which we study with Monte Carlo simulations. As we increase pH, the occupation probability of a site decreases from 1 at low pH to 0 at high pH. For sufficiently-strong interaction strengths, a phase transition occurs as the occupation probability of 1/2 is approached: the charges arrange themselves into a checkerboard pattern. This ordered phase persists over a range of pH until a transition occurs back to a disordered state. This state is the analogue of the Neel state in the antiferromagnetic Ising spin model. More complicated ordered phases are expected for sufficiently strong interactions (with occupation probabilities of 1/4 and 3/4) and if the lattice is triangular rather than square. This work was supported by NIH EY018249 (GMT).

Substitution effects on the absorption spectra of nitrophenolate isomers.

PubMed

Wanko, Marius; Houmøller, Jørgen; Støchkel, Kristian; Suhr Kirketerp, Maj-Britt; Petersen, Michael Åxman; Nielsen, Mogens Brøndsted; Nielsen, Steen Brøndsted; Rubio, Angel

2012-10-05

Charge-transfer excitations highly depend on the electronic coupling between the donor and acceptor groups. Nitrophenolates are simple examples of charge-transfer systems where the degree of coupling differs between ortho, meta and para isomers. Here we report the absorption spectra of the isolated anions in vacuo to avoid the complications of solvent effects. Gas-phase action spectroscopy was done with two different setups, an electrostatic ion storage ring and an accelerator mass spectrometer. The results are interpreted on the basis of CC2 quantum chemical calculations. We identified absorption maxima at 393, 532, and 399 nm for the para, meta, and ortho isomer, respectively, with the charge-transfer transition into the lowest excited singlet state. In the meta isomer, this π-π* transition is strongly redshifted and its oscillator strength reduced, which is related to the pronounced charge-transfer character, as a consequence of the topology of the conjugated π-system. Each isomer's different charge distribution in the ground state leads to a very different solvent shift, which in acetonitrile is bathochromic for the para and ortho, but hypsochromic for the meta isomer.

Phase transitions in local equation-of-state approximation and anomalies of spatial charge profiles in non-uniform plasma

NASA Astrophysics Data System (ADS)

Chigvintsev, A. Yu; Zorina, I. G.; Noginova, L. Yu; Iosilevskiy, I. L.

2018-01-01

Impressive appearance of discontinuities in equilibrium spatial charge profiles in non-uniform Coulomb systems is under discussions in wide number of thermoelectrostatics problems. Such discontinuities are considered as peculiar micro-level manifestation of phase transitions and intrinsic macro-level non-ideality effects in local equation of state (EOS), which should be used for description of non-ideal ionic subsystem in frames of local-density (or “pseudofluid”, or “jellium” etc) approximation. Such discontinuities were discussed already by the authors for electronic subsystems. Special emphasis is made in present paper on the mentioned above non-ideality effects in non-uniform ionic subsystems, such as micro-ions profile within screening “cloud” around macro-ion in complex (dusty, colloid etc) plasmas, equilibrium charge profile in ionic traps or (and) in the neighborhood vicinity of “charged wall” etc). Multiphase EOS for simplified ionic model of classical charged hard spheres on uniformly compressible electrostatic compensating background was constructed and several illustrative examples of discussed discontinuous ionic profiles were calculated.

Collective Dynamics and Strong Pinning near the Onset of Charge Order in La1.48Nd0.4Sr0.12CuO4

NASA Astrophysics Data System (ADS)

Baity, P. G.; Sasagawa, T.; Popović, Dragana

2018-04-01

The dynamics of charge-ordered states is one of the key issues in underdoped cuprate high-temperature superconductors, but static short-range charge-order (CO) domains have been detected in almost all cuprates. We probe the dynamics across the CO (and structural) transition in La1.48Nd0.4Sr0.12CuO4 by measuring nonequilibrium charge transport, or resistance R as the system responds to a change in temperature and to an applied magnetic field. We find evidence for metastable states, collective behavior, and criticality. The collective dynamics in the critical regime indicates strong pinning by disorder. Surprisingly, nonequilibrium effects, such as avalanches in R , are revealed only when the critical region is approached from the charge-ordered phase. Our results on La1.48Nd0.4Sr0.12CuO4 provide the long-sought evidence for the fluctuating order across the CO transition, and also set important constraints on theories of dynamic stripes.

Transition rate diagrams and excitation of titanium in a glow discharge in argon and neon

NASA Astrophysics Data System (ADS)

Weiss, Zdeněk; Steers, Edward B. M.; Pickering, Juliet C.

2018-06-01

Emission spectra of titanium in a Grimm-type glow discharge in argon and neon were studied using the formalism of transition rate diagrams. Ti I spectra in argon and neon discharges are similar, without signs of selective excitation, and populations of Ti I levels exhibit a decreasing trend as function of energy, except for some scatter. A major excitation process of Ti II in argon discharge is charge transfer from argon ions to neutral titanium. In neon discharge, a strong selective excitation was observed of Ti II levels at ≈13.3-13.4 eV relative to the Ti I ground state. It was attributed to charge transfer from doubly charged titanium ions to neutral titanium, while the Ti++ ions are produced by charge transfer and ionization of neutral titanium by neon ions. Cascade excitation is important for Ti II levels up to an energy of ≈13 eV relative to the Ti I ground state, both in argon and neon discharges.

Electrochemical reaction mechanisms under various charge-discharge operating conditions for Li1.2Ni0.13Mn0.54Co0.13O2 in a lithium-ion battery

NASA Astrophysics Data System (ADS)

Konishi, Hiroaki; Hirano, Tatsumi; Takamatsu, Daiko; Gunji, Akira; Feng, Xiaoliang; Furutsuki, Sho; Okumura, Takefumi; Terada, Shohei; Tamura, Kazuhisa

2018-06-01

The potential in each state of charge (SOC) during charging of Li1.2Ni0.13Mn0.54Co0.13O2 is higher than that during discharging. In other words, the potential hysteresis occurs between charging and discharging. Furthermore, the potential in each SOC changes according to the charge-discharge operating conditions, indicating that the charge-discharge reaction mechanism is also affected. To clarify the effect of charge-discharge operating conditions on the electrochemical reaction, Li1.2Ni0.13Mn0.54Co0.13O2 was charged and discharged under various charge-discharge operating ranges, and open-circuit potential (OCP), crystal structure, and oxidation states of the transition metals were evaluated by electrochemical measurement, X-ray diffraction (XRD), and X-ray absorption fine structure (XAFS). These results indicate that OCP, lattice parameters, and oxidation states of the transition metals of Li1.2Ni0.13Mn0.54Co0.13O2 in each SOC are not constant. The XRD results indicate that two phases, namely, LiNi0.33Mn0.33Co0.33O2-like and Li2MnO3-like, exist in Li1.2Ni0.13Mn0.54Co0.13O2. For the LiNi0.33Mn0.33Co0.33O2-like phase, the relationship between OCP, lattice parameters, and oxidation states of the transition metals in each SOC is not affected by the charge-discharge operating conditions, indicating that extraction and insertion of lithium ions for the LiNi0.33Mn0.33Co0.33O2-like phase progresses at almost the same potential. Although the extraction and insertion of lithium ions for the Li2MnO3-like phase progresses at almost the same potential in the low-SOC region, the OCP and lattice parameter in each SOC in the high-SOC region are not constant. Therefore, the extraction of lithium ions from the Li2MnO3-like phase in the high-SOC region causes the potential hysteresis of Li1.2Ni0.13Mn0.54Co0.13O2.

Influence of the quantum dot geometry on p -shell transitions in differently charged quantum dots

NASA Astrophysics Data System (ADS)

Holtkemper, M.; Reiter, D. E.; Kuhn, T.

2018-02-01

Absorption spectra of neutral, negatively, and positively charged semiconductor quantum dots are studied theoretically. We provide an overview of the main energetic structure around the p -shell transitions, including the influence of nearby nominally dark states. Based on the envelope function approximation, we treat the four-band Luttinger theory as well as the direct and short-range exchange Coulomb interactions within a configuration interaction approach. The quantum dot confinement is approximated by an anisotropic harmonic potential. We present a detailed investigation of state mixing and correlations mediated by the individual interactions. Differences and similarities between the differently charged quantum dots are highlighted. Especially large differences between negatively and positively charged quantum dots become evident. We present a visualization of energetic shifts and state mixtures due to changes in size, in-plane asymmetry, and aspect ratio. Thereby we provide a better understanding of the experimentally hard to access question of quantum dot geometry effects. Our findings show a method to determine the in-plane asymmetry from photoluminescence excitation spectra. Furthermore, we supply basic knowledge for tailoring the strength of certain state mixtures or the energetic order of particular excited states via changes of the shape of the quantum dot. Such knowledge builds the basis to find the optimal QD geometry for possible applications and experiments using excited states.

Charge carrier thermalization in organic diodes

PubMed Central

van der Kaap, N. J.; Koster, L. J. A.

2016-01-01

Charge carrier mobilities of organic semiconductors are often characterized using steady-state measurements of space charge limited diodes. These measurements assume that charge carriers are in a steady-state equilibrium. In reality, however, energetically hot carriers are introduces by photo-excitation and injection into highly energetic sites from the electrodes. These carriers perturb the equilibrium density of occupied states, and therefore change the overall charge transport properties. In this paper, we look into the effect of energetically hot carriers on the charge transport in organic semiconductors using steady state kinetic Monte Carlo simulations. For injected hot carriers in a typical organic semiconductor, rapid energetic relaxation occurs in the order of tens of nanoseconds, which is much faster than the typical transit time of a charge carrier throught the device. Furthermore, we investigate the impact of photo-generated carriers on the steady-state mobility. For a typical organic voltaic material, an increase in mobility of a factor of 1.1 is found. Therefore, we conclude that the impact of energetically hot carriers on normal device operation is limited. PMID:26791095

Triple points and phase diagrams in the extended phase space of charged Gauss-Bonnet black holes in AdS space

NASA Astrophysics Data System (ADS)

Wei, Shao-Wen; Liu, Yu-Xiao

2014-08-01

We study the triple points and phase diagrams in the extended phase space of the charged Gauss-Bonnet black holes in d-dimensional anti-de Sitter space, where the cosmological constant appears as a dynamical pressure of the system and its conjugate quantity is the thermodynamic volume of the black holes. Employing the equation of state T=T(v,P), we demonstrate that the information of the phase transition and behavior of the Gibbs free energy are potential encoded in the T-v (T-rh) line with fixed pressure P. We get the phase diagrams for the charged Gauss-Bonnet black holes with different values of the charge Q and dimension d. The result shows that the small/large black hole phase transitions appear for any d, which is reminiscent of the liquid/gas transition of a Van der Waals type. Moreover, the interesting thermodynamic phenomena, i.e., the triple points and the small/intermediate/large black hole phase transitions are observed for d=6 and Q ∈(0.1705,0.1946).

Rare earth substitutional impurities in germanium: A hybrid density functional theory study

NASA Astrophysics Data System (ADS)

Igumbor, E.; Omotoso, E.; Tunhuma, S. M.; Danga, H. T.; Meyer, W. E.

2017-10-01

The Heyd, Scuseria, and Ernzerhof (HSE06) hybrid functional by means of density functional theory has been used to model the electronic and structural properties of rare earth (RE) substitutional impurities in germanium (REGe) . The formation and charge state transition energies for the REGe (RE = Ce, Pr, Er and Eu) were calculated. The energy of formation for the neutral charge state of the REGe lies between -0.14 and 3.13 eV. The formation energy result shows that the Pr dopant in Ge (PrGe) has the lowest formation energy of -0.14 eV, and is most energetically favourable under equilibrium conditions. The REGe induced charge state transition levels within the band gap of Ge. Shallow acceptor levels were induced by both the Eu (EuGe) and Pr (PrGe) dopants in Ge. The CeGe and ErGe exhibited properties of negative-U ordering with effective-U values of -0.85 and -1.07 eV, respectively.

Ionic and Covalent Stabilization of Intermediates and Transition States in Catalysis by Solid Acids

DOE Office of Scientific and Technical Information (OSTI.GOV)

Deshlahra, Prashant; Carr, Robert T.; Iglesia, Enrique

Reactivity descriptors describe catalyst properties that determine the stability of kinetically relevant transition states and adsorbed intermediates. Theoretical descriptors, such as deprotonation energies (DPE), rigorously account for Brønsted acid strength for catalytic solids with known structure. Here, mechanistic interpretations of methanol dehydration turnover rates are used to assess how charge reorganization (covalency) and electrostatic interactions determine DPE and how such interactions are recovered when intermediates and transition states interact with the conjugate anion in W and Mo polyoxometalate (POM) clusters and gaseous mineral acids. Turnover rates are lower and kinetically relevant species are less stable on Mo than W POMmore » clusters with similar acid strength, and such species are more stable on mineral acids than that predicted from W-POM DPE–reactivity trends, indicating that DPE and acid strength are essential but incomplete reactivity descriptors. Born–Haber thermochemical cycles indicate that these differences reflect more effective charge reorganization upon deprotonation of Mo than W POM clusters and the much weaker reorganization in mineral acids. Such covalency is disrupted upon deprotonation but cannot be recovered fully upon formation of ion pairs at transition states. Predictive descriptors of reactivity for general classes of acids thus require separate assessments of the covalent and ionic DPE components. Here, we describe methods to estimate electrostatic interactions, which, taken together with energies derived from density functional theory, give the covalent and ionic energy components of protons, intermediates, and transition states. In doing so, we provide a framework to predict the reactive properties of protons for chemical reactions mediated by ion-pair transition states.« less

Stationary to nonstationary transition in crossed-field devices

DOE Office of Scientific and Technical Information (OSTI.GOV)

Marini, Samuel; Rizzato, Felipe B.; Pakter, Renato

2016-03-15

The previous results based on numerical simulations showed that a cold electron beam injected in a crossed field gap does not reach a time independent stationary state in the space charge limited regime [P. J. Christenson and Y. Y. Lau, Phys. Plasmas 1, 3725 (1994)]. In this work, the effect of finite injection temperature in the transition from stationary to nonstationary states is investigated. A fully kinetic model for the electron flow is derived and used to determine the possible stationary states of the system. It is found that although there is always a stationary solution for any set ofmore » parameters, depending on the injection temperature the electron flow becomes very sensitive to fluctuations and the stationary state is never reached. By investigating the nonlinear dynamics of a characteristic electron, a theory based on a single free parameter is constructed to predict when the transition between stationary and nonstationary states occurs. In agreement with the previous numerical results, the theory indicates that for vanishing temperatures the system never reaches the time independent stationary state in the space charge limited regime. Nevertheless, as the injection temperature is raised it is found a broad range of system parameters for which the stationary state is indeed attained. By properly adjusting the free parameter in the theory, one can be able to describe, to a very good accuracy, when the transition occurs.« less

Charge order-superfluidity transition in a two-dimensional system of hard-core bosons and emerging domain structures

NASA Astrophysics Data System (ADS)

Moskvin, A. S.; Panov, Yu. D.; Rybakov, F. N.; Borisov, A. B.

2017-11-01

We have used high-performance parallel computations by NVIDIA graphics cards applying the method of nonlinear conjugate gradients and Monte Carlo method to observe directly the developing ground state configuration of a two-dimensional hard-core boson system with decrease in temperature, and its evolution with deviation from a half-filling. This has allowed us to explore unconventional features of a charge order—superfluidity phase transition, specifically, formation of an irregular domain structure, emergence of a filamentary superfluid structure that condenses within of the charge-ordered phase domain antiphase boundaries, and formation and evolution of various topological structures.

Deflagration to detonation transition in mechanoactivated mixtures of ammonium perchlorate with aluminum

NASA Astrophysics Data System (ADS)

Shevchenko, A. A.; Dolgoborodov, A. Yu; Kirilenko, V. G.; Brazhnikov, M. A.

2016-11-01

Deflagration-to-detonation transition (DDT) in aluminum-ammonium perchlorate (Al/AP) loose-packed charges (80% porosity) has been studied. The charges were manufactured from preliminary mechanoactivated mixtures. The mixtures placed in steel tubes 10 mm in diameter were ignited by Nichrome wire. It was found that it is possible to distinguish three parts corresponding to different stages of DDT process development. Steady-state detonation velocity reached the level of 2500 m/s at the distance of 90 mm from the ignition point.

Valency configuration of transition metal impurities in ZnO

DOE Office of Scientific and Technical Information (OSTI.GOV)

Petit, Leon; Schulthess, Thomas C; Svane, Axel

2006-01-01

We use the self-interaction corrected local spin-density approximation to investigate the ground state valency configuration of transition metal (TM=Mn, Co) impurities in n- and p-type ZnO. We find that in pure Zn{sub 1-x}TM{sub x}O, the localized TM{sup 2+} configuration is energetically favored over the itinerant d-electron configuration of the local spin density (LSD) picture. Our calculations indicate furthermore that the (+/0) donor level is situated in the ZnO gap. Consequently, for n-type conditions, with the Fermi energy {epsilon}F close to the conduction band minimum, TM remains in the 2+ charge state, while for p-type conditions, with {epsilon}F close to themore » valence band maximum, the 3+ charge state is energetically preferred. In the latter scenario, modeled here by co-doping with N, the additional delocalized d-electron charge transfers into the entire states at the top of the valence band, and hole carriers will only exist, if the N concentration exceeds the TM impurity concentration.« less

Mottness Collapse in 1 T -TaS2 -xSex Transition-Metal Dichalcogenide: An Interplay between Localized and Itinerant Orbitals

NASA Astrophysics Data System (ADS)

Qiao, Shuang; Li, Xintong; Wang, Naizhou; Ruan, Wei; Ye, Cun; Cai, Peng; Hao, Zhenqi; Yao, Hong; Chen, Xianhui; Wu, Jian; Wang, Yayu; Liu, Zheng

2017-10-01

The layered transition-metal dichalcogenide 1 T -TaS2 has been recently found to undergo a Mott-insulator-to-superconductor transition induced by high pressure, charge doping, or isovalent substitution. By combining scanning tunneling microscopy measurements and first-principles calculations, we investigate the atomic scale electronic structure of the 1 T -TaS2 Mott insulator and its evolution to the metallic state upon isovalent substitution of S with Se. We identify two distinct types of orbital textures—one localized and the other extended—and demonstrate that the interplay between them is the key factor that determines the electronic structure. In particular, we show that the continuous evolution of the charge gap visualized by scanning tunneling microscopy is due to the immersion of the localized-orbital-induced Hubbard bands into the extended-orbital-spanned Fermi sea, featuring a unique evolution from a Mott gap to a charge-transfer gap. This new mechanism of Mottness collapse revealed here suggests an interesting route for creating novel electronic states and designing future electronic devices.

Ground-state oxygen holes and the metal–insulator transition in the negative charge-transfer rare-earth nickelates

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bisogni, Valentina; Catalano, Sara; Green, Robert J.

The metal-insulator transitions and the intriguing physical properties of rare-earth perovskite nickelates have attracted considerable attention in recent years. However, a complete understanding of these materials remains elusive. Here, taking a NdNiO 3 thin film as a representative example, we utilize a combination of x-ray absorption (XAS) and resonant inelastic x-ray scattering (RIXS) spectroscopies to resolve important aspects of the complex electronic structure of the rare-earth nickelates. The unusual coexistence of bound and continuum excitations observed in the RIXS spectra provides strong evidence for the abundance of oxygen 2p holes in the ground state of these materials. Using cluster calculationsmore » and Anderson impurity model interpretation, we show that these distinct spectral signatures arise from a Ni 3d 8 configuration along with holes in the oxygen 2p valence band, confirming suggestions that these materials do not obey a “conventional” positive charge-transfer picture, but instead exhibit a negative charge-transfer energy, in line with recent models interpreting the metal to insulator transition in terms of bond disproportionation.« less

Ground-state oxygen holes and the metal–insulator transition in the negative charge-transfer rare-earth nickelates

DOE PAGES

Bisogni, Valentina; Catalano, Sara; Green, Robert J.; ...

2016-10-11

The metal-insulator transitions and the intriguing physical properties of rare-earth perovskite nickelates have attracted considerable attention in recent years. However, a complete understanding of these materials remains elusive. Here, taking a NdNiO 3 thin film as a representative example, we utilize a combination of x-ray absorption (XAS) and resonant inelastic x-ray scattering (RIXS) spectroscopies to resolve important aspects of the complex electronic structure of the rare-earth nickelates. The unusual coexistence of bound and continuum excitations observed in the RIXS spectra provides strong evidence for the abundance of oxygen 2p holes in the ground state of these materials. Using cluster calculationsmore » and Anderson impurity model interpretation, we show that these distinct spectral signatures arise from a Ni 3d 8 configuration along with holes in the oxygen 2p valence band, confirming suggestions that these materials do not obey a “conventional” positive charge-transfer picture, but instead exhibit a negative charge-transfer energy, in line with recent models interpreting the metal to insulator transition in terms of bond disproportionation.« less

Ionic charge state measurements during He(+)-rich solar particle events

NASA Technical Reports Server (NTRS)

Hovestadt, D.; Klecker, B.; Scholer, M.; Gloeckler, G.

1984-01-01

Ionic charge state measurements of carbon, oxygen, and iron in He(+)-rich energetic particle events are presented. The data have been obtained with the Max-Planck-Institut/University of Maryland sensor system on the ISEE 3 spacecraft. The ionic charge states cannot be explained in terms of a model in which the coronal temperature determines a charge equilibrium which is subsequently frozen-in nor in terms of charge exchange during transition through coronal matter after acceleration. It is concluded that the acceleration and probably also the injection process is biased against particles with high mass-to-charge ratios. The plasma injected into the acceleration process must consist of material of cold (not greater than 8.5 x 10 to the 4th K) as well as hot (2.5 x 10 to the 6th K) origin. The cold material must be more abundant than the hot material.

Charge transfer transitions in optical spectra of NicMg1-cO oxides

NASA Astrophysics Data System (ADS)

Churmanov, V. N.; Sokolov, V. I.; Pustovarov, V. A.; Gruzdev, N. B.; Uimin, M. A.; Byzov, I. V.; Druzhinin, A. V.; Korolyov, A. V.; Kim, G. A.; Zatsepin, A. F.; Kuznetsova, J. A.

2017-04-01

Radiative recombination with charge transfer was observed in NicMg1-cO (c = 0.008) oxides over the 8-300 K temperature range. This recombination occurs as a result of strong hybridization of the Ni2+ ion 3d-states and the band states. The charge transfer radiation excitation spectrum shows vibrational LO repeats of two exciton lines having charge transfer energy intervals of about 35 meV. The NiO nanocrystal absorption spectrum shows two weak peaks with energies of 3.510 and 3.543 eV, which are highly dependent on temperature. They are interpreted as charge transfer excitons at the edge of NiO fundamental absorption. The distance between the charge transfer exciton lines in the NicMg1-cO oxide spectra are caused by spin-orbit splitting of the valence band peak that was formed by the p-states of the oxygen ion.

Anisotropy-driven transition from the Moore-Read state to quantum Hall stripes

NASA Astrophysics Data System (ADS)

Zhu, Zheng; Sodemann, Inti; Sheng, D. N.; Fu, Liang

2017-05-01

We investigate the nature of the quantum Hall liquid in a half-filled second Landau level (n =1 ) as a function of band mass anisotropy using numerical exact diagonalization and density matrix renormalization group methods. We find increasing the mass anisotropy induces a quantum phase transition from the Moore-Read state to a charge density wave state. By analyzing the energy spectrum, guiding center structure factors, and by adding weak pinning potentials, we show that this charge density wave is a unidirectional quantum Hall stripe, which has a periodicity of a few magnetic lengths and survives in the thermodynamic limit. We find smooth profiles for the guiding center occupation function that reveal the strong coupling nature of the array of chiral Luttinger liquids residing at the stripe edges.

Nonlinear ion dynamics in Hall thruster plasma source by ion transit-time instability

NASA Astrophysics Data System (ADS)

Lim, Youbong; Choe, Wonho; Mazouffre, Stéphane; Park, Jae Sun; Kim, Holak; Seon, Jongho; Garrigues, L.

2017-03-01

High-energy tail formation in an ion energy distribution function (IEDF) is explained in a Hall thruster plasma with the stationary crossed electric and magnetic fields whose discharge current is oscillated at the ion transit-time scale with a frequency of 360 kHz. Among ions in different charge states, singly charged Xe ions (Xe+) have an IEDF that is significantly broadened and shifted toward the high-energy side, which contributes to tail formation in the entire IEDF. Analytical and numerical investigations confirm that the IEDF tail is due to nonlinear ion dynamics in the ion transit-time oscillation.

A charge-density-wave oscillator based on an integrated tantalum disulfide-boron nitride-graphene device operating at room temperature.

PubMed

Liu, Guanxiong; Debnath, Bishwajit; Pope, Timothy R; Salguero, Tina T; Lake, Roger K; Balandin, Alexander A

2016-10-01

The charge-density-wave (CDW) phase is a macroscopic quantum state consisting of a periodic modulation of the electronic charge density accompanied by a periodic distortion of the atomic lattice in quasi-1D or layered 2D metallic crystals. Several layered transition metal dichalcogenides, including 1T-TaSe 2 , 1T-TaS 2 and 1T-TiSe 2 exhibit unusually high transition temperatures to different CDW symmetry-reducing phases. These transitions can be affected by the environmental conditions, film thickness and applied electric bias. However, device applications of these intriguing systems at room temperature or their integration with other 2D materials have not been explored. Here, we demonstrate room-temperature current switching driven by a voltage-controlled phase transition between CDW states in films of 1T-TaS 2 less than 10 nm thick. We exploit the transition between the nearly commensurate and the incommensurate CDW phases, which has a transition temperature of 350 K and gives an abrupt change in current accompanied by hysteresis. An integrated graphene transistor provides a voltage-tunable, matched, low-resistance load enabling precise voltage control of the circuit. The 1T-TaS 2 film is capped with hexagonal boron nitride to provide protection from oxidation. The integration of these three disparate 2D materials in a way that exploits the unique properties of each yields a simple, miniaturized, voltage-controlled oscillator suitable for a variety of practical applications.

Experimental and computational studies on the electronic excited states of nitrobenzene

NASA Astrophysics Data System (ADS)

Krishnakumar, Sunanda; Das, Asim Kumar; Singh, Param Jeet; Shastri, Aparna; Rajasekhar, B. N.

2016-11-01

The gas phase electronic absorption spectrum of nitrobenzene (C6H5NO2) in the 4.5-11.2 eV region is recorded using synchrotron radiation with a view to comprehend the nature of the excited states. Electronic excited states of nitrobenzene are mainly classified as local excitations within the benzene ring or nitro group and charge transfer excitations between the benzene and nitro group, with some transitions showing percentage from both. The nature of molecular orbitals, their orderings and energies are obtained from density functional theory calculations which help in assigning partially assigned/unassigned features in earlier photoelectron spectroscopy studies. Optimized geometry of ionic nitrobenzene predicts redistribution of charge density in the benzene ring rather than the nitro group resulting in stabilization of the benzene ring π orbitals in comparison to the neutral molecule. Time dependent density functional theory computations are found to describe the experimental spectra well with respect to energies, relative intensities and nature of the observed transitions in terms of valence, Rydberg or charge transfer type. New insights into the interpretation of 1B2u←1A1g and 1B1u←1A1g shifted benzene transitions in light of the present computational calculations are presented. The first few members of the ns, np and nd type Rydberg series in nitrobenzene, converging to the first six ionization potentials, identified in the spectra as weak but sharp peaks are reported for the first time. In general, transitions to the lowest three unoccupied molecular orbitals 4b1, 3a2 and 5b1 are valence or charge transfer in nature, while excitations to higher orbitals are predominantly Rydberg in nature. This work presents a consolidated experimental study and theoretical interpretation of the electronic absorption spectrum of nitrobenzene.

Equation of State of Structured Matter at Finite Temperature

NASA Astrophysics Data System (ADS)

Maruyama, T.; Yasutake, N.; Tatsumi, T.

We investigate the properties of nuclear matter at the first-order phase transitions such as liquid-gas phase transition and hadron-quark phase transition. As a general feature of the first-order phase transitions of matter consisting of many species of charged particles, there appears a mixed phases with geometrical structures called ``pasta'' due to the balance of the Coulomb repulsion and the surface tension between two phases [G.~D.~Ravenhall, C.~J.~Pethick and J.~R.~Wilson, Phys. Rev. Lett. 50 (1983), 2066. M.~Hashimoto, H.~Seki and M.~Yamada, Prog. Theor. Phys. 71 (1984), 320.] The equation of state (EOS) of mixed phase is different from the one obtained by a bulk application of the Gibbs conditions or by the Maxwell construction due to the effects of the non-uniform structure. We show that the charge screening and strong surface tension make the EOS close to that of the Maxwell construction. The thermal effects are elucidated as well as the above finite-size effects.

Ab initio studies of isolated hydrogen vacancies in graphane

NASA Astrophysics Data System (ADS)

Mapasha, R. E.; Molepo, M. P.; Chetty, N.

2016-05-01

We present a density functional study of various hydrogen vacancies located on a single hexagonal ring of graphane (fully hydrogenated graphene) considering the effects of charge states and the position of the Fermi level. We find that uncharged vacancies that lead to a carbon sublattice balance are energetically favorable and are wide band gap systems just like pristine graphane. Vacancies that do create a sublattice imbalance introduce spin polarized states into the band gap, and exhibit a half-metallic behavior with a magnetic moment of 1.00 μB per vacancy. The results show the possibility of using vacancies in graphane for novel spin-based applications. When charging such vacancy configurations, the deep donor (+1/0) and deep acceptor (0/-1) transition levels within the band gap are noted. We also note a half-metallic to metallic transition and a significant reduction of the induced magnetic moment due to both negative and positive charge doping.

Simulating the thermodynamics of charging in weak polyelectrolytes: the Debye-Hückel limit

NASA Astrophysics Data System (ADS)

Rathee, Vikramjit S.; Sikora, Benjamin J.; Sidky, Hythem; Whitmer, Jonathan K.

2018-01-01

The coil-globule transition in weak (annealed) polyelectrolytes involves a subtle balance of pH, charge strength, and solvation forces. In this work, we utilize a coarse-grained hybrid grand-canonical Monte Carlo and molecular dynamics approach to explore the swelling behavior of weak linear and star polyelectrolytes under different ionic screening conditions and pH. Importantly, we are able to quantify topology-dependent effects in charging which arise at the core of star polymers. Our results are suggestive of suppression of charging in star weak polyelectrolytes in comparison to linear weak polyelectrolytes. Furthermore, we characterize the coil-globule transition in linear and star weak polyelectrolyte through expanded ensemble density-of-states simulations which suggest a change from a first order to second order phase transition moving from linear to star polyelectrolytes. Lastly, we characterize the inhomogeneous charging across the weak star polyelectrolyte through observed shifts in {{Δ }}{{{pK}}}{{o}}, and compare with experimental work. We discuss these results in relation to surfaces functionalized by weak polyelectrolyte brushes and weak polyelectrolyte-based drug delivery applications.

Novel Electronic Behavior Driving NdNiO 3 Metal-Insulator Transition

DOE Office of Scientific and Technical Information (OSTI.GOV)

Upton, M. H.; Choi, Yongseong; Park, Hyowon

2015-07-01

We present evidence that the metal-insulator transition (MIT) in a tensile-strained NdNiO3 (NNO) film is facilitated by a redistribution of electronic density and that it neither requires Ni charge disproportionation nor a symmetry change [U. Staub et al., Phys. Rev. Lett. 88, 126402 (2002); R. Jaramillo et al., Nat. Phys. 10, 304 (2014)]. Given that epitaxial tensile strain in thin NNO films induces preferential occupancy of the e(g) d(x2-y2) orbital we propose that the larger transfer integral of this orbital state with the O 2p orbital state mediates a redistribution of electronic density from the Ni atom. A decrease inmore » the Ni d(x2-y2) orbital occupation is directly observed by resonant inelastic x-ray scattering below the MIT temperature. Furthermore, an increase in the Nd charge occupancy is measured by x-ray absorption at the Nd L-3 edge. Both spin-orbit coupling and crystal field effects combine to break the degeneracy of the Nd 5d states, shifting the energy of the Nd e(g) d(x2-y2) orbit towards the Fermi level, allowing the A site to become an active acceptor during the MIT. This work identifies the relocation of electrons from the Ni 3d to the Nd 5d orbitals across the MIT. We propose that the insulating gap opens between the Ni 3d and O 2p states, resulting from Ni 3d electron localization. The transition seems to be neither a purely Mott-Hubbard transition nor a simple charge transfer.« less

Transition from the diamagnetic insulator to ferromagnetic metal in La1-xSrxCoO3

NASA Astrophysics Data System (ADS)

Knížek, Karel; Jirák, Zdeněk; Hejtmánek, Jiří; Novák, Pavel

2010-05-01

We have analyzed, using the theoretical GGA+U calculations, different configurations of spin states (low-spin, LS; intermediate-spin, IS and high-spin, HS Co) and proposed a model that accounts for magnetic and electric transport properties of perovskite cobaltites upon doping by charge carriers. In particular, it appears that the compositional transition from the diamagnetic LS phase of LaCoO3 to the ferromagnetic metallic IS phase in La1-xSrxCoO3 ( x>0.2) involves the same mechanisms as the high-temperature transition in pure LaCoO3. The process occurs gradually via a phase-separated state, where metallic IS domains stabilized through a charge transfer between Co and Co neighbors coexist with the Co poor regions in the LS ground state (or at higher temperatures, in mixed LS/HS state). This phase separation vanishes when doping in La1-xSrxCoO3 reaches x˜0.2, and a uniform IS phase, analogous to that in pure LaCoO3 in the high-temperature limit, is established.

Nonradiative Transitions in Media of Different Polarities and Their Modeling for 12'-Apo-β-Caroten-12'-Al and 8'-Apo-β-Caroten-8'-Al

NASA Astrophysics Data System (ADS)

Pavlovich, V. S.

2014-09-01

The theory of nonradiative transitions, based on the model of orientational broadening of electronic levels, is used to interpret known data on the effect of the polarity of the medium and temperature on the lifetime of the S 1( A {/g -}) state for 12'-apo-β-caroten-12'-al and 8'-apo-β-caroten-8'-al. The effect of promoting vibrations on the rate constant for nonradiative transitions is considered. The results make it possible to hypothesize that the internal electric field created by the environment strongly perturbs the pigment molecules. Consequently, in the excited S 1( A {/g -}) state, both pigments exist as different conformers I and II. Their structures differ by a 180° rotation of the cyclohexene ring relative to the polyene chain. Conformer II predominates in polar media, and is found in an intramolecular charge-transfer state S 1( A {/g -}/ ICT). In addition, as a result of fluctuations in the internal electric field, it can also be found in a charge-separated state S 1( A {/g -}/ CS).

Long-range correction for tight-binding TD-DFT

DOE Office of Scientific and Technical Information (OSTI.GOV)

Humeniuk, Alexander; Mitrić, Roland, E-mail: roland.mitric@uni-wuerzburg.de

2015-10-07

We present two improvements to the tight-binding approximation of time-dependent density functional theory (TD-DFTB): First, we add an exact Hartree-Fock exchange term, which is switched on at large distances, to the ground state Hamiltonian and similarly to the coupling matrix that enters the linear response equations for the calculation of excited electronic states. We show that the excitation energies of charge transfer states are improved relative to the standard approach without the long-range correction by testing the method on a set of molecules from the database in Peach et al. [J. Chem. Phys. 128, 044118 (2008)] which are known tomore » exhibit problematic charge transfer states. The degree of spatial overlap between occupied and virtual orbitals indicates where TD-DFTB and long-range corrected TD-DFTB (lc-TD-DFTB) can be expected to produce large errors. Second, we improve the calculation of oscillator strengths. The transition dipoles are obtained from Slater Koster files for the dipole matrix elements between valence orbitals. In particular, excitations localized on a single atom, which appear dark when using Mulliken transition charges, acquire a more realistic oscillator strength in this way. These extensions pave the way for using lc-TD-DFTB to describe the electronic structure of large chromophoric polymers, where uncorrected TD-DFTB fails to describe the high degree of conjugation and produces spurious low-lying charge transfer states.« less

Photocarrier generation from interlayer charge-transfer transitions in WS2-graphene heterostructures

PubMed Central

Yuan, Long; Chung, Ting-Fung; Kuc, Agnieszka; Wan, Yan; Xu, Yang; Chen, Yong P.; Heine, Thomas; Huang, Libai

2018-01-01

Efficient interfacial carrier generation in van der Waals heterostructures is critical for their electronic and optoelectronic applications. We demonstrate broadband photocarrier generation in WS2-graphene heterostructures by imaging interlayer coupling–dependent charge generation using ultrafast transient absorption microscopy. Interlayer charge-transfer (CT) transitions and hot carrier injection from graphene allow carrier generation by excitation as low as 0.8 eV below the WS2 bandgap. The experimentally determined interlayer CT transition energies are consistent with those predicted from the first-principles band structure calculation. CT interactions also lead to additional carrier generation in the visible spectral range in the heterostructures compared to that in the single-layer WS2 alone. The lifetime of the charge-separated states is measured to be ~1 ps. These results suggest that interlayer interactions make graphene–two-dimensional semiconductor heterostructures very attractive for photovoltaic and photodetector applications because of the combined benefits of high carrier mobility and enhanced broadband photocarrier generation. PMID:29423439

Role of Entropy and Structural Parameters in the Spin State Transition of LaCoO3

NASA Astrophysics Data System (ADS)

Chakrabarti, Bismayan; Birol, Turan; Haule, Kristjan

The spin state transition in LaCoO3 has eluded description for decades despite concerted theoretical and experimental effort. In this study, we approach this problem using fully charge consistent Density Functional Theory + Dynamical Mean Field Theory (DFT+DMFT). We show, from first principles, that LaCoO3 cannot be described by a single, pure spin state at any temperature, but instead shows a gradual change in the population of higher spin multiples as temperature is increased. We explicitly elucidate the critical role of the lattice expansion and oxygen octahedral rotations in the spin state transition. We also show that the spin state transition and the metal-insulator transition in the compound occur at different temperatures. In addition, our results shed light on the importance of electronic entropy, which has so far been ignored in all first principles studies of this material.

Phase diagram of the underdoped cuprates at high magnetic field

NASA Astrophysics Data System (ADS)

Chakraborty, Debmalya; Morice, Corentin; Pépin, Catherine

2018-06-01

The experimentally measured phase diagram of cuprate superconductors in the temperature-applied magnetic field plane illuminates key issues in understanding the physics of these materials. At low temperature, the superconducting state gives way to a long-range charge order with increasing magnetic field; both the orders coexist in a small intermediate region. The charge order transition is strikingly insensitive to temperature and quickly reaches a transition temperature close to the zero-field superconducting Tc. We argue that such a transition along with the presence of the coexisting phase is difficult to obtain in a weak coupling competing orders formalism. We demonstrate that for some range of parameters there is an enlarged symmetry of the strongly coupled charge and superconducting orders in the system depending on their relative masses and the coupling strength of the two orders. We establish that this sharp switch from the superconducting phase to the charge order phase can be understood in the framework of a composite SU(2) order parameter comprising the charge and superconducting orders. Finally, we illustrate that there is a possibility of the coexisting phase of the competing charge and superconducting orders only when the SU(2) symmetry between them is weakly broken due to biquadratic terms in the free energy. The relation of this sharp transition to the proximity to the pseudogap quantum critical doping is also discussed.

Charge-transfer modified embedded atom method dynamic charge potential for Li-Co-O system

NASA Astrophysics Data System (ADS)

Kong, Fantai; Longo, Roberto C.; Liang, Chaoping; Nie, Yifan; Zheng, Yongping; Zhang, Chenxi; Cho, Kyeongjae

2017-11-01

To overcome the limitation of conventional fixed charge potential methods for the study of Li-ion battery cathode materials, a dynamic charge potential method, charge-transfer modified embedded atom method (CT-MEAM), has been developed and applied to the Li-Co-O ternary system. The accuracy of the potential has been tested and validated by reproducing a variety of structural and electrochemical properties of LiCoO2. A detailed analysis on the local charge distribution confirmed the capability of this potential for dynamic charge modeling. The transferability of the potential is also demonstrated by its reliability in describing Li-rich Li2CoO2 and Li-deficient LiCo2O4 compounds, including their phase stability, equilibrium volume, charge states and cathode voltages. These results demonstrate that the CT-MEAM dynamic charge potential could help to overcome the challenge of modeling complex ternary transition metal oxides. This work can promote molecular dynamics studies of Li ion cathode materials and other important transition metal oxides systems that involve complex electrochemical and catalytic reactions.

Charge-transfer modified embedded atom method dynamic charge potential for Li-Co-O system.

PubMed

Kong, Fantai; Longo, Roberto C; Liang, Chaoping; Nie, Yifan; Zheng, Yongping; Zhang, Chenxi; Cho, Kyeongjae

2017-11-29

To overcome the limitation of conventional fixed charge potential methods for the study of Li-ion battery cathode materials, a dynamic charge potential method, charge-transfer modified embedded atom method (CT-MEAM), has been developed and applied to the Li-Co-O ternary system. The accuracy of the potential has been tested and validated by reproducing a variety of structural and electrochemical properties of LiCoO 2 . A detailed analysis on the local charge distribution confirmed the capability of this potential for dynamic charge modeling. The transferability of the potential is also demonstrated by its reliability in describing Li-rich Li 2 CoO 2 and Li-deficient LiCo 2 O 4 compounds, including their phase stability, equilibrium volume, charge states and cathode voltages. These results demonstrate that the CT-MEAM dynamic charge potential could help to overcome the challenge of modeling complex ternary transition metal oxides. This work can promote molecular dynamics studies of Li ion cathode materials and other important transition metal oxides systems that involve complex electrochemical and catalytic reactions.

Models of charge pair generation in organic solar cells.

PubMed

Few, Sheridan; Frost, Jarvist M; Nelson, Jenny

2015-01-28

Efficient charge pair generation is observed in many organic photovoltaic (OPV) heterojunctions, despite nominal electron-hole binding energies which greatly exceed the average thermal energy. Empirically, the efficiency of this process appears to be related to the choice of donor and acceptor materials, the resulting sequence of excited state energy levels and the structure of the interface. In order to establish a suitable physical model for the process, a range of different theoretical studies have addressed the nature and energies of the interfacial states, the energetic profile close to the heterojunction and the dynamics of excited state transitions. In this paper, we review recent developments underpinning the theory of charge pair generation and phenomena, focussing on electronic structure calculations, electrostatic models and approaches to excited state dynamics. We discuss the remaining challenges in achieving a predictive approach to charge generation efficiency.

Point-Defect Nature of the Ultraviolet Absorption Band in AlN

NASA Astrophysics Data System (ADS)

Alden, D.; Harris, J. S.; Bryan, Z.; Baker, J. N.; Reddy, P.; Mita, S.; Callsen, G.; Hoffmann, A.; Irving, D. L.; Collazo, R.; Sitar, Z.

2018-05-01

We present an approach where point defects and defect complexes are identified using power-dependent photoluminescence excitation spectroscopy, impurity data from SIMS, and density-functional-theory (DFT)-based calculations accounting for the total charge balance in the crystal. Employing the capabilities of such an experimental computational approach, in this work, the ultraviolet-C absorption band at 4.7 eV, as well as the 2.7- and 3.9-eV luminescence bands in AlN single crystals grown via physical vapor transport (PVT) are studied in detail. Photoluminescence excitation spectroscopy measurements demonstrate the relationship between the defect luminescent bands centered at 3.9 and 2.7 eV to the commonly observed absorption band centered at 4.7 eV. Accordingly, the thermodynamic transition energy for the absorption band at 4.7 eV and the luminescence band at 3.9 eV is estimated at 4.2 eV, in agreement with the thermodynamic transition energy for the CN- point defect. Finally, the 2.7-eV PL band is the result of a donor-acceptor pair transition between the VN and CN point defects since nitrogen vacancies are predicted to be present in the crystal in concentrations similar to carbon-employing charge-balance-constrained DFT calculations. Power-dependent photoluminescence measurements reveal the presence of the deep donor state with a thermodynamic transition energy of 5.0 eV, which we hypothesize to be nitrogen vacancies in agreement with predictions based on theory. The charge state, concentration, and type of impurities in the crystal are calculated considering a fixed amount of impurities and using a DFT-based defect solver, which considers their respective formation energies and the total charge balance in the crystal. The presented results show that nitrogen vacancies are the most likely candidate for the deep donor state involved in the donor-acceptor pair transition with peak emission at 2.7 eV for the conditions relevant to PVT growth.

Zn vacancy-donor impurity complexes in ZnO

NASA Astrophysics Data System (ADS)

Frodason, Y. K.; Johansen, K. M.; Bjørheim, T. S.; Svensson, B. G.; Alkauskas, A.

2018-03-01

Results from hybrid density functional theory calculations on the thermodynamic stability and optical properties of the Zn vacancy (VZn) complexed with common donor impurities in ZnO are reported. Complexing VZn with donors successively removes its charge-state transition levels in the band gap, starting from the most negative one. Interestingly, the presence of a donor leads only to modest shifts in the positions of the VZn charge-state transition levels, the sign and magnitude of which can be interpreted from a polaron energetics model by taking hole-donor repulsion into account. By employing a one-dimensional configuration coordinate model, luminescence lineshapes and positions were calculated. Due to the aforementioned effects, the isolated VZn gradually changes from a mainly nonradiative defect with transitions in the infrared region in n -type material, to a radiative one with broad emission in the visible range when complexed with shallow donors.

Critical behavior of the extended Hubbard model with bond dimerization

NASA Astrophysics Data System (ADS)

Ejima, Satoshi; Lange, Florian; Essler, Fabian H. L.; Fehske, Holger

2018-05-01

Exploiting the matrix-product-state based density-matrix renormalization group (DMRG) technique we study the one-dimensional extended (U-V) Hubbard model with explicit bond dimerization in the half-filled band sector. In particular we investigate the nature of the quantum phase transition, taking place with growing ratio V / U between the symmetry-protected-topological and charge-density-wave insulating states. The (weak-coupling) critical line of continuous Ising transitions with central charge c = 1 / 2 terminates at a tricritical point belonging to the universality class of the dilute Ising model with c = 7 / 10 . We demonstrate that our DMRG data perfectly match with (tricritical) Ising exponents, e.g., for the order parameter β = 1 / 8 (1/24) and correlation length ν = 1 (5/9). Beyond the tricritical Ising point, in the strong-coupling regime, the quantum phase transition becomes first order.

Impact of the Valence Charge of Transition Metals on the Cobalt- and Rhodium-Catalyzed Synthesis of Indenamines, Indenols, and Isoquinolinium Salts: A Catalytic Cycle Involving MIII/MV [M = Co, Rh] for [4+2] Annulation.

PubMed

Chiou, Mong-Feng; Jayakumar, Jayachandran; Cheng, Chien-Hong; Chuang, Shih-Ching

2018-06-13

Reaction mechanisms for the synthesis of indenamines, indenols, and isoquinolinium salts through cobalt- and rhodium-catalysis were investigated using density functional theory calculations. We found that the valence charge of transition metals dramatically influences the reaction pathways. Catalytic reactions involving lower-oxidation-state transition metals (M I /M III , M = Co and Rh) generally favor a [3+2] cyclization pathway, whereas those involving higher oxidation states (M III /M V ) proceed through a [4+2] cyclization pathway. A catalytic cycle with novel M III /M V as a crucial species was successfully revealed for isoquinolinium salts synthesis, which highly valent M V was not only encountered in the [RhCp*]-catalysis but also in the [CoCp*]-catalysis.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cadiz, Fabian, E-mail: cadiz@insa-toulouse.fr; Tricard, Simon; Gay, Maxime

Developments in optoelectronics and spin-optronics based on transition metal dichalcogenide monolayers (MLs) need materials with efficient optical emission and well-defined transition energies. In as-exfoliated MoS{sub 2} MLs, the photoluminescence (PL) spectra even at low temperature consist typically of broad, overlapping contributions from neutral, charged excitons (trions) and localized states. Here, we show that in superacid treated MoS{sub 2} MLs, the PL intensity increases by up to 60 times at room temperature. The neutral and charged exciton transitions are spectrally well separated in PL and reflectivity at T = 4 K, with linewidth for the neutral exciton of 15 meV, but both transitions have similarmore » intensities compared to the ones in as-exfoliated MLs at the same temperature. Time resolved experiments uncover picoseconds recombination dynamics analyzed separately for charged and neutral exciton emissions. Using the chiral interband selection rules, we demonstrate optically induced valley polarization for both complexes and valley coherence for only the neutral exciton.« less

Photofunctional triplet excited states of cyclometalated Ir(III) complexes: beyond electroluminescence.

PubMed

You, Youngmin; Nam, Wonwoo

2012-11-07

The development of cyclometalated Ir(III) complexes has enabled important breakthroughs in electroluminescence because such complexes permit the efficient population of triplet excited states that give rise to luminescent transitions. The triplet states of Ir(III) complexes are advantageous over those of other transition metal complexes in that their electronic transitions and charge-transfer characteristics are tunable over wide ranges. These favorable properties suggest that Ir(III) complexes have significant potential in a variety of photofunctions other than electroluminescence. In this critical review, we describe recent photonic applications of novel Ir(III) complexes. Ir(III) complexes have been shown to affect the exciton statistics in the active layers of organic photovoltaic cells, thereby improving the photon-to-current conversion efficiencies. Nonlinear optical applications that take advantage of the strong charge-transfer properties of triplet transitions are also discussed. The tunability of the electrochemical potentials facilitates the development of efficient photocatalysis in the context of water photolysis or organic syntheses. The photoredox reactivities of Ir(III) complexes have been employed in studies of charge migration along DNA chains. The photoinduced cytotoxicity of Ir(III) complexes on live cells suggests that the complexes may be useful in photodynamic therapy. Potential biological applications of the complexes include phosphorescence labeling and sensing. Intriguing platforms based on cyclometalated Ir(III) complexes potentially provide novel protein tagging and ratiometric detection. We envision that future research into the photofunctionality of Ir(III) complexes will provide important breakthroughs in a variety of photonic applications.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, Yan; Sun, Zhao; Cai, Jia -Wei

Here, the mixed-valent Pbmore » $${}_{3}$$Rh $${}_{7}$$O$${}_{15}$$ undergoes a Verwey-type transition at $${T}_{{\\rm{v}}}\\approx 180$$ K, below which the development of Rh$${}^{3+}$$ /Rh$${}^{4+}$$ charge order induces an abrupt conductor-to-insulator transition in resistivity. Here we investigate the effect of pressure on the Verwey-type transition of Pb$${}_{3}$$Rh$${}_{7}$$O$${}_{15}$$ by measuring its electrical resistivity under hydrostatic pressures up to 8 GPa with a cubic anvil cell apparatus. We find that the application of high pressure can suppress the Verwey-type transition around 3 GPa, above which a metallic state is realized at temperatures below ~70 K, suggesting the melting of charge order by pressure. Interestingly, the low-temperature metallic region shrinks gradually upon further increasing pressure and disappears completely at P > 7 GPa, which indicates that the charge carriers in Pb$${}_{3}$$Rh$${}_{7}$$O$${}_{15}$$ undergo a reentrant localization under higher pressures. We have constructed a temperature-pressure phase diagram for Pb$${}_{3}$$Rh$${}_{7}$$O$${}_{15}$$ and compared to that of Fe$${}_{3}$$O$${}_{4}$$, showing an archetype Verwey transition.« less

Structural Variations in β-(BDA-TTP)2FeCl4 at Low Temperature and under Pressure: Charge-Ordered State with a Two-Fold Crystal Structure

NASA Astrophysics Data System (ADS)

Sasamori, Kota; Takahashi, Kazuyuki; Kodama, Takeshi; Fujita, Wataru; Kikuchi, Koichi; Yamada, Jun-ichi

2013-05-01

The pressure-induced organic superconductor β-(BDA-TTP)2FeCl4 [BDA-TTP = 2,5-bis(1,3-dithian-2-ylidene)-1,3,4,6-tetrathiapentalene], which shows a metal--insulator (MI) transition at TMI = 113 K under ambient pressure, has been found by X-ray study to have a two-fold crystal structure along the c-axis in the insulating state at 10 K. In the donor layer, there are four independent BDA-TTP molecules, which are divided into two charge-poor ones and two charge-rich ones on the basis of the folding dihedral angles around the intramolecular sulfur-to-sulfur axes of two outer dithiane rings in BDA-TTP. The charge separation leads to the formation of two types of dimers: a dimer consisting of two charge-poor donors and a dimer consisting of two charge-rich ones. The tight-binding band calculation revealed a band gap of 5.3 meV in the energy dispersion. The MI transition can be therefore accounted for by the charge separation. In addition, we investigated the crystal and electronic structures of β-(BDA-TTP)2FeCl4 at different pressures up to 21 kbar, and found that the application of pressures causes variations in both the conformation of donor molecule and the donor arrangement, which are responsible for almost uniform interaction in the donor stacking and for an increase in bandwidth (W). As a result, the suppression of MI transition and subsequent occurrence of superconductivity in β-(BDA-TTP)2FeCl4 would be observed with increasing pressure.

Signature of chaos in the 4 f -core-excited states for highly-charged tungsten ions

NASA Astrophysics Data System (ADS)

Safronova, Ulyana; Safronova, Alla

2014-05-01

We evaluate radiative and autoionizing transition rates in highly charged W ions in search for the signature of chaos. In particularly, previously published results for Ag-like W27+, Tm-like W5+, and Yb-like W4+ ions as well as newly obtained for I-like W21+, Xe-like W20+, Cs-like W19+, and La-like W17+ ions (with ground configuration [Kr] 4d10 4fk with k = 7, 8, 9, and 11, respectively) are considered that were calculated using the multiconfiguration relativistic Hebrew University Lawrence Livermore Atomic Code (HULLAC code) and the Hartree-Fock-Relativistic method (COWAN code). The main emphasis was on verification of Gaussian statistics of rates as a function of transition energy. There was no evidence of such statistics for above mentioned previously published results as well as for the transitions between the excited and autoionizing states for newly calculated results. However, we did find the Gaussian profile for the transitions between excited states such as the [Kr] 4d10 4fk - [Kr] 4d10 4f k - 1 5 d transitions , for newly calculated W ions. This work is supported in part by DOE under NNSA Cooperative Agreement DE-NA0001984.

Superconductor to Mott insulator transition in YBa2Cu3O7/LaCaMnO3 heterostructures.

PubMed

Gray, B A; Middey, S; Conti, G; Gray, A X; Kuo, C-T; Kaiser, A M; Ueda, S; Kobayashi, K; Meyers, D; Kareev, M; Tung, I C; Liu, Jian; Fadley, C S; Chakhalian, J; Freeland, J W

2016-09-15

The superconductor-to-insulator transition (SIT) induced by means such as external magnetic fields, disorder or spatial confinement is a vivid illustration of a quantum phase transition dramatically affecting the superconducting order parameter. In pursuit of a new realization of the SIT by interfacial charge transfer, we developed extremely thin superlattices composed of high Tc superconductor YBa2Cu3O7 (YBCO) and colossal magnetoresistance ferromagnet La0.67Ca0.33MnO3 (LCMO). By using linearly polarized resonant X-ray absorption spectroscopy and magnetic circular dichroism, combined with hard X-ray photoelectron spectroscopy, we derived a complete picture of the interfacial carrier doping in cuprate and manganite atomic layers, leading to the transition from superconducting to an unusual Mott insulating state emerging with the increase of LCMO layer thickness. In addition, contrary to the common perception that only transition metal ions may respond to the charge transfer process, we found that charge is also actively compensated by rare-earth and alkaline-earth metal ions of the interface. Such deterministic control of Tc by pure electronic doping without any hindering effects of chemical substitution is another promising route to disentangle the role of disorder on the pseudo-gap and charge density wave phases of underdoped cuprates.

Theory of Spin States of Quantum Dot Molecules

NASA Astrophysics Data System (ADS)

Ponomarev, I. V.; Reinecke, T. L.; Scheibner, M.; Stinaff, E. A.; Bracker, A. S.; Doty, M. F.; Gammon, D.; Korenev, V. L.

2007-04-01

The photoluminescence spectrum of an asymmetric pair of coupled InAs quantum dots in an applied electric field shows a rich pattern of level anticrossings, crossings and fine structure that can be understood as a superposition of charge and spin configurations. We present a theoretical model that provides a description of the energy positions and intensities of the optical transitions in exciton, biexciton and charged exciton states of coupled quantum dots molecules.

Role of entropy and structural parameters in the spin-state transition of LaCoO3

NASA Astrophysics Data System (ADS)

Chakrabarti, Bismayan; Birol, Turan; Haule, Kristjan

2017-11-01

The spin-state transition in LaCoO3 has eluded description for decades despite concerted theoretical and experimental effort. In this study, we approach this problem using fully charge self-consistent density functional theory + embedded dynamical mean field theory (DFT+DMFT). We show from first principles that LaCoO3 cannot be described by a single, pure spin state at any temperature. Instead, we observe a gradual change in the population of higher-spin multiplets with increasing temperature, with the high-spin multiplets being excited at the onset of the spin-state transition followed by the intermediate-spin multiplets being excited at the metal-insulator-transition temperature. We explicitly elucidate the critical role of lattice expansion and oxygen octahedral rotations in the spin-state transition. We also reproduce, from first principles, that the spin-state transition and the metal-insulator transition in LaCoO3 occur at different temperature scales. In addition, our results shed light on the importance of electronic entropy in driving the spin-state transition, which has so far been ignored in all first-principles studies of this material.

Absorption and luminescence spectroscopy of mass-selected flavin adenine dinucleotide mono-anions

NASA Astrophysics Data System (ADS)

Giacomozzi, L.; Kjær, C.; Langeland Knudsen, J.; Andersen, L. H.; Brøndsted Nielsen, S.; Stockett, M. H.

2018-06-01

We report the absorption profile of isolated Flavin Adenine Dinucleotide (FAD) mono-anions recorded using photo-induced dissociation action spectroscopy. In this charge state, one of the phosphoric acid groups is deprotonated and the chromophore itself is in its neutral oxidized state. These measurements cover the first four optical transitions of FAD with excitation energies from 2.3 to 6.0 eV (210-550 nm). The S0 → S2 transition is strongly blue shifted relative to aqueous solution, supporting the view that this transition has a significant charge-transfer character. The remaining bands are close to their solution-phase positions. This confirms that the large discrepancy between quantum chemical calculations of vertical transition energies and solution-phase band maxima cannot be explained by solvent effects. We also report the luminescence spectrum of FAD mono-anions in vacuo. The gas-phase Stokes shift for S1 is 3000 cm-1, which is considerably larger than any previously reported for other molecular ions and consistent with a significant displacement of the ground and excited state potential energy surfaces. Consideration of the vibronic structure is thus essential for simulating the absorption and luminescence spectra of flavins.

Fractionalized Fermi liquid with bosonic chargons as a candidate for the pseudogap metal

NASA Astrophysics Data System (ADS)

Chatterjee, Shubhayu; Sachdev, Subir

2016-11-01

Doping a Mott-insulating Z2 spin liquid can lead to a fractionalized Fermi liquid (FL*). Such a phase has several favorable features that make it a candidate for the pseudogap metal for the underdoped cuprates. We focus on a particular, simple Z2-FL* state which can undergo a confinement transition to a spatially uniform superconductor which is smoothly connected to the "plain vanilla" BCS superconductor with d -wave pairing. Such a transition occurs by the condensation of bosonic particles carrying +e charge but no spin ("chargons"). We show that modifying the dispersion of the bosonic chargons can lead to confinement transitions with charge density waves and pair density waves at the same wave vector K , coexisting with d -wave superconductivity. We also compute the evolution of the Hall number in the normal state during the transition from the plain vanilla FL* state to a Fermi liquid, and argue, following Coleman, Marston, and Schofield [Phys. Rev. B 72, 245111 (2005), 10.1103/PhysRevB.72.245111], that it exhibits a discontinuous jump near optimal doping. We note the distinction between these results and those obtained from models of the pseudogap with fermionic chargons.

Nuclear Dynamics at Molecule–Metal Interfaces: A Pseudoparticle Perspective

DOE PAGES

Galperin, Michael; Nitzan, Abraham

2015-11-20

We discuss nuclear dynamics at molecule-metal interfaces including nonequilibrium molecular junctions. Starting from the many-body states (pseudoparticle) formulation of the molecule-metal system in the molecular vibronic basis, we introduce gradient expansion to reduce the adiabatic nuclear dynamics (that is, nuclear dynamics on a single molecular potential surface) into its semiclassical form while maintaining the effect of the nonadiabatic electronic transitions between different molecular charge states. Finally, this yields a set of equations for the nuclear dynamics in the presence of these nonadiabatic transitions, which reproduce the surface-hopping formulation in the limit of small metal-molecule coupling (where broadening of the molecularmore » energy levels can be disregarded) and Ehrenfest dynamics (motion on the potential of mean force) when information on the different charging states is traced out.« less

Origin of the Counterintuitive Dynamic Charge in the Transition-Metal Dichalcogenides

NASA Astrophysics Data System (ADS)

Pike, Nicholas; van Troeye, Benoit; Dewandre, Antoine; Gonze, Xavier; Verstraete, Matthieu

Our recent first-principles calculations of the electronic and vibrational properties of the hexagonal transition-metal dichalcogenides reveal that their Born effective charges display a counterintuitive sign when compared to most other materials or transition-metal dichalcogenides with trigonal symmetry. We determine the origin of this counterintuitive sign by calculating the electronic, vibrational, and optical properties of these systems. We show that the sign of the Born effective charge is directly related to the electric field response of the electronic density, and, in turn, to the bonding characteristics of the material.There is a filled anti-bonding molecular orbital at the Fermi level, which is localized on the transition-metal atom and corresponds to a form of solid state π back-bonding in these material. We propose a method of determining if other materials display a similar counterintuitive sign, based on their bonding characteristics, and propose experiments which could measure the sign of the Born effective charge using different spectroscopies. The authors acknowledge the Belgian Fonds National de la Recherche Scientifique FNRS under PDR T.1077.15-1/7, a FRIA Grant, ULg, and from the Communauté Française de Belgique (ARC AIMED 15/19-09).

Open- and closed-state fast inactivation in sodium channels

PubMed Central

Lehmann-Horn, Frank; Holzherr, Boris D

2011-01-01

The role of sodium channel closed-state fast inactivation in membrane excitability is not well understood. We compared open- and closed-state fast inactivation, and the gating charge immobilized during these transitions, in skeletal muscle channel hNaV1.4. A significant fraction of total charge movement and its immobilization occurred in the absence of channel opening. Simulated action potentials in skeletal muscle fibers were attenuated when pre-conditioned by subthreshold depolarization. Anthopleurin A, a site-3 toxin that inhibits gating charge associated with the movement of DIVS4, was used to assess the role of this voltage sensor in closed-state fast inactivation. Anthopleurin elicited opposing effects on the gating mode, kinetics and charge immobilized during open- versus closed-state fast inactivation. This same toxin produced identical effects on recovery of channel availability and remobilization of gating charge, irrespective of route of entry into fast inactivation. Our findings suggest that depolarization promoting entry into fast inactivation from open versus closed states provides access to the IFMT receptor via different rate-limiting conformational translocations of DIVS4. PMID:21099342

Moving Towards a State of the Art Charge-Exchange Reaction Code

NASA Astrophysics Data System (ADS)

Poxon-Pearson, Terri; Nunes, Filomena; Potel, Gregory

2017-09-01

Charge-exchange reactions have a wide range of applications, including late stellar evolution, constraining the matrix elements for neutrinoless double β-decay, and exploring symmetry energy and other aspects of exotic nuclear matter. Still, much of the reaction theory needed to describe these transitions is underdeveloped and relies on assumptions and simplifications that are often extended outside of their region of validity. In this work, we have begun to move towards a state of the art charge-exchange reaction code. As a first step, we focus on Fermi transitions using a Lane potential in a few body, Distorted Wave Born Approximation (DWBA) framework. We have focused on maintaining a modular structure for the code so we can later incorporate complications such as nonlocality, breakup, and microscopic inputs. Results using this new charge-exchange code will be shown compared to the analysis in for the case of 48Ca(p,n)48Sc. This work was supported in part by the National Nuclear Security Administration under the Stewardship Science Academic Alliances program through the U.S. DOE Cooperative Agreement No. DE- FG52-08NA2855.

Spectral resolution of states relevant to photoinduced charge transfer in modified pentacene/ZnO field-effect transistors

NASA Astrophysics Data System (ADS)

Spalenka, Josef W.; Mannebach, Ehren M.; Bindl, Dominick J.; Arnold, Michael S.; Evans, Paul G.

2011-11-01

Pentacene field-effect transistors incorporating ZnO quantum dots can be used as a sensitive probe of the optical properties of a buried donor-acceptor interface. Photoinduced charge transfer between pentacene and ZnO in these devices varies with incident photon energy and reveals which energies will contribute most to charge transfer in other structures. A subsequent slow return to the dark state following the end of illumination arises from near-interface traps. Charge transfer has a sharp onset at 1.7 eV and peaks at 1.82 and 2.1 eV due to transitions associated with excitons, features absent in pentacene FETs without ZnO.

Infinite number of solvable generalizations of XY-chain, with cluster state, and with central charge c = m/2

NASA Astrophysics Data System (ADS)

Minami, Kazuhiko

2017-12-01

An infinite number of spin chains are solved and it is derived that the ground-state phase transitions belong to the universality classes with central charge c = m / 2, where m is an integer. The models are diagonalized by automatically obtained transformations, many of which are different from the Jordan-Wigner transformation. The free energies, correlation functions, string order parameters, exponents, central charges, and the phase diagram are obtained. Most of the examples consist of the stabilizers of the cluster state. A unified structure of the one-dimensional XY and cluster-type spin chains is revealed, and other series of solvable models can be obtained through this formula.

Critical behaviour in charging of electric vehicles

NASA Astrophysics Data System (ADS)

Carvalho, Rui; Buzna, Lubos; Gibbens, Richard; Kelly, Frank

2015-09-01

The increasing penetration of electric vehicles over the coming decades, taken together with the high cost to upgrade local distribution networks and consumer demand for home charging, suggest that managing congestion on low voltage networks will be a crucial component of the electric vehicle revolution and the move away from fossil fuels in transportation. Here, we model the max-flow and proportional fairness protocols for the control of congestion caused by a fleet of vehicles charging on two real-world distribution networks. We show that the system undergoes a continuous phase transition to a congested state as a function of the rate of vehicles plugging to the network to charge. We focus on the order parameter and its fluctuations close to the phase transition, and show that the critical point depends on the choice of congestion protocol. Finally, we analyse the inequality in the charging times as the vehicle arrival rate increases, and show that charging times are considerably more equitable in proportional fairness than in max-flow.

Charge disproportionation and the pressure-induced insulator–metal transition in cubic perovskite PbCrO3

PubMed Central

Cheng, Jinguang; Kweon, K. E.; Larregola, S. A.; Ding, Yang; Shirako, Y.; Marshall, L. G.; Li, Z.-Y.; Li, X.; dos Santos, António M.; Suchomel, M. R.; Matsubayashi, K.; Uwatoko, Y.; Hwang, G. S.; Goodenough, John B.; Zhou, J.-S.

2015-01-01

The perovskite PbCrO3 is an antiferromagnetic insulator. However, the fundamental interactions leading to the insulating state in this single-valent perovskite are unclear. Moreover, the origin of the unprecedented volume drop observed at a modest pressure of P = 1.6 GPa remains an outstanding problem. We report a variety of in situ pressure measurements including electron transport properties, X-ray absorption spectrum, and crystal structure study by X-ray and neutron diffraction. These studies reveal key information leading to the elucidation of the physics behind the insulating state and the pressure-induced transition. We argue that a charge disproportionation 3Cr4+ → 2Cr3+ + Cr6+ in association with the 6s-p hybridization on the Pb2+ is responsible for the insulating ground state of PbCrO3 at ambient pressure and the charge disproportionation phase is suppressed under pressure to give rise to a metallic phase at high pressure. The model is well supported by density function theory plus the correlation energy U (DFT+U) calculations. PMID:25624483

Charge disproportionation and the pressure-induced insulator–metal transition in cubic perovskite PbCrO 3

DOE PAGES

Cheng, Jinguang; Kweon, K. E.; Larregola, S. A.; ...

2015-01-26

The perovskite PbCrO 3 is an antiferromagnetic insulator. But, the fundamental interactions leading to the insulating state in this single-valent perovskite are unclear. Moreover, the origin of the unprecedented volume drop observed at a modest pressure of P = 1.6 GPa remains an outstanding problem. Our report shows a variety of in situ pressure measurements including electron transport properties, X-ray absorption spectrum, and crystal structure study by X-ray and neutron diffraction. These studies reveal key information leading to the elucidation of the physics behind the insulating state and the pressure-induced transition. Furthermore, we argue that a charge disproportionation 3Cr 4+more » → 2Cr 3+ + Cr 6+ in association with the 6s-p hybridization on the Pb 2+ is responsible for the insulating ground state of PbCrO 3 at ambient pressure and the charge disproportionation phase is suppressed under pressure to give rise to a metallic phase at high pressure. The model is well supported by density function theory plus the correlation energy U (DFT + U) calculations.« less

The phase transitions between Z n × Z n bosonic topological phases in 1 + 1D, and a constraint on the central charge for the critical points between bosonic symmetry protected topological phases

DOE PAGES

Tsui, Lokman; Huang, Yen-Ta; Jiang, Hong-Chen; ...

2017-03-27

The study of continuous phase transitions triggered by spontaneous symmetry breaking has brought revolutionary ideas to physics. Recently, through the discovery of symmetry protected topological phases, it is realized that continuous quantum phase transition can also occur between states with the same symmetry but different topology. Here in this paper we study a specific class of such phase transitions in 1+1 dimensions – the phase transition between bosonic topological phases protected by Z n × Z n. We find in all cases the critical point possesses two gap opening relevant operators: one leads to a Landau-forbidden symmetry breaking phase transitionmore » and the other to the topological phase transition. We also obtained a constraint on the central charge for general phase transitions between symmetry protected bosonic topological phases in 1+1D.« less

The phase transitions between Z n × Z n bosonic topological phases in 1 + 1D, and a constraint on the central charge for the critical points between bosonic symmetry protected topological phases

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tsui, Lokman; Huang, Yen-Ta; Jiang, Hong-Chen

The study of continuous phase transitions triggered by spontaneous symmetry breaking has brought revolutionary ideas to physics. Recently, through the discovery of symmetry protected topological phases, it is realized that continuous quantum phase transition can also occur between states with the same symmetry but different topology. Here in this paper we study a specific class of such phase transitions in 1+1 dimensions – the phase transition between bosonic topological phases protected by Z n × Z n. We find in all cases the critical point possesses two gap opening relevant operators: one leads to a Landau-forbidden symmetry breaking phase transitionmore » and the other to the topological phase transition. We also obtained a constraint on the central charge for general phase transitions between symmetry protected bosonic topological phases in 1+1D.« less

Emergence of superconductivity from the dynamically heterogeneous insulating state in La(2-x)Sr(x)CuO4.

PubMed

Shi, Xiaoyan; Logvenov, G; Bollinger, A T; Božović, I; Panagopoulos, C; Popović, Dragana

2013-01-01

A central issue for copper oxides is the nature of the insulating ground state at low carrier densities and the emergence of high-temperature superconductivity from that state with doping. Even though this superconductor-insulator transition (SIT) is a zero-temperature transition, measurements are not usually carried out at low temperatures. Here we use magnetoresistance to probe both the insulating state at very low temperatures and the presence of superconducting fluctuations in La(2-x)Sr(x)CuO(4) films, for doping levels that range from the insulator to the superconductor (x  =  0.03-0.08). We observe that the charge glass behaviour, characteristic of the insulating state, is suppressed with doping, but it coexists with superconducting fluctuations that emerge already on the insulating side of the SIT. The unexpected quenching of the superconducting fluctuations by the competing charge order at low temperatures provides a new perspective on the mechanism for the SIT.

Impurity-induced photoconductivity of narrow-gap Cadmium–Mercury–Telluride structures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kozlov, D. V., E-mail: dvkoz@impras.ru; Rumyantsev, V. V.; Morozov, S. V.

2015-12-15

The photoconductivity (PC) spectra of CdHgTe (MCT) solid solutions with a Cd fraction of 17 and 19% are measured. A simple model for calculating the states of doubly charged acceptors in MCT solid solutions, which makes it possible to describe satisfactorily the observed photoconductivity spectra, is proposed. The found lines in the photoconductivity spectra of narrow-gap MCT structures are associated with transitions between the states of both charged and neutral acceptor centers.

An unusual metallic behavior in a Ag4SSe single crystal

NASA Astrophysics Data System (ADS)

Matteppanavar, Shidaling; Bui, Nguyen Hai An; van Smaalen, Sander; Thamizhavel, A.; Ramakrishnan, S.

2018-04-01

We report the magnetic susceptibility, resistivity and heat capacity measurements on high quality single crystalline tetra silver sulphoselenide (Ag4SSe). The magnetic susceptibility and resistivity measurements show anomalies around 260 K. The large diamagnetic drop with hysteresis at the transition implies a first order transition. Such a diamagnetic drop cannot be ascribed to the formation of charge density wave (CDW) since the temperature dependence of the resistivity shows no upturn at this transition. Infact the resistivity is decreasing with decreasing temperature, indicating a metallic behavior. However, unlike normal metals, the resistivity is almost temperature independent in the temperature range from 4-180 K. Usually, when one observes a diamagnetic transition, it is assumed to be due to a drop in the density of states at the Fermi level which leads to the decrease in the Pauli paramagnetic susceptibility. Such a decrease in the density of states often results in an increase in resistivity unless mobility of the charge carriers changes significantly. Hence, we believe that in Ag4SSe, the structural transition causes an unusual Fermi surface reconstruction which in turn leads to a strange metallic behavior at low temperatures.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gendron, Frederic; Fleischauer, Valerie R.; Duignan, Thomas J.

Here, we present a combined ab initio theoretical and experimental study of the magnetic circular dichroism (MCD) spectrum of the octahedral UCl 6- complex ion in the UV-Vis spectral region. The ground state is an orbitally non-degenerate doublet E 5/2u and the MCD is a $C$-term spectrum caused by spin–orbit coupling. Calculations of the electronic spectrum at various levels of theory indicate that differential dynamic electron correlation has a strong influence on the energies of the dipole-allowed transitions and the envelope of the MCD spectrum. The experimentally observed bands are assigned to dipole-allowed ligand-to-metal charge transfer into the 5f shell,more » and 5f to 6d transitions. Charge transfer excitations into the U 6d shell appear at much higher energies. The MCD-allowed transitions can be assigned via their signs of the $C$-terms: Under O h double group symmetry, E 5/2u → E 5/2g transitions have negative $C$-terms whereas E 5/2u → F 3/2g transitions have positive $C$-terms if the ground state g-factor is negative, as it is the case for UCl 6-.« less

Disentangling Transient Charge Density and Metal–Ligand Covalency in Photoexcited Ferricyanide with Femtosecond Resonant Inelastic Soft X-ray Scattering

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jay, Raphael M.; Norell, Jesper; Eckert, Sebastian

Soft X-ray spectroscopies are ideal probes of the local valence electronic structure of photocatalytically active metal sites. Here, we apply the selectivity of time-resolved resonant inelastic X-ray scattering at the iron L-edge to the transient charge distribution of an optically excited charge-transfer state in aqueous ferricyanide. Through comparison to steady-state spectra and quantum chemical calculations, the coupled effects of valence-shell closing and ligand-hole creation are experimentally and theoretically disentangled and described in terms of orbital occupancy, metal–ligand covalency, and ligand field splitting, thereby extending established steady-state concepts to the excited-state domain. π-Back-donation is found to be mainly determined by themore » metal site occupation, whereas the ligand hole instead influences σ-donation. Here, our results demonstrate how ultrafast resonant inelastic X-ray scattering can help characterize local charge distributions around catalytic metal centers in short-lived charge-transfer excited states, as a step toward future rationalization and tailoring of photocatalytic capabilities of transition-metal complexes.« less

Disentangling Transient Charge Density and Metal–Ligand Covalency in Photoexcited Ferricyanide with Femtosecond Resonant Inelastic Soft X-ray Scattering

DOE PAGES

Jay, Raphael M.; Norell, Jesper; Eckert, Sebastian; ...

2018-06-11

Soft X-ray spectroscopies are ideal probes of the local valence electronic structure of photocatalytically active metal sites. Here, we apply the selectivity of time-resolved resonant inelastic X-ray scattering at the iron L-edge to the transient charge distribution of an optically excited charge-transfer state in aqueous ferricyanide. Through comparison to steady-state spectra and quantum chemical calculations, the coupled effects of valence-shell closing and ligand-hole creation are experimentally and theoretically disentangled and described in terms of orbital occupancy, metal–ligand covalency, and ligand field splitting, thereby extending established steady-state concepts to the excited-state domain. π-Back-donation is found to be mainly determined by themore » metal site occupation, whereas the ligand hole instead influences σ-donation. Here, our results demonstrate how ultrafast resonant inelastic X-ray scattering can help characterize local charge distributions around catalytic metal centers in short-lived charge-transfer excited states, as a step toward future rationalization and tailoring of photocatalytic capabilities of transition-metal complexes.« less

Bending and breaking of stripes in a charge ordered manganite.

PubMed

Savitzky, Benjamin H; El Baggari, Ismail; Admasu, Alemayehu S; Kim, Jaewook; Cheong, Sang-Wook; Hovden, Robert; Kourkoutis, Lena F

2017-12-01

In charge-ordered phases, broken translational symmetry emerges from couplings between charge, spin, lattice, or orbital degrees of freedom, giving rise to remarkable phenomena such as colossal magnetoresistance and metal-insulator transitions. The role of the lattice in charge-ordered states remains particularly enigmatic, soliciting characterization of the microscopic lattice behavior. Here we directly map picometer scale periodic lattice displacements at individual atomic columns in the room temperature charge-ordered manganite Bi 0.35 Sr 0.18 Ca 0.47 MnO 3 using aberration-corrected scanning transmission electron microscopy. We measure transverse, displacive lattice modulations of the cations, distinct from existing manganite charge-order models. We reveal locally unidirectional striped domains as small as ~5 nm, despite apparent bidirectionality over larger length scales. Further, we observe a direct link between disorder in one lattice modulation, in the form of dislocations and shear deformations, and nascent order in the perpendicular modulation. By examining the defects and symmetries of periodic lattice displacements near the charge ordering phase transition, we directly visualize the local competition underpinning spatial heterogeneity in a complex oxide.

Formation and fragmentation of quadruply charged molecular ions by intense femtosecond laser pulses.

PubMed

Yatsuhashi, Tomoyuki; Nakashima, Nobuaki

2010-07-22

We investigated the formation and fragmentation of multiply charged molecular ions of several aromatic molecules by intense nonresonant femtosecond laser pulses of 1.4 mum with a 130 fs pulse duration (up to 2 x 10(14) W cm(-2)). Quadruply charged states were produced for 2,3-benzofluorene and triphenylene molecular ion in large abundance, whereas naphthalene and 1,1'-binaphthyl resulted only in up to triply charged molecular ions. The laser wavelength was nonresonant with regard to the electronic transitions of the neutral molecules, and the degree of fragmentation was strongly correlated with the absorption of the singly charged cation radical. Little fragmentation was observed for naphthalene (off-resonant with cation), whereas heavy fragmentation was observed in the case of 1,1'-binaphthyl (resonant with cation). The degree of H(2) (2H) and 2H(2) (4H) elimination from molecular ions increased as the charge states increased in all the molecules examined. A striking difference was found between triply and quadruply charged 2,3-benzofluorene: significant suppression of molecular ions with loss of odd number of hydrogen was observed in the quadruply charged ions. The Coulomb explosion of protons in the quadruply charged state and succeeding fragmentation resulted in the formation of triply charged molecular ions with an odd number of hydrogens. The hydrogen elimination mechanism in the highly charged state is discussed.

A hybrid density functional study of silicon and phosphorus doped hexagonal boron nitride monolayer

NASA Astrophysics Data System (ADS)

Mapasha, R. E.; Igumbor, E.; Chetty, N.

2016-10-01

We present a hybrid density functional study of silicon (Si) and phosphorus (P) doped hexagonal boron nitride (h-BN). The local geometry, electronic structure and thermodynamic stability of Si B , Si N , P B and P N are examined using hybrid Heyd-Scuseria- Ernzerhof (HSE) functional. The defect induced buckling and the local bond distances around the defect are sensitive to charge state modulation q = -2, -1, 0, +1 and +2. The +1 charge state is found to be the most energetically stable state and significantly reduces the buckling. Based on the charge state thermodynamic transition levels, we noted that the Si N , Si N and P B defects are too deep to be ionized, and can alter the optical properties of h-BN material.

Unusual inhomogeneous microstructures in charge glass state of PbCrO3

NASA Astrophysics Data System (ADS)

Kurushima, Kosuke; Tsukasaki, Hirofumi; Ogata, Takahiro; Sakai, Yuki; Azuma, Masaki; Ishii, Yui; Mori, Shigeo

2018-05-01

We investigated the microstructures and local structures of perovskite PbCrO3, which shows a metal-to-insulator transition and a 9.8% volume collapse, by electron diffraction, high-resolution transmission electron microscopy (TEM), and high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM). It is revealed that the charge glass state is characterized by the unique coexistence of the crystalline state with a cubic symmetry on average and the noncrystalline state. HAADF-STEM observation at atomic resolution revealed that Pb ions were displaced from the ideal A site position of the cubic perovskite structure, which gives rise to characteristic diffuse scatterings around the fundamental Bragg reflections. These structural inhomogeneities are crucial to the understanding of the unique physical properties in the charge glass state of PbCrO3.

Band dependence of charge density wave in quasi-one-dimensional Ta2NiSe7 probed by orbital magnetoresistance

NASA Astrophysics Data System (ADS)

He, Jiaming; Zhang, Yiran; Wen, Libin; Yang, Yusen; Liu, Jinyu; Wu, Yueshen; Lian, Hailong; Xing, Hui; Wang, Shun; Mao, Zhiqiang; Liu, Ying

2017-07-01

Ta2NiSe7 is a quasi-one-dimensional (quasi-1D) transition-metal chalcogenide with Ta and Ni chain structures. An incommensurate charge-density wave (CDW) in this quasi-1D structure was well studied previously using tunnelling spectrum, X-ray, and electron diffraction, whereas its transport property and the relation to the underlying electronic states remain to be explored. Here, we report our results of the magnetoresistance (MR) on Ta2NiSe7. A breakdown of Kohler's rule is found upon entering the CDW state. Concomitantly, a clear change in curvature in the field dependence of MR is observed. We show that the curvature change is well described by the two-band orbital MR, with the hole density being strongly suppressed in the CDW state, indicating that the p orbitals from Se atoms dominate the change in transport through CDW transition.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jay, Raphael M.; Norell, Jesper; Eckert, Sebastian

Soft X-ray spectroscopies are ideal probes of the local valence electronic structure of photocatalytically active metal sites. Here, we apply the selectivity of time-resolved resonant inelastic X-ray scattering at the iron L-edge to the transient charge distribution of an optically excited charge-transfer state in aqueous ferricyanide. Through comparison to steady-state spectra and quantum chemical calculations, the coupled effects of valence-shell closing and ligand-hole creation are experimentally and theoretically disentangled and described in terms of orbital occupancy, metal–ligand covalency, and ligand field splitting, thereby extending established steady-state concepts to the excited-state domain. π-Back-donation is found to be mainly determined by themore » metal site occupation, whereas the ligand hole instead influences σ-donation. Here, our results demonstrate how ultrafast resonant inelastic X-ray scattering can help characterize local charge distributions around catalytic metal centers in short-lived charge-transfer excited states, as a step toward future rationalization and tailoring of photocatalytic capabilities of transition-metal complexes.« less

Structure and properties of composite films formed by cellulose nanocrystals and charged latex nanoparticles

NASA Astrophysics Data System (ADS)

Thérien-Aubin, Héloïse; Lukach, Ariella; Pitch, Natalie; Kumacheva, Eugenia

2015-04-01

We report the structural and optical properties of composite films formed from mixed suspensions of cellulose nanocrystals (CNCs) and fluorescent latex nanoparticles (NPs). We explored the effect of NP concentration, size, surface charge, glass transition temperature and film processing conditions on film structure and properties. The chiral nematic order, typical of CNC films, was preserved in films with up to 50 wt% of negatively-charged latex NPs. Composite films were characterized by macroscopically close-to-uniform fluorescence, birefringence, and circular dichroism properties. In contrast, addition of positively charged latex NPs led to gelation of CNC-latex suspensions and disruption of the chiral nematic order in the composite films. Large latex NPs disrupted the chiral nematic order to a larger extend than small NPs. Furthermore, the glass transition of latex NPs had a dramatic effect on the structure of CNC-latex films. Latex particles in the rubbery state were easily incorporated in the ordered CNC matrix and improved the structural integrity of its chiral nematic phase.We report the structural and optical properties of composite films formed from mixed suspensions of cellulose nanocrystals (CNCs) and fluorescent latex nanoparticles (NPs). We explored the effect of NP concentration, size, surface charge, glass transition temperature and film processing conditions on film structure and properties. The chiral nematic order, typical of CNC films, was preserved in films with up to 50 wt% of negatively-charged latex NPs. Composite films were characterized by macroscopically close-to-uniform fluorescence, birefringence, and circular dichroism properties. In contrast, addition of positively charged latex NPs led to gelation of CNC-latex suspensions and disruption of the chiral nematic order in the composite films. Large latex NPs disrupted the chiral nematic order to a larger extend than small NPs. Furthermore, the glass transition of latex NPs had a dramatic effect on the structure of CNC-latex films. Latex particles in the rubbery state were easily incorporated in the ordered CNC matrix and improved the structural integrity of its chiral nematic phase. Electronic supplementary information (ESI) available: Detailed latex synthesis. Additional characterization of the nanoparticles and films. See DOI: 10.1039/c5nr00660k

Superconductor to Mott insulator transition in YBa 2Cu 3O 7/LaCaMnO 3 heterostructures

DOE PAGES

Gray, B. A.; Middey, S.; Conti, G.; ...

2016-09-15

The superconductor-to-insulator transition (SIT) induced by means such as external magnetic fields, disorder or spatial confinement is a vivid illustration of a quantum phase transition dramatically affecting the superconducting order parameter. In this paper, in pursuit of a new realization of the SIT by interfacial charge transfer, we developed extremely thin superlattices composed of high Tc superconductor YBa 2Cu 3O 7 (YBCO) and colossal magnetoresistance ferromagnet La 0.67Ca 0.33MnO 3 (LCMO). By using linearly polarized resonant X-ray absorption spectroscopy and magnetic circular dichroism, combined with hard X-ray photoelectron spectroscopy, we derived a complete picture of the interfacial carrier doping inmore » cuprate and manganite atomic layers, leading to the transition from superconducting to an unusual Mott insulating state emerging with the increase of LCMO layer thickness. In addition, contrary to the common perception that only transition metal ions may respond to the charge transfer process, we found that charge is also actively compensated by rare-earth and alkaline-earth metal ions of the interface. Finally, such deterministic control of Tc by pure electronic doping without any hindering effects of chemical substitution is another promising route to disentangle the role of disorder on the pseudo-gap and charge density wave phases of underdoped cuprates.« less

Unraveling energy conversion modeling in the intrinsic persistent upconverted luminescence of solids: a study of native point defects in antiferromagnetic Er2O3.

PubMed

Huang, Bolong

2016-05-11

We investigated the mechanism of the intrinsic persistent luminescence of Er2O3 in the A-type lattice based on first-principles calculations. We found that the native point defects were engaged in mutual subtle interactions in the form of chemical reactions between different charge states. The release of energy related to lattice distortion facilitates the conversion of energy for electrons to be transported between the valence band and the trap levels or even between the deep trap levels so as to generate persistent luminescence. The defect transitions that take place along the zero-phonon line release energy to enable optical transitions, with the exact amount of negative effective correlation energy determined by the lattice distortions. Our calculations on the thermodynamic transition levels confirm that both the visible and NIR experimentally observed intrinsic persistent luminescence (phosphor or afterglow) are related to the thermodynamic transition levels of oxygen-related defects, and the thermodynamic transition levels within different charge states for these defects are independent of the chemical potentials of the given species. Lattice distortion defects such as anion Frenkel (a-Fr) pair defects play an important role in transporting O-related defects between different lattice sites. To obtain red persistent luminescence that matches the biological therapeutic window, it is suggested to increase the electron transition levels between high-coordinated O vacancies and related metastable a-Fr defects; a close-packed core-shell structure is required to quench low-coordinated O-related defects so as to reduce the green band luminescence. We further established a conversed chain reaction (CCR) model to interpret the energy conversion process of persistent luminescence in terms of the inter-reactions of native point defects between different charge states. It is advantageous to use the study of defect levels combined with formation energies to suggest limits to doping energy and explain photostimulated luminescence in terms of native point defects.

High magnetic field magnetoresistance anomalies in the charge density wave state of the quasi-two dimensional bronze KMo6O{17}

NASA Astrophysics Data System (ADS)

Guyot, H.; Dumas, J.; Marcus, J.; Schlenker, C.; Vignolles, D.

2005-12-01

We report high magnetic field magnetoresistance measurements performed in pulsed fields up to 55 T on the quasi-two dimensional charge density wave conductor KMo{6}O{17}. Magnetoresistance curves show several anomalies below 28 T. First order transitions to smaller gap states take place at low temperature above 30 T. A phase diagram T(B) has been obtained. The angular dependence of the anomalies is reported.

A model of the normal and null states of pulsars

NASA Astrophysics Data System (ADS)

Jones, P. B.

1981-12-01

A solvable three-dimensional polar cap model of pair creation and charged particle acceleration has been derived. There are no free parameters of significance apart from the polar surface magnetic flux density. The parameter determining the acceleration potential difference has been obtained by calculation of elementary nuclear and electromagnetic processes. Solutions of the model exist for both normal and null states of a pulsar, and the instability in the normal state leading to the normal to null transition has been identified. The predicted necessary condition for the transition is entirely consistent with observation.

A model of the normal and null states of pulsars

NASA Astrophysics Data System (ADS)

Jones, P. B.

A solvable three dimensional polar cap model of pair creation and charged particle acceleration is derived. There are no free parameters of significance apart from the polar surface magnetic flux density. The parameter CO determining the acceleration potential difference was obtained by calculation of elementary nuclear and electromagnetic processes. Solutions of the model exist for both normal and null states of a pulsar, and the instability in the normal state leading to the normal to null transition is identified. The predicted necessary condition for the transition is entirely consistent with observation.

Direct Evidence for Delocalization of Charge Carriers at the Fermi Level in a Doped Conducting Polymer

NASA Astrophysics Data System (ADS)

Zhuo, Jing-Mei; Zhao, Li-Hong; Chia, Perq-Jon; Sim, Wee-Sun; Friend, Richard H.; Ho, Peter K. H.

2008-05-01

The infrared absorption spectrum of the polaron charges at the Fermi level EF in a heavily p-doped conducting poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonic acid) film has been measured using interferogram-modulated Fourier-transform charge-modulation spectroscopy. The spectrum indicates softer phonons and weaker electron-phonon coupling riding on a strongly redshifted Drude-like electronic transition, different from the population-averaged “bulk” spectrum. This provides direct evidence that the EF holes are sufficiently delocalized even in such disordered materials to reside in an energy continuum (band states) while the rest of the hole population resides in self-localized gap states.

Pressure-induced electronic topological transitions in the charge-density-wave material In 4 Se 3

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, Yuhang; Song, Liyan; Shao, Xuecheng

2017-08-01

High-pressure in situ angle dispersive X-ray diffraction (ADXRD) measurements were performed on the charge-density-wave (CDW) material In4Se3 up to 48.8 GPa. Pressure-induced structural changes were observed at 7.0 and 34.2 GPa, respectively. Using the CALYPSO methodology, the first high-pressure phase was solved as an exotic Pca21 structure. The compressional behaviors of the initial Pnnm and the Pca21 phases were all determined. Combined with first-principle calculations, we find that, unexpectedly, the Pnnm phase probably experiences twice electronic topological transitions (ETTs), from the initial possible CDW state to a semimetallic state at about 2.3 GPa and then back to a possible CDWmore » state at around 3.5 GPa, which was uncovered for the first time in CDW systems. In the both possible CDW states, pressure provokes a decrease of band-gap. The observation of a bulk metallic state was ascribed to structural transition to the Pca21 phase. Besides, based on electronic band structure calculations, the thermoelectric property of the Pnnm phase under compression was discussed. Our results show that pressure play a dramatic role in tuning In4Se3's structure and transport properties.« less

The origin of nulls mode changes and timing noise in pulsars

NASA Astrophysics Data System (ADS)

Jones, P. B.

A solvable polar cap model obtained previously has normal states which may be associated with radio emission and null states. The solutions cannot be time-independent; the neutron star surface temperature T and mean surface nuclear charge Z are both functions of time. The normal and null states, and the transitions between them, form closed cycles in the T-Z plane. Normal-null transitions can occur inside a fraction of the area on the neutron star surface intersected by open magnetic flux lines. The fraction increases with pulsar period and becomes unity when the pulsar nears extinction. Frequency noise, mode changes, and pulse nulls have a common explanation in the transitions.

The origin of nulls, mode changes and timing noise in pulsars

NASA Astrophysics Data System (ADS)

Jones, P. B.

1982-09-01

A solvable polar cap model obtained previously has normal states which may be associated with radio emission, and null states. The solutions cannot be time-independent; the neutron star surface temperature T and mean surface nuclear charge Z are both functions of time. The normal and null states and the transitions between them, form closed cycles in the T-Z plane. Normal-null transitions can occur inside a fraction of the area of the neutron star surface intersected by open magnetic flux lines. The fraction increases with pulsar period and becomes unity when the pulsar nears extinction. Frequency noise, mode changes and pulse nulls have a common explanation in the transitions.

Hard X-ray photoemission study of the Fabre salts (TMTTF)2X (X = SbF6 and PF6)

NASA Astrophysics Data System (ADS)

Medjanik, Katerina; de Souza, Mariano; Kutnyakhov, Dmytro; Gloskovskii, Andrei; Müller, Jens; Lang, Michael; Pouget, Jean-Paul; Foury-Leylekian, Pascale; Moradpour, Alec; Elmers, Hans-Joachim; Schönhense, Gerd

2014-11-01

Core-level photoemission spectra of the Fabre salts with X = SbF6 and PF6 were taken using hard X-rays from PETRA III, Hamburg. In these salts TMTTF layers show a significant stack dimerization with a charge transfer of 1 e per dimer to the anion SbF6 or PF6. At room temperature and slightly below the core-level spectra exhibit single lines, characteristic for a well-screened metallic state. At reduced temperatures progressive charge localization sets in, followed by a 2nd order phase transition into a charge-ordered ground state. In both salts groups of new core-level signals occur, shifted towards lower kinetic energies. This is indicative of a reduced transverse-conductivity across the anion layers, visible as layer-dependent charge depletion for both samples. The surface potential was traced via shifts of core-level signals of an adsorbate. A well-defined potential could be established by a conducting cap layer of 5 nm aluminum which appears "transparent" due to the large probing depth of HAXPES (8-10 nm). At the transition into the charge-ordered phase the fluorine 1 s line of (TMTTF)2SbF6 shifts by 2.8 eV to higher binding energy. This is a spectroscopic fingerprint of the loss of inversion symmetry accompanied by a cooperative shift of the SbF6 anions towards the more positively charged TMTTF donors. This shift does not occur for the X = PF6 compound, most likely due to smaller charge disproportion or due to the presence of charge disorder.

Formation of unusual Cr5+ charge state in CaCr0.5Fe0.5O3 perovskite

NASA Astrophysics Data System (ADS)

Dai, Jian-Hong; Zhao, Qing; Sun, Qian; Zhang, Shuo; Wang, Xiao; Shen, Xu-Dong; Liu, Zhe-Hong; Shen, Xi; Yu, Ri-Cheng; Chan, Ting-Shan; Li, Lun-Xiong; Zhou, Guang-Hui; Yang, Yi-feng; Jin, Chang-Qing; Long, You-Wen

2018-03-01

A new oxide CaCr0.5Fe0.5O3 was prepared under high pressure and temperature conditions. It crystallizes in a B-site disordered Pbnm perovskite structure. The charge combination is determined to be Cr5+/Fe3+ with the presence of unusual Cr5+ state in octahedral coordination, although Cr4+ and Fe4+ occur in the related perovskites CaCrO3 and CaFeO3. The randomly distributed Cr5+ and Fe3+ spins lead to short-range ferromagnetic coupling, whereas an antiferromagnetic phase transition takes place near 50 K due to the Fe3+–O–Fe3+ interaction. In spite of the B-site Cr5+/Fe3+ disorder, the compound exhibits electrical insulating behavior. First-principles calculations further demonstrate the formation of {CaCr}}0.55+{Fe}}0.53+{{{O}}}3 charge combination, and the electron correlation effect of Fe3+ plays an important role for the insulting ground state. CaCr0.5Fe0.5O3 provides the first Cr5+ perovskite system with octahedral coordination, opening a new avenue to explore novel transition-metal oxides with exotic charge states. Project supported by the National Natural Science Foundation of China (Grant Nos. 11574378, 51772324, and 61404052),the National Basic Research Program of China (Grant No. 2014CB921500), and the Chinese Academy of Sciences (Grant Nos. YZ201555, QYZDB-SSW-SLH013, GJHZ1773, and XDB07030300).

Observation of extreme ultraviolet transitions in highly charged Ba{sup 16+} to Ba{sup 23+} ions with electron beam ion trap

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ali, S.; Shimizu, E.; Nakamura, N.

2016-03-15

We have investigated extreme ultraviolet emission from highly charged barium using a compact electron beam ion trap at the Tokyo EBIT laboratory. The spectra were recorded for several beam energies ranging from 440 to 740 eV, while keeping the electron beam current constant at 10 mA. Radiation from charge states Zr-like Ba{sup 16+} to As-like Ba{sup 23+} were recorded and identified by varying the electron beam energy across the ionization thresholds and comparing with calculated results. The calculations were performed with a detailed relativistic configuration interaction approach using the Flexible Atomic Code. Several new lines belonging to electric dipole transitions were observedmore » and identified.« less

Change in the frequency and intensity of the spectral lines of a hydrogen-like atom in the field of a point charge

NASA Astrophysics Data System (ADS)

Ovsyannikov, V. D.; Kamenskii, A. A.

2002-03-01

The changes in the wave functions and the energies of a hydrogen-like atom in the static field of a structureless charged particle are calculated in the asymptotic approximation. The corrections to the energy of states, as well as to the dipole matrix elements of radiative transitions caused by the interaction of the atom with the point charge at long range are calculated using the perturbation theory and the Sturm series for a reduced Coulomb Green’s function in parabolic coordinates. The analytical expressions are derived and tables of numerical values of the coefficients of asymptotic series that determine the corrections to the matrix elements and the intensities of transitions of the Lyman and Balmer series are presented.

Structural insight of the charge-ordering phenomena in manganites

NASA Astrophysics Data System (ADS)

Garcia, Joaquin

2005-03-01

Recent experiments using x-ray absorption spectroscopy (XAS) and x-ray resonant scattering (XRS) techniques show that the conventional description of the so-called charge ordering phases of manganites in terms of Mn^3+/Mn^4+ ionic ordering is far from reality. I present here the XRS study of the low temperature phase of Nd0.5Sr0.5MnO3 manganite. Strong resonances are observed in the energy dependent spectra of (300), (030) and (05/20) reflections. Their azimuthal and polarization dependencies are well explained by the anisotropy of the local geometrical structure. Two different Mn sites were found. One of them is surrounded by a tetragonal distorted oxygen octahedron, whereas the other site has a nearly regular octahedral environment. The charge separation between the intermediate valence states is less than 0.2 e-. The analysis performed resolves some of the apparent contradictions with previous XRS and XAS experiments in manganites. These results joined to those recently obtained on the Verwey transition in magnetite indicate that the electronic states in transition-metal oxides need to be described in terms of band states instead of localized ones. Colaborators: G. Sub'ias, J. Blasco, M. G. Proietti, M. S'anchez and J. Herrero-Martin

Spectroscopic Investigations of Highly Charged Tungsten Ions - Atomic Spectroscopy and Fusion Plasma Diagnostics

DOE Office of Scientific and Technical Information (OSTI.GOV)

Clementson, Joel

2010-05-01

The spectra of highly charged tungsten ions have been investigated using x-ray and extreme ultraviolet spectroscopy. These heavy ions are of interest in relativistic atomic structure theory, where high-precision wavelength measurements benchmark theoretical approaches, and in magnetic fusion research, where the ions may serve to diagnose high-temperature plasmas. The work details spectroscopic investigations of highly charged tungsten ions measured at the Livermore electron beam ion trap (EBIT) facility. Here, the EBIT-I and SuperEBIT electron beam ion traps have been employed to create, trap, and excite tungsten ions of M- and L-shell charge states. The emitted spectra have been studied inmore » high resolution using crystal, grating, and x-ray calorimeter spectrometers. In particular, wavelengths of n = 0 M-shell transitions in K-like W 55+ through Ne-like W 64+, and intershell transitions in Zn-like W 44+ through Co-like W 47+ have been measured. Special attention is given to the Ni-like W46+ ion, which has two strong electric-dipole forbidden transitions that are of interest for plasma diagnostics. The EBIT measurements are complemented by spectral modeling using the Flexible Atomic Code (FAC), and predictions for tokamak spectra are presented. The L-shell tungsten ions have been studied at electron-beam energies of up to 122 keV and transition energies measured in Ne-like W 64+ through Li-like W 71+. These spectra constitute the physics basis in the design of the ion-temperature crystal spectrometer for the ITER tokamak. Tungsten particles have furthermore been introduced into the Sustained Spheromak Physics Experiment (SSPX) spheromak in Livermore in order to investigate diagnostic possibilities of extreme ultraviolet tungsten spectra for the ITER divertor. The spheromak measurement and spectral modeling using FAC suggest that tungsten ions in charge states around Er-like W 6+ could be useful for plasma diagnostics.« less

System-size convergence of point defect properties: The case of the silicon vacancy

NASA Astrophysics Data System (ADS)

Corsetti, Fabiano; Mostofi, Arash A.

2011-07-01

We present a comprehensive study of the vacancy in bulk silicon in all its charge states from 2+ to 2-, using a supercell approach within plane-wave density-functional theory, and systematically quantify the various contributions to the well-known finite size errors associated with calculating formation energies and stable charge state transition levels of isolated defects with periodic boundary conditions. Furthermore, we find that transition levels converge faster with respect to supercell size when only the Γ-point is sampled in the Brillouin zone, as opposed to a dense k-point sampling. This arises from the fact that defect level at the Γ-point quickly converges to a fixed value which correctly describes the bonding at the defect center. Our calculated transition levels with 1000-atom supercells and Γ-point only sampling are in good agreement with available experimental results. We also demonstrate two simple and accurate approaches for calculating the valence band offsets that are required for computing formation energies of charged defects, one based on a potential averaging scheme and the other using maximally-localized Wannier functions (MLWFs). Finally, we show that MLWFs provide a clear description of the nature of the electronic bonding at the defect center that verifies the canonical Watkins model.

Spatially resolved surface valence gradient and structural transformation of lithium transition metal oxides in lithium-ion batteries.

PubMed

Liu, Hanshuo; Bugnet, Matthieu; Tessaro, Matteo Z; Harris, Kristopher J; Dunham, Mark J R; Jiang, Meng; Goward, Gillian R; Botton, Gianluigi A

2016-10-26

Layered lithium transition metal oxides are one of the most important types of cathode materials in lithium-ion batteries (LIBs) that possess high capacity and relatively low cost. Nevertheless, these layered cathode materials suffer structural changes during electrochemical cycling that could adversely affect the battery performance. Clear explanations of the cathode degradation process and its initiation, however, are still under debate and not yet fully understood. We herein systematically investigate the chemical evolution and structural transformation of the LiNi x Mn y Co 1-x-y O 2 (NMC) cathode material in order to understand the battery performance deterioration driven by the cathode degradation upon cycling. Using high-resolution electron energy loss spectroscopy (HR-EELS) we clarify the role of transition metals in the charge compensation mechanism, particularly the controversial Ni 2+ (active) and Co 3+ (stable) ions, at different states-of-charge (SOC) under 4.6 V operation voltage. The cathode evolution is studied in detail from the first-charge to long-term cycling using complementary diagnostic tools. With the bulk sensitive 7 Li nuclear magnetic resonance (NMR) measurements, we show that the local ordering of transition metal and Li layers (R3[combining macron]m structure) is well retained in the bulk material upon cycling. In complement to the bulk measurements, we locally probe the valence state distribution of cations and the surface structure of NMC particles using EELS and scanning transmission electron microscopy (STEM). The results reveal that the surface evolution of NMC is initiated in the first-charging step with a surface reduction layer formed at the particle surface. The NMC surface undergoes phase transformation from the layered structure to a poor electronic and ionic conducting transition-metal oxide rock-salt phase (R3[combining macron]m → Fm3[combining macron]m), accompanied by irreversible lithium and oxygen loss. In addition to the electrochemical cycling effect, electrolyte exposure also shows non-negligible influence on cathode surface degradation. These chemical and structural changes of the NMC cathode could contribute to the first-cycle coulombic inefficiency, restrict the charge transfer characteristics and ultimately impact the cell capacity.

Critical behavior and microscopic structure of charged AdS black holes via an alternative phase space

NASA Astrophysics Data System (ADS)

Dehyadegari, Amin; Sheykhi, Ahmad; Montakhab, Afshin

2017-05-01

It has been argued that charged Anti-de Sitter (AdS) black holes have similar thermodynamic behavior as the Van der Waals fluid system, provided one treats the cosmological constant as a thermodynamic variable (pressure) in an extended phase space. In this paper, we disclose the deep connection between charged AdS black holes and Van der Waals fluid system from an alternative point of view. We consider the mass of an AdS black hole as a function of square of the charge Q2 instead of the standard Q, i.e. M = M (S ,Q2 , P). We first justify such a change of view mathematically and then ask if a phase transition can occur as a function of Q2 for fixed P. Therefore, we write the equation of state as Q2 =Q2 (T , Ψ) where Ψ (conjugate of Q2) is the inverse of the specific volume, Ψ = 1 / v. This allows us to complete the analogy of charged AdS black holes with Van der Waals fluid system and derive the phase transition as well as critical exponents of the system. We identify a thermodynamic instability in this new picture with real analogy to Van der Waals fluid with physically relevant Maxwell construction. We therefore study the critical behavior of isotherms in Q2- Ψ diagram and deduce all the critical exponents of the system and determine that the system exhibits a small-large black hole phase transition at the critical point (Tc , Qc2 ,Ψc). This alternative view is important as one can imagine such a change for a given single black hole i.e. acquiring charge which induces the phase transition. Finally, we disclose the microscopic properties of charged AdS black holes by using thermodynamic geometry. Interestingly, we find that scalar curvature has a gap between small and large black holes, and this gap becomes exceedingly large as one moves away from the critical point along the transition line. Therefore, we are able to attribute the sudden enlargement of the black hole to the strong repulsive nature of the internal constituents at the phase transition.

Structural and electrochemical properties of iron- and nickel-substituted Li2MnO3 cathodes in charged and discharged states

NASA Astrophysics Data System (ADS)

Yuge, Ryota; Kuroshima, Sadanori; Toda, Akio; Miyazaki, Takashi; Tabuchi, Mitsuharu; Doumae, Kyosuke; Shibuya, Hideka; Tamura, Noriyuki

2017-10-01

Structural change and the charge compensation mechanism of lithium-rich layered cathode (Li1.23Fe0.15Ni0.15Mn0.46O2) in charged and discharged states were investigated. Selected area electron diffraction analysis revealed that in discharged state, an initial structure composed of a single phase of monoclinic layered rock-salt changed to a mixture of hexagonal layered rock-salt and spinel-like structures. In charged state, the spinel-like phase became dominant as transition-metal ions migrate. 57Fe Mössbauer spectroscopy, X-ray absorption spectroscopy (XAS), and Soft-XAS showed that the valence of Fe and Ni ions approximately changed from Fe3+ to Fe3.2+ and Ni2+ to Ni3.5+ during charge-discharge, although Mn ions remained as Mn4+. Various oxidation states of oxide ions such as superoxide, peroxide, and hole states have also been detected in charged state. Considering that actual discharge capacity was 255 mAh/g, the contribution to charge compensation from the valence change of Fe and Ni ions was extremely small, and it only contributed to about one-third of total capacity. Therefore, the mechanism to yield high capacity of the Li1.23Fe0.15Ni0.15Mn0.46O2 cathode relates strongly to the redox reaction of oxide ions. Moreover, the decrease in capacity during charge-discharge cycling was mainly due to the irreversible redox reaction of Mn, Fe, and oxide ions.

Cooperative photoinduced metastable phase control in strained manganite films

NASA Astrophysics Data System (ADS)

Zhang, Jingdi; Tan, Xuelian; Liu, Mengkun; Teitelbaum, S. W.; Post, K. W.; Jin, Feng; Nelson, K. A.; Basov, D. N.; Wu, Wenbin; Averitt, R. D.

2016-09-01

A major challenge in condensed-matter physics is active control of quantum phases. Dynamic control with pulsed electromagnetic fields can overcome energetic barriers, enabling access to transient or metastable states that are not thermally accessible. Here we demonstrate strain-engineered tuning of La2/3Ca1/3MnO3 into an emergent charge-ordered insulating phase with extreme photo-susceptibility, where even a single optical pulse can initiate a transition to a long-lived metastable hidden metallic phase. Comprehensive single-shot pulsed excitation measurements demonstrate that the transition is cooperative and ultrafast, requiring a critical absorbed photon density to activate local charge excitations that mediate magnetic-lattice coupling that, in turn, stabilize the metallic phase. These results reveal that strain engineering can tune emergent functionality towards proximal macroscopic states to enable dynamic ultrafast optical phase switching and control.

Nonequivalent lanthanide defects: Energy level modeling

NASA Astrophysics Data System (ADS)

Joos, Jonas J.; Poelman, Dirk; Smet, Philippe F.

2016-11-01

Empirical charge-state transition level schemes are popular tools to model the properties of lanthanide-doped materials and their construction has become standard practice. Typically, it is implicitly assumed that all lanthanide ions form isostructural defects. However, in practice, multiple nonequivalent defects related to the same lanthanide can occur or different lanthanides can even incorporate in different ways. The consequences of these complications on the impurity energy levels are discussed in this article. It seems that small structural differences around the lanthanide dopant can give rise to important spectral differences in its emission. These are not always clearly reproduced by the charge-state transition level schemes. Improvements to the existing procedure are suggested and applied to the lanthanide ions in the well-studied host crystals SrAl2O4, Sr2Si5N8 and SrGa2S4.

Effect of strain on structure and charge order transitions in epitaxial Bi0.4Ca0.6MnO3 films on perovskite (001) and (011) substrates

NASA Astrophysics Data System (ADS)

Kim, Dae Ho; Christen, Hans M.; Varela, Maria; Lee, Ho Nyung; Lowndes, Douglas H.

2006-05-01

The effect of epitaxial strain on the charge order (CO) transition in Bi0.4Ca0.6MnO3 films was studied by varying the strain's strength and symmetry via the use of SrTiO3 and LaAlO3 substrates having different crystallographic orientations. The film on pseudocubic (001) LaAlO3, under symmetric compressive strain, exhibits a clear CO transition. In the film on a (001) SrTiO3 substrate, under symmetric tensile strain, highly segregated line-shaped features in the Bi distribution are seen in Z-contrast scanning transmission microscopy, accompanied by a strongly broadened CO transition. The asymmetric tensile stress on (011) SrTiO3 results in an apparent compressive strain state with a deviation from tetragonality (i.e., γ ≠90°), accompanied by the sharpest CO transition. These comparisons illustrate the importance of considering both the strength and symmetry of epitaxial strain.

Spin-polarized charge transport in HgTe/CdTe quantum well topological insulator under a ferromagnetic metal strip

NASA Astrophysics Data System (ADS)

Wu, Zhenhua; Luo, Kun; Yu, Jiahan; Wu, Xiaobo; Lin, Liangzhong

2018-02-01

Electron tunneling through a single magnetic barrier in a HgTe topological insulator has been theoretically investigated. We find that the perpendicular magnetic field would not lead to spin-flip of the edge states due to the conservation of the angular moment. By tuning the magnetic field and the Fermi energy, the edge channels can be transited from switch-on states to switch-off states and the current from unpolarized states can be filtered to fully spin polarized states. These features offer us an efficient way to control charge/spin transport in a HgTe/CdTe quantum well, and pave a way to construct the nanoelectronic devices utilizing the topological edge states.

Frequency metrology using highly charged ions

NASA Astrophysics Data System (ADS)

Crespo López-Urrutia, J. R.

2016-06-01

Due to the scaling laws of relativistic fine structure splitting, many forbidden optical transitions appear within the ground state configurations of highly charged ions (HCI). In some hydrogen-like ions, even the hyperfine splitting of the 1s ground state gives rise to optical transitions. Given the very low polarizability of HCI, such laser-accessible transitions are extremely impervious to external perturbations and systematics that limit optical clock performance and arise from AC and DC Stark effects, such as black-body radiation and light shifts. Moreover, AC and DC Zeeman splitting are symmetric due to the much larger relativistic spin-orbit coupling and corresponding fine-structure splitting. Appropriate choice of states or magnetic sub-states with suitable total angular momentum and magnetic quantum numbers can lead to a cancellation of residual quadrupolar shifts. All these properties are very advantageous for the proposed use of HCI forbidden lines as optical frequency standards. Extremely magnified relativistic, quantum electrodynamic, and nuclear size contributions to the binding energies of the optically active electrons make HCI ideal tools for fundamental research, as in proposed studies of a possible time variation of the fine structure constant. Beyond this, HCI that cannot be photoionized by vacuum-ultraviolet photons could also provide frequency standards for future lasers operating in that range.

Charge-induced geometrical reorganization of DNA oligonucleotides studied by tandem mass spectrometry and ion mobility.

PubMed

Ickert, Stefanie; Hofmann, Johanna; Riedel, Jens; Beck, Sebastian; Pagel, Kevin; Linscheid, Michael W

2018-04-01

Mass spectrometry is applied as a tool for the elucidation of molecular structures. This premises that gas-phase structures reflect the original geometry of the analytes, while it requires a thorough understanding and investigation of the forces controlling and affecting the gas-phase structures. However, only little is known about conformational changes of oligonucleotides in the gas phase. In this study, a series of multiply charged DNA oligonucleotides (n = 15-40) has been subjected to a comprehensive tandem mass spectrometric study to unravel transitions between different ionic gas-phase structures. The nucleobase sequence and the chain length were varied to gain insights into their influence on the geometrical oligonucleotide organization. Altogether, 23 oligonucleotides were analyzed using collision-induced fragmentation. All sequences showed comparable correlation regarding the characteristic collision energy. This value that is also a measure for stability, strongly correlates with the net charge density of the precursor ions. With decreasing charge of the oligonucleotides, an increase in the fragmentation energy was observed. At a distinct charge density, a deviation from linearity was observed for all studied species, indicating a structural reorganization. To corroborate the proposed geometrical change, collisional cross-sections of the oligonucleotides at different charge states were determined using ion mobility-mass spectrometry. The results clearly indicate that an increase in charge density and thus Coulomb repulsion results in the transition from a folded, compact form to elongated structures of the precursor ions. Our data show this structural transition to depend mainly on the charge density, whereas sequence and size do not have an influence.

Effects of excess carriers on charged defect concentrations in wide bandgap semiconductors

NASA Astrophysics Data System (ADS)

Alberi, Kirstin; Scarpulla, Michael A.

2018-05-01

Unintentional doping and doping limits in semiconductors are typically caused by compensating defects with low formation energies. Since the formation enthalpy of a charged defect depends linearly on the Fermi level, doping limits can be especially pronounced in wide bandgap semiconductors where the Fermi level can vary substantially. Introduction of non-equilibrium carrier concentrations during growth or processing alters the chemical potentials of band carriers and allows populations of charged defects to be modified in ways impossible at thermal equilibrium. We demonstrate that in the presence of excess carriers, the rates of carrier capture and emission involving a defect charge transition level determine the admixture of electron and hole quasi-Fermi levels involved in the formation enthalpy of non-zero charge defect states. To understand the range of possible responses, we investigate the behavior of a single donor-like defect as functions of extrinsic doping and charge transition level energy. We find that that excess carriers will increase the formation enthalpy of compensating defects for most values of the charge transition level in the bandgap. Thus, it may be possible to use non-equilibrium carrier concentrations to overcome limitations on doping imposed by native defects. Cases also exist in which the concentration of defects with the same charge polarity as the majority dopant is either left unchanged or actually increases. This surprising effect arises when emission rates are suppressed relative to the capture rates and is most pronounced in wide bandgap semiconductors. We provide guidelines for carrying out experimental tests of this model.

Relativistic many-body calculations of excitation energies, oscillator strengths, transition rates, and lifetimes in samarium like ions

NASA Astrophysics Data System (ADS)

Safronova, Ulyana; Safronova, Alla; Beiersdorfer, Peter

2013-05-01

Excitation energies, oscillator strengths, transition probabilities, and lifetimes are calculated for (5s2 + 5p2 + 5d2 + 5 s 5 d + 5 s 5 g + 5 p 5 f) - (5 s 5 p + 5 s 5 f + 5 p 5 d + 5 p 5 g) electric dipole transitions in Sm-like ions with nuclear charge Z ranging from 74 to 100. Relativistic many-body perturbation theory (RMBPT), including the Breit interaction, is used to evaluate retarded E1 matrix elements in length and velocity forms. The calculations start from a 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 4d10 4f14 Dirac-Fock potential. First-order perturbation theory is used to obtain intermediate coupling coefficients, and the second-order RMBPT is used to determine the matrix elements. The contributions from negative-energy states are included in the second-order E1 matrix elements to achieve agreement between length-form and velocity-form amplitudes. The resulting transition energies and transition probabilities, and lifetimes for Sm-like W12+ are compared with results obtained by the relativistic Hartree-Fock approximation (COWAN code) to estimate contribution of the 4 f -core-excited states. Trends of excitation energies and oscillator strengths as function of nuclear charge Z are shown graphically for selected states and transitions. This work provides a number of yet unmeasured properti. This research was sponsored by the grant DE-FG02-08ER54951.

Effect of temperature-driven phase transition on energy-storage and -release properties of Pb0.97La0.02[Zr0.55Sn0.30Ti0.15]O3 ceramics

NASA Astrophysics Data System (ADS)

Xu, Ran; Tian, Jingjing; Zhu, Qingshan; Feng, Yujun; Wei, Xiaoyong; Xu, Zhuo

2017-07-01

Temperature-driven phase transition of Pb0.97La0.02[Zr0.55Sn0.30Ti0.15]O3 ceramics was studied, and the consecutive ferroelectric-antiferroelectric-paraelectric (FE-AFE-PE) switching was confirmed. The materials have better dielectric tunability (-82% to 50%) in the AFE state than in the FE state. Also, the phase transition influences the energy-storage and -release performance significantly. A sharp increase in releasable energy density and efficiency was observed due to the temperature-driven FE-AFE transition. Highest releasable energy density, current density, and peak power density were achieved at 130 °C, which was attributed to the highest backward transition field. The stored charge was released completely in AFE and PE states in the microseconds scale, while only a small part of it was released in the FE state. The above results indicate the huge impact of temperature-driven phase transition on dielectrics' performance, which is significant when developing AFE materials working in a wide temperature range.

Inducement of ferromagnetic-metallic phase in intermediate-doped charge-ordered Pr0.75Na0.25MnO3 manganite by K+ substitution

NASA Astrophysics Data System (ADS)

Rozilah, R.; Ibrahim, N.; Mohamed, Z.; Yahya, A. K.; Khan, Nawazish A.; Khan, M. Nasir

2017-09-01

Polycrystalline Pr0.75Na0.25-xKxMnO3 (x = 0, 0.05, 0.10, 0.15 and 0.20) ceramics were prepared using conventional solid-state method and their structural, magnetic and electrical transport properties were investigated. Magnetization versus temperature measurements showed un-substituted sample exhibited paramagnetic behavior with charge-ordered temperature, TCO around 218 K followed by antiferromagnetic behavior at transition temperature, TN ∼ 170 K. K+-substitution initially weakened CO state for x = 0.05-0.10 then successfully suppressed the CO state for x = 0.15-0.20 and inducing ferromagnetic-paramagnetic transition with Curie temperature, TC increased with x. In addition, deviation of the temperature dependence of inverse magnetic susceptibility curves from the Curie-Weiss law suggests the existence of Griffiths phase-like increased with x. Magnetization versus magnetic field curves show existence of hysteresis loops at T < 260 K (x = 0) and T < 180 K (x = 0.05-0.10), which related to metamagnetic transition occurring at critical field. Electrical resistivity measurements showed an insulating behavior for x = 0 sample while for x = 0.05-0.20 samples showed metal-insulator transition and transition temperature, TMI increased with x. The increased in TC and TMI are attributed to the increase in tolerance factor which indicates reduction in MnO6 octahedral distortion consequently enhanced double exchange interaction.

Computationally designed and experimentally confirmed diastereoselective rhodium-catalyzed Pauson-Khand reaction at room temperature.

PubMed

Baik, Mu-Hyun; Mazumder, Shivnath; Ricci, Paolo; Sawyer, James R; Song, Ye-Geun; Wang, Huijun; Evans, P Andrew

2011-05-25

The computational analysis of the rhodium-catalyzed Pauson-Khand reaction indicates that the key transition state is highly charge-polarized, wherein different diastereoisomers have distinctively different charge polarization patterns. Experimental studies demonstrate that chloro-enynes provide the optimal σ-electron-withdrawing group to promote polarization and thereby reduce the activation barrier to provide a highly diastereoselective reaction at room temperature.

Absorption Spectra and Photoreactivity of p-Aminobenzophenone by Time-dependent Density Functional Theory

NASA Astrophysics Data System (ADS)

Cheng, Xue-mei; Huang, Yao; Ma, Jian-yi; Li, Xiang-yuan

2007-06-01

The absorption spectral properties of para-aminobenzophenone (p-ABP) were investigated in gas phase and in solution by time-dependent density functional theory. Calculations suggest that the singlet states vary greatly with the solvent polarities. In various polar solvents, including acetonitrile, methanol, ethanol, dimethyl sulfoxide, and dimethyl formamide, the excited S1 states with charge transfer character result from π → π* transitions. However, in nonpolar solvents, cyclohexane, and benzene, the S1 states are the result of n → π* transitions related to local excitation in the carbonyl group. The excited T1 states were calculated to have ππ* character in various solvents. From the variation of the calculated excited states, the band due to π → π* transition undergoes a redshift with an increase in solvent polarity, while the band due to n → π* transition undergoes a blueshift with an increase in solvent polarity. In addition, the triplet yields and the photoreactivities of p-ABP in various solvents are discussed.

Circuits and methods for determination and control of signal transition rates in electrochemical cells

DOEpatents

Jamison, David Kay

2016-04-12

A charge/discharge input is for respectively supplying charge to, or drawing charge from, an electrochemical cell. A transition modifying circuit is coupled between the charge/discharge input and a terminal of the electrochemical cell and includes at least one of an inductive constituent, a capacitive constituent and a resistive constituent selected to generate an adjusted transition rate on the terminal sufficient to reduce degradation of a charge capacity characteristic of the electrochemical cell. A method determines characteristics of the transition modifying circuit. A degradation characteristic of the electrochemical cell is analyzed relative to a transition rate of the charge/discharge input applied to the electrochemical cell. An adjusted transition rate is determined for a signal to be applied to the electrochemical cell that will reduce the degradation characteristic. At least one of an inductance, a capacitance, and a resistance is selected for the transition modifying circuit to achieve the adjusted transition rate.

Nanodisperse transition metal electrodes (NTME) for electrochemical cells

DOEpatents

Striebel, Kathryn A.; Wen, Shi-Jie

2000-01-01

Disclosed are transition metal electrodes for electrochemical cells using gel-state and solid-state polymers. The electrodes are suitable for use in primary and secondary cells. The electrodes (either negative electrode or positive electrode) are characterized by uniform dispersion of the transition metal at the nanoscale in the polymer. The transition metal moiety is structurally amorphous, so no capacity fade should occur due to lattice expansion/contraction mechanisms. The small grain size, amorphous structure and homogeneous distribution provide improved charge/discharge cycling performance, and a higher initial discharge rate capability. The cells can be cycled at high current densities, limited only by the electrolyte conductivity. A method of making the electrodes (positive and negative), and their usage in electrochemical cells are disclosed.

Ground-State Charge-Density Distribution in a Crystal of the Luminescent ortho-Phenylenediboronic Acid Complex with 8-Hydroxyquinoline.

PubMed

Jarzembska, Katarzyna N; Kamiński, Radosław; Durka, Krzysztof; Woźniak, Krzysztof

2018-05-10

This contribution is devoted to the first electron density studies of a luminescent oxyquinolinato boron complex in the solid state. ortho-Phenylenediboronic acid mixed with 8-hydroxyquinoline in dioxane forms high-quality single crystals via slow solvent evaporation, which allows successful high resolution data collection (sin θ/λ = 1.2 Å -1 ) and charge density distribution modeling. Particular attention has been paid to the boron-oxygen fragment connecting the two parts of the complex, and to the solvent species exhibiting anharmonic thermal motion. The experiment and theory compared rather well in terms of atomic charges and volumes, except for the boron centers. Boron atoms, as expected, constitute the most electron-deficient species in the complex molecule, whereas the neighboring oxygen and carbon atoms are the most significantly negatively charged ones. This part of the molecule appears to be very much involved in the charge transfer occurring between the acid fragment and oxyquinoline moiety leading to the observed fluorescence, as supported by the time-dependent density functional theory (TDDFT) results and the generated transition density maps. TDDFT calculations indicated that p-type atomic orbitals contributing to the HOMO-1, HOMO, and LUMO play the major role in the lowest energy transitions, and enabled further comparison with the charge density features, which is discussed in details. Furthermore, the results confirmed the known fact the Q ligand character is most important for the spectroscopic properties of this class of complexes.

La 139 and Cu 63 NMR investigation of charge order in La 2 CuO 4 + y ( T c = 42 K)

DOE PAGES

Imai, T.; Lee, Y. S.

2018-03-14

Here, we report 139La and 63Cu NMR investigation of the successive charge order, spin order, and superconducting transitions in superoxygenated La 2CuO 4+y single crystal with stage-4 excess oxygen order at T stage≃290 K. We show that the stage-4 order induces tilting of CuO 6 octahedra below T stage, which in turn causes 139La NMR line broadening. The structural distortion continues to develop far below Tstage, and completes at T charge≃60 K, where charge order sets in. This sequence is reminiscent of the the charge-order transition in Nd codoped La 1.88Sr 0.12CuO 4 that sets in once the low-temperature tetragonalmore » phase is established. We also show that the paramagnetic 63Cu NMR signals are progressively wiped out below T charge due to enhanced low-frequency spin fluctuations in charge-ordered domains, but the residual 63Cu NMR signals continue to exhibit the characteristics expected for optimally doped superconducting CuO 2 planes. This indicates that charge order in La 2CuO 4+y does not take place uniformly in space. In addition, unlike the typical second-order magnetic phase transitions, low-frequency Cu spin fluctuations as probed by 139La nuclear spin-lattice relaxation rate do not exhibit critical divergence at T spin(≃T c) =42 K. These findings, including the spatially inhomogeneous nature of the charge-ordered state, are qualitatively similar to the case of La 1.885Sr 0.115CuO 4, but both charge and spin order take place more sharply in the present case.« less

La 139 and Cu 63 NMR investigation of charge order in La 2 CuO 4 + y ( T c = 42 K)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Imai, T.; Lee, Y. S.

Here, we report 139La and 63Cu NMR investigation of the successive charge order, spin order, and superconducting transitions in superoxygenated La 2CuO 4+y single crystal with stage-4 excess oxygen order at T stage≃290 K. We show that the stage-4 order induces tilting of CuO 6 octahedra below T stage, which in turn causes 139La NMR line broadening. The structural distortion continues to develop far below Tstage, and completes at T charge≃60 K, where charge order sets in. This sequence is reminiscent of the the charge-order transition in Nd codoped La 1.88Sr 0.12CuO 4 that sets in once the low-temperature tetragonalmore » phase is established. We also show that the paramagnetic 63Cu NMR signals are progressively wiped out below T charge due to enhanced low-frequency spin fluctuations in charge-ordered domains, but the residual 63Cu NMR signals continue to exhibit the characteristics expected for optimally doped superconducting CuO 2 planes. This indicates that charge order in La 2CuO 4+y does not take place uniformly in space. In addition, unlike the typical second-order magnetic phase transitions, low-frequency Cu spin fluctuations as probed by 139La nuclear spin-lattice relaxation rate do not exhibit critical divergence at T spin(≃T c) =42 K. These findings, including the spatially inhomogeneous nature of the charge-ordered state, are qualitatively similar to the case of La 1.885Sr 0.115CuO 4, but both charge and spin order take place more sharply in the present case.« less

On the nature of the Mott transition in multiorbital systems

NASA Astrophysics Data System (ADS)

Facio, Jorge I.; Vildosola, V.; García, D. J.; Cornaglia, Pablo S.

2017-02-01

We analyze the nature of a Mott metal-insulator transition in multiorbital systems using dynamical mean-field theory. The auxiliary multiorbital quantum impurity problem is solved using continuous-time quantum Monte Carlo and the rotationally invariant slave-boson (RISB) mean-field approximation. We focus our analysis on the Kanamori Hamiltonian and find that there are two markedly different regimes determined by the nature of the lowest-energy excitations of the atomic Hamiltonian. The RISB results at T →0 suggest the following rule of thumb for the order of the transition at zero temperature: a second-order transition is to be expected if the lowest-lying excitations of the atomic Hamiltonian are charge excitations, while the transition tends to be first order if the lowest-lying excitations are in the same charge sector as the atomic ground state. At finite temperatures, the transition is first order and its strength, as measured, e.g., by the jump in the quasiparticle weight at the transition, is stronger in the parameter regime where the RISB method predicts a first-order transition at zero temperature. Interestingly, these results seem to apply to a wide variety of models and parameter regimes.

Charge-transfer channel in quantum dot-graphene hybrid materials

NASA Astrophysics Data System (ADS)

Cao, Shuo; Wang, Jingang; Ma, Fengcai; Sun, Mengtao

2018-04-01

The energy band theory of a classical semiconductor can qualitatively explain the charge-transfer process in low-dimensional hybrid colloidal quantum dot (QD)-graphene (GR) materials; however, the definite charge-transfer channels are not clear. Using density functional theory (DFT) and time-dependent DFT, we simulate the hybrid QD-GR nanostructure, and by constructing its orbital interaction diagram, we show the quantitative coupling characteristics of the molecular orbitals (MOs) of the hybrid structure. The main MOs are derived from the fragment MOs (FOs) of GR, and the Cd13Se13 QD FOs merge with the GR FOs in a certain proportion to afford the hybrid system. Upon photoexcitation, electrons in the GR FOs jump to the QD FOs, leaving holes in the GR FOs, and the definite charge-transfer channels can be found by analyzing the complex MOs coupling. The excited electrons and remaining holes can also be localized in the GR or the QD or transfer between the QD and GR with different absorption energies. The charge-transfer process for the selected excited states of the hybrid QD-GR structure are testified by the charge difference density isosurface. The natural transition orbitals, charge-transfer length analysis and 2D site representation of the transition density matrix also verify the electron-hole delocalization, localization, or coherence chacracteristics of the selected excited states. Therefore, our research enhances understanding of the coupling mechanism of low-dimensional hybrid materials and will aid in the design and manipulation of hybrid photoelectric devices for practical application in many fields.

Charge-transfer channel in quantum dot-graphene hybrid materials.

PubMed

Cao, Shuo; Wang, Jingang; Ma, Fengcai; Sun, Mengtao

2018-04-06

The energy band theory of a classical semiconductor can qualitatively explain the charge-transfer process in low-dimensional hybrid colloidal quantum dot (QD)-graphene (GR) materials; however, the definite charge-transfer channels are not clear. Using density functional theory (DFT) and time-dependent DFT, we simulate the hybrid QD-GR nanostructure, and by constructing its orbital interaction diagram, we show the quantitative coupling characteristics of the molecular orbitals (MOs) of the hybrid structure. The main MOs are derived from the fragment MOs (FOs) of GR, and the Cd 13 Se 13 QD FOs merge with the GR FOs in a certain proportion to afford the hybrid system. Upon photoexcitation, electrons in the GR FOs jump to the QD FOs, leaving holes in the GR FOs, and the definite charge-transfer channels can be found by analyzing the complex MOs coupling. The excited electrons and remaining holes can also be localized in the GR or the QD or transfer between the QD and GR with different absorption energies. The charge-transfer process for the selected excited states of the hybrid QD-GR structure are testified by the charge difference density isosurface. The natural transition orbitals, charge-transfer length analysis and 2D site representation of the transition density matrix also verify the electron-hole delocalization, localization, or coherence chacracteristics of the selected excited states. Therefore, our research enhances understanding of the coupling mechanism of low-dimensional hybrid materials and will aid in the design and manipulation of hybrid photoelectric devices for practical application in many fields.

Effect of solvent hydrogen bonding on the photophysical properties of intramolecular charge transfer probe trans-ethyl p-(dimethylamino) cinamate and its derivative

NASA Astrophysics Data System (ADS)

Singh, T. Sanjoy; Moyon, N. S.; Mitra, Sivaprasad

2009-08-01

Intramolecular charge transfer (ICT) behavior of trans-ethyl p-(dimethylamino) cinamate (EDAC) and 4-(dimethylamino) cinnamic acid (DMACA) were studied by steady state absorption and emission, picosecond time-resolved fluorescence experiments in various pure and mixed solvent systems. The large fluorescence spectral shift in more polar solvents indicates an efficient charge transfer from the donor site to the acceptor moiety in the excited state compared to the ground state. The energy for 0,0 transition ( ν0,0) for EDAC shows very good linear correlation with static solvent dielectric property; however, fluorescence emission maximum, stokes shift and fluorescence quantum yield show significant deviation from linearity in polar protic solvents, indicating a large contribution of solvent hydrogen bonding on the excited state relaxation mechanism. A quantitative estimation of contribution from different solvatochromic parameters was made using linear free energy relationship based on Kamlet-Taft equation.

Donor-σ-Acceptor Motifs: Thermally Activated Delayed Fluorescence Emitters with Dual Upconversion.

PubMed

Geng, Yan; D'Aleo, Anthony; Inada, Ko; Cui, Lin-Song; Kim, Jong Uk; Nakanotani, Hajime; Adachi, Chihaya

2017-12-22

A family of organic emitters with a donor-σ-acceptor (D-σ-A) motif is presented. Owing to the weakly coupled D-σ-A intramolecular charge-transfer state, a transition from the localized excited triplet state ( 3 LE) and charge-transfer triplet state ( 3 CT) to the charge-transfer singlet state ( 1 CT) occurred with a small activation energy and high photoluminescence quantum efficiency. Two thermally activated delayed fluorescence (TADF) components were identified, one of which has a very short lifetime of 200-400 ns and the other a longer TADF lifetime of the order of microseconds. In particular, the two D-σ-A materials presented strong blue emission with TADF properties in toluene. These results will shed light on the molecular design of new TADF emitters with short delayed lifetimes. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Ligand field splittings in core level transitions for transition metal (TM) oxides: Tanabe-Sugano diagrams and (TM) dangling bonds in vacated O-atom defects

NASA Astrophysics Data System (ADS)

Lucovsky, Gerry; Wu, Kun; Pappas, Brian; Whitten, Jerry

2013-04-01

Defect states in the forbidden band-gap below the conduction band edge are active as electron traps in nano-grain high-) transition metal (TM) oxides with thickness >0.3 nm, e.g., ZrO2 and HfO2. These oxides have received considerable attention as gate-dielectrics in complementary metal oxide semiconductor (CMOS) devices, and more recently are emerging as candidates for charge storage and memory devices. To provide a theoretical basis for device functionality, ab-initio many-electron theory is combined with X-ray absorption spectroscopy (XAS) to study O K edge and TM core level transitions. These studies identify ligand field splittings (ΔLF) for defect state features,. When compared with those obtained from O-atom and TM-atom core spectroscopic transitions, this provides direct information about defect state sun-nm bonding arrangements. comparisons are made for (i) elemental TiO2 and Ti2O3 with different formal ionic charges, Ti4+ and Ti3+ and for (ii) Magneli Phase alloys, TinO2n-1, n is an integer 9>=n>3, and (TiO2)x(HfO2)1-x alloys. The alloys display multi-valent behavior from (i) different ionic-charge states, (ii} local bond-strain, and (iii) metallic hopping transport. The intrinsic bonding defects in TM oxides are identified as pairs of singly occupied dangling bonds. For 6-fold coordinated Ti-oxides defect excited states in 2nd derivative O K pre-edge spectra are essentially the same as single Ti-atom d2 transitions in Tanabe-Sugano (T-S) diagrams. O-vacated site defects in 8-fold coordinated ZrO2 and HfO2 are described by d8 T-S diagrams. T-S defect state ordering and splittings are functions of the coordination and symmetry of vacated site bordering TM atoms. ΔLF values from the analysis of T-S diagrams indicate medium range order (MRO) extending to 3rd and 4th nearest-neighbor (NN) TM-atoms. Values are different for 6-fold Ti, and 8-fold ZrO2 and HfO2, and scale inversely with differences in respective formal ionic radii. O-vacated site bonding defects in TM nano-grain oxides are qualitatively similar to vacant-site defects in non-crystalline SiO2 and GeO2 for ulta-thin films, < 0.2 nm thick, and yield similar performance in MOSCAPs on Ge substrates heralding applications in aggressively-scale CMOS devices.

Jahn-Teller effects in transition-metal compounds with small charge-transfer energy

NASA Astrophysics Data System (ADS)

Mizokawa, Takashi

2013-04-01

We have studied Jahn-Teller effects in Cs2Au2Br6, ACu3Co4O12(A=Ca or Y), and IrTe2 in which the ligand p-to-transition-metal d charge-transfer energy is small or negative. The Au+/Au3+ charge disproportionation of Cs2Au2Br6 manifests in Au 4f photoemission spectra. In Cs2Au2Br6 with negative Δ and intermediate U, the charge disproportionation can be described using effective d orbitals constructed from the Au 5d and Br 4p orbitals and is stabilized by the Jahn-Teller distortion of the Au3+ site with low-spin d8 configuration. In ACu3Co4O12, Δs for Cu3+ and Co4+ are negative and Us are very large. The Zhang-Rice picture is valid to describe the electronic state, and the valence change from Cu2+/Co4+ to Cu3+/Co3+ can be viewed as the O 2p hole transfer from Co to Cu or d9 + d6L → d9L + d6. In IrTe2, both Δ and U are small and the Ir 5d and Te 5p electrons are itinerant to form the multi-band Fermi surfaces. The ideas of band Jahn-Teller transition and Peierls transition are useful to describe the structural instabilities.

Spin-valley locking in the normal state of a transition-metal dichalcogenide superconductor.

PubMed

Bawden, L; Cooil, S P; Mazzola, F; Riley, J M; Collins-McIntyre, L J; Sunko, V; Hunvik, K W B; Leandersson, M; Polley, C M; Balasubramanian, T; Kim, T K; Hoesch, M; Wells, J W; Balakrishnan, G; Bahramy, M S; King, P D C

2016-05-23

Metallic transition-metal dichalcogenides (TMDCs) are benchmark systems for studying and controlling intertwined electronic orders in solids, with superconductivity developing from a charge-density wave state. The interplay between such phases is thought to play a critical role in the unconventional superconductivity of cuprates, Fe-based and heavy-fermion systems, yet even for the more moderately-correlated TMDCs, their nature and origins have proved controversial. Here, we study a prototypical example, 2H-NbSe2, by spin- and angle-resolved photoemission and first-principles theory. We find that the normal state, from which its hallmark collective phases emerge, is characterized by quasiparticles whose spin is locked to their valley pseudospin. This results from a combination of strong spin-orbit interactions and local inversion symmetry breaking, while interlayer coupling further drives a rich three-dimensional momentum dependence of the underlying Fermi-surface spin texture. These findings necessitate a re-investigation of the nature of charge order and superconducting pairing in NbSe2 and related TMDCs.

Analogous Gamow-Teller and M1 Transitions in Tz = ±½ Mirror Nuclei and in Tz = ±1, 0 Triplet Nuclei relevant to Low-energy Super GT state

NASA Astrophysics Data System (ADS)

Fujita, Yoshitaka; Fujita, Hirohiko; Tanumura, Yusuke

2018-05-01

Nuclei have spin- and isospin-degrees of freedom. Therefore, Gamow-Teller (GT) transitions caused by the στ operator (spin-isospin operator) are unique tools for the studies of nuclear structure as well as nuclear interactions. They can be studied in β decays as well as charge-exchange (CE) reactions. Similarly, M1 γ decays are mainly caused by the στ operator. Combined studies of these transitions caused by Weak, Strong, and Electro-Magnetic interactions provide us a deeper understanding of nuclear spin-isospin-type transitions. We first compare the strengths of analogous GT and M1 transitions in the A = 27, Tz = ±½ mirror nuclei 27Al and 27Si. The comparison is extended to the Tz = ±1, 0 nuclei. The strength of GT transition from the ground state (g.s.) of 42Ca to the 0.611 MeV first Jπ = 1+ state in 42Sc is compared with that of the analogous M1 transition from the 0.611 MeV state to the T = 1, 0+ g.s. (isobaric analog state: IAS) in 42Sc. The 0.611 MeV state has the property of Low-energy Super GT (LeSGT) state, because it carries the main part of the GT strength of all available transitions from the g.s. of 42Ca (and 42Ti) to the Jπ = 1+ GT states in 42Sc.

Narrowband noise study of sliding charge density waves in NbSe3 nanoribbons

NASA Astrophysics Data System (ADS)

Onishi, Seita; Jamei, Mehdi; Zettl, Alex

2017-02-01

Transport properties (dc electrical resistivity, threshold electric field, and narrow-band noise) are reported for nanoribbon specimens of NbSe3 with thicknesses as low as 18 nm. As the sample thickness decreases, the resistive anomalies characteristic of the charge density wave (CDW) state are suppressed and the threshold fields for nonlinear CDW conduction apparently diverge. Narrow-band noise measurements allow determination of the concentration of carriers condensed in the CDW state n c , reflective of the CDW order parameter Δ. Although the CDW transition temperatures are relatively independent of sample thickness, in the lower CDW state Δ decreases dramatically with decreasing sample thickness.

Ultrafast photoinduced charge transport in Pt(II) donor-acceptor assembly bearing naphthalimide electron acceptor and phenothiazine electron donor.

PubMed

Sazanovich, Igor V; Best, Jonathan; Scattergood, Paul A; Towrie, Michael; Tikhomirov, Sergei A; Bouganov, Oleg V; Meijer, Anthony J H M; Weinstein, Julia A

2014-12-21

Visible light-induced charge transfer dynamics were investigated in a novel transition metal triad acceptor-chromophore-donor, (NDI-phen)Pt(II)(-C≡C-Ph-CH2-PTZ)2 (1), designed for photoinduced charge separation using a combination of time-resolved infrared (TRIR) and femtosecond electronic transient absorption (TA) spectroscopy. In 1, the electron acceptor is 1,4,5,8-naphthalene diimide (NDI), and the electron donor is phenothiazine (PTZ), and [(phen)Pt(-C≡C-Ph-)], where phen is 1,10-phenanthroline, represents the chromophoric core. The first excited state observed in 1 is a (3)MLCT/LL'CT, with {Pt(II)-acetylide}-to-phen character. Following that, charge transfer from the phen-anion onto the NDI subunit to form NDI(-)-phen-[Pt-(C≡C)2](+)-PTZ2 occurs with a time constant of 2.3 ps. This transition is characterised by appearance of the prominent NDI-anion features in both TRIR and TA spectra. The final step of the charge separation in 1 proceeds with a time constant of ∼15 ps during which the hole migrates from the [Pt-(C≡C)2] subunit to one of the PTZ groups. Charge recombination in 1 then occurs with two distinct time constants of 36 ns and 107 ns, corresponding to the back electron transfer to each of the two donor groups; a rather rare occurrence which manifests that the hole in the final charge-separated state is localised on one of the two donor PTZ groups. The assignment of the nature of the excited states and dynamics in 1 was assisted by TRIR investigations of the analogous previously reported ((COOEt)2bpy)Pt(C≡C-Ph-CH2-PTZ)2 (2), (J. E. McGarrah and R. Eisenberg, Inorg. Chem., 2003, 42, 4355; J. E. McGarrah, J. T. Hupp and S. N. Smirnov, J. Phys. Chem. A, 2009, 113, 6430) as well as (bpy)Pt(C≡C-Ph-C7H15)2, which represent the acceptor-free dyad, and the chromophoric core, respectively. Thus, the step-wise formation of the full charge-separated state on the picosecond time scale and charge recombination via tunnelling have been established; and the presence of two distinct charge recombination pathways has been observed.

Black p-branes versus black holes in non-asymptotically flat Einstein-Yang-Mills theory

NASA Astrophysics Data System (ADS)

Habib Mazharimousavi, S.; Halilsoy, M.

2016-09-01

We present a class of non-asymptotically flat (NAF) charged black p-branes (BpB) with p-compact dimensions in higher-dimensional Einstein-Yang-Mills theory. Asymptotically the NAF structure manifests itself as an anti-de sitter spacetime. We determine the total mass/energy enclosed in a thin shell located outside the event horizon. By comparing the entropies of BpB with those of black holes in the same dimensions we derive transition criteria between the two types of black objects. Given certain conditions satisfied, our analysis shows that BpB can be considered excited states of black holes. An event horizon r+ versus charge square Q2 plot for the BpB reveals such a transition where r+ is related to the horizon radius rh of the black hole (BH) both with the common charge Q.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Xu, Jing; Hu, Enyuan; Nordlund, Dennis

The phase transition, charge compensation, and local chemical environment of Ni in LiNiO 2 were investigated to understand the degradation mechanism. The electrode was subjected to a variety of bulk and surface-sensitive characterization techniques under different charge–discharge cycling conditions. We observed the phase transition from the original hexagonal H1 phase to another two hexagonal phases (H2 and H3) upon Li deintercalation. Moreover, the gradual loss of H3-phase features was revealed during the repeated charges. The reduction in Ni redox activity occurred at both the charge and the discharge states, and it appeared both in the bulk and at the surfacemore » over the extended cycles. In conclusion, the degradation of crystal structure significantly contributes to the reduction of Ni redox activity, which in turn causes the cycling performance decay of LiNiO 2.« less

Gamow-Teller transitions in the 64Ni(3He, t)64Cu reaction

NASA Astrophysics Data System (ADS)

Popescu, L.; Adachi, T.; Berg, G. P. A.; von Brentano, P.; De Frenne, D.; Fujita, K.; Fujita, Y.; Hatanaka, K.; Jacobs, E.; Negret, A.; Nakanishi, K.; Sakemi, Y.; Shimbara, Y.; Shimizu, Y.; Tameshige, Y.; Tamii, A.; Uchida, M.; Yosoi, M.

2005-10-01

In order to study the Gamow-Teller (GT) transitions in the fp-shell nucleus 64Cu, the 64Ni(3He, t)64Cu charge-exchange reaction was investigated at E3He= 140 MeV/nucleon [1]. The outgoing tritons were momentum analysed by the Grand Raiden spectrometer at 0°. The very high energy resolution of 35 keV (FWHM) allowed the separation of individual levels in the excitation energy region from 0 to 3.5 MeV. An angular distribution analysis was performed for the observed transitions to these states. In addition to the ground state (g.s.), known to be a Jπ = 1+ GT state, several excited states showed L = 0 nature, making them candidates of GT states. At higher excitation energies, the level density becomes very high and a bump-like structure, the so-called GT Giant Resonance, dominates the spectrum.

Ultrafast dynamics of multi-exciton state coupled to coherent vibration in zinc chlorin aggregates for artificial photosynthesis.

PubMed

Shi, Tongchao; Liu, Zhengzheng; Miyatake, Tomohiro; Tamiaki, Hitoshi; Kobayashi, Takayoshi; Zhang, Zeyu; Du, Juan; Leng, Yuxin

2017-11-27

Ultrafast vibronic dynamics induced by the interaction of the Frenkel exciton with the coherent molecular vibrations in a layer-structured zinc chlorin aggregates prepared for artificial photosynthesis have been studied by 7.1 fs real-time vibrational spectroscopy with multi-spectrum detection. The fast decay of 100 ± 5fs is ascribed to the relaxation from the higher multi-exciton state (MES) to the one-exciton state, and the slow one of 863 ± 70fs is assigned to the relaxation from Q-exciton state to the dark nonfluorescent charge-transfer (CT) state, respectively. In addition, the wavelength dependences of the exciton-vibration coupling strength are found to follow the zeroth derivative of the transient absorption spectra of the exciton. It could be explained in term of the transition dipole moment modulated by dynamic intensity borrowing between the B transition and the Q transition through the vibronic interactions.

Cu doped diamond: Effect of charge state and defect aggregation on spin interactions in a 3d transition metal doped wide band-gap semiconductor

NASA Astrophysics Data System (ADS)

Benecha, E. M.; Lombardi, E. B.

2018-05-01

We present a first principles study of Cu in diamond using DFT+U electronic structure methods, by carefully considering the impact of co-doping, charge state, and Fermi level position on its stability, lattice location, spin states, and electronic properties. We show that the energetic stability and spin states of Cu are strongly dependent on the Fermi level position and the type of diamond co-doping, with Cu being energetically more favorable in n-type or p-type co-doped diamond compared to intrinsic diamond. Since Cu has been predicted to order magnetically in a number of other wide band-gap semiconductors, we have also evaluated this possibility for Cu doped diamond. We show that while Cu exhibits strong spin interactions at specific interatomic separations in diamond, a detailed consideration of the impact of Fermi level position and Cu aggregation precludes magnetic ordering, with Cu forming non-magnetic, antiferromagnetic, or paramagnetic clusters. These results have important implications in the understanding of the properties of transition metal dopants in diamond for device applications.

Steady-state and time-resolved studies on the photophysical properties of fullerene-pyropheophorbide a complexes in polar and nonpolar solvents

NASA Astrophysics Data System (ADS)

Ermilov, E. A.; Al-Omari, S.; Helmreich, M.; Jux, N.; Hirsch, A.; Röder, B.

2004-04-01

A novel monofullerene-bis(pyropheophorbide a) dyad has been photophysically characterized by steady-state as well as time-resolved techniques. It was revealed that in this complex strong and fast quenching of the first excited singlet state of the pyropheophorbide a (pyroPheo) molecule occurs by efficient photoinduced electron transfer to the fullerene moiety in both polar (DMF) and nonpolar (toluene) solvents. In DMF the energy of the charge-separated state is 0.94 eV and it undergoes directly transition to the ground state resulting in a very low value of photosensitized singlet oxygen generation. In contrast to the situation in a polar solvent, in toluene the charge-separated state lies above the exited triplet state of pyroPheo as well as that of C 60. It has been shown that in a nonpolar solvent a sufficient amount of singlet oxygen was generated by energy transfer from the excited triplet state of pyroPheo which has been populated via relaxation of the charge-separated state.

Transition metal redox and Mn disproportional reaction in LiMn0.5Fe0.5PO4 electrodes cycled with aqueous electrolyte

NASA Astrophysics Data System (ADS)

Zhuo, Zengqing; Hu, Jiangtao; Duan, Yandong; Yang, Wanli; Pan, Feng

2016-07-01

We performed soft x-ray absorption spectroscopy (sXAS) and a quantitative analysis of the transition metal redox in the LiMn0.5Fe0.5PO4 electrodes upon electrochemical cycling. In order to circumvent the complication of the surface reactions with organic electrolyte at high potential, the LiMn0.5Fe0.5PO4 electrodes are cycled with aqueous electrolyte. The analysis of the transitional metal L-edge spectra allows a quantitative determination of the redox evolution of Mn and Fe during the electrochemical cycling. The sXAS analysis reveals the evolving Mn oxidation states in LiMn0.5Fe0.5PO4. We found that electrochemically inactive Mn2+ is formed on the electrode surface during cycling. Additionally, the signal indicates about 20% concentration of Mn4+ at the charged state, providing a strong experimental evidence of the disproportional reaction of Mn3+ to Mn2+ and Mn4+ on the surface of the charged LiMn0.5Fe0.5PO4 electrodes.

Band structure dynamics in indium wires

NASA Astrophysics Data System (ADS)

Chávez-Cervantes, M.; Krause, R.; Aeschlimann, S.; Gierz, I.

2018-05-01

One-dimensional indium wires grown on Si(111) substrates, which are metallic at high temperatures, become insulating below ˜100 K due to the formation of a charge density wave (CDW). The physics of this transition is not conventional and involves a multiband Peierls instability with strong interband coupling. This CDW ground state is readily destroyed with femtosecond laser pulses resulting in a light-induced insulator-to-metal phase transition. The current understanding of this transition remains incomplete, requiring measurements of the transient electronic structure to complement previous investigations of the lattice dynamics. Time- and angle-resolved photoemission spectroscopy with extreme ultraviolet radiation is applied to this end. We find that the transition from the insulating to the metallic band structure occurs within ˜660 fs, which is a fraction of the amplitude mode period. The long lifetime of the transient state (>100 ps) is attributed to trapping in a metastable state in accordance with previous work.

Facilitating a Major Staffing Transition in a State Psychiatric Hospital With Changes to Nursing Orientation.

PubMed

Birnbaum, Shira; Sperber-Weiss, Doreen; Dimitrios, Timothy; Eckel, Donald; Monroy-Miller, Cherry; Monroe, Janet J; Friedman, Ross; Ologbosele, Mathias; Epo, Grace; Sharpe, Debra; Zarski, Yongsuk

A large state psychiatric hospital experienced a state-mandated Reduction in Force that resulted in the abrupt loss and rapid turnover of more than 40% of its nursing and paraprofessional staff. The change exemplified current national trends toward downsizing and facility closure. This article describes revisions to the nursing orientation program that supported cost containment and fidelity to mission and clinical practices during the transition. An existing nursing orientation program was reconfigured in alignment with principles of rational instructional design and a core-competencies model of curriculum development, evidence-based practices that provided tactical clarity and commonality of purpose during a complex and emotionally charged transition period. Program redesign enabled efficiencies that facilitated the transition, with no evidence of associated negative effects. The process described here offers an example for hospitals facing similar workforce reorganization in an era of public sector downsizing.

Transition energy measurements in hydrogenlike and heliumlike ions strongly supporting bound-state QED calculations

NASA Astrophysics Data System (ADS)

Kubiček, K.; Mokler, P. H.; Mäckel, V.; Ullrich, J.; López-Urrutia, J. R. Crespo

2014-09-01

For the hydrogenlike Ar17+ ion, the 1s Lamb shift was absolutely determined with a 1.4% accuracy based on Lyman-α wavelength measurements that have negligible uncertainties from nuclear size effects. The result agrees with state-of-the-art quantum electrodynamics (QED) calculations, and demonstrates the suitability of Lyman-α transitions in highly charged ions as x-ray energy standards, accurate at the five parts-per-million level. For the heliumlike Ar16+ ion the transition energy for the 1s2p1P1→1s21S0 line was also absolutely determined on an even higher level of accuracy. Additionally, we present relative measurements of transitions in S15+,S14+, and Fe24+ ions. The data for the heliumlike S14+,Ar16+, and Fe24+ ions stringently confirm advanced bound-state QED predictions including screened QED terms that had recently been contested.

Theory of hydrodynamic transport in fluctuating electronic charge density wave states

NASA Astrophysics Data System (ADS)

Delacrétaz, Luca V.; Goutéraux, Blaise; Hartnoll, Sean A.; Karlsson, Anna

2017-11-01

We describe the collective hydrodynamic motion of an incommensurate charge density wave state in a clean electronic system. Our description simultaneously incorporates the effects of both pinning due to weak disorder and also phase relaxation due to proliferating dislocations. We show that the interplay between these two phenomena has important consequences for charge and momentum transport. For instance, it can lead to metal-insulator transitions. We furthermore identify signatures of fluctuating density waves in frequency and spatially resolved conductivities. Phase disordering is well known to lead to a large viscosity. We derive a precise formula for the phase relaxation rate in terms of the viscosity in the dislocation cores. We thereby determine the viscosity of the superconducting state of BSCCO from the observed melting dynamics of Abrikosov lattices and show that the result is consistent with dissipation into Bogoliubov quasiparticles.

Pressure-temperature phase diagram of a charge-ordered organic conductor studied by C13 NMR

NASA Astrophysics Data System (ADS)

Itou, T.; Miyagawa, K.; Nakamura, J.; Kanoda, K.; Hiraki, K.; Takahashi, T.

2014-07-01

We performed C13 NMR measurements on the quasi-one-dimensional (Q1D) charge-ordered system (DI-DCNQI)2Ag under ambient and applied pressure to clarify the pressure-temperature phase diagram. For pressures up to 15 kbar, the NMR spectra exhibit complicated splitting at low temperatures, indicating a "generalized 3D Wigner crystal" state. In this pressure region, we find that increased pressure causes a decrease in the charge disproportionation ratio, along with a decrease in the transition temperature of the generalized 3D Wigner crystal. In the high-pressure region, near 20 kbar, where a 1D confined liquid crosses over to a 3D Fermi liquid at high temperatures, the ground state is replaced by a nonmagnetic insulating state that is qualitatively different from the generalized 3D Wigner crystal.

Materials for Nonlinear Optics Chemical Perspectives

DTIC Science & Technology

1991-01-01

formation of these polarized states has been referred to in terms of " viru transitions". The polarization behavior can be written in terms of the...MATERIALS FOR NONUNEAR OPTICS: CHEMICAL PERSPECTIVES also be corona -poled. Either way, the films are ideally suited for guided wave applications. With...electrodes, or a corona charging station, similar to that used in electrophotographic copiers, can be used to apply charged particles to the insulating

Stacked charge stripes in the quasi-2D trilayer nickelate La4Ni3O8

NASA Astrophysics Data System (ADS)

Zhang, Junjie; Chen, Yu-Sheng; Phelan, D.; Zheng, Hong; Norman, M. R.; Mitchell, J. F.

2016-08-01

The quasi-2D nickelate La4Ni3O8 (La-438), consisting of trilayer networks of square planar Ni ions, is a member of the so-called T' family, which is derived from the Ruddlesden-Popper (R-P) parent compound La4Ni3O10-x by removing two oxygen atoms and rearranging the rock salt layers to fluorite-type layers. Although previous studies on polycrystalline samples have identified a 105-K phase transition with a pronounced electronic and magnetic response but weak lattice character, no consensus on the origin of this transition has been reached. Here, we show using synchrotron X-ray diffraction on high-pO2 floating zone-grown single crystals that this transition is associated with a real space ordering of charge into a quasi-2D charge stripe ground state. The charge stripe superlattice propagation vector, q = (2/3, 0, 1), corresponds with that found in the related 1/3-hole doped single-layer R-P nickelate, La5/3Sr1/3NiO4 (LSNO-1/3; Ni2.33+), with orientation at 45° to the Ni-O bonds. The charge stripes in La-438 are weakly correlated along c to form a staggered ABAB stacking that reduces the Coulomb repulsion among the stripes. Surprisingly, however, we find that the charge stripes within each trilayer of La-438 are stacked in phase from one layer to the next, at odds with any simple Coulomb repulsion argument.

Hall effect in quantum critical charge-cluster glass

DOE PAGES

Bozovic, Ivan; Wu, Jie; Bollinger, Anthony T.; ...

2016-04-04

Upon doping, cuprates undergo a quantum phase transition from an insulator to a d-wave superconductor. The nature of this transition and of the insulating state is vividly debated. Here, we study the Hall effect in La 2-xSr xCuO 4 (LSCO) samples doped near the quantum critical point at x ≈ 0.06. Dramatic fluctuations in the Hall resistance appear below T CG ≈ 1.5 K and increase as the sample is cooled down further, signaling quantum critical behavior. We explore the doping dependence of this effect in detail, by studying a combinatorial LSCO library in which the Sr content is variedmore » in extremely fine steps, Δx ≈ 0.00008. Furthermore, we observe that quantum charge fluctuations wash out when superconductivity emerges but can be restored when the latter is suppressed by applying a magnetic field, showing that the two instabilities compete for the ground state.« less

Hall effect in quantum critical charge-cluster glass

PubMed Central

Wu, Jie; Bollinger, Anthony T.; Sun, Yujie; Božović, Ivan

2016-01-01

Upon doping, cuprates undergo a quantum phase transition from an insulator to a d-wave superconductor. The nature of this transition and of the insulating state is vividly debated. Here, we study the Hall effect in La2-xSrxCuO4 (LSCO) samples doped near the quantum critical point at x ∼ 0.06. Dramatic fluctuations in the Hall resistance appear below TCG ∼ 1.5 K and increase as the sample is cooled down further, signaling quantum critical behavior. We explore the doping dependence of this effect in detail, by studying a combinatorial LSCO library in which the Sr content is varied in extremely fine steps, Δx ∼ 0.00008. We observe that quantum charge fluctuations wash out when superconductivity emerges but can be restored when the latter is suppressed by applying a magnetic field, showing that the two instabilities compete for the ground state. PMID:27044081

Hall effect in quantum critical charge-cluster glass.

PubMed

Wu, Jie; Bollinger, Anthony T; Sun, Yujie; Božović, Ivan

2016-04-19

Upon doping, cuprates undergo a quantum phase transition from an insulator to a d-wave superconductor. The nature of this transition and of the insulating state is vividly debated. Here, we study the Hall effect in La2-xSrxCuO4(LSCO) samples doped near the quantum critical point atx∼ 0.06. Dramatic fluctuations in the Hall resistance appear belowTCG∼ 1.5 K and increase as the sample is cooled down further, signaling quantum critical behavior. We explore the doping dependence of this effect in detail, by studying a combinatorial LSCO library in which the Sr content is varied in extremely fine steps,Δx∼ 0.00008. We observe that quantum charge fluctuations wash out when superconductivity emerges but can be restored when the latter is suppressed by applying a magnetic field, showing that the two instabilities compete for the ground state.

Structural instability and electronic localization in the 2:1 salts: The case of the Fabre and the (DMtTTF){2}CIO{4}salts

NASA Astrophysics Data System (ADS)

Ravy, S.; Foury-Leylekian, P.; Le Bolloc'h, D.; Pouget, J.-P.; Fabre, J. M.; Prado, R. J.; Lagarde, P.

2004-04-01

The charge ordering observed in the (TMTTF){2}X family has been studied by X-ray absorption spectroscopy. XANES measurements at the Sulfur K-edge show no evidence of charge disproportionation larger than 0.5 e, and EXAFS at the Phosphorus K-edge indicate no displacements of the PF{6} anion larger than 0.05 Å. The difficulty to observe a structural signature of this charge ordering is due to the triclinic symmetry of these salts. By contrast, in the monoclinic charge transfer salt (DMtTTF){2}ClO{4}, a screw axis symmetry constrains the molecular stacks to be uniform. In this real 1/4-filled system, charge localization is observed at about 150 K. We show that around this temperature an incommensurate modulation of reduced wave vector (0.58,0,-0.275) is stabilized. The transition is strongly hysteretic, but no long range order is established. We suggest that this modulation, which has the 4k{F} periodicity in the chain direction, stabilizes a local antiferroelectric state similar to the one previously observed in (TMTTF){2}SCN. Key words. Charge ordering, Structural phase transition.

Symmetry-broken states in a system of interacting bosons on a two-leg ladder with a uniform Abelian gauge field

NASA Astrophysics Data System (ADS)

Greschner, S.; Piraud, M.; Heidrich-Meisner, F.; McCulloch, I. P.; Schollwöck, U.; Vekua, T.

2016-12-01

We study the quantum phases of bosons with repulsive contact interactions on a two-leg ladder in the presence of a uniform Abelian gauge field. The model realizes many interesting states, including Meissner phases, vortex fluids, vortex lattices, charge density waves, and the biased-ladder phase. Our work focuses on the subset of these states that breaks a discrete symmetry. We use density matrix renormalization group simulations to demonstrate the existence of three vortex-lattice states at different vortex densities and we characterize the phase transitions from these phases into neighboring states. Furthermore, we provide an intuitive explanation of the chiral-current reversal effect that is tied to some of these vortex lattices. We also study a charge-density-wave state that exists at 1/4 particle filling at large interaction strengths and flux values close to half a flux quantum. By changing the system parameters, this state can transition into a completely gapped vortex-lattice Mott-insulating state. We elucidate the stability of these phases against nearest-neighbor interactions on the rungs of the ladder relevant for experimental realizations with a synthetic lattice dimension. A charge-density-wave state at 1/3 particle filling can be stabilized for flux values close to half a flux quantum and for very strong on-site interactions in the presence of strong repulsion on the rungs. Finally, we analytically describe the emergence of these phases in the low-density regime, and, in particular, we obtain the boundaries of the biased-ladder phase, i.e., the phase that features a density imbalance between the legs. We make contact with recent quantum-gas experiments that realized related models and discuss signatures of these quantum states in experimentally accessible observables.

Monolayer optical memory cells based on artificial trap-mediated charge storage and release

NASA Astrophysics Data System (ADS)

Lee, Juwon; Pak, Sangyeon; Lee, Young-Woo; Cho, Yuljae; Hong, John; Giraud, Paul; Shin, Hyeon Suk; Morris, Stephen M.; Sohn, Jung Inn; Cha, Seungnam; Kim, Jong Min

2017-03-01

Monolayer transition metal dichalcogenides are considered to be promising candidates for flexible and transparent optoelectronics applications due to their direct bandgap and strong light-matter interactions. Although several monolayer-based photodetectors have been demonstrated, single-layered optical memory devices suitable for high-quality image sensing have received little attention. Here we report a concept for monolayer MoS2 optoelectronic memory devices using artificially-structured charge trap layers through the functionalization of the monolayer/dielectric interfaces, leading to localized electronic states that serve as a basis for electrically-induced charge trapping and optically-mediated charge release. Our devices exhibit excellent photo-responsive memory characteristics with a large linear dynamic range of ~4,700 (73.4 dB) coupled with a low OFF-state current (<4 pA), and a long storage lifetime of over 104 s. In addition, the multi-level detection of up to 8 optical states is successfully demonstrated. These results represent a significant step toward the development of future monolayer optoelectronic memory devices.

Angular studies of the magnetoresistance in the density wave state of the quasi-two-dimensional purple bronze KMo6O17

NASA Astrophysics Data System (ADS)

Guyot, H.; Dumas, J.; Kartsovnik, M. V.; Marcus, J.; Schlenker, C.; Sheikin, I.; Vignolles, D.

2007-07-01

The purple molybdenum bronze KMo6O17 is a quasi-two-dimensional compound which shows a Peierls transition towards a commensurate metallic charge density wave (CDW) state. High magnetic field measurements have revealed several transitions at low temperature and have provided an unusual phase diagram “temperature-magnetic field”. Angular studies of the interlayer magnetoresistance are now reported. The results suggest that the orbital coupling of the magnetic field to the CDW is the most likely mechanism for the field induced transitions. The angular dependence of the magnetoresistance is discussed on the basis of a warped quasi-cylindrical Fermi surface and provides information on the geometry of the Fermi surface in the low temperature density wave state.

Strongly correlated superconductivity and quantum criticality

NASA Astrophysics Data System (ADS)

Tremblay, A.-M. S.

Doped Mott insulators and doped charge-transfer insulators describe classes of materials that can exhibit unconventional superconducting ground states. Examples include the cuprates and the layered organic superconductors of the BEDT family. I present results obtained from plaquette cellular dynamical mean-field theory. Continuous-time quantum Monte Carlo evaluation of the hybridization expansion allows one to study the models in the large interaction limit where quasiparticles can disappear. The normal state which is unstable to the superconducting state exhibits a first-order transition between a pseudogap and a correlated metal phase. That transition is the finite-doping extension of the metal-insulator transition obtained at half-filling. This transition serves as an organizing principle for the normal and superconducting states of both cuprates and doped organic superconductors. In the less strongly correlated limit, these methods also describe the more conventional case where the superconducting dome surrounds an antiferromagnetic quantum critical point. Sponsored by NSERC RGPIN-2014-04584, CIFAR, Research Chair in the Theory of Quantum Materials.

Communication: Fragment-based Hamiltonian model of electronic charge-excitation gaps and gap closure

DOE Office of Scientific and Technical Information (OSTI.GOV)

Valone, S. M.; Pilania, G.; Liu, X. Y.

2015-11-14

Capturing key electronic properties such as charge excitation gaps within models at or above the atomic scale presents an ongoing challenge to understanding molecular, nanoscale, and condensed phase systems. One strategy is to describe the system in terms of properties of interacting material fragments, but it is unclear how to accomplish this for charge-excitation and charge-transfer phenomena. Hamiltonian models such as the Hubbard model provide formal frameworks for analyzing gap properties but are couched purely in terms of states of electrons, rather than the states of the fragments at the scale of interest. The recently introduced Fragment Hamiltonian (FH) modelmore » uses fragments in different charge states as its building blocks, enabling a uniform, quantum-mechanical treatment that captures the charge-excitation gap. These gaps are preserved in terms of inter-fragment charge-transfer hopping integrals T and on-fragment parameters U{sup (FH)}. The FH model generalizes the standard Hubbard model (a single intra-band hopping integral t and on-site repulsion U) from quantum states for electrons to quantum states for fragments. We demonstrate that even for simple two-fragment and multi-fragment systems, gap closure is enabled once T exceeds the threshold set by U{sup (FH)}, thus providing new insight into the nature of metal-insulator transitions. This result is in contrast to the standard Hubbard model for 1d rings, for which Lieb and Wu proved that gap closure was impossible, regardless of the choices for t and U.« less

Direct evidence for radiative charge transfer after inner-shell excitation and ionization of large clusters

NASA Astrophysics Data System (ADS)

Hans, Andreas; Stumpf, Vasili; Holzapfel, Xaver; Wiegandt, Florian; Schmidt, Philipp; Ozga, Christian; Reiß, Philipp; Ben Ltaief, Ltaief; Küstner-Wetekam, Catmarna; Jahnke, Till; Ehresmann, Arno; Demekhin, Philipp V.; Gokhberg, Kirill; Knie, André

2018-01-01

We directly observe radiative charge transfer (RCT) in Ne clusters by dispersed vacuum-ultraviolet photon detection. The doubly ionized Ne2+-{{{N}}{{e}}}n-1 initial states of RCT are populated after resonant 1s-3p photoexcitation or 1s photoionization of Ne n clusters with < n> ≈ 2800. These states relax further producing Ne+-Ne+-{{{N}}{{e}}}n-2 final states, and the RCT photon is emitted. Ab initio calculations assign the observed RCT signal to the{}{{{N}}{{e}}}2+(2{{{p}}}-2{[}1{{D}}]){--}{{{N}}{{e}}}n-1 initial state, while transitions from other possible initial states are proposed to be quenched by competing relaxation processes. The present results are in agreement with the commonly discussed scenario, where the doubly ionized atom in a noble gas cluster forms a dimer which dissipates its vibrational energy on a picosecond timescale. Our study complements the picture of the RCT process in weakly bound clusters, providing information which is inaccessible by charged particle detection techniques.

Quantum phase transition with dissipative frustration

NASA Astrophysics Data System (ADS)

Maile, D.; Andergassen, S.; Belzig, W.; Rastelli, G.

2018-04-01

We study the quantum phase transition of the one-dimensional phase model in the presence of dissipative frustration, provided by an interaction of the system with the environment through two noncommuting operators. Such a model can be realized in Josephson junction chains with shunt resistances and resistances between the chain and the ground. Using a self-consistent harmonic approximation, we determine the phase diagram at zero temperature which exhibits a quantum phase transition between an ordered phase, corresponding to the superconducting state, and a disordered phase, corresponding to the insulating state with localized superconducting charge. Interestingly, we find that the critical line separating the two phases has a nonmonotonic behavior as a function of the dissipative coupling strength. This result is a consequence of the frustration between (i) one dissipative coupling that quenches the quantum phase fluctuations favoring the ordered phase and (ii) one that quenches the quantum momentum (charge) fluctuations leading to a vanishing phase coherence. Moreover, within the self-consistent harmonic approximation, we analyze the dissipation induced crossover between a first and second order phase transition, showing that quantum frustration increases the range in which the phase transition is second order. The nonmonotonic behavior is reflected also in the purity of the system that quantifies the degree of correlation between the system and the environment, and in the logarithmic negativity as an entanglement measure that encodes the internal quantum correlations in the chain.

Insights into the Effects of Zinc Doping on Structural Phase Transition of P2-Type Sodium Nickel Manganese Oxide Cathodes for High-Energy Sodium Ion Batteries.

PubMed

Wu, Xuehang; Xu, Gui-Liang; Zhong, Guiming; Gong, Zhengliang; McDonald, Matthew J; Zheng, Shiyao; Fu, Riqiang; Chen, Zonghai; Amine, Khalil; Yang, Yong

2016-08-31

P2-type sodium nickel manganese oxide-based cathode materials with higher energy densities are prime candidates for applications in rechargeable sodium ion batteries. A systematic study combining in situ high energy X-ray diffraction (HEXRD), ex situ X-ray absorption fine spectroscopy (XAFS), transmission electron microscopy (TEM), and solid-state nuclear magnetic resonance (SS-NMR) techniques was carried out to gain a deep insight into the structural evolution of P2-Na0.66Ni0.33-xZnxMn0.67O2 (x = 0, 0.07) during cycling. In situ HEXRD and ex situ TEM measurements indicate that an irreversible phase transition occurs upon sodium insertion-extraction of Na0.66Ni0.33Mn0.67O2. Zinc doping of this system results in a high structural reversibility. XAFS measurements indicate that both materials are almost completely dependent on the Ni(4+)/Ni(3+)/Ni(2+) redox couple to provide charge/discharge capacity. SS-NMR measurements indicate that both reversible and irreversible migration of transition metal ions into the sodium layer occurs in the material at the fully charged state. The irreversible migration of transition metal ions triggers a structural distortion, leading to the observed capacity and voltage fading. Our results allow a new understanding of the importance of improving the stability of transition metal layers.

Theoretical and Experimental Studies of N,N-Dimethyl-N'-Picryl-4,4'-Stilbenediamine.

PubMed

Papper, Vladislav; Wu, Yuanyuan; Kharlanov, Vladimir; Sukharaharja, Ayrine; Steele, Terry W J; Marks, Robert S

2018-01-01

N,N-dimethyl-N'-picryl-4,4'-stilbenediamine (DMPSDA) was prepared, purified and crystallised in a form of black lustrous crystals, and its absorption and fluorescence spectra were recorded in cyclohexane, acetonitrile and dimethyl sulfoxide. Non-emissive intramolecular charge transfer state (ICT) was clearly observed in this molecule in all three solvents. Theoretical calculations demonstrating a betaine electronic structure of the trinitrophenyl group in the ground state of the molecule and a charge transfer nature of the long wavelength transition S 0  → S 1 supported the experimental observations of the ICT formation in the molecule.

Relativistic Coulomb Problem for Z Larger than 137

NASA Astrophysics Data System (ADS)

Alhaidari, A. D.

We propose a relativistic one-parameter Hermitian theory for the Coulomb problem with an electric charge greater than 137. In the nonrelativistic limit, the theory becomes identical to the Schrödinger-Coulomb problem for all Z. Moreover, it agrees with the Dirac-Coulomb problem to order (αZ)2, where α is the fine structure constant. The vacuum in the theory is stable and does not suffer from the "charged vacuum" problem for all Z. Moreover, transition between positive and negative energy states could be eliminated. The relativistic bound states energy spectrum and corresponding spinor wave functions are obtained.

Stable-unstable transition for a Bose-Hubbard chain coupled to an environment

NASA Astrophysics Data System (ADS)

Guo, Chu; de Vega, Ines; Schollwöck, Ulrich; Poletti, Dario

2018-05-01

Interactions in quantum systems may induce transitions to exotic correlated phases of matter which can be vulnerable to coupling to an environment. Here, we study the stability of a Bose-Hubbard chain coupled to a bosonic bath at zero and nonzero temperature. We show that only above a critical interaction the chain loses bosons and its properties are significantly affected. The transition is of a different nature than the superfluid-Mott-insulator transition and occurs at a different critical interaction. We explain such a stable-unstable transition by the opening of a global charge gap. The comparison of accurate matrix product state simulations to approximative approaches that miss this transition reveals its many-body origin.

The effect of UV irradiation on the refractive index modulation in photo-thermo-refractive glasses: Mechanisms and application

NASA Astrophysics Data System (ADS)

Chernakov, Dmitry I.; Sidorov, Alexander I.; Stolyarchuk, Maxim V.; Kozlova, Darya A.; Krykova, Victoria A.; Nikonorov, Nikolay V.

2018-02-01

It is shown experimentally that in photo-thermo-refractive glasses the transformation of charged silver subnanosized molecular clusters to neutral state by UV irradiation results in the increase of glass refractive index. The increment of the refractive index reaches Δn = 0.76·10-4. Computer simulation has shown that the polarizability of neutral molecular clusters is by 20-40% larger than of charged ones. The reason of this is the increase of electron density and volume of electron density surfaces during the transformation of molecular cluster to the neutral state. The transition molecular cluster from the ground state to the excited state also results in the increase of its polarizability.

Recent Topics of Organic Superconductors

NASA Astrophysics Data System (ADS)

Ardavan, Arzhang; Brown, Stuart; Kagoshima, Seiichi; Kanoda, Kazushi; Kuroki, Kazuhiko; Mori, Hatsumi; Ogata, Masao; Uji, Shinya; Wosnitza, Jochen

2012-01-01

Recent developments in research into superconductivity in organic materials are reviewed. In the epoch-defining quasi-one-dimensional TMTSF superconductors with Tc ˜ 1 K, Tc decreases monotonically with increasing pressure, as do signatures of spin fluctuations in the normal state, providing good evidence for magnetically-mediated pairing. Upper critical fields exceed the Zeeman-limiting field by several times, suggesting triplet pairing or a transition to an inhomogeneous superconducting state at high magnetic fields, while triplet pairing is ruled out at low fields by NMR Knight-shift measurements. Evidence for a spatially inhomogeneous superconducting state, Fulde--Ferrel--Larkin--Ovchinnikov state, which has long been sought in various superconducting systems, is now captured by thermodynamic and transport measurements for clean and highly two-dimensional BEDT-TTF and BETS superconductors. Some of the layered superconductors also serve as model systems for Mott physics on anisotropic triangular lattice. For example, the Nernst effect and the pseudo-gap behavior in NMR relaxation are enhanced near to the Mott transition. In the case of increasing spin frustration, the superconducting transition temperature is depressed, and antiferromagnetic ordering is eliminated altogether in the adjacent Mott insulating phase. There is an increasing number of materials exhibiting superconductivity in competition or cooperation with charge order. Theoretical studies shed light on the role of spin and/or charge fluctuations for superconductivity appearing under conditions close to those of correlation-induced insulating phases in the diversity of organic materials.

Mapping of Residues Forming the Voltage Sensor of the Voltage-Dependent Anion-Selective Channel

NASA Astrophysics Data System (ADS)

Thomas, Lorie; Blachly-Dyson, Elizabeth; Colombini, Marco; Forte, Michael

1993-06-01

Voltage-gated ion-channel proteins contain "voltage-sensing" domains that drive the conformational transitions between open and closed states in response to changes in transmembrane voltage. We have used site-directed mutagenesis to identify residues affecting the voltage sensitivity of a mitochondrial channel, the voltage-dependent anion-selective channel (VDAC). Although charge changes at many sites had no effect, at other sites substitutions that increased positive charge also increased the steepness of voltage dependance and substitutions that decreased positive charge decreased voltage dependance by an appropriate amount. In contrast to the plasma membrane K^+ and Na^+ channels, these residues are distributed over large parts of the VDAC protein. These results have been used to define the conformational transitions that accompany voltage gating of an ion channel. This gating mechanism requires the movement of large portions of the VDAC protein through the membrane.

X-Ray Sum Frequency Diffraction for Direct Imaging of Ultrafast Electron Dynamics

NASA Astrophysics Data System (ADS)

Rouxel, Jérémy R.; Kowalewski, Markus; Bennett, Kochise; Mukamel, Shaul

2018-06-01

X-ray diffraction from molecules in the ground state produces an image of their charge density, and time-resolved x-ray diffraction can thus monitor the motion of the nuclei. However, the density change of excited valence electrons upon optical excitation can barely be monitored with regular diffraction techniques due to the overwhelming background contribution of the core electrons. We present a nonlinear x-ray technique made possible by novel free electron laser sources, which provides a spatial electron density image of valence electron excitations. The technique, sum frequency generation carried out with a visible pump and a broadband x-ray diffraction pulse, yields snapshots of the transition charge densities, which represent the electron density variations upon optical excitation. The technique is illustrated by ab initio simulations of transition charge density imaging for the optically induced electronic dynamics in a donor or acceptor substituted stilbene.

Understanding the Degradation Mechanism of Lithium Nickel Oxide Cathodes for Li-Ion Batteries

DOE PAGES

Xu, Jing; Hu, Enyuan; Nordlund, Dennis; ...

2016-11-01

The phase transition, charge compensation, and local chemical environment of Ni in LiNiO 2 were investigated to understand the degradation mechanism. The electrode was subjected to a variety of bulk and surface-sensitive characterization techniques under different charge–discharge cycling conditions. We observed the phase transition from the original hexagonal H1 phase to another two hexagonal phases (H2 and H3) upon Li deintercalation. Moreover, the gradual loss of H3-phase features was revealed during the repeated charges. The reduction in Ni redox activity occurred at both the charge and the discharge states, and it appeared both in the bulk and at the surfacemore » over the extended cycles. In conclusion, the degradation of crystal structure significantly contributes to the reduction of Ni redox activity, which in turn causes the cycling performance decay of LiNiO 2.« less

Phase stabilisation of hexagonal barium titanate doped with transition metals: A computational study

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dawson, J.A., E-mail: mtp09jd@sheffield.ac.uk; Freeman, C.L.; Harding, J.H.

Interatomic potentials recently developed for the modelling of BaTiO{sub 3} have been used to explore the stabilisation of the hexagonal polymorph of BaTiO{sub 3} by doping with transition metals (namely Mn, Co, Fe and Ni) at the Ti-site. Classical simulations have been completed on both the cubic and hexagonal polymorphs to investigate the energetic consequences of transition metal doping on each polymorph. Ti-site charge compensation mechanisms have been used for the multi-valent transition metal ions and cluster binding energies have been considered. Simulations show a significant energetic gain when doping occurs at Ti sites in the face sharing dimers (Ti{submore » 2} sites) of the hexagonal polymorph compared with the doping of the cubic polymorph. This energetic difference between the two polymorphs is true for all transition metals tested and all charge states and in the case of tri- and tetra-valent dopants negative solution energies are found for the hexagonal polymorph suggesting actual polymorph stabilisation occurs with the incorporation of these ions as observed experimentally. Oxidation during incorporation of Ni{sup 2+} and Fe{sup 3+} ions has also been considered. - Graphical abstract: The representation of the strongest binding energy clusters for tri-valent dopants—(a) Ti{sub 2}/O{sub 1} cluster and (b) Ti{sub 2}/O{sub 2} cluster. Highlights: ► Classical simulations show a significant energetic gain when doping occurs at Ti sites in the face sharing dimers (Ti2 sites) of the hexagonal polymorph compared with the doping of the cubic polymorph. ► This energetic difference between the two polymorphs is true for all transition metals tested and all charge states. ► In the case of tri- and tetra- valent dopants negative solution energies are found for the hexagonal polymorph suggesting actual polymorph stabilisation occurs with the incorporation of these ions.« less

Insulator-semimetallic transition in quasi-1D charged impurity-infected armchair boron-nitride nanoribbons

NASA Astrophysics Data System (ADS)

Dinh Hoi, Bui; Yarmohammadi, Mohsen

2018-04-01

We address control of electronic phase transition in charged impurity-infected armchair-edged boron-nitride nanoribbons (ABNNRs) with the local variation of Fermi energy. In particular, the density of states of disordered ribbons produces the main features in the context of pretty simple tight-binding model and Green's functions approach. To this end, the Born approximation has been implemented to find the effect of π-band electron-impurity interactions. A modulation of the π-band depending on the impurity concentrations and scattering potentials leads to the phase transition from insulator to semimetallic. We present here a detailed physical meaning of this transition by studying the treatment of massive Dirac fermions. From our findings, it is found that the ribbon width plays a crucial role in determining the electronic phase of disordered ABNNRs. The obtained results in controllable gap engineering are useful for future experiments. Also, the observations in this study have also fueled interest in the electronic properties of other 2D materials.

On the reversibility of the Meissner effect and the angular momentum puzzle

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hirsch, J.E., E-mail: jhirsch@ucsd.edu

It is generally believed that the laws of thermodynamics govern superconductivity as an equilibrium state of matter, and hence that the normal-superconductor transition in a magnetic field is reversible under ideal conditions. Because eddy currents are generated during the transition as the magnetic flux changes, the transition has to proceed infinitely slowly to generate no entropy. Experiments showed that to a high degree of accuracy no entropy was generated in these transitions. However, in this paper we point out that for the length of times over which these experiments extended, a much higher degree of irreversibility due to decay ofmore » eddy currents should have been detected than was actually observed. We also point out that within the conventional theory of superconductivity no explanation exists for why no Joule heat is generated in the superconductor to normal transition when the supercurrent stops. In addition we point out that within the conventional theory of superconductivity no mechanism exists for the transfer of momentum between the supercurrent and the body as a whole, which is necessary to ensure that the transition in the presence of a magnetic field respects momentum conservation. We propose a solution to all these questions based on the alternative theory of hole superconductivity. The theory proposes that in the normal-superconductor transition there is a flow and backflow of charge in direction perpendicular to the phase boundary when the phase boundary moves. We show that this flow and backflow explains the absence of Joule heat generated by Faraday eddy currents, the absence of Joule heat generated in the process of the supercurrent stopping, and the reversible transfer of momentum between the supercurrent and the body, provided the current carriers in the normal state are holes. - Highlights: • The normal-superconductor phase transition is reversible. • Within the conventional theory, Foucault currents give rise to irreversibility. • To suppress Foucault currents, charge has to flow in direction perpendicular to the phase boundary. • The charge carriers have to be holes. • This solves also the angular momentum puzzle associated with the Meissner effect.« less

Speeding Up Sigmatropic Shifts-To Halve or to Hold.

PubMed

Tantillo, Dean J

2016-04-19

Catalysis is common. Rational catalyst design, however, is at the frontier of chemical science. Although the histories of physical organic and synthetic organic chemistry boast key chapters involving [3s,3s] sigmatropic shifts, catalysis of these reactions is much less common than catalysis of ostensibly more complex processes. The comparative dearth of catalysts for sigmatropic shifts is perhaps a result of the perception that transition state structures for these reactions, like their reactants, are nonpolar and therefore not amenable to selective stabilization and its associated barrier lowering. However, as demonstrated in this Account, transition state structures for [3s,3s] sigmatropic shifts can in fact have charge distributions that differ significantly from those of reactants, even for hydrocarbon substrates, allowing for barriers to be decreased and rates increased. In some cases, differences in charge distribution result from the inclusion of heteroatoms at specific positions in reactants, but in other cases differences are actually induced by catalysts. Perhaps surprisingly, strategies for complexation of transition state structures that remain nonpolar are also possible. In general, the strategies for catalysis employed can be characterized as involving either mechanistic intervention, where a catalyst induces a change from the concerted mechanism expected for a [3s,3s] sigmatropic shift to a multistep process (cutting the transformation into halves or smaller pieces) whose overall barrier is decreased relative to the concerted process, or transition state complexation, where a catalyst simply binds (holds) more tightly to the transition state structure for a [3s,3s] sigmatropic shift than to the reactant, leading to a lower barrier in the presence of the catalyst. Both of these strategies can be considered to be biomimetic in that enzymes frequently induce multistep processes and utilize selective transition state stabilization for the steps involved. In addition, transition state complexation was the principle around which catalytic antibodies were originally designed. The field of catalysis of sigmatropic shifts is now ready for rational design. The studies described here all provide evidence for the origins of rate acceleration, derived in large part from the results of quantum chemical calculations, that can now be applied to the design of new catalysts for [3s,3s] and other sigmatropic shifts.

Devil's staircase of odd-number charge order modulations in divalent β -vanadium bronzes under pressure

NASA Astrophysics Data System (ADS)

Yamauchi, Touru; Ueda, Hiroaki; Ohwada, Kenji; Nakao, Hironori; Ueda, Yutaka

2018-03-01

A common characteristic of quasi-one-dimensional (q1D) conductors β -A0.33V2O5 (A = Li, Na, and Ag) is that the charge ordering (CO), the ground state (GS) at ambient pressure, and the superconducting (SC) phases, the GS under high pressure, are competing with each other. We have explored high-pressure properties of divalent β -vanadium bronzes, β -A0.33V2O5 (A = Ca, Sr, and Pb), which are A -cation stoichiometry finely controlled single-crystal/powder samples, and found the absence of the SC phase. In these observations, however, we observed enormous and novel phase transitions, a kind of "devil's staircase"-type phase transitions in the charge ordering (CO) phases. The most surprising discovery in this devil's staircase, which was found mainly in β -Sr0.33V2O5 , is that all the charge modulation vectors of many kinds of CO phases can be represented as a primitive lattice translation vector along the b axis multiplied by several odd numbers. This discovery surely demonstrates interplay between the charge degree freedom and the crystallographic symmetry. We propose two possible mechanisms to explain this phenomenon: "self-charge transfer (carrier redistribution)" between the two subsystems in these compounds and "sequential symmetry reduction" that was discussed in Landau theory of phase transitions. In β -Ca0.33V2O5 we also found a P -T phase diagram similar in outlook but different in detail. The devil's staircase was also observed but it is an incomplete one. Furthermore, the charge modulation vectors in it are shorter than those in β -Sr0.33V2O5 . In β -Pb0.33V2O5 , which has no CO phase at ambient pressure, the pressure-induced antiferromagnetic ordering was observed at around 50 K above 0.5 GPa. Using these two kinds of mechanisms, we also explain the global high-pressure properties in all the stoichiometric divalent β -vanadium bronzes, which were observed as a wide variety of electromagnetic states. In addition, we also discuss a possible key for the presence/absence of the SC phase under pressure.

Electronic structure of charge-density-wave state in quasi-2D KMo6O17 purple bronze characterized by angle resolved photoemission spectroscopy

NASA Astrophysics Data System (ADS)

Valbuena, M. A.; Avila, J.; Drouard, S.; Guyot, H.; Asensio, M. C.

2006-01-01

We report on an angle-resolved-photoemission spectroscopy (ARPES) investigation of layered quasi-two dimensional (2D) Molybdenum purple bronze KMo6O17 in order to study and characterizes the transition to a charge-density-wave (CDW) state. We have performed photoemission temperature dependent measurements cooling down from room temperature (RT) to 32 K, well below the Peierls transition for this material, with CDW transition temperature Tc =110 K. The spectra have been taken at a selected kF point of the Fermi surface (FS) that satisfies the nesting condition of the FS, looking for the characteristic pseudo-gap opening in this kind of materials. The pseudogap has been estimated and it result to be in agreement with our previous works. The shift to lower binding energy of crossing Fermi level ARPES feature have been also confirmed and studied as a function of temperature, showing a rough like BCS behaviour. Finally we have also focused on ARPES measurements along ΓM¯ high symmetry direction for both room and low temperature states finding some insight for ‘shadow’ or back folded bands indicating the new periodicity of real lattice after the CDW lattice distortion.

Universality of the Berezinskii-Kosterlitz-Thouless type of phase transition in the dipolar XY-model

NASA Astrophysics Data System (ADS)

Vasiliev, A. Yu; Tarkhov, A. E.; Menshikov, L. I.; Fedichev, P. O.; Fischer, Uwe R.

2014-05-01

We investigate the nature of the phase transition occurring in a planar XY-model spin system with dipole-dipole interactions. It is demonstrated that a Berezinskii-Kosterlitz-Thouless (BKT) type of phase transition always takes place at a finite temperature separating the ordered (ferro) and the disordered (para) phases. The low-temperature phase corresponds to an ordered state with thermal fluctuations, composed of a ‘gas’ of bound vortex-antivortex pairs, which would, when considered isolated, be characterized by a constant vortex-antivortex attraction force which is due to the dipolar interaction term in the Hamiltonian. Using a topological charge model, we show that small bound pairs are easily polarized, and screen the vortex-antivortex interaction in sufficiently large pairs. Screening changes the linear attraction potential of vortices to a logarithmic one, and leads to the familiar pair dissociation mechanism of the BKT type phase transition. The topological charge model is confirmed by numerical simulations, in which we demonstrate that the transition temperature slightly increases when compared with the BKT result for short-range interactions.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bugaris, Daniel E.; Malliakas, Christos D.; Han, Fei

A new polymorph of the RE 2Ru 3Ge 5 (RE = Pr, Sm, Dy) compounds has been grown as single crystals via an indium flux. These compounds crystallize in tetragonal space group P4/mnc with the Sc 2Fe 3Si 5-type structure, having lattice parameters a = 11.020(2) Å and c = 5.853(1) Å for RE = Pr, a = 10.982(2) Å and c = 5.777(1) Å for RE = Sm, and a = 10.927(2) Å and c = 5.697(1) Å for RE = Dy. These materials exhibit a structural transition at low temperature, which is attributed to an apparent charge densitymore » wave (CDW). Both the high-temperature average crystal structure and the low-temperature incommensurately modulated crystal structure (for Sm 2Ru 3Ge 5 as a representative) have been solved. The charge density wave order is manifested by periodic distortions of the onedimensional zigzag Ge chains. From X-ray diffraction, charge transport (electrical resistivity, Hall effect, magnetoresistance), magnetic measurements, and heat capacity, the ordering temperatures (T CDW) observed in the Pr and Sm analogues are ~200 and ~175 K, respectively. The charge transport measurement results indicate an electronic state transition happening simultaneously with the CDW transition. X-ray absorption near-edge spectroscopy (XANES) and electronic band structure results are also reported.« less

Narrowband noise study of sliding charge density waves in NbSe 3 nanoribbons

DOE PAGES

Onishi, Seita; Jamei, Mehdi; Zettl, Alex

2017-01-12

Transport properties (dc electrical resistivity, threshold electric field, and narrow-band noise) are reported for nanoribbon specimens of NbSe 3 with thicknesses as low as 18 nm. As the sample thickness decreases, the resistive anomalies characteristic of the charge density wave (CDW) state are suppressed and the threshold fields for nonlinear CDW conduction apparently diverge. Narrow-band noise measurements allow determination of the concentration of carriers condensed in the CDW state n c , reflective of the CDW order parameter Δ. Although the CDW transition temperatures are relatively independent of sample thickness, in the lower CDW state Δ decreases dramatically with decreasingmore » sample thickness.« less

Secondary ion emission from Ti, V, Cu, Ag and Au surfaces under KeV Cs + irradiation

NASA Astrophysics Data System (ADS)

van der Heide, P. A. W.

2005-02-01

Low energy mono-atomic singly charged secondary ion emissions from Ti, V, Cu, Ag and Au substrates during the initial stages of sputtering with Cs + primary ions have been studied. With the exception of the Ag - secondary ions, all exhibited exponential like correlations with the Cs induced work function changes. This, along with the lack of variations in the valence band structure around the Fermi edge, is consistent with resonance charge transfer to/from states located at the Fermi edge. The insensitivity of Ag - to work function appears to stem from the dominance of a separate ion formation process, namely charge transfer into vacant 4d states in the sputtered population, which themselves appear to be produced through collective oscillations. A similar excitation-mediated process involving different levels also appears to be active in the formation of other negatively charged transition metal ions, albeit to a much lesser degree.

Quantum spin liquids and the metal-insulator transition in doped semiconductors.

PubMed

Potter, Andrew C; Barkeshli, Maissam; McGreevy, John; Senthil, T

2012-08-17

We describe a new possible route to the metal-insulator transition in doped semiconductors such as Si:P or Si:B. We explore the possibility that the loss of metallic transport occurs through Mott localization of electrons into a quantum spin liquid state with diffusive charge neutral "spinon" excitations. Such a quantum spin liquid state can appear as an intermediate phase between the metal and the Anderson-Mott insulator. An immediate testable consequence is the presence of metallic thermal conductivity at low temperature in the electrical insulator near the metal-insulator transition. Further, we show that though the transition is second order, the zero temperature residual electrical conductivity will jump as the transition is approached from the metallic side. However, the electrical conductivity will have a nonmonotonic temperature dependence that may complicate the extrapolation to zero temperature. Signatures in other experiments and some comparisons with existing data are made.

Disorder-induced localization in crystalline phase-change materials.

PubMed

Siegrist, T; Jost, P; Volker, H; Woda, M; Merkelbach, P; Schlockermann, C; Wuttig, M

2011-03-01

Localization of charge carriers in crystalline solids has been the subject of numerous investigations over more than half a century. Materials that show a metal-insulator transition without a structural change are therefore of interest. Mechanisms leading to metal-insulator transition include electron correlation (Mott transition) or disorder (Anderson localization), but a clear distinction is difficult. Here we report on a metal-insulator transition on increasing annealing temperature for a group of crystalline phase-change materials, where the metal-insulator transition is due to strong disorder usually associated only with amorphous solids. With pronounced disorder but weak electron correlation, these phase-change materials form an unparalleled quantum state of matter. Their universal electronic behaviour seems to be at the origin of the remarkable reproducibility of the resistance switching that is crucial to their applications in non-volatile-memory devices. Controlling the degree of disorder in crystalline phase-change materials might enable multilevel resistance states in upcoming storage devices.

Possible observation of the Berezinskii-Kosterlitz-Thouless transition in boron-doped diamond films

NASA Astrophysics Data System (ADS)

Coleman, Christopher; Bhattacharyya, Somnath

2017-11-01

The occurrence of the Berezinskii-Kosterlitz-Thouless (BKT) transition is investigated in heavily boron-doped nanocrystalline diamond films through a combination of current-voltage and resistance measurements. We observe transport features suggesting a robust BKT transition along with transport features related to vortex pinning in nanocrystalline diamond films with smaller grain size. The vortex core energy determined through analysis of the resistance temperature curves was found to be anti-correlated to the BKT transition temperatures. It is also observed that the higher BKT temperature is related to an increased vortex-antivortex binding energy derived from the activated transport regions. Further, the magnetic field induced superconductor insulator transition shows the possibility of the charge glass state. The consequences of granularity such as localization and vortex pinning can lead to tuneable BKT temperatures and strongly affects the field induced insulating state.

Origins of the structural phase transitions in MoTe2 and WTe2

NASA Astrophysics Data System (ADS)

Kim, Hyun-Jung; Kang, Seoung-Hun; Hamada, Ikutaro; Son, Young-Woo

2017-05-01

Layered transition metal dichalcogenides MoTe2 and WTe2 share almost similar lattice constants as well as topological electronic properties except their structural phase transitions. While the former shows a first-order phase transition between monoclinic and orthorhombic structures, the latter does not. Using a recently proposed van der Waals density functional method, we investigate structural stability of the two materials and uncover that the disparate phase transitions originate from delicate differences between their interlayer bonding states near the Fermi energy. By exploiting the relation between the structural phase transitions and the low energy electronic properties, we show that a charge doping can control the transition substantially, thereby suggesting a way to stabilize or to eliminate their topological electronic energy bands.

Unconventional charge order in a co-doped high-Tc superconductor

PubMed Central

Pelc, D.; Vučković, M.; Grafe, H. -J.; Baek, S. -H.; Požek, M.

2016-01-01

Charge-stripe order has recently been established as an important aspect of cuprate high-Tc superconductors. However, owing to the complex interplay between competing phases and the influence of disorder, it is unclear how it emerges from the parent high-temperature state. Here we report on the discovery of an unconventional ordered phase between charge-stripe order and (pseudogapped) metal in the cuprate La1.8−xEu0.2SrxCuO4. We use three complementary experiments—nuclear quadrupole resonance, nonlinear conductivity and specific heat—to demonstrate that the order appears through a sharp phase transition and exists in a dome-shaped region of the phase diagram. Our results imply that the new phase is a state, which preserves translational symmetry: a charge nematic. We thus resolve the process of charge-stripe development in cuprates, show that this nematic phase is distinct from high-temperature pseudogap and establish a link with other strongly correlated electronic materials with prominent nematic order. PMID:27605152

Ferroelectric ferrimagnetic LiFe2F6 : Charge-ordering-mediated magnetoelectricity

NASA Astrophysics Data System (ADS)

Lin, Ling-Fang; Xu, Qiao-Ru; Zhang, Yang; Zhang, Jun-Jie; Liang, Yan-Ping; Dong, Shuai

2017-12-01

Trirutile-type LiFe2F6 is a charge-ordered material with an Fe2 +/Fe3 + configuration. Here, its physical properties, including magnetism, electronic structure, phase transition, and charge ordering, are studied theoretically. On one hand, the charge ordering leads to improper ferroelectricity with a large polarization. On the other hand, its magnetic ground state can be tuned from the antiferromagnetic to ferrimagnetic by moderate compressive strain. Thus, LiFe2F6 can be a rare multiferroic with both large magnetization and polarization. Most importantly, since the charge ordering is the common ingredient for both ferroelectricity and magnetization, the net magnetization may be fully switched by flipping the polarization, rendering intrinsically strong magnetoelectric effects and desirable functions.

Crystal nucleation and metastable bcc phase in charged colloids: A molecular dynamics study

NASA Astrophysics Data System (ADS)

Ji, Xinqiang; Sun, Zhiwei; Ouyang, Wenze; Xu, Shenghua

2018-05-01

The dynamic process of homogenous nucleation in charged colloids is investigated by brute-force molecular dynamics simulation. To check if the liquid-solid transition will pass through metastable bcc, simulations are performed at the state points that definitely lie in the phase region of thermodynamically stable fcc. The simulation results confirm that, in all of these cases, the preordered precursors, acting as the seeds of nucleation, always have predominant bcc symmetry consistent with Ostwald's step rule and the Alexander-McTague mechanism. However, the polymorph selection is not straightforward because the crystal structures formed are not often determined by the symmetry of intermediate precursors but have different characters under different state points. The region of the state point where bcc crystal structures of large enough size are formed during crystallization is narrow, which gives a reasonable explanation as to why the metastable bcc phase in charged colloidal suspensions is rarely detected in macroscopic experiments.

Charge transfer mechanism for the formation of metallic states at the KTaO3/SrTiO3 interface

NASA Astrophysics Data System (ADS)

Nazir, S.; Singh, N.; Schwingenschlögl, U.

2011-03-01

The electronic and optical properties of the KTaO3/SrTiO3 heterointerface are analyzed by the full-potential linearized augmented plane-wave approach of density functional theory. Optimization of the atomic positions points at subordinate changes in the crystal structure and chemical bonding near the interface, which is due to a minimal lattice mismatch. The creation of metallic interface states thus is not affected by structural relaxation but can be explained by charge transfer between transition metal and oxygen atoms. It is to be expected that a charge transfer is likewise important for related interfaces such as LaAlO3/SrTiO3. The KTaO3/SrTiO3 system is ideal for disentangling the complex behavior of metallic interface states, since almost no structural relaxation takes place.

Low-energy charge transfer excitations in NiO

NASA Astrophysics Data System (ADS)

Sokolov, V. I.; Pustovarov, V. A.; Churmanov, V. N.; Ivanov, V. Yu; Yermakov, A. Ye; Uimin, M. A.; Gruzdev, N. B.; Sokolov, P. S.; Baranov, A. N.; Moskvin, A. S.

2012-08-01

Comparative analysis of photoluminescence (PL) and photoluminescence excitation (PLE) spectra of NiO poly- and nanocrystals in the spectral range 2-5.5 eV reveals two PLE bands peaked near 3.7 and 4.6 eV with a dramatic rise in the low-temperature PLE spectral weight of the 3.7 eV PLE band in the nanocrystalline NiO as compared with its polycrystalline counterpart. In frames of a cluster model approach we assign the 3.7 eV PLE band to the low-energy bulk-forbidden p-d (t1g(π)-eg) charge transfer (CT) transition which becomes the allowed one in the nanocrystalline state while the 4.6 eV PLE band is related to a bulk allowed d-d (eg-eg) CT transition scarcely susceptible to the nanocrystallization. The PLE spectroscopy of the nanocrystalline materials appears to be a novel informative technique for inspection of different CT transitions.

Nontrivial transition of transmission in a highly open quantum point contact in the quantum Hall regime

NASA Astrophysics Data System (ADS)

Hong, Changki; Park, Jinhong; Chung, Yunchul; Choi, Hyungkook; Umansky, Vladimir

2017-11-01

Transmission through a quantum point contact (QPC) in the quantum Hall regime usually exhibits multiple resonances as a function of gate voltage and high nonlinearity in bias. Such behavior is unpredictable and changes sample by sample. Here, we report the observation of a sharp transition of the transmission through an open QPC at finite bias, which was observed consistently for all the tested QPCs. It is found that the bias dependence of the transition can be fitted to the Fermi-Dirac distribution function through universal scaling. The fitted temperature matches quite nicely to the electron temperature measured via shot-noise thermometry. While the origin of the transition is unclear, we propose a phenomenological model based on our experimental results that may help to understand such a sharp transition. Similar transitions are observed in the fractional quantum Hall regime, and it is found that the temperature of the system can be measured by rescaling the quasiparticle energy with the effective charge (e*=e /3 ). We believe that the observed phenomena can be exploited as a tool for measuring the electron temperature of the system and for studying the quasiparticle charges of the fractional quantum Hall states.

Charge and spin control of ultrafast electron and hole dynamics in single CdSe/ZnSe quantum dots

NASA Astrophysics Data System (ADS)

Hinz, C.; Gumbsheimer, P.; Traum, C.; Holtkemper, M.; Bauer, B.; Haase, J.; Mahapatra, S.; Frey, A.; Brunner, K.; Reiter, D. E.; Kuhn, T.; Seletskiy, D. V.; Leitenstorfer, A.

2018-01-01

We study the dynamics of photoexcited electrons and holes in single negatively charged CdSe/ZnSe quantum dots with two-color femtosecond pump-probe spectroscopy. An initial characterization of the energy level structure is performed at low temperatures and magnetic fields of up to 5 T. Emission and absorption resonances are assigned to specific transitions between few-fermion states by a theoretical model based on a configuration interaction approach. To analyze the dynamics of individual charge carriers, we initialize the quantum system into excited trion states with defined energy and spin. Subsequently, the time-dependent occupation of the trion ground state is monitored by spectrally resolved differential transmission measurements. We observe subpicosecond dynamics for a hole excited to the D shell. The energy dependence of this D -to-S shell intraband transition is investigated in quantum dots of varying size. Excitation of an electron-hole pair in the respective p shells leads to the formation of singlet and triplet spin configurations. Relaxation of the p -shell singlet is observed to occur on a time scale of a few picoseconds. Pumping of p -shell triplet transitions opens up two pathways with distinctly different scattering times. These processes are shown to be governed by the mixing of singlet and triplet states due to exchange interactions enabling simultaneous electron and hole spin flips. To isolate the relaxation channels, we align the spin of the residual electron by a magnetic field and employ laser pulses of defined helicity. This step provides ultrafast preparation of a fully inverted trion ground state of the quantum dot with near unity probability, enabling deterministic addition of a single photon to the probe pulse. Therefore our experiments represent a significant step towards using single quantum emitters with well-controled inversion to manipulate the photon statistics of ultrafast light pulses.

Near-Field Nanoscopy of Metal-Insulator Phase Transitions Towards Synthesis of Novel Correlated Transition Metal Oxides and Their Interaction with Plasmon Resonances

DTIC Science & Technology

2016-01-05

and to utilize the phase transtion states of VO2 to control and manipulate local plasmon resonaces. First, we imaged the charge dynamics in (MIT) of...Then we studied the interaction of VO2 with plasmons . Both the film VO2 and the crystal VO2 were 1. REPORT DATE (DD-MM-YYYY) 4. TITLE AND SUBTITLE 13...Novel Correlated Transition Metal Oxides and Their Interaction with Plasmon Resonances The views, opinions and/or findings contained in this report are

Stacked charge stripes in the quasi-2D trilayer nickelate La 4 Ni 3 O 8

DOE PAGES

Zhang, Junjie; Chen, Yu-Sheng; Phelan, D.; ...

2016-07-26

The quasi-2D nickelate La 4Ni 3O 8 (La-438), consisting of trilayer networks of square planar Ni ions, is a member of the so-called T' family, which is derived from the Ruddlesden-Popper (R-P) parent compound La 4Ni 3O 10-x by removing two oxygen atoms and rearranging the rock salt layers to fluorite-type layers. Although previous studies on polycrystalline samples have identified a 105-K phase transition with a pronounced electronic and magnetic response but weak lattice character, no consensus on the origin of this transition has been reached. We show using synchrotron X-ray diffraction on high-pO(2) floating zone-grown single crystals that thismore » transition is associated with a real space ordering of charge into a quasi-2D charge stripe ground state. We found that the charge stripe superlattice propagation vector, q = (2/3, 0, 1), corresponds with that those in the related 1/3-hole doped single- layer R-P nickelate, La 5/3Sr 1/3NiO 4 (LSNO-1/3; Ni 2.33+), with orientation at 45 degrees to the Ni-O bonds. Furthermore, the charge stripes in La-438 are weakly correlated along c to form a staggered ABAB stacking that reduces the Coulomb repulsion among the stripes. Surprisingly, however, we find that the charge stripes within each trilayer of La-438 are stacked in phase from one layer to the next, at odds with any simple Coulomb repulsion argument.« less

Stacked charge stripes in the quasi-2D trilayer nickelate La 4 Ni 3 O 8

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, Junjie; Chen, Yu-Sheng; Phelan, D.

The quasi-2D nickelate La 4Ni 3O 8 (La-438), consisting of trilayer networks of square planar Ni ions, is a member of the so-called T' family, which is derived from the Ruddlesden-Popper (R-P) parent compound La 4Ni 3O 10-x by removing two oxygen atoms and rearranging the rock salt layers to fluorite-type layers. Although previous studies on polycrystalline samples have identified a 105-K phase transition with a pronounced electronic and magnetic response but weak lattice character, no consensus on the origin of this transition has been reached. We show using synchrotron X-ray diffraction on high-pO(2) floating zone-grown single crystals that thismore » transition is associated with a real space ordering of charge into a quasi-2D charge stripe ground state. We found that the charge stripe superlattice propagation vector, q = (2/3, 0, 1), corresponds with that those in the related 1/3-hole doped single- layer R-P nickelate, La 5/3Sr 1/3NiO 4 (LSNO-1/3; Ni 2.33+), with orientation at 45 degrees to the Ni-O bonds. Furthermore, the charge stripes in La-438 are weakly correlated along c to form a staggered ABAB stacking that reduces the Coulomb repulsion among the stripes. Surprisingly, however, we find that the charge stripes within each trilayer of La-438 are stacked in phase from one layer to the next, at odds with any simple Coulomb repulsion argument.« less

Glutamate Induced Thermal Equilibrium Intermediate and Counteracting Effect on Chemical Denaturation of Proteins.

PubMed

Anumalla, Bramhini; Prabhu, N Prakash

2018-01-25

When organisms are subjected to stress conditions, one of their adaptive responses is accumulation of small organic molecules called osmolytes. These osmolytes affect the structure and stability of the biological macromolecules including proteins. The present study examines the effect of a negatively charged amino acid osmolyte, glutamate (Glu), on two model proteins, ribonuclease A (RNase A) and α-lactalbumin (α-LA), which have positive and negative surface charges at pH 7, respectively. These proteins follow two-state unfolding transitions during both heat and chemical induced denaturation processes. The addition of Glu stabilizes the proteins against temperature and induces an early equilibrium intermediate during unfolding. The stability is found to be enthalpy-driven, and the free energy of stabilization is more for α-LA compared to RNase A. The decrease in the partial molar volume and compressibility of both of the proteins in the presence of Glu suggests that the proteins attain a more compact state through surface hydration which could provide a more stable conformation. This is also supported by molecule dynamic simulation studies which demonstrate that the water density around the proteins is increased upon the addition of Glu. Further, the intermediates could be completely destabilized by lower concentrations (∼0.5 M) of guanidinium chloride and salt. However, urea subverts the Glu-induced intermediate formed by α-LA, whereas it only slightly destabilizes in the case of RNase A which has a positive surface charge and could possess charge-charge interactions with Glu. This suggests that, apart from hydration, columbic interactions might also contribute to the stability of the intermediate. Gdm-induced denaturation of RNase A and α-LA in the absence and the presence of Glu at different temperatures was carried out. These results also show the Glu-induced stabilization of both of the proteins; however, all of the unfolding transitions followed two-state transitions during chemical denaturation. The extent of stability exerted by Glu is higher for RNase A at higher temperature, whereas it provides more stability for α-LA at lower temperature. Thus, the experiments indicate that Glu induces a thermal equilibrium intermediate and increases the thermodynamic stability of proteins irrespective of their surface charges. The extent of stability varies between the proteins in a temperature-dependent manner.

High-resolution study of Gamow-Teller transitions in the 47Ti(3He,t)47V reaction

NASA Astrophysics Data System (ADS)

Ganioǧlu, E.; Fujita, H.; Fujita, Y.; Adachi, T.; Algora, A.; Csatlós, M.; Deaven, J. M.; Estevez-Aguado, E.; Guess, C. J.; Gulyás, J.; Hatanaka, K.; Hirota, K.; Honma, M.; Ishikawa, D.; Krasznahorkay, A.; Matsubara, H.; Meharchand, R.; Molina, F.; Okamura, H.; Ong, H. J.; Otsuka, T.; Perdikakis, G.; Rubio, B.; Scholl, C.; Shimbara, Y.; Susoy, G.; Suzuki, T.; Tamii, A.; Thies, J. H.; Zegers, R. G. T.; Zenihiro, J.

2013-01-01

Given the importance of Gamow-Teller (GT) transitions in nuclear structure and astrophysical nuclear processes, we have studied Tz=+3/2→+1/2, GT transitions starting from the 47Ti nucleus in the (3He,t) charge-exchange reaction at 0∘ and at an intermediate incident energy of 140 MeV/nucleon. The experiments were carried out at the Research Center for Nuclear Physics (RCNP), Osaka, using the high-resolution facility with a high-dispersion beam line and the Grand-Raiden spectrometer. With an energy resolution of 20 keV, individual GT transitions were observed and GT strength was derived for each state populated up to an excitation energy (Ex) of 12.5 MeV. The GT strength was widely distributed from low excitation energy up to 12.5 MeV, where we had to stop the analysis because of the high level density. The distribution of the GT strengths was compared with the results of shell model calculations using the GXPF1 interaction. The calculations could reproduce the experimental GT distributions well. The GT transitions from the ground state of 47Ti and the M1 transitions from the isobaric analog state in 47V to the same low-lying states in 47V are analogous. It was found that the ratios of GT transition strengths to the ground state, the 0.088-MeV state, and the 0.146-MeV state are similar to the ratios of the strengths of the analogous M1 transitions from the isobaric analog state (IAS) to these states. The measured distribution of the GT strengths was also compared with those starting from the Tz=+3/2 nucleus 41K to the Tz=+1/2 nucleus 41Ca.

Metal-insulator transitions

NASA Astrophysics Data System (ADS)

Imada, Masatoshi; Fujimori, Atsushi; Tokura, Yoshinori

1998-10-01

Metal-insulator transitions are accompanied by huge resistivity changes, even over tens of orders of magnitude, and are widely observed in condensed-matter systems. This article presents the observations and current understanding of the metal-insulator transition with a pedagogical introduction to the subject. Especially important are the transitions driven by correlation effects associated with the electron-electron interaction. The insulating phase caused by the correlation effects is categorized as the Mott Insulator. Near the transition point the metallic state shows fluctuations and orderings in the spin, charge, and orbital degrees of freedom. The properties of these metals are frequently quite different from those of ordinary metals, as measured by transport, optical, and magnetic probes. The review first describes theoretical approaches to the unusual metallic states and to the metal-insulator transition. The Fermi-liquid theory treats the correlations that can be adiabatically connected with the noninteracting picture. Strong-coupling models that do not require Fermi-liquid behavior have also been developed. Much work has also been done on the scaling theory of the transition. A central issue for this review is the evaluation of these approaches in simple theoretical systems such as the Hubbard model and t-J models. Another key issue is strong competition among various orderings as in the interplay of spin and orbital fluctuations. Experimentally, the unusual properties of the metallic state near the insulating transition have been most extensively studied in d-electron systems. In particular, there is revived interest in transition-metal oxides, motivated by the epoch-making findings of high-temperature superconductivity in cuprates and colossal magnetoresistance in manganites. The article reviews the rich phenomena of anomalous metallicity, taking as examples Ti, V, Cr, Mn, Fe, Co, Ni, Cu, and Ru compounds. The diverse phenomena include strong spin and orbital fluctuations, mass renormalization effects, incoherence of charge dynamics, and phase transitions under control of key parameters such as band filling, bandwidth, and dimensionality. These parameters are experimentally varied by doping, pressure, chemical composition, and magnetic fields. Much of the observed behavior can be described by the current theory. Open questions and future problems are also extracted from comparison between experimental results and theoretical achievements.

Reversible Hydrogel–Solution System of Silk with High Beta-Sheet Content

PubMed Central

2015-01-01

Silkworm silk has been widely used as a textile fiber, as biomaterials and in optically functional materials due to its extraordinary properties. The β-sheet-rich natural nanofiber units of about 10–50 nm in diameter are often considered the origin of these properties, yet it remains unclear how silk self-assembles into these hierarchical structures. A new system composed of β-sheet-rich silk nanofibers about 10–20 nm in diameter is reported here, where these nanofibers formed into “flowing hydrogels” at 0.5–2% solutions and could be transformed back into the solution state at lower concentrations, even with a high β-sheet content. This is in contrast with other silk processed materials, where significant β-sheet content negates reversibility between solution and solid states. These fibers are formed by regulating the self-assembly process of silk in aqueous solution, which changes the distribution of negative charges while still supporting β-sheet formation in the structures. Mechanistically, there appears to be a shift toward negative charges along the outside of the silk nanofibers in our present study, resulting in a higher zeta potential (above −50 mV) than previous silk materials which tend to be below −30 mV. The higher negative charge on silk nanofibers resulted in electrostatic repulsion strong enough to negate further assembly of the nanofibers. Changing silk concentration changed the balance between hydrophobic interactions and electrostatic repulsion of β-sheet-rich silk nanofibers, resulting in reversible hydrogel–solution transitions. Furthermore, the silk nanofibers could be disassembled into shorter fibers and even nanoparticles upon ultrasonic treatment following the transition from hydrogel to solution due to the increased dispersion of hydrophobic smaller particles, without the loss of β-sheet content, and with retention of the ability to transition between hydrogel and solution states through reversion to longer nanofibers during self-assembly. These reversible solution-hydrogel transitions were tunable with ultrasonic intensity, time, or temperature. PMID:25056606

Enhance luminescence by introducing alkali metal ions (R+ = Li+, Na+ and K+) in SrAl2O4:Eu3+ phosphor by solid-state reaction method

NASA Astrophysics Data System (ADS)

Prasad Sahu, Ishwar

2016-05-01

In the present article, the role of charge compensator ions (R+ = Li+, Na+ and K+) in europium-doped strontium aluminate (SrAl2O4:Eu3+) phosphors was synthesized by the high-temperature, solid-state reaction method. The crystal structures of sintered phosphors were in a monoclinic phase with space group P21. The trap parameters which are mainly activation energy (E), frequency factor (s) and order of the kinetics (b) were evaluated by using the peak shape method. The calculated trap depths are in the range from 0.76 to 0.84 eV. Photoluminescence measurements showed that the phosphor exhibited emission peak with good intensity at 595 nm, corresponding to 5D0-7F1 (514 nm) orange emission and weak 5D0-7F2 (614 nm) red emission. The excitation spectra monitored at 595 nm show a broad band from 220 to 320 nm ascribed to O-Eu charge-transfer state transition and the other peaks in the range of 350-500 nm originated from f-f transitions of Eu3+ ions. The strongest band at 394 nm can be assigned to 7F0-5L6 transition of Eu3+ ions due to the typical f-f transitions within Eu3+ of 4f6 configuration. The latter lies in near ultraviolet (350-500 nm) emission of UV LED. CIE color chromaticity diagram and thermoluminescence spectra confirm that the synthesized phosphors would emit an orange-red color. Incorporating R+ = Li+, Na+ and K+ as the compensator charge, the emission intensity of SrAl2O4:Eu3+ phosphor can be obviously enhanced and the emission intensity of SrAl2O4:Eu3+ doping Li+ is higher than that of Na+ or K+ ions.

Reversible hydrogel-solution system of silk with high beta-sheet content.

PubMed

Bai, Shumeng; Zhang, Xiuli; Lu, Qiang; Sheng, Weiqin; Liu, Lijie; Dong, Boju; Kaplan, David L; Zhu, Hesun

2014-08-11

Silkworm silk has been widely used as a textile fiber, as biomaterials and in optically functional materials due to its extraordinary properties. The β-sheet-rich natural nanofiber units of about 10-50 nm in diameter are often considered the origin of these properties, yet it remains unclear how silk self-assembles into these hierarchical structures. A new system composed of β-sheet-rich silk nanofibers about 10-20 nm in diameter is reported here, where these nanofibers formed into "flowing hydrogels" at 0.5-2% solutions and could be transformed back into the solution state at lower concentrations, even with a high β-sheet content. This is in contrast with other silk processed materials, where significant β-sheet content negates reversibility between solution and solid states. These fibers are formed by regulating the self-assembly process of silk in aqueous solution, which changes the distribution of negative charges while still supporting β-sheet formation in the structures. Mechanistically, there appears to be a shift toward negative charges along the outside of the silk nanofibers in our present study, resulting in a higher zeta potential (above -50 mV) than previous silk materials which tend to be below -30 mV. The higher negative charge on silk nanofibers resulted in electrostatic repulsion strong enough to negate further assembly of the nanofibers. Changing silk concentration changed the balance between hydrophobic interactions and electrostatic repulsion of β-sheet-rich silk nanofibers, resulting in reversible hydrogel-solution transitions. Furthermore, the silk nanofibers could be disassembled into shorter fibers and even nanoparticles upon ultrasonic treatment following the transition from hydrogel to solution due to the increased dispersion of hydrophobic smaller particles, without the loss of β-sheet content, and with retention of the ability to transition between hydrogel and solution states through reversion to longer nanofibers during self-assembly. These reversible solution-hydrogel transitions were tunable with ultrasonic intensity, time, or temperature.

Electronic doping of transition metal oxide perovskites

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cammarata, Antonio, E-mail: cammaant@fel.cvut.cz; Rondinelli, James M.

2016-05-23

CaFeO{sub 3} is a prototypical negative charge transfer oxide that undergoes electronic metal-insulator transition concomitant with a dilation and contraction of nearly rigid octahedra. Altering the charge neutrality of the bulk system destroys the electronic transition, while the structure is significantly modified at high charge content. Using density functional theory simulations, we predict an alternative avenue to modulate the structure and the electronic transition in CaFeO{sub 3}. Charge distribution can be modulated using strain-rotation coupling and thin film engineering strategies, proposing themselves as a promising avenue for fine tuning electronic features in transition metal-oxide perovskites.

Ground-state magnetic phase diagram of bow-tie graphene nanoflakes in external magnetic field

NASA Astrophysics Data System (ADS)

Szałowski, Karol

2013-12-01

The magnetic phase diagram of a ground state is studied theoretically for graphene nanoflakes of bow-tie shape and various sizes in external in-plane magnetic field. The tight-binding Hamiltonian supplemented with Hubbard term is used to model the electronic structure of the systems in question. The existence of the antiferromagnetic phase with magnetic moments localized at the sides of the bow-tie is found for low field and a field-induced spin-flip transition to ferromagnetic state is predicted to occur in charge-undoped structures. For small nanoflake doped with a single charge carrier, the low-field phase is ferrimagnetic and a metamagnetic transition to ferromagnetic ordering can be forced by the field. The critical field is found to decrease with increasing size of the nanoflake. The influence of diagonal and off-diagonal disorder on the mentioned magnetic properties is studied. The effect of off-diagonal disorder is found to be more important than that of diagonal disorder, leading to significantly widened distribution of critical fields for disordered population of nanoflakes.

Communication: Fragment-based Hamiltonian model of electronic charge-excitation gaps and gap closure

DOE Office of Scientific and Technical Information (OSTI.GOV)

Valone, Steven Michael; Pilania, Ghanshyam; Liu, Xiang-Yang

Capturing key electronic properties such as charge excitation gaps within models at or above the atomic scale presents an ongoing challenge to understanding molecular, nanoscale, and condensed phase systems. One strategy is to describe the system in terms of properties of interacting material fragments, but it is unclear how to accomplish this for charge-excitation and charge-transfer phenomena. Hamiltonian models such as the Hubbard model provide formal frameworks for analyzing gap properties but are couched purely in terms of states of electrons, rather than the states of the fragments at the scale of interest. The recently introduced Fragment Hamiltonian (FH) modelmore » uses fragments in different charge states as its building blocks, enabling a uniform, quantum-mechanical treatment that captures the charge-excitation gap. These gaps are preserved in terms of inter-fragment charge-transferhopping integrals T and on-fragment parameters U (FH). The FH model generalizes the standard Hubbard model (a single intra-band hopping integral t and on-site repulsion U) from quantum states for electrons to quantum states for fragments. In this paper, we demonstrate that even for simple two-fragment and multi-fragment systems, gap closure is enabled once T exceeds the threshold set by U (FH), thus providing new insight into the nature of metal-insulator transitions. Finally, this result is in contrast to the standard Hubbard model for 1d rings, for which Lieb and Wu proved that gap closure was impossible, regardless of the choices for t and U.« less

Communication: Fragment-based Hamiltonian model of electronic charge-excitation gaps and gap closure

DOE PAGES

Valone, Steven Michael; Pilania, Ghanshyam; Liu, Xiang-Yang; ...

2015-11-13

Capturing key electronic properties such as charge excitation gaps within models at or above the atomic scale presents an ongoing challenge to understanding molecular, nanoscale, and condensed phase systems. One strategy is to describe the system in terms of properties of interacting material fragments, but it is unclear how to accomplish this for charge-excitation and charge-transfer phenomena. Hamiltonian models such as the Hubbard model provide formal frameworks for analyzing gap properties but are couched purely in terms of states of electrons, rather than the states of the fragments at the scale of interest. The recently introduced Fragment Hamiltonian (FH) modelmore » uses fragments in different charge states as its building blocks, enabling a uniform, quantum-mechanical treatment that captures the charge-excitation gap. These gaps are preserved in terms of inter-fragment charge-transferhopping integrals T and on-fragment parameters U (FH). The FH model generalizes the standard Hubbard model (a single intra-band hopping integral t and on-site repulsion U) from quantum states for electrons to quantum states for fragments. In this paper, we demonstrate that even for simple two-fragment and multi-fragment systems, gap closure is enabled once T exceeds the threshold set by U (FH), thus providing new insight into the nature of metal-insulator transitions. Finally, this result is in contrast to the standard Hubbard model for 1d rings, for which Lieb and Wu proved that gap closure was impossible, regardless of the choices for t and U.« less

Role of the Muon in Semiconductor Research

NASA Astrophysics Data System (ADS)

Mengyan, Rick (P. W.)

Muons are used in semiconductor research as an experimentally accessible analog to the isolated Hydrogen (H) impurity - a complex that is very difficult (or impossible) to study by other means. Hydrogen impurities of any concentration can modify the electrical, optical or magnetic properties of the host. For instance, H can be incorporated to remove electrically active levels from the energy gap (i.e. passivation) while some can form isolated centers that tend to be responsible for the trap and release of charge carriers and participate in site and charge-state dynamics which certainly affect the electrical properties of the host. Therefore, it can be quite useful to characterize these impurities in semiconducting materials that are of interest for use in devices. A muon has the same charge and spin as a proton but a mass that is nine times lighter. When implanted in a target material, a positively charged muon can behave as a light proton or bind with an electron to form a complex known as Muonium (Mu) with properties that are very similar to that of ionic or neutral H, respectively. A result of these similarities and direct non-destructive implantation is that Mu provides a direct measure of local electronic structure, thermal stability and charge-state transitions of these impurity centers. Since any material can be subjected to muon implantation and it is the muons themselves that mimic the H impurity centers, these measurements do not depend (at all) on the host's solubility of hydrogen nor do they require some minimum concentration; unlike many other techniques, such as EPR, ENDOR, NMR, or IR vibrational spectroscopy. Here we summarize major contributions muons have made to the field of semiconductor research followed by a few case studies to demonstrate the technique and detailed knowledge of the physical and electronic structures as well as dynamics (e.g.: charge-state and site transitions; local motion; long-range diffusion) of Mu/H that can be obtained.

Relativistic all-order many-body calculation of energies, wavelengths, and M 1 and E 2 transition rates for the 3 dn configurations in tungsten ions

NASA Astrophysics Data System (ADS)

Safronova, M. S.; Safronova, U. I.; Porsev, S. G.; Kozlov, M. G.; Ralchenko, Yu.

2018-01-01

Energy levels, wavelengths, magnetic-dipole and electric-quadrupole transition rates between the low-lying states are evaluated for W51 + to W54 + ions with 3 dn (n =2 to 5) electronic configurations by using an approach combining configuration interaction with the linearized coupled-cluster single-double method. The QED corrections are directly incorporated into the calculations and their effect is studied in detail. Uncertainties of the calculations are discussed. This study of such highly charged ions with the present method opens the way for future applications allowing an accurate prediction of properties for a very wide range of highly charged ions aimed at providing precision benchmarks for various applications.

ESR, SIMS and TEMF of an Y-Ba-Cu-O superconductor

NASA Technical Reports Server (NTRS)

Kirschner, I.; Giber, J.; Halasz, I.

1995-01-01

Superconducting transition comes into being between 92 K and 82 K in the samples having a Meissner's state value of 68 vol. percent. The main material content has an orthorhombic unit cell of Y1Ba2Cu408 accompanied by low quantity CuO and a sporadic phase. A proof of anisotropic superconductivity, an unusually high Cu ion concentration and a temperature dependent transition of charge carriers have been observed.

Enhanced charge ordering transition in doped CaFeO3 through steric templating

NASA Astrophysics Data System (ADS)

Jiang, Lai; Saldana-Greco, Diomedes; Schick, Joseph T.; Rappe, Andrew M.

2014-06-01

We report a density functional theory investigation of B-site doped CaFeO3, a prototypical charge ordered perovskite. At 290 K, CaFeO3 undergoes a metal-insulator transition and a charge disproportionation reaction 2Fe4+→Fe5++Fe3+. We observe that when Zr dopants occupy a (001) layer, the band gap of the resulting solid solution increases to 0.93 eV due to a two-dimensional Jahn-Teller-type distortion, where FeO6 cages on the xy plane elongate along x and y alternatively between neighboring Fe sites. Furthermore, we show that the rock-salt ordering of the Fe5+ and Fe3+ cations can be enhanced when the B-site dopants are arranged in a (111) plane due to a collective steric effect that facilitates the size discrepancy between the Fe5+O6 and Fe3+O6 octahedra and therefore gives rise to a larger band gap. The enhanced charge disproportionation in these solid solutions is verified by rigorously calculating the oxidation states of the Fe cations with different octahedral cage sizes. We therefore predict that the corresponding transition temperature will increase due to the enhanced charge ordering and larger band gap. The compositional, structural, and electrical relationships exploited in this paper can be extended to a variety of perovskites and nonperovskite oxides, providing guidance in the structural manipulation of electrical properties of functional materials.

Effect of Zn2+ binding and enzyme active site on the transition state for RNA 2'-O-transphosphorylation interpreted through kinetic isotope effects.

PubMed

Chen, Haoyuan; Piccirilli, Joseph A; Harris, Michael E; York, Darrin M

2015-11-01

Divalent metal ions, due to their ability to stabilize high concentrations of negative charge, are important for RNA folding and catalysis. Detailed models derived from the structures and kinetics of enzymes and from computational simulations have been developed. However, in most cases the specific catalytic modes involving metal ions and their mechanistic roles and effects on transition state structures remain controversial. Valuable information about the nature of the transition state is provided by measurement of kinetic isotope effects (KIEs). However, KIEs reflect changes in all bond vibrational modes that differ between the ground state and transition state. QM calculations are therefore essential for developing structural models of the transition state and evaluating mechanistic alternatives. Herein, we present computational models for Zn2+ binding to RNA 2'O-transphosphorylation reaction models that aid in the interpretation of KIE experiments. Different Zn2+ binding modes produce distinct KIE signatures, and one binding mode involving two zinc ions is in close agreement with KIEs measured for non-enzymatic catalysis by Zn2+ aquo ions alone. Interestingly, the KIE signatures in this specific model are also very close to those in RNase A catalysis. These results allow a quantitative connection to be made between experimental KIE measurements and transition state structure and bonding, and provide insight into RNA 2'O-ransphosphorylation reactions catalyzed by metal ions and enzymes. This article is part of a Special Issue entitled: Enzyme Transition States from Theory and Experiment. Copyright © 2015. Published by Elsevier B.V.

Vacancies and Vacancy-Mediated Self Diffusion in Cr 2 O 3 : A First-Principles Study

DOE Office of Scientific and Technical Information (OSTI.GOV)

Medasani, Bharat; Sushko, Maria L.; Rosso, Kevin M.

Charged and neutral vacancies and vacancy mediated self diffusion in alpha-Cr2O3 were investigated using first principles density functional theory (DFT) and periodic supercell formalism. The vacancy formation energies of charged defects were calculated using the electrostatic finite-size corrections to account for electrostatic interactions between supercells and the corrections for the bandgap underestimation in DFT. Calculations predict that neutral oxygen (O) vacancies are predominant in chromium (Cr)-rich conditions and Cr vacancies with -2 charge state are the dominant defects in O-rich conditions. The charge transition levels of both O and Cr vacancies are deep within the bandgap indicating the stability ofmore » these defects. Transport calculations indicate that vacancy mediated diffusion along the basal plane has lower energy barriers for both O and Cr ions. The most favorable vacancy mediated self diffusion processes correspond to the diffusion of Cr ion in 3+ charge state and O ion in 2- state, respectively. Our calculations reveal that Cr triple defects comprised of Cr in octahedral interstitial sites with two adjacent Cr vacancies along the c-axis have a lower formation energy compared to that of charged Cr vacancies. The formation of such triple defects facilitate Cr self diffusion along the c-axis.« less

Testing Electrostatic Complementarity in Enzyme Catalysis: Hydrogen Bonding in the Ketosteroid Isomerase Oxyanion Hole

PubMed Central

Kraut, Daniel A; Sigala, Paul A; Pybus, Brandon; Liu, Corey W; Ringe, Dagmar; Petsko, Gregory A

2006-01-01

A longstanding proposal in enzymology is that enzymes are electrostatically and geometrically complementary to the transition states of the reactions they catalyze and that this complementarity contributes to catalysis. Experimental evaluation of this contribution, however, has been difficult. We have systematically dissected the potential contribution to catalysis from electrostatic complementarity in ketosteroid isomerase. Phenolates, analogs of the transition state and reaction intermediate, bind and accept two hydrogen bonds in an active site oxyanion hole. The binding of substituted phenolates of constant molecular shape but increasing p K a models the charge accumulation in the oxyanion hole during the enzymatic reaction. As charge localization increases, the NMR chemical shifts of protons involved in oxyanion hole hydrogen bonds increase by 0.50–0.76 ppm/p K a unit, suggesting a bond shortening of ˜0.02 Å/p K a unit. Nevertheless, there is little change in binding affinity across a series of substituted phenolates (ΔΔG = −0.2 kcal/mol/p K a unit). The small effect of increased charge localization on affinity occurs despite the shortening of the hydrogen bonds and a large favorable change in binding enthalpy (ΔΔH = −2.0 kcal/mol/p K a unit). This shallow dependence of binding affinity suggests that electrostatic complementarity in the oxyanion hole makes at most a modest contribution to catalysis of ˜300-fold. We propose that geometrical complementarity between the oxyanion hole hydrogen-bond donors and the transition state oxyanion provides a significant catalytic contribution, and suggest that KSI, like other enzymes, achieves its catalytic prowess through a combination of modest contributions from several mechanisms rather than from a single dominant contribution. PMID:16602823

Shot-noise evidence of fractional quasiparticle creation in a local fractional quantum Hall state.

PubMed

Hashisaka, Masayuki; Ota, Tomoaki; Muraki, Koji; Fujisawa, Toshimasa

2015-02-06

We experimentally identify fractional quasiparticle creation in a tunneling process through a local fractional quantum Hall (FQH) state. The local FQH state is prepared in a low-density region near a quantum point contact in an integer quantum Hall (IQH) system. Shot-noise measurements reveal a clear transition from elementary-charge tunneling at low bias to fractional-charge tunneling at high bias. The fractional shot noise is proportional to T(1)(1-T(1)) over a wide range of T(1), where T(1) is the transmission probability of the IQH edge channel. This binomial distribution indicates that fractional quasiparticles emerge from the IQH state to be transmitted through the local FQH state. The study of this tunneling process enables us to elucidate the dynamics of Laughlin quasiparticles in FQH systems.

Biology's built-in Faraday cages

NASA Astrophysics Data System (ADS)

Klee, Maurice M.

2014-05-01

Biological fluids are water-based, ionic conductors. As such, they have both high relative dielectric constants and substantial conductivities, meaning they are lossy dielectrics. These fluids contain charged molecules (free charges), whose movements play roles in essentially all cellular processes from metabolism to communication with other cells. Using the problem of a point source in air above a biological fluid of semi-infinite extent, the bound charges in the fluid are shown to perform the function of a fast-acting Faraday cage, which protects the interior of the fluid from external electric fields. Free charges replace bound charges in accordance with the fluid's relaxation time, thereby providing a smooth transition between the initial protection provided by the bound charges and the steady state protection provided by the free charges. The electric fields within the biological fluid are thus small for all times just as they would be inside a classical Faraday cage.

Radio frequency charge parity meter.

PubMed

Schroer, M D; Jung, M; Petersson, K D; Petta, J R

2012-10-19

We demonstrate a total charge parity measurement by detecting the radio frequency signal that is reflected by a lumped-element resonator coupled to a single InAs nanowire double quantum dot. The high frequency response of the circuit is used to probe the effects of the Pauli exclusion principle at interdot charge transitions. Even parity charge transitions show a striking magnetic field dependence that is due to a singlet-triplet transition, while odd parity transitions are relatively insensitive to a magnetic field. The measured response agrees well with cavity input-output theory, allowing accurate measurements of the interdot tunnel coupling and the resonator-charge coupling rate g(c)/2π~17 MHz.

Insights into the Effects of Zinc Doping on Structural Phase Transition of P2-Type Sodium Nickel Manganese Oxide Cathodes for High-Energy Sodium Ion Batteries

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wu, Xuehang; Xu, Gui-Liang; Zhong, Guiming

P2-type sodium nickel manganese oxide-based cathode materials with higher energy densities are prime candidates for applications in rechargeable sodium ion batteries. A systematic study combining in situ high energy X-ray diffraction (HEXRD), ex situ Xray absorption fine spectroscopy (XAFS), transmission electron microscopy (TEM), and solid-state nuclear magnetic resonance (SSNMR) techniques was carried out to gain a deep insight into the structural evolution of P2-Na 0.66Ni 0.33-xZn xMn 0.67O 2 (x = 0, 0.07) during cycling. In situ HEXRD and ex situ TEM measurements indicate that an irreversible phase transition occurs upon sodium insertion-extraction of Na 0.66Ni 0.33Mn 0.67O 2. Zincmore » doping of this system results in a high structural reversibility. XAFS measurements indicate that both materials are almost completely dependent on the Ni 4+/Ni 3+/ Ni 2+ redox couple to provide charge/discharge capacity. SS-NMR measurements indicate that both reversible and irreversible migration of transition metal ions into the sodium layer occurs in the material at the fully charged state. The irreversible migration of transition metal ions triggers a structural distortion, leading to the observed capacity and voltage fading. Our results allow a new understanding of the importance of improving the stability of transition metal layers.« less

Coexistence of magnetic and charge order in a two-component order parameter description of the layered superconductors

NASA Astrophysics Data System (ADS)

Doria, Mauro M.; Vargas-Paredes, Alfredo A.; Cariglia, Marco

2014-12-01

We consider an effective theory of superconductivity for layered superconductors using a two-component order parameter, and show that it allows the formation of a condensate with magnetic and charge degrees of freedom. This condensate is an inhomogeneous state, topologically stable, that exists without the presence of an applied magnetic field. In particular, it is associated to a charge density in the superconducting layers. We show that well defined angular momentum states have for their lowest moment an hexadecapole charge distribution, i.e. quartic in the momenta. Our approach is based on solving first order equations (FOE) that generalize the Abrikosov-Bogomolny equations of the Ginzburg-Landau theory with one order parameter. The FOE solve the variational equations of the theory in the limit of a small order parameter, which is achieved for the special temperature that corresponds to the crossing of the superconducting dome and the pseudogap transition line. This topologically stable state is a condensate of skyrmions that breaks time reversal symmetry and produces a weak local magnetic field below the threshold of experimental observation.

Strain controlled ferromagnetic-ferrimagnetic transition and vacancy formation energy of defective graphene.

PubMed

Zhang, Yajun; Sahoo, Mpk; Wang, Jie

2016-09-23

Single vacancy (SV)-induced magnetism in graphene has attracted much attention motivated by its potential in achieving new functionalities. However, a much higher vacancy formation energy limits its direct application in electronic devices and the dependency of spin interaction on the strain is unclear. Here, through first-principles density-functional theory calculations, we investigate the possibility of strain engineering towards lowering vacancy formation energy and inducing new magnetic states in defective graphene. It is found that the SV-graphene undergoes a phase transition from an initial ferromagnetic state to a ferrimagnetic state under a biaxial tensile strain. At the same time, the biaxial tensile strain significantly lowers the vacancy formation energy. The charge density, density of states and band theory successfully identify the origin and underlying physics of the transition. The predicted magnetic phase transition is attributed to the strain driven spin flipping at the C-atoms nearest to the SV-site. The magnetic semiconducting graphene induced by defect and strain engineering suggests an effective way to modulate both spin and electronic degrees of freedom in future spintronic devices.

Chirality and orbital order in charge density waves

NASA Astrophysics Data System (ADS)

van Wezel, Jasper

2011-12-01

Helical arrangements of spins are common among magnetic materials. The first material to harbor a corkscrew pattern of charge density, on the other hand, was discovered only very recently. The nature of the order parameter is of key relevance, since rotating a magnetic vector around any propagation vector trivially yields a helical pattern. In contrast, the purely scalar charge density cannot straightforwardly support a chiral state. Here we use a Landau order parameter analysis to resolve this paradox, and show that the chiral charge order may be understood as a form of orbital ordering. We discuss the microscopic mechanism driving the transition and show it to be of a general form, thus allowing for a broad class of materials to display this novel type of orbital-ordered chiral charge density wave.

Effect of Zn2+ binding and enzyme active site on the transition state for RNA 2′-O-transphosphorylation interpreted through kinetic isotope effects

PubMed Central

Chen, Haoyuan; Piccirilli, Joseph A.; Harris, Michael E.; York, Darrin M.

2016-01-01

Divalent metal ions, due to their ability to stabilize high concentrations of negative charge, are important for RNA folding and catalysis. Detailed models derived from the structures and kinetics of enzymes and from computational simulations have been developed. However, in most cases the specific catalytic modes involving metal ions and their mechanistic roles and effects on transition state structures remains controversial. Valuable information about the nature of the transition state is provided by measurement of kinetic isotope effects (KIEs). However, KIEs reflect changes in all bond vibrational modes that differ between the ground state and transition state. QM calculations are therefore essential for developing structural models of the transition state and evaluating mechanistic alternatives. Herein, we present computational models for Zn2+ binding to RNA 2′O-transphosphorylation reaction models that aid in the interpretation of KIE experiments. Different Zn2+ binding modes produce distinct KIE signatures, and one binding mode involving two zinc ions is in close agreement with KIEs measured for non-enzymatic catalysis by Zn2+ aquo ions alone. Interestingly, the KIE signatures in this specific model are also very close to those in RNase A catalysis. These results allow a quantitative connection to be made between experimental KIE measurements and transition state structure and bonding, and provide insight into RNA 2′O-transphosphorylation reactions catalyzed by metal ions and enzymes. PMID:25812974

Sequence charge decoration dictates coil-globule transition in intrinsically disordered proteins.

PubMed

Firman, Taylor; Ghosh, Kingshuk

2018-03-28

We present an analytical theory to compute conformations of heteropolymers-applicable to describe disordered proteins-as a function of temperature and charge sequence. The theory describes coil-globule transition for a given protein sequence when temperature is varied and has been benchmarked against the all-atom Monte Carlo simulation (using CAMPARI) of intrinsically disordered proteins (IDPs). In addition, the model quantitatively shows how subtle alterations of charge placement in the primary sequence-while maintaining the same charge composition-can lead to significant changes in conformation, even as drastic as a coil (swelled above a purely random coil) to globule (collapsed below a random coil) and vice versa. The theory provides insights on how to control (enhance or suppress) these changes by tuning the temperature (or solution condition) and charge decoration. As an application, we predict the distribution of conformations (at room temperature) of all naturally occurring IDPs in the DisProt database and notice significant size variation even among IDPs with a similar composition of positive and negative charges. Based on this, we provide a new diagram-of-states delineating the sequence-conformation relation for proteins in the DisProt database. Next, we study the effect of post-translational modification, e.g., phosphorylation, on IDP conformations. Modifications as little as two-site phosphorylation can significantly alter the size of an IDP with everything else being constant (temperature, salt concentration, etc.). However, not all possible modification sites have the same effect on protein conformations; there are certain "hot spots" that can cause maximal change in conformation. The location of these "hot spots" in the parent sequence can readily be identified by using a sequence charge decoration metric originally introduced by Sawle and Ghosh. The ability of our model to predict conformations (both expanded and collapsed states) of IDPs at a high-throughput level can provide valuable insights into the different mechanisms by which phosphorylation/charge mutation controls IDP function.

Sequence charge decoration dictates coil-globule transition in intrinsically disordered proteins

NASA Astrophysics Data System (ADS)

Firman, Taylor; Ghosh, Kingshuk

2018-03-01

We present an analytical theory to compute conformations of heteropolymers—applicable to describe disordered proteins—as a function of temperature and charge sequence. The theory describes coil-globule transition for a given protein sequence when temperature is varied and has been benchmarked against the all-atom Monte Carlo simulation (using CAMPARI) of intrinsically disordered proteins (IDPs). In addition, the model quantitatively shows how subtle alterations of charge placement in the primary sequence—while maintaining the same charge composition—can lead to significant changes in conformation, even as drastic as a coil (swelled above a purely random coil) to globule (collapsed below a random coil) and vice versa. The theory provides insights on how to control (enhance or suppress) these changes by tuning the temperature (or solution condition) and charge decoration. As an application, we predict the distribution of conformations (at room temperature) of all naturally occurring IDPs in the DisProt database and notice significant size variation even among IDPs with a similar composition of positive and negative charges. Based on this, we provide a new diagram-of-states delineating the sequence-conformation relation for proteins in the DisProt database. Next, we study the effect of post-translational modification, e.g., phosphorylation, on IDP conformations. Modifications as little as two-site phosphorylation can significantly alter the size of an IDP with everything else being constant (temperature, salt concentration, etc.). However, not all possible modification sites have the same effect on protein conformations; there are certain "hot spots" that can cause maximal change in conformation. The location of these "hot spots" in the parent sequence can readily be identified by using a sequence charge decoration metric originally introduced by Sawle and Ghosh. The ability of our model to predict conformations (both expanded and collapsed states) of IDPs at a high-throughput level can provide valuable insights into the different mechanisms by which phosphorylation/charge mutation controls IDP function.

Origin of Capacity Fading in Nano-Sized Co3O4 Electrodes: Electrochemical Impedance Spectroscopy Study

NASA Astrophysics Data System (ADS)

Kang, Jin-Gu; Ko, Young-Dae; Park, Jae-Gwan; Kim, Dong-Wan

2008-10-01

Transition metal oxides have been suggested as innovative, high-energy electrode materials for lithium-ion batteries because their electrochemical conversion reactions can transfer two to six electrons. However, nano-sized transition metal oxides, especially Co3O4, exhibit drastic capacity decay during discharge/charge cycling, which hinders their practical use in lithium-ion batteries. Herein, we prepared nano-sized Co3O4 with high crystallinity using a simple citrate-gel method and used electrochemical impedance spectroscopy method to examine the origin for the drastic capacity fading observed in the nano-sized Co3O4 anode system. During cycling, AC impedance responses were collected at the first discharged state and at every subsequent tenth discharged state until the 100th cycle. By examining the separable relaxation time of each electrochemical reaction and the goodness-of-fit results, a direct relation between the charge transfer process and cycling performance was clearly observed.

Ground state of underdoped cuprates in vicinity of superconductor-to-insulator transition

DOE PAGES

Wu, Jie; Bollinger, Anthony T.; Sun, Yujie; ...

2016-08-15

When an insulating underdoped cuprate is doped beyond a critical concentration (x c), high-temperature superconductivity emerges. We have synthesized a series of La 2–xSr xCuO 4 (LSCO) samples using the combinatorial spread technique that allows us to traverse the superconductor-to-insulator transition (SIT) in extremely fine doping steps, Δx≈0.00008. We have measured the Hall resistivity (ρ H) as a function of temperature down to 300 mK in magnetic fields up to 9 T. At very low temperatures, ρ H shows an erratic behavior, jumps and fluctuations exceeding 100%, hysteresis, and memory effects, indicating that the insulating ground state is a charge-clustermore » glass (CCG). Furthermore, based on the phase diagram depicted in our experiment, we propose a unified picture to account for the anomalous electric transport in the vicinity of the SIT, suggesting that the CCG is in fact a disordered and glassy version of the charge density wave.« less

Atomistic origin of an ordered superstructure induced superconductivity in layered chalcogenides.

PubMed

Ang, R; Wang, Z C; Chen, C L; Tang, J; Liu, N; Liu, Y; Lu, W J; Sun, Y P; Mori, T; Ikuhara, Y

2015-01-27

Interplay among various collective electronic states such as charge density wave and superconductivity is of tremendous significance in low-dimensional electron systems. However, the atomistic and physical nature of the electronic structures underlying the interplay of exotic states, which is critical to clarifying its effect on remarkable properties of the electron systems, remains elusive, limiting our understanding of the superconducting mechanism. Here, we show evidence that an ordering of selenium and sulphur atoms surrounding tantalum within star-of-David clusters can boost superconductivity in a layered chalcogenide 1T-TaS2-xSex, which undergoes a superconducting transition in the nearly commensurate charge density wave phase. Advanced electron microscopy investigations reveal that such an ordered superstructure forms only in the x area, where the superconductivity manifests, and is destructible to the occurrence of the Mott metal-insulator transition. The present findings provide a novel dimension in understanding the relationship between lattice and electronic degrees of freedom.

Frenkel-Charge-Transfer exciton intermixing theory for molecular crystals with two isolated Frenkel exciton states.

NASA Astrophysics Data System (ADS)

Bondarev, Igor; Popescu, Adrian

We develop an analytical theory for the intra-intermolecular exciton intermixing in periodic 1D chains of planar organic molecules with two isolated low-lying Frenkel exciton states, typical of copper phthalocyanine (CuPc) and other transition metal phthalocyanine molecules. We formulate the Hamiltonian and use the exact Bogoliubov diagonalization procedure to derive the eigen energy spectrum for the two lowest intramolecular Frenkel excitons coupled to the intermolecular charge transfer (CT) exciton state. By comparing our theoretical spectrum with available experimental CuPc absorption data, we obtain the parameters of the Frenkel-CT exciton intermixing in CuPc thin films. The two Frenkel exciton states here are spaced apart by 0.26 eV, and the charge transfer exciton state is 50 meV above the lowest Frenkel exciton. Both Frenkel excitons are strongly mixed with the CT exciton, showing the coupling constant 0.17 eV in agreement with earlier electron transport experiments. Our results can be used for the proper interpretation of the physical properties of crystalline phthalocyanines. DOE-DE-SC0007117 (I.B.), UNC-GA ROI Grant (A.P.).

Vesicle Adhesion and Fusion Studied by Small-Angle X-Ray Scattering.

PubMed

Komorowski, Karlo; Salditt, Annalena; Xu, Yihui; Yavuz, Halenur; Brennich, Martha; Jahn, Reinhard; Salditt, Tim

2018-04-24

We have studied the adhesion state (also denoted by docking state) of lipid vesicles as induced by the divalent ions Ca 2+ or Mg 2+ at well-controlled ion concentration, lipid composition, and charge density. The bilayer structure and the interbilayer distance in the docking state were analyzed by small-angle x-ray scattering. A strong adhesion state was observed for DOPC:DOPS vesicles, indicating like-charge attraction resulting from ion correlations. The observed interbilayer separations of ∼1.6 nm agree quantitatively with the predictions of electrostatics in the strong coupling regime. Although this phenomenon was observed when mixing anionic and zwitterionic (or neutral) lipids, pure anionic membranes (DOPS) with highest charge density σ resulted in a direct phase transition to a multilamellar state, which must be accompanied by rupture and fusion of vesicles. To extend the structural assay toward protein-controlled docking and fusion, we have characterized reconstituted N-ethylmaleimide-sensitive factor attachment protein receptors in controlled proteoliposome suspensions by small-angle x-ray scattering. Copyright © 2018 Biophysical Society. Published by Elsevier Inc. All rights reserved.

Anomalous magneto-elastic and charge doping effects in thallium-doped BaFe 2As 2

DOE PAGES

Sefat, Athena S.; Li, Li; Cao, Huibo B.; ...

2016-02-12

Within the BaFe 2As 2 crystal lattice, we partially substitute thallium for barium and report the effects of interlayer coupling in Ba 1-xTl xFe 2As 2 crystals. We demonstrate the unusual effects of magneto-elastic coupling and charge doping in this iron-arsenide material, whereby Néel temperature rises with small x, and then falls with additional x. Specifically, we find that Néel and structural transitions in BaFe 2As 2 (T N = T s = 133 K) increase for x = 0.05 (T N = 138 K, T s = 140 K) from magnetization, heat capacity, resistivity, and neutron diffraction measurements. Evidencemore » from single crystal X-ray diffraction and first principles calculations attributes the stronger magnetism in x = 0.05 to magneto-elastic coupling related to the shorter intraplanar Fe-Fe bond distance. With further thallium substitution, the transition temperatures decrease for x = 0.09 (T N = T s = 131 K), and this is due to charge doping. Lastly, we illustrate that small changes related to 3d transition-metal state can have profound effects on magnetism.« less

Anomalous magneto-elastic and charge doping effects in thallium-doped BaFe2As2

PubMed Central

Sefat, Athena S.; Li, Li; Cao, Huibo B.; McGuire, Michael A.; Sales, Brian; Custelcean, Radu; Parker, David S.

2016-01-01

Within the BaFe2As2 crystal lattice, we partially substitute thallium for barium and report the effects of interlayer coupling in Ba1-xTlxFe2As2 crystals. We demonstrate the unusual effects of magneto-elastic coupling and charge doping in this iron-arsenide material, whereby Néel temperature rises with small x, and then falls with additional x. Specifically, we find that Néel and structural transitions in BaFe2As2 (TN = Ts = 133 K) increase for x = 0.05 (TN = 138 K, Ts = 140 K) from magnetization, heat capacity, resistivity, and neutron diffraction measurements. Evidence from single crystal X-ray diffraction and first principles calculations attributes the stronger magnetism in x = 0.05 to magneto-elastic coupling related to the shorter intraplanar Fe-Fe bond distance. With further thallium substitution, the transition temperatures decrease for x = 0.09 (TN = Ts = 131 K), and this is due to charge doping. We illustrate that small changes related to 3d transition-metal state can have profound effects on magnetism. PMID:26867821

Decoupling the Lattice Distortion and Charge Doping Effects on the Phase Transition Behavior of VO2 by Titanium (Ti4+) Doping

PubMed Central

Wu, Yanfei; Fan, Lele; Liu, Qinghua; Chen, Shi; Huang, Weifeng; Chen, Feihu; Liao, Guangming; Zou, Chongwen; Wu, Ziyu

2015-01-01

The mechanism for regulating the critical temperature (TC) of metal-insulator transition (MIT) in ions-doped VO2 systems is still a matter of debate, in particular, the unclear roles of lattice distortion and charge doping effects. To rule out the charge doping effect on the regulation of TC, we investigated Ti4+-doped VO2 (TixV1-xO2) system. It was observed that the TC of TixV1-xO2 samples first slightly decreased and then increased with increasing Ti concentration. X-ray absorption fine structure (XAFS) spectroscopy was used to explore the electronic states and local lattice structures around both Ti and V atoms in TixV1-xO2 samples. Our results revealed the local structure evolution from the initial anatase to the rutile-like structure around the Ti dopants. Furthermore, the host monoclinic VO2 lattice, specifically, the VO6 octahedra would be subtly distorted by Ti doping. The distortion of VO6 octahedra and the variation of TC showed almost the similar trend, confirming the direct effect of local structural perturbations on the phase transition behavior. By comparing other ion-doping systems, we point out that the charge doping is more effective than the lattice distortion in modulating the MIT behavior of VO2 materials. PMID:25950809

Influence of Coherent Tunneling and Incoherent Hopping on the Charge Transfer Mechanism in Linear Donor-Bridge-Acceptor Systems.

PubMed

Li, Guangqi; Govind, Niranjan; Ratner, Mark A; Cramer, Christopher J; Gagliardi, Laura

2015-12-17

The mechanism of charge transfer has been observed to change from tunneling to hopping with increasing numbers of DNA base pairs in polynucleotides and with the length of molecular wires. The aim of this paper is to investigate this transition by examining the population dynamics using a tight-binding Hamiltonian with model parameters to describe a linear donor-bridge-acceptor (D-B-A) system. The model includes a primary vibration and an electron-vibration coupling at each site. A further coupling of the primary vibration with a secondary phonon bath allows the system to dissipate energy to the environment and reach a steady state. We apply the quantum master equation (QME) approach, based on second-order perturbation theory in a quantum dissipative system, to examine the dynamical processes involved in charge-transfer and follow the population transfer rate at the acceptor, ka, to shed light on the transition from tunneling to hopping. With a small tunneling parameter, V, the on-site population tends to localize and form polarons, and the hopping mechanism dominates the transfer process. With increasing V, the population tends to be delocalized and the tunneling mechanism dominates. The competition between incoherent hopping and coherent tunneling governs the mechanism of charge transfer. By varying V and the total number of sites, we also examine the onset of the transition from tunneling to hopping with increasing length.

On the calculation of charge transfer transitions with standard density functionals using constrained variational density functional theory.

PubMed

Ziegler, Tom; Krykunov, Mykhaylo

2010-08-21

It is well known that time-dependent density functional theory (TD-DFT) based on standard gradient corrected functionals affords both a quantitative and qualitative incorrect picture of charge transfer transitions between two spatially separated regions. It is shown here that the well known failure can be traced back to the use of linear response theory. Further, it is demonstrated that the inclusion of higher order terms readily affords a qualitatively correct picture even for simple functionals based on the local density approximation. The inclusion of these terms is done within the framework of a newly developed variational approach to excitation energies called constrained variational density functional theory (CV-DFT). To second order [CV(2)-DFT] this theory is identical to adiabatic TD-DFT within the Tamm-Dancoff approximation. With inclusion of fourth order corrections [CV(4)-DFT] it affords a qualitative correct description of charge transfer transitions. It is finally demonstrated that the relaxation of the ground state Kohn-Sham orbitals to first order in response to the change in density on excitation together with CV(4)-DFT affords charge transfer excitations in good agreement with experiment. The new relaxed theory is termed R-CV(4)-DFT. The relaxed scheme represents an effective way in which to introduce double replacements into the description of single electron excitations, something that would otherwise require a frequency dependent kernel.

Modulation doping of quantum dot laser active area and its impact on lasing performance

NASA Astrophysics Data System (ADS)

Konoplev, S. S.; Savelyev, A. V.; Korenev, V. V.; Maximov, M. V.; Zhukov, A. E.

2015-11-01

We present a theoretical study of modulation doping of active region in the quantum dot (QD) laser and corresponding issues of QD charge neutrality violation, a band diagram of the laser and charge carriers distribution in the structure. Modulation doping is discussed as a possible technique to control laser output characteristics. It was shown that modulation doping leads to an increase of threshold current of lasing through excited QD optical transition together with power emission from QD ground state.

Density functional tight-binding and infrequent metadynamics can capture entropic effects in intramolecular hydrogen transfer reactions

NASA Astrophysics Data System (ADS)

Oliveira, Luiz F. L.; Fu, Christopher D.; Pfaendtner, Jim

2018-04-01

Infrequent metadynamics uses biased simulations to estimate the unbiased kinetics of a system, facilitating the calculation of rates and barriers. Here the method is applied to study intramolecular hydrogen transfer reactions involving peroxy radicals, a class of reactions that is challenging to model due to the entropic contributions of the formation of ring structures in the transition state. Using the self-consistent charge density-functional based tight-binding (DFTB) method, we applied infrequent metadynamics to the study of four intramolecular H-transfer reactions, demonstrating that the method can qualitatively reproduce these high entropic contributions, as observed in experiments and those predicted by transition state theory modeled by higher levels of theory. We also show that infrequent metadynamics and DFTB are successful in describing the relationship between transition state ring size and kinetic coefficients (e.g., activation energies and the pre-exponential factors).

Optical Absorption and Electric Resistivity of an l-Cysteine Film

NASA Astrophysics Data System (ADS)

Kamada, Masao; Hideshima, Takuya; Azuma, Junpei; Yamamoto, Isamu; Imamura, Masaki; Takahashi, Kazutoshi

2016-12-01

The optical and electric properties of an l-cysteine film have been investigated to understand its applicability to bioelectronics. The fundamental absorption is the allowed transition having the threshold at 5.8 eV and the absorption is due to the charge-transfer type transition from sulfur-3sp to oxygen-2p and/or carbon-2p states, while absorptions more than 9 eV can be explained with intra-atomic transitions in the functional groups. The electric resistivity is 2.0 × 104 Ω m at room temperature and increases as the sample temperature decreases. The results indicate that the l-cysteine film is a p-type semiconductor showing the hole conduction caused by the sulfur-3sp occupied states and unknown impurity or defect states as acceptors. The electron affinity of the l-cysteine film is derived as ≦-0.3 eV.

Theoretical study of metal noble-gas positive ions

NASA Technical Reports Server (NTRS)

Bauschlicher, Charles W., Jr.; Partridge, Harry; Langhoff, Stephen R.

1989-01-01

Theoretical calculations have been performed to determine the spectroscopic constant for the ground and selected low-lying electronic states of the transition-metal noble-gas ions Var(+), FeAr(+), CoAr(+), CuHe(+), CuAr(+), and CuKr(+). Analogous calculations have been performed for the ground states of the alkali noble-gas ions LiAr(+), LiKr(+), NaAr(+), and KAr(+) and the alkaline-earth noble-gas ion MgAr(+) to contrast the difference in binding energies between the simple and transition-metal noble-gas ions. The binding energies increase with increasing polarizability of the noble-gas ions, as expected for a charge-induced dipole bonding mechanism. It is found that the spectroscopic constants of the X 1Sigma(+) states of the alkali noble-gas ions are well described at the self-consistent field level. In contrast, the binding energies of the transition-metal noble-gas ions are substantially increased by electron correlation.

Strain-induced Weyl and Dirac states and direct-indirect gap transitions in group-V materials

NASA Astrophysics Data System (ADS)

Moynihan, Glenn; Sanvito, Stefano; O'Regan, David D.

2017-12-01

We perform comprehensive density-functional theory calculations on strained two-dimensional phosphorus (P), arsenic (As) and antimony (Sb) in the monolayer, bilayer, and bulk α-phase, from which we compute the key mechanical and electronic properties of these materials. Specifically, we compute their electronic band structures, band gaps, and charge-carrier effective masses, and identify the qualitative electronic and structural transitions that may occur. Moreover, we compute the elastic properties such as the Young’s modulus Y; shear modulus G; bulk modulus B ; and Poisson ratio ν and present their isotropic averages of as well as their dependence on the in-plane orientation, for which the relevant expressions are derived. We predict strain-induced Dirac states in the monolayers of As and Sb and the bilayers of P, As, and Sb, as well as the possible existence of Weyl states in the bulk phases of P and As. These phases are predicted to support charge velocities up to 106 m {{\\text{s}}-1} and, in some highly anisotropic cases, permit one-dimensional ballistic conductivity in the puckered direction. We also predict numerous band gap transitions for moderate in-plane stresses. Our results contribute to the mounting evidence for the utility of these materials, made possible by their broad range in tuneable properties, and facilitate the directed exploration of their potential application in next-generation electronics.

Tempo: A Toolkit for the Timed Input/Output Automata Formalism

DTIC Science & Technology

2008-01-30

generation of distributed code from specifications. F .4.3 [Formal Languages]: Tempo;, D.3 [Programming Many distributed systems involve a combination of...and require The chek (i) transition is enabled when process i’s program the simulator to check the assertions after every single step counter is set to...output foo (n:Int) The Tempo simulator addresses this issue by putting the states x: Int : = 10;transitions modeler in charge of resolving the non

Coexisting charge and magnetic orders in the dimer-chain iridate Ba 5AlIr 2O 11

DOE PAGES

Terzic, J.; Wang, J. C.; Ye, Feng; ...

2015-06-29

In this paper, we have synthesized and studied single-crystal Ba 5AlIr 2O 11 that features dimer chains of two inequivalent octahedra occupied by tetravalent Ir 4+(5d 5) and pentavalent Ir 5+(5d 4) ions, respectively. Ba 5AlIr 2O 11 is a Mott insulator that undergoes a subtle structural phase transition near T S=210K and a magnetic transition at T M=4.5K; the latter transition is surprisingly resistant to applied magnetic fields μ oH≤12T but more sensitive to modest applied pressure (dT M/dp ≈ +0.61K/GPa). All results indicate that the phase transition at T S signals an enhanced charge order that induces electricalmore » dipoles and strong dielectric response near T S. It is clear that the strong covalency and spin-orbit interaction (SOI) suppress double exchange in Ir dimers and stabilize a novel magnetic state that is neither S=3/2 nor J=1/2, but rather lies in an “intermediate” regime between these two states. Finally, the novel behavior of Ba 5AlIr 2O 11 therefore provides unique insights into the physics of SOI along with strong covalency in competition with double-exchange interactions of comparable strength.« less

Stretch-collapse transition of polyelectrolyte brushes in a poor solvent

NASA Astrophysics Data System (ADS)

von Goeler, F.; Muthukumar, M.

1996-12-01

This paper describes the behavior of charged, polymer brushes in electrolyte solutions of varying solvent quality. The brush height, d, dependence on the chain length, L (=Nl, where l is the Kuhn length), the grafting density σ, and solvent conditions is determined. We consider a monomer-monomer potential consisting of three components: (1) a long-ranged, screened Coulombic component of strength v¯/l (l is the Kuhn length) and range κ-1; (2) a short-ranged, two-body component of strength w¯l; and (3) a short-ranged, three-body component of strength ūl3. In particular, we examine the transition from a stretched state to a collapsed state in a poor solvent (w¯<0) as the solvent quality is decreased. Using dimensional analysis, Monte Carlo methods, and a variational technique, a first order transition is observed as predicted by the scaling arguments of Ross et al. and Borisov et al. for high charge/grafting densities. Using a variational procedure, we derive an analytical expression for the brush size and determine, quantitatively, the critical conditions for a first order transition in terms of key dimensionless variables, vN5/2, κlN1/2, wN3/2, and uN2 (where v=2πσl2v¯, w=σl2w¯, and u=σ2l4ū).

Femtosecond Fluorescence Upconversion Study of a Naphthalimide-Bithiophene-Triphenylamine Push-Pull Dye in Solution.

PubMed

Maffeis, Valentin; Brisse, Romain; Labet, Vanessa; Jousselme, Bruno; Gustavsson, Thomas

2018-06-13

There is a high interest in the development of new push-pull dyes for the use in dye sensitized solar cells. The pronounced charge transfer character of the directly photoexcited state is in principle favorable for a charge injection. Here, we report a time-resolved fluorescence study of a triphenylamine-bithiophene-naphthalimide dye in four solvents of varying polarity using fluorescence upconversion. The recording of femtosecond time-resolved fluorescence spectra corrected for the group velocity dispersion allows for a detailed analysis discriminating between spectral shifts and total intensity decays. After photoexcitation, the directly populated state (S 1 /FC) evolves toward a relaxed charge transfer state (S 1 /CT). This S 1 /CT state is characterized by a lower radiative transition moment and a higher nonradiative quenching. The fast dynamic shift of the fluorescence band is well described by solvation dynamics in polar solvents, but less so in nonpolar solvents, hinting that the excited-state relaxation process occurs on a free energy surface whose topology is strongly governed by the solvent polarity. This study underlines the influence of the environment on the intramolecular charge transfer (ICT) process, and the necessity to analyze time-resolved data in detail when solvation and ICT occur simultaneously.

Operation of a quantum dot in the finite-state machine mode: Single-electron dynamic memory

DOE Office of Scientific and Technical Information (OSTI.GOV)

Klymenko, M. V.; Klein, M.; Levine, R. D.

2016-07-14

A single electron dynamic memory is designed based on the non-equilibrium dynamics of charge states in electrostatically defined metallic quantum dots. Using the orthodox theory for computing the transfer rates and a master equation, we model the dynamical response of devices consisting of a charge sensor coupled to either a single and or a double quantum dot subjected to a pulsed gate voltage. We show that transition rates between charge states in metallic quantum dots are characterized by an asymmetry that can be controlled by the gate voltage. This effect is more pronounced when the switching between charge states correspondsmore » to a Markovian process involving electron transport through a chain of several quantum dots. By simulating the dynamics of electron transport we demonstrate that the quantum box operates as a finite-state machine that can be addressed by choosing suitable shapes and switching rates of the gate pulses. We further show that writing times in the ns range and retention memory times six orders of magnitude longer, in the ms range, can be achieved on the double quantum dot system using experimentally feasible parameters, thereby demonstrating that the device can operate as a dynamic single electron memory.« less

State-to-State Internal Energy Relaxation Following the Quantum-Kinetic Model in DSMC

NASA Technical Reports Server (NTRS)

Liechty, Derek S.

2014-01-01

A new model for chemical reactions, the Quantum-Kinetic (Q-K) model of Bird, has recently been introduced that does not depend on macroscopic rate equations or values of local flow field data. Subsequently, the Q-K model has been extended to include reactions involving charged species and electronic energy level transitions. Although this is a phenomenological model, it has been shown to accurately reproduce both equilibrium and non-equilibrium reaction rates. The usefulness of this model becomes clear as local flow conditions either exceed the conditions used to build previous models or when they depart from an equilibrium distribution. Presently, the applicability of the relaxation technique is investigated for the vibrational internal energy mode. The Forced Harmonic Oscillator (FHO) theory for vibrational energy level transitions is combined with the Q-K energy level transition model to accurately reproduce energy level transitions at a reduced computational cost compared to the older FHO models.

Charge density wave properties of the quasi two-dimensional purple molybdenum bronze KMo 6O 17

NASA Astrophysics Data System (ADS)

Balaska, H.; Dumas, J.; Guyot, H.; Mallet, P.; Marcus, J.; Schlenker, C.; Veuillen, J. Y.; Vignolles, D.

2005-06-01

The purple molybdenum bronze KMo 6O 17 is a quasi-two-dimensional compound which shows a Peierls transition towards a commensurate metallic CDW state. Electron spectroscopy (ARUPS), Scanning Tunnelling Microscopy (STM) and spectroscopy (STS) as well as high magnetic field studies are reported. ARUPS studies corroborate the model of the hidden nesting and provide a value of the CDW vector in good agreement with other measurements. STM studies visualize the triple- q CDW in real space. This is consistent with other measurements of the CDW vector. STS studies provide a value of several 10 meV for the average CDW gap. High magnetic field measurements performed in pulsed fields up to 55 T establish that first order transitions to smaller gap states take place at low temperature. These transitions are ascribed to Pauli type coupling. A phase diagram summarizing all observed anomalies and transitions is presented.

139La and 63Cu NMR investigation of charge order in La2CuO4 +y (Tc=42 K)

NASA Astrophysics Data System (ADS)

Imai, T.; Lee, Y. S.

2018-03-01

We report 139La and 63Cu NMR investigation of the successive charge order, spin order, and superconducting transitions in superoxygenated La2CuO4 +y single crystal with stage-4 excess oxygen order at Tstage≃290 K. We show that the stage-4 order induces tilting of CuO6 octahedra below Tstage, which in turn causes 139La NMR line broadening. The structural distortion continues to develop far below Tstage, and completes at Tcharge≃60 K, where charge order sets in. This sequence is reminiscent of the the charge-order transition in Nd codoped La1.88Sr0.12CuO4 that sets in once the low-temperature tetragonal phase is established. We also show that the paramagnetic 63Cu NMR signals are progressively wiped out below Tcharge due to enhanced low-frequency spin fluctuations in charge-ordered domains, but the residual 63Cu NMR signals continue to exhibit the characteristics expected for optimally doped superconducting CuO2 planes. This indicates that charge order in La2CuO4 +y does not take place uniformly in space. In addition, unlike the typical second-order magnetic phase transitions, low-frequency Cu spin fluctuations as probed by 139La nuclear spin-lattice relaxation rate do not exhibit critical divergence at Tspin(≃Tc ) =42 K. These findings, including the spatially inhomogeneous nature of the charge-ordered state, are qualitatively similar to the case of La1.885Sr0.115CuO4 [Imai et al., Phys. Rev. B 96, 224508 (2017), 10.1103/PhysRevB.96.224508 and Arsenault et al., Phys. Rev. B 97, 064511 (2018), 10.1103/PhysRevB.97.064511], but both charge and spin order take place more sharply in the present case.

Electronic phase transition in hollandite titanates BaxTi8O16 +δ

NASA Astrophysics Data System (ADS)

Murata, R.; Sato, T.; Okuda, T.; Horibe, Y.; Tsukasaki, H.; Mori, S.; Yamaguchi, N.; Sugimoto, K.; Kawaguchi, S.; Takata, M.; Katsufuji, T.

2015-12-01

We studied the physical properties of hollandite titanates, BaxTi8O16 +δ , which have double chains of edge-sharing TiO6 octahedra with d electrons in the t2 g states. We found that there is an electronic phase transition at ˜220 K, at which various properties exhibit anomalies. This phase transition is characterized by a modulation in the TiO6 chains and a spectral weight transfer of over 2 eV in the optical conductivity spectrum, which are presumably caused by charge and orbital ordering of the Ti t2 g electrons.

Automatic charge control system for satellites

NASA Technical Reports Server (NTRS)

Shuman, B. M.; Cohen, H. A.

1985-01-01

The SCATHA and the ATS-5 and 6 spacecraft provided insights to the problem of spacecraft charging at geosychronous altitudes. Reduction of the levels of both absolute and differential charging was indicated, by the emission of low energy neutral plasma. It is appropriate to complete the transition from experimental results to the development of a system that will sense the state-of-charge of a spacecraft, and, when a predetermined threshold is reached, will respond automatically to reduce it. A development program was initiated utilizing sensors comparable to the proton electrostatic analyzer, the surface potential monitor, and the transient pulse monitor that flew in SCATHA, and combine these outputs through a microprocessor controller to operate a rapid-start, low energy plasma source.

Engineering the Ground State of Complex Oxides

NASA Astrophysics Data System (ADS)

Meyers, Derek Joseph

Transition metal oxides featuring strong electron-electron interactions have been at the forefront of condensed matter physics research in the past few decades due to the myriad of novel and exciting phases derived from their competing interactions. Beyond their numerous intriguing properties displayed in the bulk they have also shown to be quite susceptible to externally applied perturbation in various forms. The dominant theme of this work is the exploration of three emerging methods for engineering the ground states of these materials to access both their applicability and their deficiencies. The first of the three methods involves a relatively new set of compounds which adhere to a unique paradigm in chemical doping, a-site ordered perovskites. These compounds are iso-structural, i.e. constant symmetry, despite changing the dopant ions. We find that these materials, featuring Cu at the doped A-site, display the Zhang-Rice state, to varying degrees, found in high temperature superconducting cuprates, with the choice of B-site allowing "self-doping" within the material. Further, we find that within CaCu3Ir 4O12 the Cu gains a localized magnetic moment and leads to the experimentally observed heavy fermion state in the materials, one of only two such non-f-electron heavy fermion materials. Next, epitaxial constraint is used to modify the ground state of the rare-earth nickelates in ultra thin film form. Application of compressive (tensile) strain is found to suppress (maintain) the temperature at which the material goes through a Mott metal-insulator transition. Further, while for EuNiO3 thin films the typical bulk-like magnetic and charge ordering is found to occur, epitaxial strain is found to suppress the charge ordering in NdNiO3 thin films due to pinning to the substrate and the relatively weak tendency to monoclinically distort. Finally, the creation of superlattices of EuNiO3 and LaNiO3 was shown to not only allow the selection of the temperature at which the metal-insulator transition occurs, but through digital control the Ni site symmetry can be artificially broken leading to a previously unseen monoclinic metallic phase. Further, by creating a structure which does or does not match the bulk-like rock salt charge order pattern it was found this transition can be either strongly enhanced or removed entirely.

Novel photoinduced phase transitions in transition metal oxides and diluted magnetic semiconductors.

PubMed

Mizokawa, Takashi

2012-10-23

Some transition metal oxides have frustrated electronic states under multiphase competition due to strongly correlated d electrons with spin, charge, and orbital degrees of freedom and exhibit drastic responses to external stimuli such as optical excitation. Here, we present photoemission studies on Pr0.55(Ca1 - ySry)0.45MnO3 (y = 0.25), SrTiO3, and Ti1 - xCoxO2 (x = 0.05, 0.10) under laser illumination and discuss electronic structural changes induced by optical excitation in these strongly correlated oxides. We discuss the novel photoinduced phase transitions in these transition metal oxides and diluted magnetic semiconductors on the basis of polaronic pictures such as orbital, ferromagnetic, and ferroelectric polarons.

Transition-state optimization by the free energy gradient method: Application to aqueous-phase Menshutkin reaction between ammonia and methyl chloride

NASA Astrophysics Data System (ADS)

Hirao, Hajime; Nagae, Yukihiko; Nagaoka, Masataka

2001-11-01

The transition state (TS) for the Menshutkin reaction H 3N+CH 3Cl→H 3NCH 3++Cl - in aqueous solution was located on the free energy surface (FES) by the free energy gradient (FEG) method. The solute-solvent system was described by a hybrid quantum mechanical and molecular mechanical (QM/MM) method. The reaction path in water was found to deviate largely from that in the gas phase. It was concluded that, in such a reaction including charge separation, TS structure optimization on an FES is inevitable for obtaining valid information about a TS in solution.

Quasi-superradiant soliton state of matter in quantum metamaterials

NASA Astrophysics Data System (ADS)

Asai, Hidehiro; Kawabata, Shiro; Savel'ev, Sergey E.; Zagoskin, Alexandre M.

2018-02-01

Strong interaction of a system of quantum emitters (e.g., two-level atoms) with electromagnetic field induces specific correlations in the system accompanied by a drastic increase of emitted radiation (superradiation or superfluorescence). Despite the fact that since its prediction this phenomenon was subject to a vigorous experimental and theoretical research, there remain open question, in particular, concerning the possibility of a first order phase transition to the superradiant state from the vacuum state. In systems of natural and charge-based artificial atom this transition is prohibited by "no-go" theorems. Here we demonstrate numerically and confirm analytically a similar transition in a one-dimensional quantum metamaterial - a chain of artificial atoms (qubits) strongly interacting with classical electromagnetic fields in a transmission line. The system switches from vacuum state to the quasi-superradiant (QS) phase with one or several magnetic solitons and finite average occupation of qubit excited states along the transmission line. A quantum metamaterial in the QS phase circumvents the "no-go" restrictions by considerably decreasing its total energy relative to the vacuum state by exciting nonlinear electromagnetic solitons.

Frenkel and Charge-Transfer Excitations in Donor-acceptor Complexes from Many-Body Green's Functions Theory.

PubMed

Baumeier, Björn; Andrienko, Denis; Rohlfing, Michael

2012-08-14

Excited states of donor-acceptor dimers are studied using many-body Green's functions theory within the GW approximation and the Bethe-Salpeter equation. For a series of prototypical small-molecule based pairs, this method predicts energies of local Frenkel and intermolecular charge-transfer excitations with the accuracy of tens of meV. Application to larger systems is possible and allowed us to analyze energy levels and binding energies of excitons in representative dimers of dicyanovinyl-substituted quarterthiophene and fullerene, a donor-acceptor pair used in state of the art organic solar cells. In these dimers, the transition from Frenkel to charge transfer excitons is endothermic and the binding energy of charge transfer excitons is still of the order of 1.5-2 eV. Hence, even such an accurate dimer-based description does not yield internal energetics favorable for the generation of free charges either by thermal energy or an external electric field. These results confirm that, for qualitative predictions of solar cell functionality, accounting for the explicit molecular environment is as important as the accurate knowledge of internal dimer energies.

Optical study of phase transitions in single-crystalline RuP

NASA Astrophysics Data System (ADS)

Chen, R. Y.; Shi, Y. G.; Zheng, P.; Wang, L.; Dong, T.; Wang, N. L.

2015-03-01

RuP single crystals of MnP-type orthorhombic structure were synthesized by the Sn flux method. Temperature-dependent x-ray diffraction measurements reveal that the compound experiences two structural phase transitions, which are further confirmed by enormous anomalies shown in temperature-dependent resistivity and magnetic susceptibility. Particularly, the resistivity drops monotonically upon temperature cooling below the second transition, indicating that the material shows metallic behavior, in sharp contrast with the insulating ground state of polycrystalline samples. Optical conductivity measurements were also performed in order to unravel the mechanism of these two transitions. The measurement revealed a sudden reconstruction of band structure over a broad energy scale and a significant removal of conducting carriers below the first phase transition, while a charge-density-wave-like energy gap opens below the second phase transition.

Imaging metal-like monoclinic phase stabilized by surface coordination effect in vanadium dioxide nanobeam

PubMed Central

Li, Zejun; Wu, Jiajing; Hu, Zhenpeng; Lin, Yue; Chen, Qi; Guo, Yuqiao; Liu, Yuhua; Zhao, Yingcheng; Peng, Jing; Chu, Wangsheng; Wu, Changzheng; Xie, Yi

2017-01-01

In correlated systems, intermediate states usually appear transiently across phase transitions even at the femtosecond scale. It therefore remains an open question how to determine these intermediate states—a critical issue for understanding the origin of their correlated behaviour. Here we report a surface coordination route to successfully stabilize and directly image an intermediate state in the metal-insulator transition of vanadium dioxide. As a prototype metal-insulator transition material, we capture an unusual metal-like monoclinic phase at room temperature that has long been predicted. Coordinate bonding of L-ascorbic acid molecules with vanadium dioxide nanobeams induces charge-carrier density reorganization and stabilizes metallic monoclinic vanadium dioxide, unravelling orbital-selective Mott correlation for gap opening of the vanadium dioxide metal–insulator transition. Our study contributes to completing phase-evolution pathways in the metal-insulator transition process, and we anticipate that coordination chemistry may be a powerful tool for engineering properties of low-dimensional correlated solids. PMID:28613281

The effect of solvent relaxation time constants on free energy gap law for ultrafast charge recombination following photoinduced charge separation.

PubMed

Mikhailova, Valentina A; Malykhin, Roman E; Ivanov, Anatoly I

2018-05-16

To elucidate the regularities inherent in the kinetics of ultrafast charge recombination following photoinduced charge separation in donor-acceptor dyads in solutions, the simulations of the kinetics have been performed within the stochastic multichannel point-transition model. Increasing the solvent relaxation time scales has been shown to strongly vary the dependence of the charge recombination rate constant on the free energy gap. In slow relaxing solvents the non-equilibrium charge recombination occurring in parallel with solvent relaxation is very effective so that the charge recombination terminates at the non-equilibrium stage. This results in a crucial difference between the free energy gap laws for the ultrafast charge recombination and the thermal charge transfer. For the thermal reactions the well-known Marcus bell-shaped dependence of the rate constant on the free energy gap is realized while for the ultrafast charge recombination only a descending branch is predicted in the whole area of the free energy gap exceeding 0.2 eV. From the available experimental data on the population kinetics of the second and first excited states for a series of Zn-porphyrin-imide dyads in toluene and tetrahydrofuran solutions, an effective rate constant of the charge recombination into the first excited state has been calculated. The obtained rate constant being very high is nearly invariable in the area of the charge recombination free energy gap from 0.2 to 0.6 eV that supports the theoretical prediction.

Charge storage in oxygen deficient phases of TiO2: defect Physics without defects.

PubMed

Padilha, A C M; Raebiger, H; Rocha, A R; Dalpian, G M

2016-07-01

Defects in semiconductors can exhibit multiple charge states, which can be used for charge storage applications. Here we consider such charge storage in a series of oxygen deficient phases of TiO2, known as Magnéli phases. These Magnéli phases (TinO2n-1) present well-defined crystalline structures, i.e., their deviation from stoichiometry is accommodated by changes in space group as opposed to point defects. We show that these phases exhibit intermediate bands with an electronic quadruple donor transitions akin to interstitial Ti defect levels in rutile TiO2. Thus, the Magnéli phases behave as if they contained a very large pseudo-defect density: ½ per formula unit TinO2n-1. Depending on the Fermi Energy the whole material will become charged. These crystals are natural charge storage materials with a storage capacity that rivals the best known supercapacitors.

The Role of Solution Conditions in the Bacteriophage PP7 Capsid Charge Regulation

DOE PAGES

Nap, Rikkert J.; Bozic, Anze Losdorfer; Szleifer, Igal; ...

2014-10-21

Here, we investigate and quantify the effects of pH and salt concentration on the charge regulation of the bacteriophage PP7 capsid. These effects are found to be extremely important and substantial, introducing qualitative changes in the charge state of the capsid such as a transition from net-positive to net-negative charge depending on the solution pH. The overall charge of the virus capsid arises as a consequence of a complicated balance with the chemical dissociation equilibrium of the amino acids and the electrostatic interaction between them, and the translational entropy of the mobile solution ions, i.e., counterion release. We show thatmore » to properly describe and predict the charging equilibrium of viral capsids in general, one needs to include molecular details as exemplified by the acid-base equilibrium of the detailed distribution of amino acids in the proteinaceous capsid shell.« less

Symmetry and charge order in Fe2OBO3 studied through polarized resonant x-ray diffraction

NASA Astrophysics Data System (ADS)

Bland, S. R.; Angst, M.; Adiga, S.; Scagnoli, V.; Johnson, R. D.; Herrero-Martín, J.; Hatton, P. D.

2010-09-01

Bond valence sum calculations have previously suggested that iron oxyborate exhibits charge order of the Fe ions with integer 2+/3+ valence states. Meanwhile transition metal oxides typically show much smaller, fractional charge disproportionations. Using resonant x-ray diffraction at the iron K edge, we find resonant features which are much larger than those ordinarily observed in charge ordered oxides. Simulations were subsequently performed using a cluster-based, monoelectronic code. The nanoscale domain structure prevents precise fitting; nevertheless the simulations confirm the diagonal charge order symmetry, as well as the unusually large charge disproportionation. We have demonstrated the conversion of linearly to nonlinearly polarized light and vice versa through full polarization analysis. Simulations show that this effect principally results from interference between the isotropic and anisotropic scattering terms. This mechanism is likely to account for similar observations in alternative systems.

Transition state analysis of Trypanosoma cruzi uridine phosphorylase-catalyzed arsenolysis of uridine

PubMed Central

Silva, Rafael G.; Vetticatt, Mathew J.; Merino, Emilio F.; Cassera, Maria B.; Schramm, Vern L.

2011-01-01

Uridine phosphorylase catalyzes the reversible phosphorolysis of uridine and 2′-deoxyuridine to generate uracil and (2-deoxy)ribose 1-phosphate, an important step in the pyrimidine salvage pathway. The coding sequence annotated as a putative nucleoside phosphorylase in the Trypanosoma cruzi genome was overexpressed in Escherichia coli, purified to homogeneity, and shown to be a homodimeric uridine phosphorylase, with similar specificity for uridine and 2′-deoxyuridine, and undetectable activity towards thymidine and purine nucleosides. Competitive kinetic isotope effects (KIEs) were measured and corrected for a forward commitment factor using arsenate as the nucleophile. The intrinsic KIEs are: 1′-14C = 1.103, 1,3-15N2 = 1.034, 3-15N = 1.004, 1-15N = 1.030, 1′-3H = 1.132, 2′-2H = 1.086 and 5′-3H2 = 1.041 for this reaction. Density functional theory was employed to quantitatively interpret the KIEs in terms of transition state structure and geometry. Matching of experimental KIEs to proposed transition state structures suggests an almost synchronous, SN2-like transition state model, in which the ribosyl moiety possesses significant bond order to both nucleophile and leaving group. Natural bond orbital analysis allowed a comparison of the charge distribution pattern between the ground state and the transition state model. PMID:21599004

Mechanosensitive channel activation by diffusio-osmotic force.

PubMed

Bonthuis, Douwe Jan; Golestanian, Ramin

2014-10-03

For ion channel gating, the appearance of two distinct conformational states and the discrete transitions between them are essential, and therefore of crucial importance to all living organisms. We show that the physical interplay between two structural elements that are commonly present in bacterial mechanosensitive channels--namely, a charged vestibule and a hydrophobic constriction--creates two distinct conformational states, open and closed, as well as the gating between them. We solve the nonequilibrium Stokes-Poisson-Nernst-Planck equations, extended to include a molecular potential of mean force, and show that a first order transition between the closed and open states arises naturally from the diffusio-osmotic stress caused by the ions and the water inside the channel and the elastic restoring force from the membrane.

Influence of Coulombic repulsion on the dissociation pathways and energetics of multiprotein complexes in the gas phase.

PubMed

Sinelnikov, Igor; Kitova, Elena N; Klassen, John S

2007-04-01

Thermal dissociation experiments, implemented with blackbody infrared radiative dissociation and Fourier-transform ion cyclotron resonance mass spectrometry, are performed on gaseous protonated and deprotonated ions of the homopentameric B subunits of Shiga toxin 1 (Stx1 B5) and Shiga toxin 2 (Stx2 B5) and the homotetramer streptavidin (S4). Dissociation of the gaseous, multisubunit complexes proceeds predominantly by the loss of a single subunit. Notably, the fractional partitioning of charge between the product ions, i.e., the leaving subunit and the resulting multimer, for a given complex is, within error, constant over the range of charge states investigated. The Arrhenius activation parameters (E(a), A) measured for the loss of subunit decrease with increasing charge state of the complex. However, the parameters for the protonated and deprotonated ions, with the same number of charges, are indistinguishable. The influence of the complex charge state on the dissociation pathways and the magnitude of the dissociation E(a) are modeled theoretically with the discrete charge droplet model (DCDM) and the protein structure model (PSM), wherein the structure of the subunits is considered. Importantly, the major subunit charge states observed experimentally for the Stx1 B5(n+/-) ions correspond to the minimum energy charge distribution predicted by DCDM and PSM assuming a late dissociative transition-state (TS); while for structurally-related Stx2 B5(n+) ions, the experimental charge distribution corresponds to an early TS. It is proposed that the lateness of the TS is related, in part, to the degree of unfolding of the leaving subunit, with Stx1 B being more unfolded than Stx2 B. PSM, incorporating significant subunit unfolding is necessary to account for the product ions observed for the S4(n+) ions. The contribution of Coulombic repulsion to the dissociation E(a) is quantified and the intrinsic activation energy is estimated for the first time.

Charge exchange of highly charged argon ions as a function of projectile energy

NASA Astrophysics Data System (ADS)

Allen, F. I.; Biedermann, C.; Radtke, R.; Fussmann, G.

2007-03-01

X-ray emission of highly charged argon ions following charge exchange collisions with argon atoms has been measured as a function of projectile energy. The ions are extracted from the Electron Beam Ion Trap (EBIT) in Berlin and selected according to their massto-charge ratios. Experiments focussed on hydrogen-like and bare argon ions which were decelerated from 125q eV/amu to below 0.25q eV/amu prior to interaction with an argon gas target. The x-ray spectra recorded probe the cascading transitions resulting from electron capture into Rydberg states and are found to vary significantly with collision velocity. This indicates a shift in the orbital angular momentum of the capture state. Hardness ratios are observed to increase with decreasing projectile energy though at a rate which differs from the results of simulations. For comparison, measurements of the x-ray emission following charge exchange within the trap were carried out and are in agreement with the findings of the EBIT group at LLNL. Both of these in situ measurements, however, are in discrepancy with the results of the experiments using extracted ions.

Density functional theory study of hydrogen atom abstraction from a series of para-substituted phenols: why is the Hammett σ(p)+ constant able to represent radical reaction rates?

PubMed

Yoshida, Tatsusada; Hirozumi, Koji; Harada, Masataka; Hitaoka, Seiji; Chuman, Hiroshi

2011-06-03

The rate of hydrogen atom abstraction from phenolic compounds by a radical is known to be often linear with the Hammett substitution constant σ(+), defined using the S(N)1 solvolysis rates of substituted cumyl chlorides. Nevertheless, a physicochemical reason for the above "empirical fact" has not been fully revealed. The transition states of complexes between the 2,2-diphenyl-1-picrylhydrazyl radical (dpph·) and a series of para-substituted phenols were determined by DFT (Density Functional Theory) calculations, and then the activation energy as well as the homolytic bond dissociation energy of the O-H bond and charge distribution in the transition state were calculated. The heterolytic bond dissociation energy of the C-Cl bond and charge distribution in the corresponding para-substituted cumyl chlorides were calculated in parallel. Excellent correlations among σ(+), charge distribution, and activation and bond dissociation energies revealed quantitatively that there is a strong similarity between the two reactions, showing that the electron-deficiency of the π-electron system conjugated with a substituent plays a crucial role in determining rates of the two reactions. The results provide a new insight into and physicochemical understanding of σ(+) in the hydrogen abstraction from substituted phenols by a radical.

Electrically active induced energy levels and metastability of B and N vacancy-complexes in 4H–SiC

NASA Astrophysics Data System (ADS)

Igumbor, E.; Olaniyan, O.; Mapasha, R. E.; Danga, H. T.; Omotoso, E.; Meyer, W. E.

2018-05-01

Electrically active induced energy levels in semiconductor devices could be beneficial to the discovery of an enhanced p or n-type semiconductor. Nitrogen (N) implanted into 4H–SiC is a high energy process that produced high defect concentrations which could be removed during dopant activation annealing. On the other hand, boron (B) substituted for silicon in SiC causes a reduction in the number of defects. This scenario leads to a decrease in the dielectric properties and induced deep donor and shallow acceptor levels. Complexes formed by the N, such as the nitrogen-vacancy centre, have been reported to play a significant role in the application of quantum bits. In this paper, results of charge states thermodynamic transition level of the N and B vacancy-complexes in 4H–SiC are presented. We explore complexes where substitutional N/N or B/B sits near a Si (V) or C (V) vacancy to form vacancy-complexes (NV, NV, NV, NV, BV, BV, BV and BV). The energies of formation of the N related vacancy-complexes showed the NV to be energetically stable close to the valence band maximum in its double positive charge state. The NV is more energetically stable in the double negative charge state close to the conduction band minimum. The NV on the other hand, induced double donor level and the NV induced a double acceptor level. For B related complexes, the BV and BV were energetically stable in their single positive charge state close to the valence band maximum. As the Fermi energy is varied across the band gap, the neutral and single negative charge states of the BV become more stable at different energy levels. B and N related complexes exhibited charge state controlled metastability behaviour.

Origins of microstructural transformations in charged vesicle suspensions: the crowding hypothesis.

PubMed

Seth, Mansi; Ramachandran, Arun; Murch, Bruce P; Leal, L Gary

2014-09-02

It is observed that charged unilamellar vesicles in a suspension can spontaneously deflate and subsequently transition to form bilamellar vesicles, even in the absence of externally applied triggers such as salt or temperature gradients. We provide strong evidence that the driving force for this deflation-induced transition is the repulsive electrostatic pressure between charged vesicles in concentrated suspensions, above a critical effective volume fraction. We use volume fraction measurements and cryogenic transmission electron microscopy imaging to quantitatively follow both the macroscopic and microstructural time-evolution of cationic diC18:1 DEEDMAC vesicle suspensions at different surfactant and salt concentrations. A simple model is developed to estimate the extent of deflation of unilamellar vesicles caused by electrostatic interactions with neighboring vesicles. It is determined that when the effective volume fraction of the suspension exceeds a critical value, charged vesicles in a suspension can experience "crowding" due to overlap of their electrical double layers, which can result in deflation and subsequent microstructural transformations to reduce the effective volume fraction of the suspension. Ordinarily in polydisperse colloidal suspensions, particles interacting via a repulsive potential transform into a glassy state above a critical volume fraction. The behavior of charged vesicle suspensions reported in this paper thus represents a new mechanism for the relaxation of repulsive interactions in crowded situations.

Diplomats in the Foxhole: The Evolution of the State Department During Irregular Conflicts

DTIC Science & Technology

2014-05-22

transitioning of Iraq,” and the Project and Contracting Office ( PCO ) which was a DOD-led organization charged with contract acquisition and project...JUL - DOS S/CRS established • IRMO established • PCO established • SETs introduced • APR. Battle of Fallujah • Central Revolutionary

Spin ordering and electronic texture in the bilayer iridate Sr3Ir2O7

NASA Astrophysics Data System (ADS)

Dhital, Chetan; Khadka, Sovit; Yamani, Z.; de la Cruz, Clarina; Hogan, T. C.; Disseler, S. M.; Pokharel, Mani; Lukas, K. C.; Tian, Wei; Opeil, C. P.; Wang, Ziqiang; Wilson, Stephen D.

2012-09-01

Through a neutron scattering, charge transport, and magnetization study, the correlated ground state in the bilayer iridium oxide Sr3Ir2O7 is explored. Our combined results resolve scattering consistent with a high temperature magnetic phase that persists above 600 K, reorients at the previously defined TAF=280 K, and coexists with an electronic ground state whose phase behavior suggests the formation of a fluctuating charge or orbital phase that freezes below T*≈70 K. Our study provides a window into the emergence of multiple electronic order parameters near the boundary of the metal to insulator phase transition of the 5d Jeff=1/2 Mott phase.

The Thomas-Fermi model in the theory of systems of charged particles above the surface of liquid dielectrics

NASA Astrophysics Data System (ADS)

Lytvtnenko, D. M.; Slyusarenko, Yu. V.; Kirdin, A. I.

2012-10-01

A consistent theory of equilibrium states of same sign charges above the surface of liquid dielectric film located on solid substrate in the presence of external attracting constant electric field is proposed. The approach to the development of the theory is based on the Thomas-Fermi model generalized to the systems under consideration and on the variational principle. The using of self-consistent field model allows formulating a theory containing no adjustable constants. In the framework of the variational principle we obtain the self-consistency equations for the parameters describing the system: the distribution function of charges above the liquid dielectric surface, the electrostatic field potentials in all regions of the system and the surface profile of the liquid dielectric. The self-consistency equations are used to describe the phase transition associated with the formation of spatially periodic structures in the system of charges on liquid dielectric surface. Assuming the non-degeneracy of the gas of charges above the surface of liquid dielectric film the solutions of the self-consistency equations near the critical point are obtained. In the case of the symmetric phase we obtain the expressions for the potentials and electric fields in all regions of the studied system. The distribution of the charges above the surface of liquid dielectric film for the symmetric phase is derived. The system parameters of the phase transition to nonsymmetric phase - the states with a spatially periodic ordering are obtained. We derive the expression determining the period of two-dimensional lattice as a function of physical parameters of the problem - the temperature, the external attractive electric field, the number of electrons per unit of the flat surface area of the liquid dielectric, the density of the dielectric, its surface tension and permittivity, and the permittivity of the solid substrate. The possibility of generalizing the developed theory in the case of degenerate gas of like-charged particles above the liquid dielectric surface is discussed.

Charge dynamics of 57Fe probe atoms in La2Li0.5Cu0.5O4

NASA Astrophysics Data System (ADS)

Presniakov, I. A.; Sobolev, A. V.; Rusakov, V. S.; Moskvin, A. S.; Baranov, A. V.

2018-06-01

The objective of this study is to characterize the electronic state and local surrounding of 57Fe Mössbauer probe atoms within iron-doped layered perovskite La2Li0.5Cu0.5O4 containing transition metal in unusual formal oxidation states "+3". An approach based on the qualitative energy diagrams analysis and the calculations within the cluster configuration interaction method have been developed. It was shown that a large amount of charge is transferred via Cu-O bonds from the O: 2p bands to the Cu: 3d orbitals and the ground state is dominated by the d9L configuration ("Cu2+-O-" state). The dominant d9L ground state for the (CuO6) sublattice induces in the environment of the 57Fe probe cations a charge transfer Fe3+ + O-(L) → Fe4+ + O2-, which transforms "Fe3+" into "Fe4+" state. The experimental spectra in the entire temperature range 77-300 K were described with the use of the stochastic two-level model based on the assumption of dynamic equilibrium between two Fe3+↔Fe4+ valence states related to the iron atom in the [Fe(1)O4]4- center. The relaxation frequencies and activation energies of the corresponding charge fluctuations were estimated based on Mössbauer data. The results are discussed assuming a temperature-induced change in the electronic state of the [CuO4]5- clusters in the layered perovskite.

Static charge-density-wave order in the superconducting state of La 2 - x Ba x CuO 4

DOE PAGES

Thampy, V.; Chen, X. M.; Cao, Y.; ...

2017-06-15

Charge-density-wave (CDW) correlations feature prominently in the phase diagram of the cuprates, motivating competing theories of whether fluctuating CDW correlations aid superconductivity or whether static CDW order coexists with superconductivity in inhomogeneous or spatially modulated states. Here we report Cu L-edge resonant x-ray photon correlation spectroscopy measurements of CDW correlations in superconducting La 2–xBa xCuO 4, x = 0.11. Static CDW order is shown to exist in the superconducting state at low temperatures and to persist up to at least 85% of the CDW transition temperature. As a result, we discuss the implications of our observations for how nominally competingmore » order parameters can coexist in the cuprates.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Radzihovsky, Leo

Motivated by a realization of imbalanced Feshbach-resonant atomic Fermi gases, we formulate a low-energy theory of the Fulde-Ferrell and the Larkin-Ovchinnikov (LO) states and use it to analyze fluctuations, stability, and phase transitions in these enigmatic finite momentum-paired superfluids. Focusing on the unidirectional LO pair-density-wave state, which spontaneously breaks the continuous rotational and translational symmetries, we show that it is characterized by two Goldstone modes, corresponding to a superfluid phase and a smectic phonon. Because of the liquid-crystalline ''softness'' of the latter, at finite temperature the three-dimensional state is characterized by a vanishing LO order parameter, quasi-Bragg peaks in themore » structure and momentum distribution functions, and a ''charge''-4, paired-Cooper-pairs, off-diagonal long-range order, with a superfluid-stiffness anisotropy that diverges near a transition into a nonsuperfluid state. In addition to conventional integer vortices and dislocations, the LO superfluid smectic exhibits composite half-integer vortex-dislocation defects. A proliferation of defects leads to a rich variety of descendant states, such as the charge-4 superfluid and Fermi-liquid nematics and topologically ordered nonsuperfluid states, that generically intervene between the LO state and the conventional superfluid and the polarized Fermi liquid at low and high imbalance, respectively. The fermionic sector of the LO gapless superconductor is also quite unique, exhibiting a Fermi surface of Bogoliubov quasiparticles associated with the Andreev band of states, localized on the array of the LO domain walls.« less

Conformational transition of κ-casein in micellar environment: Insight from the tryptophan fluorescence

NASA Astrophysics Data System (ADS)

Mishra, Smruti; Meher, Geetanjali; Chakraborty, Hirak

2017-11-01

Intrinsically disordered proteins (IDPs) are under intense analysis due to their structural flexibility and importance in biological functions. Minuscule modulation in the microenvironment induces significant conformational changes in IDPs, and these non-native conformations of the IDPs often induce aggregation and cause cell death. Changes in the membrane composition often change the microenvironment, which promote conformational change and aggregation of IDPs. κ-Casein, an important milk protein, belongs to the class of IDPs containing net negative charges. In this present work, we have studied the interaction of κ-casein with cetyltrimethyl ammonium bromide (CTAB), a positively charged surfactant, utilizing various steady state fluorescence, time-resolved fluorescence and circular dichroism spectroscopy. Our results clearly indicate that κ-casein undergoes at least two conformational transitions in presence of various concentrations of CTAB. The intrinsically disordered κ-casein assumes a partially folded conformation at lower concentration of CTAB, which adopts an unstructured conformation at higher concentration of CTAB. The partially folded conformation of κ-casein at a lower CTAB concentration might be induced by the favorable electrostatic interaction between the positively charged surfactant headgroup and net negative charges of the protein, whereas surfactant nature of CTAB is being pronounced at higher concentration of CTAB.

Hyperfine induced transition probabilities from 4{f}^{14}5s5p{}^{3}{{\\rm{P}}}_{0,2}^{o} states in Sm-like ions

NASA Astrophysics Data System (ADS)

Zhou, Fuyang; Li, Jiguang; Qu, Yizhi; Wang, Jianguo

2017-11-01

The hyperfine induced 4{f}145s5p{}3{{{P}}}0,2o-4{f}145{s}2{}1{{{S}}}0 transition probabilities for highly charged Sm-like ions are calculated within the framework of the multiconfiguration Dirac-Hartree-Fock method. Electron correlation, the Breit interaction and quantum electrodynamical effects are taken into account. For ions ranging from Z = 79 to Z=94,4{f}145s5p{}3{{{P}}}0o is the first excited state, and the hyperfine induced transition (HIT) is a dominant decay channel. For the 4{f}145s5p{}3{{{P}}}2o state, the HIT rates of Sm-like ions with Z=82-94 are reported as well as the magnetic dipole (M1) {}3{{{P}}}2o-{}3{{{P}}}1o, the electric quadrupole (E2) {}3{{{P}}}2o-{}3{{{P}}}0,1o, and the magnetic quadrupole (M2) {}3{{{P}}}2o-{}1{{{S}}}0 transition probabilities. It is found that M1 transition from the 4{f}145s5p{}3{{{P}}}2o state is the most important decay channel in this range on Z≥slant 82.

Selection rule engineering of forbidden transitions of a hydrogen atom near a nanogap

NASA Astrophysics Data System (ADS)

Kim, Hyunyoung Y.; Kim, Daisik S.

2018-01-01

We perform an analytical study on the allowance of forbidden transitions for a hydrogen atom placed near line dipole sources, mimicking light emanating from a one-dimensional metallic nanogap. It is shown that the rapid variation of the electric field vector, inevitable in the near zone, completely breaks the selection rule of Δl=±1. While the forbidden transitions between spherically symmetric S states, such as 2S to 1S or 3S to 1S (Δl=0), are rather robust against selection rule breakage, Δl=±2 transitions such as between 3D and 1S or 3D and 2S states are very vulnerable to the spatial variation of the perturbing electric field. Transitions between 2S and 3D states are enhanced by many orders of magnitude, aided by the quadratic nature of both the perturbing Hamiltonian and D wavefunctions. The forbidden dipole moment, which approaches one Bohr radius times the electric charge in the vicinity of the gap, can be written in a simple closed form owing to the one-dimensional nature of our gap. With large enough effective volume together with the symmetric nature of the excited state wavefunctions, our work paves way towards atomic physics application of infinitely long nanogaps.

An allosteric model of the molecular interactions of excitation- contraction coupling in skeletal muscle

PubMed Central

1993-01-01

A contact interaction is proposed to exist between the voltage sensor of the transverse tubular membrane of skeletal muscle and the calcium release channel of the sarcoplasmic reticulum. This interaction is given a quantitative formulation inspired in the Monod, Wyman, and Changeux model of allosteric transitions in hemoglobin (Monod, J., J. Wyman, and J.-P. Changeux. 1965. Journal of Molecular Biology. 12:88- 118), and analogous to one proposed by Marks and Jones for voltage- dependent Ca channels (Marks, T. N., and S. W. Jones. 1992. Journal of General Physiology. 99:367-390). The allosteric protein is the calcium release channel, a homotetramer, with two accessible states, closed and open. The kinetics and equilibrium of this transition are modulated by voltage sensors (dihydropyridine receptors) pictured as four units per release channel, each undergoing independent voltage-driven transitions between two states (resting and activating). For each voltage sensor that moves to the activating state, the tendency of the channel to open increases by an equal (large) factor. The equilibrium and kinetic equations of the model are solved and shown to reproduce well a number of experimentally measured relationships including: charge movement (Q) vs. voltage, open probability of the release channel (Po) vs. voltage, the transfer function relationship Po vs. Q, and the kinetics of charge movement, release activation, and deactivation. The main consequence of the assumption of allosteric coupling is that primary effects on the release channel are transmitted backward to the voltage sensor and give secondary effects. Thus, the model reproduces well the effects of perchlorate, described in the two previous articles, under the assumption that the primary effect is to increase the intrinsic tendency of the release channel to open, with no direct effects on the voltage sensor. This modification of the open-closed equilibrium of the release channel causes a shift in the equilibrium dependency of charge movement with voltage. The paradoxical slowing of charge movement by perchlorate also results from reciprocal effects of the channel on the allosterically coupled voltage sensors. The observations of the previous articles plus the simulations in this article constitute functional evidence of allosteric transmission. PMID:8245819

48 CFR 47.305-13 - Transit arrangements.

Code of Federal Regulations, 2010 CFR

2010-10-01

..., as specified in carrier tariffs or rate tenders. A single through rate is charged from origin to final destination plus a transit or other related charge, rather than a more expensive combination of... contractors' earned commercial transit credits, which are recorded with the carriers. A transit credit...

Temperature Dependence of Magnetically Active Charge Excitations in Magnetite across the Verwey Transition

NASA Astrophysics Data System (ADS)

Taguchi, M.; Chainani, A.; Ueda, S.; Matsunami, M.; Ishida, Y.; Eguchi, R.; Tsuda, S.; Takata, Y.; Yabashi, M.; Tamasaku, K.; Nishino, Y.; Ishikawa, T.; Daimon, H.; Todo, S.; Tanaka, H.; Oura, M.; Senba, Y.; Ohashi, H.; Shin, S.

2015-12-01

We study the electronic structure of bulk single crystals and epitaxial films of Fe3 O4 . Fe 2 p core level spectra show clear differences between hard x-ray (HAX) and soft x-ray photoemission spectroscopy (PES). The bulk-sensitive spectra exhibit temperature (T ) dependence across the Verwey transition, which is missing in the surface-sensitive spectra. By using an extended impurity Anderson full-multiplet model—and in contrast to an earlier peak assignment—we show that the two distinct Fe species (A and B site) and the charge modulation at the B site are responsible for the newly found double peaks in the main peak above TV and its T -dependent evolution. The Fe 2 p HAXPES spectra show a clear magnetic circular dichroism (MCD) in the metallic phase of magnetized 100-nm-thick films. The model calculations also reproduce the MCD and identify the contributions from magnetically distinct A and B sites. Valence band HAXPES shows a finite density of states at EF for the polaronic half metal with a remnant order above TV and a clear gap formation below TV. The results indicate that the Verwey transition is driven by changes in the strongly correlated and magnetically active B -site electronic states, consistent with resistivity and optical spectra.

Coulombic charge ice

NASA Astrophysics Data System (ADS)

McClarty, P. A.; O'Brien, A.; Pollmann, F.

2014-05-01

We consider a classical model of charges ±q on a pyrochlore lattice in the presence of long-range Coulomb interactions. This model first appeared in the early literature on charge order in magnetite [P. W. Anderson, Phys. Rev. 102, 1008 (1956), 10.1103/PhysRev.102.1008]. In the limit where the interactions become short ranged, the model has a ground state with an extensive entropy and dipolar charge-charge correlations. When long-range interactions are introduced, the exact degeneracy is broken. We study the thermodynamics of the model and show the presence of a correlated charge liquid within a temperature window in which the physics is well described as a liquid of screened charged defects. The structure factor in this phase, which has smeared pinch points at the reciprocal lattice points, may be used to detect charge ice experimentally. In addition, the model exhibits fractionally charged excitations ±q/2 which are shown to interact via a 1/r potential. At lower temperatures, the model exhibits a transition to a long-range ordered phase. We are able to treat the Coulombic charge ice model and the dipolar spin ice model on an equal footing by mapping both to a constrained charge model on the diamond lattice. We find that states of the two ice models are related by a staggering field which is reflected in the energetics of these two models. From this perspective, we can understand the origin of the spin ice and charge ice ground states as coming from a dipolar model on a diamond lattice. We study the properties of charge ice in an external electric field, finding that the correlated liquid is robust to the presence of a field in contrast to the case of spin ice in a magnetic field. Finally, we comment on the transport properties of Coulombic charge ice in the correlated liquid phase.

A nonconjugated radical polymer glass with high electrical conductivity

NASA Astrophysics Data System (ADS)

Joo, Yongho; Agarkar, Varad; Sung, Seung Hyun; Savoie, Brett M.; Boudouris, Bryan W.

2018-03-01

Solid-state conducting polymers usually have highly conjugated macromolecular backbones and require intentional doping in order to achieve high electrical conductivities. Conversely, single-component, charge-neutral macromolecules could be synthetically simpler and have improved processibility and ambient stability. We show that poly(4-glycidyloxy-2,2,6,6-tetramethylpiperidine-1-oxyl), a nonconjugated radical polymer with a subambient glass transition temperature, underwent rapid solid-state charge transfer reactions and had an electrical conductivity of up to 28 siemens per meter over channel lengths up to 0.6 micrometers. The charge transport through the radical polymer film was enabled with thermal annealing at 80°C, which allowed for the formation of a percolating network of open-shell sites in electronic communication with one another. The electrical conductivity was not enhanced by intentional doping, and thin films of this material showed high optical transparency.

Fast-timing study of the l -forbidden 1 /2+→3 /2+ M 1 transition in 129Sn

NASA Astrophysics Data System (ADS)

Licǎ, R.; Mach, H.; Fraile, L. M.; Gargano, A.; Borge, M. J. G.; Mǎrginean, N.; Sotty, C. O.; Vedia, V.; Andreyev, A. N.; Benzoni, G.; Bomans, P.; Borcea, R.; Coraggio, L.; Costache, C.; De Witte, H.; Flavigny, F.; Fynbo, H.; Gaffney, L. P.; Greenlees, P. T.; Harkness-Brennan, L. J.; Huyse, M.; Ibáñez, P.; Judson, D. S.; Konki, J.; Korgul, A.; Kröll, T.; Kurcewicz, J.; Lalkovski, S.; Lazarus, I.; Lund, M. V.; Madurga, M.; Mǎrginean, R.; Marroquín, I.; Mihai, C.; Mihai, R. E.; Morales, A. I.; Nácher, E.; Negret, A.; Page, R. D.; Pakarinen, J.; Pascu, S.; Paziy, V.; Perea, A.; Pérez-Liva, M.; Picado, E.; Pucknell, V.; Rapisarda, E.; Rahkila, P.; Rotaru, F.; Swartz, J. A.; Tengblad, O.; Van Duppen, P.; Vidal, M.; Wadsworth, R.; Walters, W. B.; Warr, N.; IDS Collaboration

2016-04-01

The levels in 129Sn populated from the β- decay of 129In isomers were investigated at the ISOLDE facility of CERN using the newly commissioned ISOLDE Decay Station (IDS). The lowest 1 /2+ state and the 3 /2+ ground state in 129Sn are expected to have configurations dominated by the neutron s1 /2 (l =0 ) and d3 /2 (l =2 ) single-particle states, respectively. Consequently, these states should be connected by a somewhat slow l -forbidden M 1 transition. Using fast-timing spectroscopy we have measured the half-life of the 1 /2+ 315.3-keV state, T1 /2= 19(10) ps, which corresponds to a moderately fast M 1 transition. Shell-model calculations using the CD-Bonn effective interaction, with standard effective charges and g factors, predict a 4-ns half-life for this level. We can reconcile the shell-model calculations to the measured T1 /2 value by the renormalization of the M 1 effective operator for neutron holes.

Unusual ground states in {R_5T_4X_{10}} (R  =  rare earth; T  =  Rh, Ir; and X  =  Si, Ge, Sn): a review

NASA Astrophysics Data System (ADS)

Ramakrishnan, S.; van Smaalen, Sander

2017-11-01

Rare earth compounds of the type R_5T_4X10 (R  =  rare earth; T  =  Rh, Ir, and X  =  Si, Ge, Sn) display a variety of phase transitions towards exotic states, including charge density waves (CDW), local moment magnetism, antiferromagnetism in the heavy fermion state, superconductivity and giant positive magnetoresistance. They support strongly correlated electron systems. In particular, R 5Ir4 Si10 (R  =  Dy-Lu) exhibit strong coupling CDWs with high transition temperatures, and superconductivity or magnetic ordering at lower temperatures. R_5T4 Ge10 (R  =  Gd-Tm T  =  Co, Rh, Ir) show multiple magnetic transitions with large magnetoresistance below the magnetic transitions. Finally, the light rare earth series R_5T4 Sn10 (R  =  Ce, Pr, Nd; T  =  Rh, Ir) display heavy fermion behaviour (for Ce and Pr) or possess giant positive magnetoresistance (for Nd) at low temperatures. This review provides a comprehensive overview of compounds, crystal structures and phase transitions. This is followed by an in-depth discussion of the mechanisms of the phase transitions and the properties of the ordered states.

Effects of Excess Carriers on Charged Defect Concentrations in Wide Bandgap Semiconductors

DOE Office of Scientific and Technical Information (OSTI.GOV)

Alberi, Kirstin M; Scarpulla, Michael A.

Unintentional doping and doping limits in semiconductors are typically caused by compensating defects with low formation energies. Since the formation enthalpy of a charged defect depends linearly on the Fermi level, doping limits can be especially pronounced in wide bandgap semiconductors where the Fermi level can vary substantially. Introduction of non-equilibrium carrier concentrations during growth or processing alters the chemical potentials of band carriers and allows populations of charged defects to be modified in ways impossible at thermal equilibrium. We demonstrate that in the presence of excess carriers, the rates of carrier capture and emission involving a defect charge transitionmore » level determine the admixture of electron and hole quasi-Fermi levels involved in the formation enthalpy of non-zero charge defect states. To understand the range of possible responses, we investigate the behavior of a single donor-like defect as functions of extrinsic doping and charge transition level energy. We find that that excess carriers will increase the formation enthalpy of compensating defects for most values of the charge transition level in the bandgap. Thus, it may be possible to use non-equilibrium carrier concentrations to overcome limitations on doping imposed by native defects. Cases also exist in which the concentration of defects with the same charge polarity as the majority dopant is either left unchanged or actually increases. This surprising effect arises when emission rates are suppressed relative to the capture rates and is most pronounced in wide bandgap semiconductors. We provide guidelines for carrying out experimental tests of this model.« less

Holographic Van der Waals phase transition of the higher-dimensional electrically charged hairy black hole

NASA Astrophysics Data System (ADS)

Li, Hui-Ling; Feng, Zhong-Wen; Zu, Xiao-Tao

2018-01-01

With motivation by holography, employing black hole entropy, two-point connection function and entanglement entropy, we show that, for the higher-dimensional Anti-de Sitter charged hairy black hole in the fixed charged ensemble, a Van der Waals-like phase transition can be observed. Furthermore, based on the Maxwell equal-area construction, we check numerically the equal-area law for a first order phase transition in order to further characterize the Van der Waals-like phase transition.

Ion Mobility Spectrometry-Hydrogen Deuterium Exchange Mass Spectrometry of Anions: Part 1. Peptides to Proteins

NASA Astrophysics Data System (ADS)

Donohoe, Gregory C.; Khakinejad, Mahdiar; Valentine, Stephen J.

2015-04-01

Ion mobility spectrometry (IMS) coupled with hydrogen deuterium exchange (HDX)-mass spectrometry (MS) has been used to study the conformations of negatively-charged peptide and protein ions. Results are presented for ion conformers of angiotensin 1, a synthetic peptide (SP), bovine insulin, ubiquitin, and equine cytochrome c. In general, the SP ion conformers demonstrate a greater level of HDX efficiency as a greater proportion of the sites undergo HDX. Additionally, these ions exhibit the fastest rates of exchange. Comparatively, the angiotensin 1 ions exhibit a lower rate of exchange and HDX level presumably because of decreased accessibility of exchange sites by charge sites. The latter are likely confined to the peptide termini. Insulin ions show dramatically reduced HDX levels and exchange rates, which can be attributed to decreased conformational flexibility resulting from the disulfide bonds. For the larger ubiquitin and protein ions, increased HDX is observed for larger ions of higher charge state. For ubiquitin, a conformational transition from compact to more elongated species (from lower to higher charge states) is reflected by an increase in HDX levels. These results can be explained by a combination of interior site protection by compact conformers as well as decreased access by charge sites. The elongated cytochrome c ions provide the largest HDX levels where higher values correlate with charge state. These results are consistent with increased exchange site accessibility by additional charge sites. The data from these enhanced IMS-HDX experiments are described in terms of charge site location, conformer rigidity, and interior site protection.

Synthesis of a metal oxide with a room-temperature photoreversible phase transition.

PubMed

Ohkoshi, Shin-Ichi; Tsunobuchi, Yoshihide; Matsuda, Tomoyuki; Hashimoto, Kazuhito; Namai, Asuka; Hakoe, Fumiyoshi; Tokoro, Hiroko

2010-07-01

Photoinduced phase-transition materials, such as chalcogenides, spin-crossover complexes, photochromic organic compounds and charge-transfer materials, are of interest because of their application to optical data storage. Here we report a photoreversible metal-semiconductor phase transition at room temperature with a unique phase of Ti(3)O(5), lambda-Ti(3)O(5). lambda-Ti(3)O(5) nanocrystals are made by the combination of reverse-micelle and sol-gel techniques. Thermodynamic analysis suggests that the photoinduced phase transition originates from a particular state of lambda-Ti(3)O(5) trapped at a thermodynamic local energy minimum. Light irradiation causes reversible switching between this trapped state (lambda-Ti(3)O(5)) and the other energy-minimum state (beta-Ti(3)O(5)), both of which are persistent phases. This is the first demonstration of a photorewritable phenomenon at room temperature in a metal oxide. lambda-Ti(3)O(5) satisfies the operation conditions required for a practical optical storage system (operational temperature, writing data by short wavelength light and the appropriate threshold laser power).

Fine-tuning the Mott metal-insulator transition and critical charge carrier dynamics in molecular conductors

NASA Astrophysics Data System (ADS)

Müller, Jens; Hartmann, Benedikt; Sasaki, Takahiko

2017-12-01

The unique possibilities of fine-tuning their physical properties in the vicinity of the Mott metal-insulator transition make the quasi-two-dimensional organic charge-transfer salts ?-(BEDT-TTF)?X unprecedented model systems for studying the fundamentals of electron-electron correlations and the coupling between charge, spin and lattice degrees of freedom in reduced dimensions. The critical properties and the universality class of the Mott transition, however, are controversially debated for these materials, and information on the low-frequency dynamical properties of the correlated electrons is rather limited. By introducing fluctuation (noise) spectroscopy as a powerful new tool for studying the slow dynamics of charge carriers, in the past years we have been able to extract spectroscopic information on the coupling of charge carriers to the vibrational degrees of freedom of the crystal lattice. This is related to a glassy freezing of the BEDT-TTF molecules' ethylene end-group (EEG) rotations at elevated temperatures, which (i) results in a small amount of (intrinsic) disorder and (ii) crucially influences the ratio of bandwidth to on-site Coulomb repulsion (W / U) and therefore the samples' position in the phase diagram, i.e. the electronic ground state. The low-frequency resistance fluctuations show a dramatic enhancement and divergent behaviour when tuning the sample close to the critical point of the Mott transition, accompanied by a strong shift of spectral weight to low frequencies and the onset of non-Gaussian behaviour. This indicates the critical slowing down of the order-parameter (doublon density) fluctuations and suggests a collective dynamics of the correlated electrons. In order to enable detailed investigations of this hypothesis in future experiments, by exploiting the structural EEG relaxation, a 'warming cycle' protocol can be established that allows for fine-tuning the sample across the Mott transition and therefore precisely accessing the finite-temperature critical endpoint. We 'calibrate' this procedure by a comparison to pressure-tuning experiments on the same sample. This method will allow to map out the region of ergodicity breaking around the critical endpoint and its dependence on disorder.

Effect of Fe-doping on CDW state in 1T-TaS2 investigated by STM/STS

NASA Astrophysics Data System (ADS)

Fujisawa, Y.; Shimabukuro, T.; Kojima, H.; Kobayashi, K.; Demura, S.; Sakata, H.

2017-07-01

1T-TaS2 has been known to undergo Mott transition from nearly commensurate charge density wave (CDW) state to commensurate CDW state at about 200 K. Recently, Fe doping was found to suppress the Mott transition and induce superconductivity. In this study, we report on the scanning tunneling microscopy (STM) and spectroscopy (STS) study on Fe doped 1T-TaS2 with different Fe concentration. STM observations reveal that the CDW superlattice becomes irregular as increasing Fe concentration. STS measurements uncover the spatial change in the local density of state (LDOS). We find two types of David-star: one has symmetric LDOS with respect to Fermi energy, and the other has asymmetric one. We identify that the asymmetric spectrum is due to an Fe dopant.

Nanoscale ferromagnetism in phase-separated manganites

NASA Astrophysics Data System (ADS)

Mori, S.; Horibe, Y.; Asaka, T.; Matsui, Y.; Chen, C. H.; Cheong, S. W.

2007-03-01

Magnetic domain structures in phase-separated manganites were investigated by low-temperature Lorentz electron microscopy, in order to understand some unusual physical properties such as a colossal magnetoresistance (CMR) effect and a metal-to-insulator transition. In particular, we examined a spatial distribution of the charge/orbital-ordered (CO/OO) insulator state and the ferromagnetic (FM) metallic one in phase-separated manganites; Cr-doped Nd0.5Ca0.5MnO3 and ( La1-xPrx)CaMnO3 with x=0.375, by obtaining both the dark-field images and Lorentz electron microscopic ones. It is found that an unusual coexistence of the CO/OO and FM metallic states below a FM transition temperature in the two compounds. The present experimental results clearly demonstrated the coexisting state of the two distinct ground states in manganites.

Synthesis of bis-Phosphate Iminoaltritol Enantiomers and Structural Characterization with Adenine Phosphoribosyltransferase.

PubMed

Harris, Lawrence D; Harijan, Rajesh K; Ducati, Rodrigo G; Evans, Gary B; Hirsch, Brett M; Schramm, Vern L

2018-01-19

Phosphoribosyl transferases (PRTs) are essential in nucleotide synthesis and salvage, amino acid, and vitamin synthesis. Transition state analysis of several PRTs has demonstrated ribocation-like transition states with a partial positive charge residing on the pentose ring. Core chemistry for synthesis of transition state analogues related to the 5-phospho-α-d-ribosyl 1-pyrophosphate (PRPP) reactant of these enzymes could be developed by stereospecific placement of bis-phosphate groups on an iminoaltritol ring. Cationic character is provided by the imino group and the bis-phosphates anchor both the 1- and 5-phosphate binding sites. We provide a facile synthetic path to these molecules. Cyclic-nitrone redox methodology was applied to the stereocontrolled synthesis of three stereoisomers of a selectively monoprotected diol relevant to the synthesis of transition-state analogue inhibitors. These polyhydroxylated pyrrolidine natural product analogues were bis-phosphorylated to generate analogues of the ribocationic form of 5-phosphoribosyl 1-phosphate. A safe, high yielding synthesis of the key intermediate represents a new route to these transition state mimics. An enantiomeric pair of iminoaltritol bis-phosphates (L-DIAB and D-DIAB) was prepared and shown to display inhibition of Plasmodium falciparum orotate phosphoribosyltransferase and Saccharomyces cerevisiae adenine phosphoribosyltransferase (ScAPRT). Crystallographic inhibitor binding analysis of L- and D-DIAB bound to the catalytic sites of ScAPRT demonstrates accommodation of both enantiomers by altered ring geometry and bis-phosphate catalytic site contacts.

Collective charge excitations and the metal-insulator transition in the square lattice Hubbard-Coulomb model

DOE PAGES

Ulybyshev, Maksim; Winterowd, Christopher; Zafeiropoulos, Savvas

2017-11-09

Here in this article, we discuss the nontrivial collective charge excitations (plasmons) of the extended square lattice Hubbard model. Using a fully nonperturbative approach, we employ the hybrid Monte Carlo algorithm to simulate the system at half-filling. A modified Backus-Gilbert method is introduced to obtain the spectral functions via numerical analytic continuation. We directly compute the single-particle density of states which demonstrates the formation of Hubbard bands in the strongly correlated phase. The momentum-resolved charge susceptibility also is computed on the basis of the Euclidean charge-density-density correlator. In agreement with previous extended dynamical mean-field theory studies, we find that, atmore » high strength of the electron-electron interaction, the plasmon dispersion develops two branches.« less

Collective charge excitations and the metal-insulator transition in the square lattice Hubbard-Coulomb model

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ulybyshev, Maksim; Winterowd, Christopher; Zafeiropoulos, Savvas

Here in this article, we discuss the nontrivial collective charge excitations (plasmons) of the extended square lattice Hubbard model. Using a fully nonperturbative approach, we employ the hybrid Monte Carlo algorithm to simulate the system at half-filling. A modified Backus-Gilbert method is introduced to obtain the spectral functions via numerical analytic continuation. We directly compute the single-particle density of states which demonstrates the formation of Hubbard bands in the strongly correlated phase. The momentum-resolved charge susceptibility also is computed on the basis of the Euclidean charge-density-density correlator. In agreement with previous extended dynamical mean-field theory studies, we find that, atmore » high strength of the electron-electron interaction, the plasmon dispersion develops two branches.« less

Quantitative Probes of Electron-Phonon Coupling in an Organic Charge-Transfer Material

NASA Astrophysics Data System (ADS)

Rury, Aaron; Sorenson, Shayne; Driscoll, Eric; Dawlaty, Jahan

While organic charge transfer (CT) materials may provide alternatives to inorganic materials in electronics and photonics applications, properties central to applications remain understudied in these organic materials. Specifically, electron-phonon coupling plays a pivotal role in electronic applications yet this coupling in CT materials remains difficult to directly characterize. To better understand the suitability of organic CT materials for electronic applications, we have devised an experimental technique that can directly assess electron-phonon coupling in a model organic CT material. Upon non-resonant interaction with an ultrafast laser pulse, we show that coherent excitation of Raman-active lattice vibrations of quinhydrone, a 1:1 co-crystal of the hydroquinone and p-benzoquinone, modulates the energies of electronic transitions probed by a white light pulse. Using a well-established theoretical framework of vibrational quantum beat spectra across the probe bandwidth, we quantitatively extract the parameters describing these electronic transitions to characterize electron-phonon coupling in this material. In conjunction with temperature-dependent resonance Raman measurements, we assess the hypothesis that several sharp transitions in the near-IR correspond to previously unknown excitonic states of this material. These results and their interpretation set the foundation for further elucidation of the one of the most important parameters in the application of organic charge-transfer materials to electronics and photonics.

Low-Frequency Raman Modes of 2H-TaSe2 in the Charge Density Wave Phase

NASA Astrophysics Data System (ADS)

Chowdhury, Sugata; Simpson, J.; Einstein, T. L.; Hight Walker, A. R.; Theoretical Collaboration

With changes in temperatures, tantalum diselenide (2H-TaSe2) , a layered, transition metal chalcogenides (TMD) exhibits unique super-lattice structures. The metallic ground state changes to an incommensurate charge density wave (CDW) state at 122?K followed by a commensurate CDW state at 90?K, and eventually a superconducting state 0.14 K. These phase transitions are driven by strong electron-phonon coupling and favored by the particular form of the Fermi surface of these systems. Here we theoretically studied the structural origin of low-frequency Raman modes of bulk 2H-TaSe2\\ in the CDW phases. Our calculations reveal that changes observed in the Raman modes are associated with the thermal expansion in the basal plane of 2H-TaSe2. The Grüneisen parameters of these two Raman modes increase in the CDW phases. Changes in the lattice parameter ``a'' are large compared to ``c'' which induces strain along the a-axis. We compared our results with experimental data which show low-frequency Raman phonon modes are very sensitive to temperature and are not observed in the metallic room-temperature state. In addition, we found that cation displacement is more than anion in CDW phase. Our results may shed more light on exact nature of the CDW instability and optical properties in this system.

Importance of electronegativity differences and surface structure in molecular dissociation reactions at transition metal surfaces.

PubMed

Crawford, Paul; Hu, P

2006-12-14

The dissociative adsorption of N2 has been studied at both monatomic steps and flat regions on the surfaces of the 4d transition metals from Zr to Pd. Using density functional theory (DFT) calculations, we have determined and analyzed the trends in both straight reactivity and structure sensitivity across the periodic table. With regards to reactivity, we find that the trend in activation energy (Ea) is determined mainly by a charge transfer from the surface metal atoms to the N atoms during transition state formation, namely, the degree of ionicity of the N-surface bond at the transition state. Indeed, we find that the strength of the metal-N bond at the transition state (and therefore the trend in Ea) can be predicted by the difference in Mulliken electronegativity between the metal and N. Structure sensitivity is analyzed in terms of geometric and electronic effects. We find that the lowering of Ea due to steps is more pronounced on the right-hand side of the periodic table. It is found that for the early transition metals the geometric and electronic effects work in opposition when going from terrace to step active site. In the case of the late 4d metals, however, these effects work in combination, producing a more marked reduction in Ea.

Superconducting transmission line particle detector

DOEpatents

Gray, K.E.

1988-07-28

A microvertex particle detector for use in a high energy physic collider including a plurality of parallel superconducting thin film strips separated from a superconducting ground plane by an insulating layer to form a plurality of superconducting waveguides. The microvertex particle detector indicates passage of a charged subatomic particle by measuring a voltage pulse measured across a superconducting waveguide caused by the transition of the superconducting thin film strip from a superconducting to a non- superconducting state in response to the passage of a charged particle. A plurality of superconducting thin film strips in two orthogonal planes plus the slow electromagnetic wave propagating in a superconducting transmission line are used to resolve N/sup 2/ ambiguity of charged particle events. 6 figs.

Superconducting transmission line particle detector

DOEpatents

Gray, Kenneth E.

1989-01-01

A microvertex particle detector for use in a high energy physic collider including a plurality of parallel superconducting thin film strips separated from a superconducting ground plane by an insulating layer to form a plurality of superconducting waveguides. The microvertex particle detector indicates passage of a charged subatomic particle by measuring a voltage pulse measured across a superconducting waveguide caused by the transition of the superconducting thin film strip from a superconducting to a non-superconducting state in response to the passage of a charged particle. A plurality of superconducting thin film strips in two orthogonal planes plus the slow electromagnetic wave propogating in a superconducting transmission line are used to resolve N.sup.2 ambiguity of charged particle events.

Anomalous metallic state with strong charge fluctuations in BaxTi8O16 +δ revealed by hard x-ray photoemission spectroscopy

NASA Astrophysics Data System (ADS)

Dash, S.; Kajita, T.; Okawa, M.; Saitoh, T.; Ikenaga, E.; Saini, N. L.; Katsufuji, T.; Mizokawa, T.

2018-04-01

We have studied a charge-orbital driven metal-insulator transition (MIT) in hollandite-type BaxTi8O16 +δ by means of hard x-ray photoemission spectroscopy (HAXPES). The Ti 2 p HAXPES indicates strong Ti3 +/Ti4 + charge fluctuation in the metallic phase above the MIT temperature. The metallic phase is characterized by a power-law spectral function near the Fermi level which would be a signature of bad metal with non-Drude polaronic behavior. The power-law spectral shape is associated with the large Seebeck coefficient of the metallic phase in BaxTi8O16 +δ .

Monitoring nonadiabatic avoided crossing dynamics in molecules by ultrafast X-ray diffraction

DOE PAGES

Kowalewski, Markus; Bennett, Kochise; Mukamel, Shaul

2017-05-26

We examine time-resolved X-ray diffraction from molecules in the gas phase which undergo nonadiabatic avoided-crossing dynamics involving strongly coupled electrons and nuclei. Several contributions to the signal are identified, representing (in decreasing strength) elastic scattering, contributions of the electronic coherences created by nonadiabatic couplings in the avoided crossing regime, and inelastic scattering. The former probes the charge density and delivers direct information on the evolving molecular geometry. The latter two contributions are weaker and carry spatial information through the transition charge densities (off-diagonal elements of the charge-density operator). Furthermore, simulations are presented for the nonadiabatic harpooning process in the excitedmore » state of sodium fluoride.« less

Zygotic Genome Activation in Vertebrates.

PubMed

Jukam, David; Shariati, S Ali M; Skotheim, Jan M

2017-08-21

The first major developmental transition in vertebrate embryos is the maternal-to-zygotic transition (MZT) when maternal mRNAs are degraded and zygotic transcription begins. During the MZT, the embryo takes charge of gene expression to control cell differentiation and further development. This spectacular organismal transition requires nuclear reprogramming and the initiation of RNAPII at thousands of promoters. Zygotic genome activation (ZGA) is mechanistically coordinated with other embryonic events, including changes in the cell cycle, chromatin state, and nuclear-to-cytoplasmic component ratios. Here, we review progress in understanding vertebrate ZGA dynamics in frogs, fish, mice, and humans to explore differences and emphasize common features. Copyright © 2017 Elsevier Inc. All rights reserved.

Structure and properties of B20Si-/0/+ clusters

NASA Astrophysics Data System (ADS)

Lu, Qi Liang; Luo, Qi Quan; Li, Yi De; Huang, Shou Guo

2018-06-01

A global search for the lowest energy structure of B20Si-, B20Si0 and B20Si+ clusters is conducted. Structural transitions at different charge states are observed. B20Si- is a 2D planar configuration with no polygonal holes, and Si atom occupies a peripheral position. B20Si+ adopts a 3D tubular shape, and each Si is bonded with four B atoms. But for B20Si0, competition among quasi-planar, tubular and cage like structures is found. These structures differ greatly from that of pure B21 - cluster. The structural transition may result from changes in the framework of bonding, sp 2 hybridization, and structural mechanics. Some of the clusters' properties including frontier molecular orbital, on-site charge on Si atom, electron density, and magnetism are also discussed.

Investigation on charge transfer bands of Ce 4+ in Sr 2CeO 4 blue phosphor

NASA Astrophysics Data System (ADS)

Li, Ling; Zhou, Shihong; Zhang, Siyuan

2008-03-01

Bulk and nano-materials Sr2CeO4 were prepared by solid-state reaction and sol-gel technique, respectively. Photoluminescence shows that luminescence has the characteristic of a ligand-to-metal charge transfer (CT) emission. Compared with bulk Sr2CeO4, the nano-material exhibits stronger emission intensity, longer decay time, and higher CT excitation energy. Three CT excitation peaks were observed in both bulk and nano samples. Based on the theoretical calculations of the average energy gap of the chemical bond using the dielectric theory of complex crystal, the highest and the lowest energy CT bands were assigned to the transitions O1 → Ce4+ and O2 → Ce4+, respectively. The middle bands were due to the superposition of the transitions Ce-O1 and Ce-O2.

Optimal Charge-to-Spin Conversion in Graphene on Transition-Metal Dichalcogenides

NASA Astrophysics Data System (ADS)

Offidani, Manuel; Milletarı, Mirco; Raimondi, Roberto; Ferreira, Aires

2017-11-01

When graphene is placed on a monolayer of semiconducting transition metal dichalcogenide (TMD) its band structure develops rich spin textures due to proximity spin-orbital effects with interfacial breaking of inversion symmetry. In this work, we show that the characteristic spin winding of low-energy states in graphene on a TMD monolayer enables current-driven spin polarization, a phenomenon known as the inverse spin galvanic effect (ISGE). By introducing a proper figure of merit, we quantify the efficiency of charge-to-spin conversion and show it is close to unity when the Fermi level approaches the spin minority band. Remarkably, at high electronic density, even though subbands with opposite spin helicities are occupied, the efficiency decays only algebraically. The giant ISGE predicted for graphene on TMD monolayers is robust against disorder and remains large at room temperature.

Localization of electrons and excitations

NASA Astrophysics Data System (ADS)

Larsson, Sven

2006-07-01

Electrons, electron holes, or excitations in finite or infinite 'multimer systems' may be localized or delocalized. In the theory of Hush, localization depends on the ratio Δ/ λ ( Δ/2 = coupling; λ = reorganization energy). The latter theory has been extended to the infinite system [S. Larsson, A. Klimkāns, Mol. Cryst. Liq. Cryst. 355 (2000) 217]. The metal/insulator transition often takes place abruptly as a function of Δ/ λ. It is argued that localization in a system with un-filled bands cannot be determined on the basis of Mott-Hubbard U alone, but depends on the number of accessible valence states, reorganization energy λ and coupling Δ (=2t). In fact U = 0 does not necessarily imply delocalization. The analysis here shows that there are many different situations for an insulator to metal transition. Charge transfer in doped NiO is characterized by Ni 2+ - Ni 3+ exchange while charge transfer in pure NiO is characterized by a disproportionation 2Ni 2+ → Ni + + Ni 3+. In spite of the great differences between these two cases, U has been applied without discrimination to both. The relevant localization parameters appear to be Δ and λ in the first case, with only two oxidation states, and U, Δ and λ in the second case with three oxidation states. The analysis is extended to insulator-metal transitions, giant magnetic resistance (GMR) and high Tc superconductivity (SC). λ and Δ can be determined quite accurately in quantum mechanical calculations involving only one and two monomers, respectively.

Manipulating charge density waves in 1 T -TaS2 by charge-carrier doping: A first-principles investigation

NASA Astrophysics Data System (ADS)

Shao, D. F.; Xiao, R. C.; Lu, W. J.; Lv, H. Y.; Li, J. Y.; Zhu, X. B.; Sun, Y. P.

2016-09-01

The transition-metal dichalcogenide 1 T -TaS2 exhibits a rich set of charge-density-wave (CDW) orders. Recent investigations suggested that using light or an electric field can manipulate the commensurate CDW (CCDW) ground state. Such manipulations are considered to be determined by charge-carrier doping. Here we use first-principles calculations to simulate the carrier-doping effect on the CCDW in 1 T -TaS2 . We investigate the charge-doping effects on the electronic structures and phonon instabilities of the 1 T structure, and we analyze the doping-induced energy and distortion ratio variations in the CCDW structure. We found that both in bulk and monolayer 1 T -TaS2 , the CCDW is stable upon electron doping, while hole doping can significantly suppress the CCDW, implying different mechanisms of such reported manipulations. Light or positive perpendicular electric-field-induced hole doping increases the energy of the CCDW, so that the system transforms to a nearly commensurate CDW or a similar metastable state. On the other hand, even though the CCDW distortion is more stable upon in-plane electric-field-induced electron injection, some accompanied effects can drive the system to cross over the energy barrier from the CCDW to a nearly commensurate CDW or a similar metastable state. We also estimate that hole doping can introduce potential superconductivity with a Tc of 6-7 K. Controllable switching of different states such as a CCDW/Mott insulating state, a metallic state, and even a superconducting state can be realized in 1 T -TaS2 . As a result, this material may have very promising applications in future electronic devices.

Field-induced thermal metal-to-insulator transition in underdoped La(2-x)Sr(x)CuO(4+delta).

PubMed

Hawthorn, D G; Hill, R W; Proust, C; Ronning, F; Sutherland, Mike; Boaknin, Etienne; Lupien, C; Tanatar, M A; Paglione, Johnpierre; Wakimoto, S; Zhang, H; Taillefer, Louis; Kimura, T; Nohara, M; Takagi, H; Hussey, N E

2003-05-16

The transport of heat and charge in cuprates was measured in single crystals of La(2-x)Sr(x)CuO(4+delta) (LSCO) across the doping phase diagram at low temperatures. In underdoped LSCO, the thermal conductivity is found to decrease with increasing magnetic field in the T-->0 limit, in striking contrast to the increase observed in all superconductors, including cuprates at higher doping. In heavily underdoped LSCO, where superconductivity can be entirely suppressed with an applied magnetic field, we show that a novel thermal metal-to-insulator transition takes place upon going from the superconducting state to the field-induced normal state.

Antiferromagnetic d-Electron Exchange via a Spin-Singlet π-Electron Ground State in an Organic Conductor

NASA Astrophysics Data System (ADS)

Tokumoto, T.; Brooks, J. S.; Oshima, Y.; Choi, E. S.; Brunel, L. C.; Akutsu, H.; Kaihatsu, T.; Yamada, J.; van Tol, J.

2008-04-01

Electron spin resonance reveals the spin behavior of conduction (π) and localized (d) electrons in β-(BDA-TTP)2MCl4 (M=Fe, Ga). Both the Ga3+(S=0) and Fe3+(S=5/2) compounds exhibit a metal-insulator transition at 113 K with the simultaneous formation of a spin-singlet ground state in the π electron system of the donor molecules. The behavior is consistent with charge ordering in β-(BDA-TTP)2MCl4 at the metal-insulator transition. At 5 K, the Fe3+ compound orders antiferromagnetically, even though the π electrons, which normally would facilitate magnetic exchange, are localized nonmagnetic singlets.

Graduate Student Support for Quantum Computing With Superconducting Charge States

DTIC Science & Technology

2005-08-31

cavity resonance frequency ωr, the atomic transition frequency Ω, and the strength of the atom- photon coupling g appearing in the Jaynes - Cummings ...the atom through the cavity. In the absence of damping, exact diagonalization of the Jaynes - Cumming Hamiltonian yields the excited eigen- states...cillating terms and omitting damping for the moment, 5 Eq. (16) reduces to the Jaynes - Cummings Hamiltonian (1) with Ω = EJ/~ and the vacuum Rabi frequency

BKT phase transition in a 2D system with long-range dipole-dipole interaction

NASA Astrophysics Data System (ADS)

Fedichev, P. O.; Men'shikov, L. I.

2012-01-01

We consider phase transitions in 2D XY-like systems with long-range dipole-dipole interactions and demonstrate that BKT-type phase transition always occurs separating the ordered (ferroelectric) and the disordered (paraelectric) phases. The low-temperature phase corresponds to a thermal state with bound vortex-antivortex pairs characterized by linear attraction at large distances. Using the Maier-Schwabl topological charge model, we show that bound vortex pairs polarize and screen the vortex-antivortex interaction, leaving only the logarithmic attraction at sufficiently large separations between the vortices. At higher temperatures the pairs dissociate and the phase transition similar to BKT occurs, though at a larger temperature than in a system without the dipole-dipole interaction.

Phase transitions of a water overlayer on charged graphene: from electromelting to electrofreezing.

PubMed

Zhu, Xueyan; Yuan, Quanzi; Zhao, Ya-Pu

2014-05-21

We show by using molecular dynamics simulations that a water overlayer on charged graphene experiences first-order ice-to-liquid (electromelting), and then liquid-to-ice (electrofreezing) phase transitions with the increase of the charge value. Corresponding to the ice-liquid-ice transition, the variations of the order parameters indicate an order-disorder-order transition. The key to this novel phenomenon is the surface charge induced change of the orientations of water dipoles, which leads to the change of the water-water interactions from being attractive to repulsive at a critical charge value qc. To further uncover how the orientations of water dipoles influence the interaction strength between water molecules, a theoretical model considering both the Coulomb and van der Waals interactions is established. The results show that with the increase of the charge value, the interaction strength between water molecules decreases below qc, then increases above qc. These two inverse processes lead to electromelting and electrofreezing, respectively. Combining this model with the Eyring equation, the diffusion coefficient is obtained, the variation of which is in qualitative agreement with the simulation results. Our findings not only expand our knowledge of the graphene-water interface, but related analyses could also help recognize the controversial role of the surface charge or electric field in promoting phase transitions of water.

Nonequilibrium Phase Transitions and a Nonequilibrium Critical Point from Anti-de Sitter Space and Conformal Field Theory Correspondence

NASA Astrophysics Data System (ADS)

Nakamura, Shin

2012-09-01

We find novel phase transitions and critical phenomena that occur only outside the linear-response regime of current-driven nonequilibrium states. We consider the strongly interacting (3+1)-dimensional N=4 large-Nc SU(Nc) supersymmetric Yang-Mills theory with a single flavor of fundamental N=2 hypermultiplet as a microscopic theory. We compute its nonlinear nonballistic quark-charge conductivity by using the AdS/CFT correspondence. We find that the system exhibits a novel nonequilibrium first-order phase transition where the conductivity jumps and the sign of the differential conductivity flips at finite current density. A nonequilibrium critical point is discovered at the end point of the first-order regime. We propose a nonequilibrium steady-state analogue of thermodynamic potential in terms of the gravity-dual theory in order to define the transition point. Nonequilibrium analogues of critical exponents are proposed as well. The critical behavior of the conductivity is numerically confirmed on the basis of these proposals. The present work provides a new example of nonequilibrium phase transitions and nonequilibrium critical points.

The transition mechanism from a symmetric single period discharge to a period-doubling discharge in atmospheric helium dielectric-barrier discharge

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, Dingzong; Wang, Yanhui; Wang, Dezhen

2013-06-15

Period-doubling and chaos phenomenon have been frequently observed in atmospheric-pressure dielectric-barrier discharges. However, how a normal single period discharge bifurcates into period-doubling state is still unclear. In this paper, by changing the driving frequency, we study numerically the transition mechanisms from a normal single period discharge to a period-doubling state using a one-dimensional self-consistent fluid model. The results show that before a discharge bifurcates into a period-doubling state, it first deviates from its normal operation and transforms into an asymmetric single period discharge mode. Then the weaker discharge in this asymmetric discharge will be enhanced gradually with increasing of themore » frequency until it makes the subsequent discharge weaken and results in the discharge entering a period-doubling state. In the whole transition process, the spatial distribution of the charged particle density and the electric field plays a definitive role. The conclusions are further confirmed by changing the gap width and the amplitude of the applied voltage.« less

Self-doping processes between planes and chains in the metal-to-superconductor transition of YBa2Cu3O6.9.

PubMed

Magnuson, M; Schmitt, T; Strocov, V N; Schlappa, J; Kalabukhov, A S; Duda, L-C

2014-11-12

The interplay between the quasi 1-dimensional CuO-chains and the 2-dimensional CuO2 planes of YBa(2)Cu(3)O(6+x) (YBCO) has been in focus for a long time. Although the CuO-chains are known to be important as charge reservoirs that enable superconductivity for a range of oxygen doping levels in YBCO, the understanding of the dynamics of its temperature-driven metal-superconductor transition (MST) remains a challenge. We present a combined study using x-ray absorption spectroscopy and resonant inelastic x-ray scattering (RIXS) revealing how a reconstruction of the apical O(4)-derived interplanar orbitals during the MST of optimally doped YBCO leads to substantial hole-transfer from the chains into the planes, i.e. self-doping. Our ionic model calculations show that localized divalent charge-transfer configurations are expected to be abundant in the chains of YBCO. While these indeed appear in the RIXS spectra from YBCO in the normal, metallic, state, they are largely suppressed in the superconducting state and, instead, signatures of Cu trivalent charge-transfer configurations in the planes become enhanced. In the quest for understanding the fundamental mechanism for high-Tc-superconductivity (HTSC) in perovskite cuprate materials, the observation of such an interplanar self-doping process in YBCO opens a unique novel channel for studying the dynamics of HTSC.

QED theory of multiphoton transitions in atoms and ions

NASA Astrophysics Data System (ADS)

Zalialiutdinov, Timur A.; Solovyev, Dmitry A.; Labzowsky, Leonti N.; Plunien, Günter

2018-03-01

This review surveys the quantum theory of electromagnetic radiation for atomic systems. In particular, a review of current theoretical studies of multiphoton processes in one and two-electron atoms and highly charged ions is provided. Grounded on the quantum electrodynamics description the multiphoton transitions in presence of cascades, spin-statistic behaviour of equivalent photons and influence of external electric fields on multiphoton in atoms and anti-atoms are discussed. Finally, the nonresonant corrections which define the validity of the concept of the excited state energy levels are introduced.

Evolution of structural and transport properties in Y-doped double perovskite Sr2FeIrO6

NASA Astrophysics Data System (ADS)

Kharkwal, K. C.; Pramanik, A. K.

2018-05-01

The structural and transport properties of Yttrium doped double perovskite Sr2FeIrO6 have been investigated. Structural properties have been investigated by means of x-ray diffraction measurement and Rietveld analysis. Structural transition has not been observed although lattice parameters evolve with the Yttrium doping. All samples have been found to be insulating over the whole temperature range where the resistivity increases with doping. This increase in resistivity with doping may be due to the change in charge state of transition metal.

Electron impact excitation of highly charged sodium-like ions

NASA Technical Reports Server (NTRS)

Blaha, M.; Davis, J.

1978-01-01

Optical transition probabilities and electron collision strengths for Ca X, Fe XVI, Zn XX, Kr XXVI and Mo XXXII are calculated for transitions between n equal to 3 and n equal to 4 levels. The calculations neglect relativistic effects on the radial functions. A semi-empirical approach provides wave functions of the excited states; a distorted wave function without exchange is employed to obtain the excitation cross sections. The density dependence of the relative intensities of certain emission lines in the sodium isoelectronic sequence is also discussed.

Charge State of the Globular Histone Core Controls Stability of the Nucleosome

PubMed Central

Fenley, Andrew T.; Adams, David A.; Onufriev, Alexey V.

2010-01-01

Presented here is a quantitative model of the wrapping and unwrapping of the DNA around the histone core of the nucleosome that suggests a mechanism by which this transition can be controlled: alteration of the charge state of the globular histone core. The mechanism is relevant to several classes of posttranslational modifications such as histone acetylation and phosphorylation; several specific scenarios consistent with recent in vivo experiments are considered. The model integrates a description based on an idealized geometry with one based on the atomistic structure of the nucleosome, and the model consistently accounts for both the electrostatic and nonelectrostatic contributions to the nucleosome free energy. Under physiological conditions, isolated nucleosomes are predicted to be very stable (38 ± 7 kcal/mol). However, a decrease in the charge of the globular histone core by one unit charge, for example due to acetylation of a single lysine residue, can lead to a significant decrease in the strength of association with its DNA. In contrast to the globular histone core, comparable changes in the charge state of the histone tail regions have relatively little effect on the nucleosome's stability. The combination of high stability and sensitivity explains how the nucleosome is able to satisfy the seemingly contradictory requirements for thermodynamic stability while allowing quick access to its DNA informational content when needed by specific cellular processes such as transcription. PMID:20816070

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sinitsyn, Nikolai A.

In this paper, I identify a nontrivial four-state Landau-Zener model for which transition probabilities between any pair of diabatic states can be determined analytically and exactly. The model describes an experimentally accessible system of two interacting qubits, such as a localized state in a Dirac material with both valley and spin degrees of freedom or a singly charged quantum dot (QD) molecule with spin orbit coupling. Application of the linearly time-dependent magnetic field induces a sequence of quantum level crossings with possibility of interference of different trajectories in a semiclassical picture. I argue that this system satisfies the criteria ofmore » integrability in the multistate Landau-Zener theory, which allows one to derive explicit exact analytical expressions for the transition probability matrix. Finally, I also argue that this model is likely a special case of a larger class of solvable systems, and present a six-state generalization as an example.« less

Estimation of electronic coupling in π-stacked donor-bridge-acceptor systems: Correction of the two-state model

NASA Astrophysics Data System (ADS)

Voityuk, Alexander A.

2006-02-01

Comparison of donor-acceptor electronic couplings calculated within two-state and three-state models suggests that the two-state treatment can provide unreliable estimates of Vda because of neglecting the multistate effects. We show that in most cases accurate values of the electronic coupling in a π stack, where donor and acceptor are separated by a bridging unit, can be obtained as Ṽda=(E2-E1)μ12/Rda+(2E3-E1-E2)2μ13μ23/Rda2, where E1, E2, and E3 are adiabatic energies of the ground, charge-transfer, and bridge states, respectively, μij is the transition dipole moments between the states i and j, and Rda is the distance between the planes of donor and acceptor. In this expression based on the generalized Mulliken-Hush approach, the first term corresponds to the coupling derived within a two-state model, whereas the second term is the superexchange correction accounting for the bridge effect. The formula is extended to bridges consisting of several subunits. The influence of the donor-acceptor energy mismatch on the excess charge distribution, adiabatic dipole and transition moments, and electronic couplings is examined. A diagnostic is developed to determine whether the two-state approach can be applied. Based on numerical results, we showed that the superexchange correction considerably improves estimates of the donor-acceptor coupling derived within a two-state approach. In most cases when the two-state scheme fails, the formula gives reliable results which are in good agreement (within 5%) with the data of the three-state generalized Mulliken-Hush model.

Estimation of electronic coupling in pi-stacked donor-bridge-acceptor systems: correction of the two-state model.

PubMed

Voityuk, Alexander A

2006-02-14

Comparison of donor-acceptor electronic couplings calculated within two-state and three-state models suggests that the two-state treatment can provide unreliable estimates of V(da) because of neglecting the multistate effects. We show that in most cases accurate values of the electronic coupling in a pi stack, where donor and acceptor are separated by a bridging unit, can be obtained as V(da) = (E(2)-E(1))mu(12)R(da) + (2E(3)-E(1)-E(2))2mu(13)mu(23)R(da) (2), where E(1), E(2), and E(3) are adiabatic energies of the ground, charge-transfer, and bridge states, respectively, mu(ij) is the transition dipole moments between the states i and j, and R(da) is the distance between the planes of donor and acceptor. In this expression based on the generalized Mulliken-Hush approach, the first term corresponds to the coupling derived within a two-state model, whereas the second term is the superexchange correction accounting for the bridge effect. The formula is extended to bridges consisting of several subunits. The influence of the donor-acceptor energy mismatch on the excess charge distribution, adiabatic dipole and transition moments, and electronic couplings is examined. A diagnostic is developed to determine whether the two-state approach can be applied. Based on numerical results, we showed that the superexchange correction considerably improves estimates of the donor-acceptor coupling derived within a two-state approach. In most cases when the two-state scheme fails, the formula gives reliable results which are in good agreement (within 5%) with the data of the three-state generalized Mulliken-Hush model.

Ultrafast large-amplitude relocation of electronic charge in ionic crystals

PubMed Central

Zamponi, Flavio; Rothhardt, Philip; Stingl, Johannes; Woerner, Michael; Elsaesser, Thomas

2012-01-01

The interplay of vibrational motion and electronic charge relocation in an ionic hydrogen-bonded crystal is mapped by X-ray powder diffraction with a 100 fs time resolution. Photoexcitation of the prototype material KH2PO4 induces coherent low-frequency motions of the PO4 tetrahedra in the electronically excited state of the crystal while the average atomic positions remain unchanged. Time-dependent maps of electron density derived from the diffraction data demonstrate an oscillatory relocation of electronic charge with a spatial amplitude two orders of magnitude larger than the underlying vibrational lattice motions. Coherent longitudinal optical and tranverse optical phonon motions that dephase on a time scale of several picoseconds, drive the charge relocation, similar to a soft (transverse optical) mode driven phase transition between the ferro- and paraelectric phase of KH2PO4. PMID:22431621

Absorption spectrometric study of charge transfer complex formation between 4-acetamidophenol (paracetamol) and a series of quinones including Vitamin K 3

NASA Astrophysics Data System (ADS)

Saha, Avijit; Mukherjee, Asok K.

2004-07-01

The formation of charge transfer (CT) complexes of 4-acetamidophenol (commonly called 'paracetamol') and a series of quinones (including Vitamin K 3) has been studied spectrophotometrically in ethanol medium. The vertical ionisation potential of paracetamol and the degrees of charge transfer of the complexes in their ground state has been estimated from the trends in the charge transfer bands. The oscillator and transition dipole strengths of the complexes have been determined from the CT absorption spectra at 298 K. The complexes have been found by Job's method of continuous variation to have the uncommon 2:1 (paracetamol:quinone) stoichiometry in each case. The enthalpies and entropies of formation of the complexes have been obtained by determining their formation constants at five different temperatures.

Resonant coherent excitation of 390 MeV/u Ar ions planar channeled in Si crystals

NASA Astrophysics Data System (ADS)

Komaki, K.; Azuma, T.; Ito, T.; Takabayashi, Y.; Yamazaki, Y.; Sano, M.; Torikoshi, M.; Kitagawa, A.; Takada, E.; Murakami, T.

1998-12-01

Resonant coherent excitation of the 1s electron to n=2 states in a hydrogen-like ion was studied through measurements of the survived fraction of 390 MeV/u Ar17+ planar channeled in a Si crystal. Adopting a totally depleted Si surface barrier detector as a target crystal, the charge state of the individual emerged ion was measured in coincidence with the energy deposition in the target. By changing the incident direction along the (2 overline2 0), (0 0 4), and (1 overline1 1) planes, a series of clear resonances were observed as the decrease in the survived charge fraction due to higher electron loss probability for the excited state. Each resonance profile reflects energy splitting of the n=2 manifold originated from l-s interaction and Stark effect due to the crystal field. From the correlation between the energy loss and survived charge fraction, transition energy as a function of the ion trajectory amplitude is deduced which is in good agreement with calculated results.

Electronic signatures of dimerization in IrTe2

NASA Astrophysics Data System (ADS)

Dai, Jixia; Wu, Weida; Oh, Yoon Seok; Cheong, S.-W.; Yang, J. J.

2014-03-01

Recently, the mysterious phase transition around Tc ~ 260 K in IrTe2 has been intensively studied. A structural supermodulation with q =1/5 was identified below Tc. A variety of microscopic mechanisms have been proposed to account for this transition, including charge-density wave due to Fermi surface nesting, Te p-orbital driven structure instability, anionic depolymerization, ionic dimerization, and so on. However, there has not been an unified picture on the nature of this transition. To address this issue, we have performed low-temperature scanning tunneling microscopy and spectroscopy (STM/STS) experiments on IrTe2 and IrTe2-xSex. Our STM data clearly shows a strong bias dependence in both topography and local density of states (STS) maps. High resolution spectroscopic data further confirms the stripe-like electronic states modulation, which provides insight to the ionic dimerization revealed by X-ray diffraction.

Mott insulator-to-metal transition in yttrium-doped CaIrO₃.

PubMed

Gunasekera, J; Chen, Y; Kremenak, J W; Miceli, P F; Singh, D K

2015-02-11

We report on the study of insulator-to-metal transition in post-perovskite compound CaIrO3. It is discovered that a gradual chemical substitution of calcium by yttrium leads to the onset of strong metallic behavior in this compound. This observation is in stark contrast to BaIrO3, which preserves its Mott insulating behavior despite excess of the charge carriers due to yttrium doping. Magnetic measurements reveal that both compounds tend to exhibit magnetic character irrespective of the chemical substitution of Ca or Ba. We analyze these unusual observations in light of recent researches that suggest that CaIrO3 does not necessarily possess j = 1/2 ground state due to structural distortion. The insulator-to-metal transition in CaIrO3 will spur new researches to explore more exotic ground state, including superconductivity, in post-perovskite Mott insulators.

Photoinduced Charge Shifts and Electron Transfer in Viologen-Tetraphenylborate Complexes: Push-Pull Character of the Exciplex.

PubMed

Santos, Willy G; Budkina, Darya S; Deflon, Victor M; Tarnovsky, Alexander N; Cardoso, Daniel R; Forbes, Malcolm D E

2017-06-14

Viologen-tetraarylborate ion-pair complexes were prepared and investigated by steady-state and time-resolved spectroscopic techniques such as fluorescence and femtosecond transient absorption. The results highlight a charge transfer transition that leads to changes in the viologen structure in the excited singlet state. Femtosecond transient absorption reveals the formation of excited-state absorption and stimulated emission bands assigned to the planar (k obs < 10 12 s -1 ) and twisted (k obs ∼ 10 10 s -1 ) structures between two pyridinium groups in the viologen ion. An efficient photoinduced electron transfer from the tetraphenylborate anionic moiety to the viologen dication was observed less than 1 μs after excitation. This is a consequence of the push-pull character of the electron donor twisted viologen structure, which helps formation of the borate triplet state. The borate triplet state is deactivated further via a second electron transfer process, generating viologen cation radical (V •+ ).

Conjugated ionic state and its distribution in perylene bisimide doped film: A characterization of Z-scanning in confocal Raman spectroscopy.

PubMed

Zhou, Xuehong; Zhang, Wenqiang; Wang, Cong; Zhou, Jiadong; Liu, Linlin; Xie, Zengqi; Ma, Yuguang

2018-04-27

Ion-doped states are significant for improving the performance in organic semiconductor-based devices, which require clear characterization to understand their relationship with conductivity and charge transporting mechanisms. In this paper, Raman spectroscopy is used to track the evolution of a dianion-anion-neutral mixture in a perylene bisimide (PBI)-doped film under air, with z-scanning carried out in the confocal mode. The precise distribution for the different states along the film depth is realized within 3.5 μm. The whole film is clearly divided into three regions: the ion-poor state, transition region and ion-rich state. The ion ratio and distribution are strongly related to the film conductivity and the onset voltage shift. Changes in the distribution of the ionic species during oxidation and electrode catalysis are clearly recorded by z-scanning, which is beneficial for understanding the charge transfer properties as well as the mechanism underlying working devices. Copyright © 2018 Elsevier B.V. All rights reserved.

Spectroscopic and structural investigation for the ground and excited states of CaNa+ molecular ion

NASA Astrophysics Data System (ADS)

Jellali, Soulef; Habli, Héla; Mejrissi, Leila; Hamdi, Rafika; Oujia, Brahim; Xavier Gadéa, Florent

2018-04-01

In the current theoretical study, we investigated several electronic states correlated with the {Ca+Na+} and {Ca++Na} asymptotic limits of different symmetries (Σ+, Π, Δ). Our calculations were based on ab intio method using semi-empirical pseudo-potential theory of both cores Na+ and Ca2+ and Full Configuration Interaction (FCI). Hence, we computed the adiabatic potential energy curves (PECs) and vibrational levels of the ground state along with several higher states of (CaNa)+ molecular ion. From these curves, we extracted all related spectroscopic parameters (De, D0, Te, Re, Be, ωe and ωeχe). Dipolar properties of (CaNa)+ such as Permanent and Transition Dipole Moments (PDM, TDM) were determined and analyzed. Numerous Avoided Crossings (ACs) were detected in PECs and their reflections were clearly observed in PDM and TDM functions. The strong interactions could lead to significant charge or excitation transfer for atom-ion collisions in the diverse charge or excited states.

Metal-to-metal charge transfer transitions - Interpretation of visible-region spectra of the moon and lunar materials

NASA Technical Reports Server (NTRS)

Loeffler, B. M.; Burns, R. G.; Tossell, J. A.

1975-01-01

Prominent bands in the spectral profiles of Fe-Ti phases in lunar samples have been attributed to charge-transfer transitions between Fe and Ti cations, and a model is presented for calculating charge transfer energies from energy levels computed by the SCF-X(alpha) scattered wave molecular orbital method for isolated MO6 octahedral coordination clusters containing Fe(2+), Fe(3+), Ti(3+), and Ti(4+) cations. The calculated charge transfer energy for the Fe(2+) to Ti(4+) transition correlates well with a measured spectral feature around 0.6 micron in ilmenite, and, since ilmenite is a major constituent of mare basalts and dark-mantling material, the observed darkness and blueness of the regolith in lunar black spots is attributed primarily to this transition. The Ti(3+) to Ti(4+) transition is thought to contribute to some phases.

Electrical detection of proton-spin motion in a polymer device at room temperature

NASA Astrophysics Data System (ADS)

Boehme, Christoph

With the emergence of spintronics concepts based on organic semiconductors there has been renewed interest in the role of both, electron as well as nuclear spin states for the magneto-optoelectronic properties of these materials. In spite of decades of research on these molecular systems, there is still much need for an understanding of some of the fundamental properties of spin-controlled charge carrier transport and recombination processes. This presentation focuses on mechanisms that allow proton spin states to influence electronic transition rates in organic semiconductors. Remarkably, even at low-magnetic field conditions and room temperature, nuclear spin states with energy splittings orders of magnitude below thermal energies are able to influence observables like magnetoresistance and fluorescence. While proton spins couple to charge carrier spins via hyperfine interaction, there has been considerable debate about the nature of the electronic processes that are highly susceptible to these weak hyperfine fields. Here, experiments are presented which show how the magnetic resonant manipulation of electron and nuclear spin states in a π-conjugated polymer device causes changes of the device current. The experiments confirm the extraordinary sensitivity of electronic transitions to very weak magnetic field changes and underscore the potential significance of spin-selection rules for highly sensitive absolute magnetic fields sensor concepts. However, the relevance of these magnetic-field sensitive spin-dependent electron transitions is not just limited to semiconductor materials but also radical pair chemistry and even avian magnetoreceptors This work was supported by the US Department of Energy, Office of Basic Energy Sciences, Division of Materials Sciences and Engineering under Award #DE-SC0000909. The Utah NSF - MRSEC program #DMR 1121252 is acknowledged for instrumentation support.

STATIC QUARK ANTI-QUARK FREE AND INTERNAL ENERGY IN 2-FLAVOR QCD AND BOUND STATES IN THE QGP.

DOE Office of Scientific and Technical Information (OSTI.GOV)

ZANTOW, F.; KACZMAREK, O.

2005-07-25

We present results on heavy quark free energies in 2-flavour QCD. The temperature dependence of the interaction between static quark anti-quark pairs will be analyzed in terms of temperature dependent screening radii, which give a first estimate on the medium modification of (heavy quark) bound states in the quark gluon plasma. Comparing those radii to the (zero temperature) mean squared charge radii of chasmonium states indicates that the J/{Psi} may survive the phase transition as a bound state, while {chi}{sub c} and {Psi}{prime} are expected to show significant thermal modifications at temperatures close to the transition. Furthermore we will analyzemore » the relation between heavy quark free energies, entropy contributions and internal energy and discuss their relation to potential models used to analyze the melting of heavy quark bound states above the deconfinement temperature. Results of different groups and various potential models for bound states in the deconfined phase of QCD are compared.« less

Mechanisms for pressure-induced crystal-crystal transition, amorphization, and devitrification of SnI{sub 4}

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liu, H.; Tse, J. S., E-mail: john.tse@usask.ca; Hu, M. Y.

2015-10-28

The pressure-induced amorphization and subsequent recrystallization of SnI{sub 4} have been investigated using first principles molecular dynamics calculations together with high-pressure {sup 119}Sn nuclear resonant inelastic x-ray scattering measurements. Above ∼8 GPa, we observe a transformation from an ambient crystalline phase to an intermediate crystal structure and a subsequent recrystallization into a cubic phase at ∼64 GPa. The crystalline-to-amorphous transition was identified on the basis of elastic compatibility criteria. The measured tin vibrational density of states shows large amplitude librations of SnI{sub 4} under ambient conditions. Although high pressure structures of SnI{sub 4} were thought to be determined by randommore » packing of equal-sized spheres, we detected electron charge transfer in each phase. This charge transfer results in a crystal structure packing determined by larger than expected iodine atoms.« less

Mechanisms for pressure-induced crystal-crystal transition, amorphization, and devitrification of Snl 4

DOE PAGES

Liu, Hanyu; Tse, John S.; Hu, Michael Y.; ...

2015-10-27

The pressure-induced amorphization and subsequent recrystallization of SnI 4 have been investigated using first principles molecular dynamics calculations together with high-pressure 119Sn nuclear resonant inelastic x-ray scattering measurements. Above ~8 GPa, we observe a transformation from an ambient crystalline phase to an intermediate crystal structure and a subsequent recrystallization into a cubic phase at ~64 GPa. The crystalline-to-amorphous transition was identified on the basis of elastic compatibility criteria. The measured tin vibrational density of states shows large amplitude librations of SnI 4 under ambient conditions. Although high pressure structures of SnI 4 were thought to be determined by random packingmore » of equal-sized spheres, we detected electron charge transfer in each phase. As a result, this charge transfer results in a crystal structure packing determined by larger than expected iodine atoms. (C) 2015 AIP Publishing LLC.« less

Mechanisms for pressure-induced crystal-crystal transition, amorphization, and devitrification of SnI4.

PubMed

Liu, H; Tse, J S; Hu, M Y; Bi, W; Zhao, J; Alp, E E; Pasternak, M; Taylor, R D; Lashley, J C

2015-10-28

The pressure-induced amorphization and subsequent recrystallization of SnI4 have been investigated using first principles molecular dynamics calculations together with high-pressure (119)Sn nuclear resonant inelastic x-ray scattering measurements. Above ∼8 GPa, we observe a transformation from an ambient crystalline phase to an intermediate crystal structure and a subsequent recrystallization into a cubic phase at ∼64 GPa. The crystalline-to-amorphous transition was identified on the basis of elastic compatibility criteria. The measured tin vibrational density of states shows large amplitude librations of SnI4 under ambient conditions. Although high pressure structures of SnI4 were thought to be determined by random packing of equal-sized spheres, we detected electron charge transfer in each phase. This charge transfer results in a crystal structure packing determined by larger than expected iodine atoms.

Photochemistry of the α-Al 2O 3-PETN interface

DOE PAGES

Tsyshevsky, Roman V.; Zverev, Anton; Mitrofanov, Anatoly; ...

2016-02-29

Optical absorption measurements are combined with electronic structure calculations to explore photochemistry of an α-Al 2O 3-PETN interface formed by a nitroester (pentaerythritol tetranitrate, PETN, C 5H 8N 4O 12) and a wide band gap aluminum oxide (α-Al 2O 3) substrate. The first principles modeling is used to deconstruct and interpret the α-Al 2O 3-PETN absorption spectrum that has distinct peaks attributed to surface F 0-centers and surfacePETN transitions. We predict the low energy α-Al 2O 3 F 0-centerPETN transition, producing the excited triplet state, and α-Al 2O 3 F- 0-centerPETN charge transfer, generating the PETN anion radical. This impliesmore » that irradiation by commonly used lasers can easily initiate photodecomposition of both excited and charged PETN at the interface. As a result, the feasible mechanism of the photodecomposition is proposed.« less

Structural and electronic phase transitions of MoTe2 induced by Li ionic gating

NASA Astrophysics Data System (ADS)

Hwang, Jeongwoon; Zhang, Chenxi; Cho, Kyeongjae

2017-12-01

Monolayer MoTe2 has semiconducting and semimetallic phases with small energy difference, and the relative stability is readily reversed by gating. By first-principles calculations, we investigate the changes in atomic structure, electronic structure, and relative stability of two phases induced by Li ionic gating. To model Li ionic gating, we employ two approaches; one is direct adsorption of Li on MoTe2 and the other is introducing non-contacting Li plate over MoTe2. We show phonon instability in H-phase of MoTe2 with increasing the amount of charge transfer from Li, which implies a large electron-phonon coupling in the system resulting in a charge density wave state. Structural distortion is also observed in highly doped T d phase. The transition energy barrier from distorted H phase to distorted T d phase is reduced considerably compared to that of pristine MoTe2.

Stochastic many-particle model for LFP electrodes

NASA Astrophysics Data System (ADS)

Guhlke, Clemens; Gajewski, Paul; Maurelli, Mario; Friz, Peter K.; Dreyer, Wolfgang

2018-02-01

In the framework of non-equilibrium thermodynamics, we derive a new model for many-particle electrodes. The model is applied to LiFePO4 (LFP) electrodes consisting of many LFP particles of nanometer size. The phase transition from a lithium-poor to a lithium-rich phase within LFP electrodes is controlled by both different particle sizes and surface fluctuations leading to a system of stochastic differential equations. An explicit relation between battery voltage and current controlled by the thermodynamic state variables is derived. This voltage-current relation reveals that in thin LFP electrodes lithium intercalation from the particle surfaces into the LFP particles is the principal rate-limiting process. There are only two constant kinetic parameters in the model describing the intercalation rate and the fluctuation strength, respectively. The model correctly predicts several features of LFP electrodes, viz. the phase transition, the observed voltage plateaus, hysteresis and the rate-limiting capacity. Moreover we study the impact of both the particle size distribution and the active surface area on the voltage-charge characteristics of the electrode. Finally we carefully discuss the phase transition for varying charging/discharging rates.

Optimization by infusion of multiple reaction monitoring transitions for sensitive quantification of peptides by liquid chromatography/mass spectrometry.

PubMed

Alghanem, Bandar; Nikitin, Frédéric; Stricker, Thomas; Duchoslav, Eva; Luban, Jeremy; Strambio-De-Castillia, Caterina; Muller, Markus; Lisacek, Frédérique; Varesio, Emmanuel; Hopfgartner, Gérard

2017-05-15

In peptide quantification by liquid chromatography/mass spectrometry (LC/MS), the optimization of multiple reaction monitoring (MRM) parameters is essential for sensitive detection. We have compared different approaches to build MRM assays, based either on flow injection analysis (FIA) of isotopically labelled peptides, or on the knowledge and the prediction of the best settings for MRM transitions and collision energies (CE). In this context, we introduce MRMOptimizer, an open-source software tool that processes spectra and assists the user in selecting transitions in the FIA workflow. MS/MS spectral libraries with CE voltages from 10 to 70 V are automatically acquired in FIA mode for isotopically labelled peptides. Then MRMOptimizer determines the optimal MRM settings for each peptide. To assess the quantitative performance of our approach, 155 peptides, representing 84 proteins, were analysed by LC/MRM-MS and the peak areas were compared between: (A) the MRMOptimizer-based workflow, (B1) the SRMAtlas transitions set used 'as-is'; (B2) the same SRMAtlas set with CE parameters optimized by Skyline. 51% of the three most intense transitions per peptide were shown to be common to both A and B1/B2 methods, and displayed similar sensitivity and peak area distributions. The peak areas obtained with MRMOptimizer for transitions sharing either the precursor ion charge state or the fragment ions with the SRMAtlas set at unique transitions were increased 1.8- to 2.3-fold. The gain in sensitivity using MRMOptimizer for transitions with different precursor ion charge state and fragment ions (8% of the total), reaches a ~ 11-fold increase. Isotopically labelled peptides can be used to optimize MRM transitions more efficiently in FIA than by searching databases. The MRMOptimizer software is MS independent and enables the post-acquisition selection of MRM parameters. Coefficients of variation for optimal CE values are lower than those obtained with the SRMAtlas approach (B2) and one additional peptide was detected. Copyright © 2017 John Wiley & Sons, Ltd. Copyright © 2017 John Wiley & Sons, Ltd.

DFT Study of Optical Properties of Pt-based Complexes

NASA Astrophysics Data System (ADS)

Oprea, Corneliu I.; Dumbravǎ, Anca; Moscalu, Florin; Nicolaides, Atnanassios; Gîrţu, Mihai A.

2010-01-01

We report Density Functional Theory (DFT) calculations providing the geometrical and electronic structures, as well as the vibrational and optical properties of the homologous series of Pt-pyramidalized olefin complexes (CH2)n-(C8H10)Pt(PH3)2, where n = 0, 1, and 2, in their neutral and oxidized states. All complexes were geometry optimized for the singlet ground state in vacuum using DFT methods with B3LYP exchange-correlation functional and the Effective Core Potential LANL2DZ basis set, within the frame of Gaussian03 quantum chemistry package. We find the coordination geometry of Pt to be distorted square planar, with dihedral angles ranging from 0°, for n = 0 and 1, which have C2V symmetry to 3.4°, for n = 2 with C2 symmetry. The Mulliken charge analysis allows a discussion of the oxidation state of the Pt ion. Electronic transitions were calculated at the same level of theory by means of Time Dependant-DFT. For n = 2 the electronic absorption bands are located in the UV region of the spectrum, the transitions being assigned to metal to ligand charge transfers. The relevance of these Pt-based compounds as possible pigments for dye-sensitized solar cells is discussed.

Molecular dynamics simulation of bovine pancreatic ribonuclease A-CpA and transition state-like complexes.

PubMed

Formoso, Elena; Matxain, Jon M; Lopez, Xabier; York, Darrin M

2010-06-03

The mechanisms of enzymes are intimately connected with their overall structure and dynamics in solution. Experimentally, it is considerably challenging to provide detailed atomic level information about the conformational events that occur at different stages along the chemical reaction path. Here, theoretical tools may offer new potential insights that complement those obtained from experiments that may not yield an unambiguous mechanistic interpretation. In this study, we apply molecular dynamics simulations of bovine pancreatic ribonuclease A, an archetype ribonuclease, to study the conformational dynamics, structural relaxation, and differential solvation that occur at discrete stages of the transesterification and cleavage reaction. Simulations were performed with explicit solvation with rigorous electrostatics and utilize recently developed molecular mechanical force field parameters for transphosphorylation and hydrolysis transition state analogues. Herein, we present results for the enzyme complexed with the dinucleotide substrate cytidilyl-3',5'-adenosine (CpA) in the reactant, and transphosphorylation and hydrolysis transition states. A detailed analysis of active site structures and hydrogen-bond patterns is presented and compared. The integrity of the overall backbone structure is preserved in the simulations and supports a mechanism whereby His12 stabilizes accumulating negative charge at the transition states through hydrogen-bond donation to the nonbridge oxygens. Lys41 is shown to be highly versatile along the reaction coordinate and can aid in the stabilization of the dianionic transition state, while being poised to act as a general acid catalyst in the hydrolysis step.

Molecular Dynamics Simulation of Bovine Pancreatic Ribonuclease A - CpA and Transition State-like Complexes

PubMed Central

Formoso, Elena; Matxain, Jon M.; Lopez, Xabier; York, Darrin M.

2010-01-01

The mechanisms of enzymes are intimately connected with their overall structure and dynamics in solution. Experimentally it is considerably challenging to provide detailed atomic level information about the conformational events that occur at different stages along the chemical reaction path. Here, theoretical tools may offer new potential insights that complement those obtained from experiments that may not yield an unambiguous mechanistic interpretation. In this study we apply molecular dynamics simulations of bovine pancreatic ribonuclease A, an archetype ribonuclease, in order to study the conformational dynamics, structural relaxation, and differential solvation that occurs at discreet stages of the transesterification and cleavage reaction. Simulations were performed with explicit solvation with rigorous electrostatics, and utilize recently developed molecular mechanical force field parameters for transphosphorylation and hydrolysis transition state analogs. Herein, we present results for the enzyme complexed with the dinucleotide substrate cytidilyl-3′,5′-adenosine (CpA) in the reactant, and transphosphorylation and hydrolysis transition states. A detailed analysis of active site structures and hydrogen bond patterns are presented and compared. The integrity of the overall backbone structure is preserved in the simulations, and support a mechanism whereby His12 stabilizes accumulating negative charge at the transition states through hydrogen bond donation to the non-bridge oxygens. Lys41 is shown to be highly versatile along the reaction coordinate, and can aid in the stabilization of the dianionic transition state, while being poised to act as a general acid catalyst in the hydrolysis step. PMID:20455590

Superconducting transmission line particle detector

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gray, K.E.

This paper describes a microvertex particle detector for use in a high energy physic collider including a plurality of parallel superconducting thin film strips separated from a superconducting ground plane by an insulating layer to form a plurality of superconducting waveguides. The microvertex particle detector indicates passage of a charged subatomic particle by measuring a voltage pulse measured across a superconducting waveguide caused by the transition of the superconducting thin film strip from a superconducting to a non-superconducting state in response to the passage of a charged particle. A plurality of superconducting thin film strips in two orthogonal planes plusmore » the slow electromagnetic wave propogating in a superconducting transmission line are used to resolve N{sup 2} ambiguity of charged particle events.« less

Superconducting transmission line particle detector

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gray, K.E.

A microvertex particle detector for use in a high energy physic collider including a plurality of parallel superconducting thin film strips separated from a superconducting ground plane by an insulating layer to form a plurality of superconducting waveguides. The microvertex particle detector indicates passage of a charged subatomic particle by measuring a voltage pulse measured across a superconducting waveguide caused by the transition of the superconducting thin film strip from a superconducting to a non- superconducting state in response to the passage of a charged particle. A plurality of superconducting thin film strips in two orthogonal planes plus the slowmore » electromagnetic wave propagating in a superconducting transmission line are used to resolve N/sup 2/ ambiguity of charged particle events. 6 figs.« less

Unity quantum yield of photogenerated charges and band-like transport in quantum-dot solids.

PubMed

Talgorn, Elise; Gao, Yunan; Aerts, Michiel; Kunneman, Lucas T; Schins, Juleon M; Savenije, T J; van Huis, Marijn A; van der Zant, Herre S J; Houtepen, Arjan J; Siebbeles, Laurens D A

2011-09-25

Solid films of colloidal quantum dots show promise in the manufacture of photodetectors and solar cells. These devices require high yields of photogenerated charges and high carrier mobilities, which are difficult to achieve in quantum-dot films owing to a strong electron-hole interaction and quantum confinement. Here, we show that the quantum yield of photogenerated charges in strongly coupled PbSe quantum-dot films is unity over a large temperature range. At high photoexcitation density, a transition takes place from hopping between localized states to band-like transport. These strongly coupled quantum-dot films have electrical properties that approach those of crystalline bulk semiconductors, while retaining the size tunability and cheap processing properties of colloidal quantum dots.

Two-channel Kondo effect and renormalization flow with macroscopic quantum charge states.

PubMed

Iftikhar, Z; Jezouin, S; Anthore, A; Gennser, U; Parmentier, F D; Cavanna, A; Pierre, F

2015-10-08

Many-body correlations and macroscopic quantum behaviours are fascinating condensed matter problems. A powerful test-bed for the many-body concepts and methods is the Kondo effect, which entails the coupling of a quantum impurity to a continuum of states. It is central in highly correlated systems and can be explored with tunable nanostructures. Although Kondo physics is usually associated with the hybridization of itinerant electrons with microscopic magnetic moments, theory predicts that it can arise whenever degenerate quantum states are coupled to a continuum. Here we demonstrate the previously elusive 'charge' Kondo effect in a hybrid metal-semiconductor implementation of a single-electron transistor, with a quantum pseudospin of 1/2 constituted by two degenerate macroscopic charge states of a metallic island. In contrast to other Kondo nanostructures, each conduction channel connecting the island to an electrode constitutes a distinct and fully tunable Kondo channel, thereby providing unprecedented access to the two-channel Kondo effect and a clear path to multi-channel Kondo physics. Using a weakly coupled probe, we find the renormalization flow, as temperature is reduced, of two Kondo channels competing to screen the charge pseudospin. This provides a direct view of how the predicted quantum phase transition develops across the symmetric quantum critical point. Detuning the pseudospin away from degeneracy, we demonstrate, on a fully characterized device, quantitative agreement with the predictions for the finite-temperature crossover from quantum criticality.

Band Alignment and Charge Transfer in Complex Oxide Interfaces

NASA Astrophysics Data System (ADS)

Zhong, Zhicheng; Hansmann, Philipp

2017-01-01

The synthesis of transition metal heterostructures is currently one of the most vivid fields in the design of novel functional materials. In this paper, we propose a simple scheme to predict band alignment and charge transfer in complex oxide interfaces. For semiconductor heterostructures, band-alignment rules like the well-known Anderson or Schottky-Mott rule are based on comparison of the work function or electron affinity of the bulk components. This scheme breaks down for oxides because of the invalidity of a single work-function approximation as recently shown in [Phys. Rev. B 93, 235116 (2016), 10.1103/PhysRevB.93.235116; Adv. Funct. Mater. 26, 5471 (2016), 10.1002/adfm.201600243]. Here, we propose a new scheme that is built on a continuity condition of valence states originating in the compounds' shared network of oxygen. It allows for the prediction of sign and relative amplitude of the intrinsic charge transfer, taking as input only information about the bulk properties of the components. We support our claims by numerical density functional theory simulations as well as (where available) experimental evidence. Specific applications include (i) controlled doping of SrTiO3 layers with the use of 4 d and 5 d transition metal oxides and (ii) the control of magnetic ordering in manganites through tuned charge transfer.

Symmetry of Isoscalar Matrix Elements and Systematics in the sd and beginning of fp shells

NASA Astrophysics Data System (ADS)

Orce, J. N.; Petkov, P.; Velázquez, V.; McKay, C. J.; Lesher, S. R.; Choudry, S.; Mynk, M.; Linnemann, A.; Jolie, J.; von Brentano, P.; Werner, V.; Yates, S. W.; McEllistrem, M. T.

2006-03-01

A careful determination of the lifetime and measurement of the branching ratio for decay of the first 2T=1+ state in 42Sc has allowed an accurate experimental test of charge independence in the A = 42 isobaric triplet. A lifetime of 69(17) fs was measured at the University of Kentucky, while relative intensities for the 975 keV and 1586 keV transitions depopulating the first 2T=1+ state have been determined at the University of Cologne as 100(1) and 8(1), respectively. Both measurements give an isoscalar matrix element, M0, of 6.4(9) (W.u.)1/2. This result confirms charge independence for the A=42 isobaric triplet. Shell model calculations have been carried out for understanding the global trend of M0 values for A = 4n + 2 isobaric triplets ranging from A = 18 to A = 42. The 21 (T=1)+ → 01 (T=1)+ transition energies, reduced transition probabilities and M0 values are reproduced to a high degree of accuracy. The trend of M0 strength along the sd shell is interpreted in terms of the shell structure. Certain discrepancies arise at the extremes of the sd shell, for the A = 18 and A = 38 isobaric triplets, which might be explained in terms of the low valence space at the extremes of the sd shell.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Orce, J. N.; McKay, C. J.; Lesher, S. R.

A careful determination of the lifetime and measurement of the branching ratio for decay of the first 2{sub T=1}{sup +} state in 42Sc has allowed an accurate experimental test of charge independence in the A = 42 isobaric triplet. A lifetime of 69(17) fs was measured at the University of Kentucky, while relative intensities for the 975 keV and 1586 keV transitions depopulating the first 2{sub T=1}{sup +} state have been determined at the University of Cologne as 100(1) and 8(1), respectively. Both measurements give an isoscalar matrix element, M0, of 6.4(9) (W.u.)1/2. This result confirms charge independence for themore » A=42 isobaric triplet. Shell model calculations have been carried out for understanding the global trend of M0 values for A = 4n + 2 isobaric triplets ranging from A = 18 to A = 42. The 2{sub 1(T=1)}{sup +} {yields} 0{sub 1(T=1)}{sup +} transition energies, reduced transition probabilities and M0 values are reproduced to a high degree of accuracy. The trend of M0 strength along the sd shell is interpreted in terms of the shell structure. Certain discrepancies arise at the extremes of the sd shell, for the A = 18 and A 38 isobaric triplets, which might be explained in terms of the low valence space at the extremes of the sd shell.« less

Thermoelectric material including a multiple transition metal-doped type I clathrate crystal structure

DOEpatents

Yang, Jihui [Lakeshore, CA; Shi, Xun [Troy, MI; Bai, Shengqiang [Shanghai, CN; Zhang, Wenqing [Shanghai, CN; Chen, Lidong [Shanghai, CN; Yang, Jiong [Shanghai, CN

2012-01-17

A thermoelectric material includes a multiple transition metal-doped type I clathrate crystal structure having the formula A.sub.8TM.sub.y.sub.1.sup.1TM.sub.y.sub.2.sup.2 . . . TM.sub.y.sub.n.sup.nM.sub.zX.sub.46-y.sub.1.sub.-y.sub.2.sub.- . . . -y.sub.n.sub.-z. In the formula, A is selected from the group consisting of barium, strontium, and europium; X is selected from the group consisting of silicon, germanium, and tin; M is selected from the group consisting of aluminum, gallium, and indium; TM.sup.1, TM.sup.2, and TM.sup.n are independently selected from the group consisting of 3d, 4d, and 5d transition metals; and y.sub.1, y.sub.2, y.sub.n and Z are actual compositions of TM.sup.1, TM.sup.2, TM.sup.n, and M, respectively. The actual compositions are based upon nominal compositions derived from the following equation: z=8q.sub.A-|.DELTA.q.sub.1|y.sub.1-|.DELTA.q.sub.2|y.sub.2- . . . -|.DELTA.q.sub.n|y.sub.n, wherein q.sub.A is a charge state of A, and wherein .DELTA.q.sub.1, .DELTA.q.sub.2, .DELTA.q.sub.n are, respectively, the nominal charge state of the first, second, and n-th TM.

Prospects and applications near ferroelectric quantum phase transitions: a key issues review.

PubMed

Chandra, P; Lonzarich, G G; Rowley, S E; Scott, J F

2017-11-01

The emergence of complex and fascinating states of quantum matter in the neighborhood of zero temperature phase transitions suggests that such quantum phenomena should be studied in a variety of settings. Advanced technologies of the future may be fabricated from materials where the cooperative behavior of charge, spin and current can be manipulated at cryogenic temperatures. The progagating lattice dynamics of displacive ferroelectrics make them appealing for the study of quantum critical phenomena that is characterized by both space- and time-dependent quantities. In this key issues article we aim to provide a self-contained overview of ferroelectrics near quantum phase transitions. Unlike most magnetic cases, the ferroelectric quantum critical point can be tuned experimentally to reside at, above or below its upper critical dimension; this feature allows for detailed interplay between experiment and theory using both scaling and self-consistent field models. Empirically the sensitivity of the ferroelectric T c 's to external and to chemical pressure gives practical access to a broad range of temperature behavior over several hundreds of Kelvin. Additional degrees of freedom like charge and spin can be added and characterized systematically. Satellite memories, electrocaloric cooling and low-loss phased-array radar are among possible applications of low-temperature ferroelectrics. We end with open questions for future research that include textured polarization states and unusual forms of superconductivity that remain to be understood theoretically.

Prospects and applications near ferroelectric quantum phase transitions: a key issues review

NASA Astrophysics Data System (ADS)

Chandra, P.; Lonzarich, G. G.; Rowley, S. E.; Scott, J. F.

2017-11-01

The emergence of complex and fascinating states of quantum matter in the neighborhood of zero temperature phase transitions suggests that such quantum phenomena should be studied in a variety of settings. Advanced technologies of the future may be fabricated from materials where the cooperative behavior of charge, spin and current can be manipulated at cryogenic temperatures. The progagating lattice dynamics of displacive ferroelectrics make them appealing for the study of quantum critical phenomena that is characterized by both space- and time-dependent quantities. In this key issues article we aim to provide a self-contained overview of ferroelectrics near quantum phase transitions. Unlike most magnetic cases, the ferroelectric quantum critical point can be tuned experimentally to reside at, above or below its upper critical dimension; this feature allows for detailed interplay between experiment and theory using both scaling and self-consistent field models. Empirically the sensitivity of the ferroelectric T c’s to external and to chemical pressure gives practical access to a broad range of temperature behavior over several hundreds of Kelvin. Additional degrees of freedom like charge and spin can be added and characterized systematically. Satellite memories, electrocaloric cooling and low-loss phased-array radar are among possible applications of low-temperature ferroelectrics. We end with open questions for future research that include textured polarization states and unusual forms of superconductivity that remain to be understood theoretically.

Dynamics of electronic transitions and reemission spectra of attosecond electromagnetic pulses

NASA Astrophysics Data System (ADS)

Matveev, V. I.; Makarov, D. N.

2014-05-01

The processes of reemission of attosecond electromagnetic pulses by systems in nonstationary states have been considered. The probabilities of the reemission of attosecond electromagnetic pulses at the resonance charge exchange of a proton on a hydrogen atom and at the decay of a quasistationary state, as well as the probabilities of the reemission of attosecond pulses by a system in a resonance external field, have been calculated as examples. The developed method can be applied to more complex targets, including targets in the collision state, and to various chemical reactions.

Novel phase transitions in coupled dipolar chains.

NASA Astrophysics Data System (ADS)

Mellado, Paula

We study the properties of a classical magnetic system realized by two chains of U(1) rotors coupled via Coulomb interactions in the dumbbell approach. Magnets in chain I and chain II rotate in the x-z and y-z planes respectively. Ground state correlations and the system wave excitation spectrum are found using spin wave theory. The displacement ''d'' of chain II from chain I induces dynamics in the system and yields two first order magnetic phase transitions. The transitions happen at critical displacements, which notably, are independent of the magnetic charge at the tips of the magnets, suggesting a geometrical origin. This work was supported by Fondecyt under Grant No. 1160239.

Exciton fission in monolayer transition metal dichalcogenide semiconductors.

PubMed

Steinhoff, A; Florian, M; Rösner, M; Schönhoff, G; Wehling, T O; Jahnke, F

2017-10-27

When electron-hole pairs are excited in a semiconductor, it is a priori not clear if they form a plasma of unbound fermionic particles or a gas of composite bosons called excitons. Usually, the exciton phase is associated with low temperatures. In atomically thin transition metal dichalcogenide semiconductors, excitons are particularly important even at room temperature due to strong Coulomb interaction and a large exciton density of states. Using state-of-the-art many-body theory, we show that the thermodynamic fission-fusion balance of excitons and electron-hole plasma can be efficiently tuned via the dielectric environment as well as charge carrier doping. We propose the observation of these effects by studying exciton satellites in photoemission and tunneling spectroscopy, which present direct solid-state counterparts of high-energy collider experiments on the induced fission of composite particles.

Driving spin transition at interface: Role of adsorption configurations

NASA Astrophysics Data System (ADS)

Zhang, Yachao

2018-01-01

A clear insight into the electrical manipulation of molecular spins at interface is crucial to the design of molecule-based spintronic devices. Here we report on the electrically driven spin transition in manganocene physisorbed on a metallic surface in two different adsorption configurations predicted by ab initio techniques, including a Hubbard-U correction at the manganese site and accounting for the long-range van der Waals interactions. We show that the application of an electric field at the interface induces a high-spin to low-spin transition in the flat-lying manganocene, while it could hardly alter the high-spin ground state of the standing-up molecule. This phenomenon cannot be explained by either the molecule-metal charge transfer or the local electron correlation effects. We demonstrate a linear dependence of the intra-molecular spin-state splitting on the energy difference between crystal-field splitting and on-site Coulomb repulsion. After considering the molecule-surface binding energy shifts upon spin transition, we reproduce the obtained spin-state energetics. We find that the configuration-dependent responses of the spin-transition originate from the binding energy shifts instead of the variation of the local ligand field. Through these analyses, we obtain an intuitive understanding of the effects of molecule-surface contact on spin-crossover under electrical bias.

Rapid Mapping of Lithiation Dynamics in Transition Metal Oxide Particles with Operando X-ray Absorption Spectroscopy.

PubMed

Nowack, Lea; Grolimund, Daniel; Samson, Vallerie; Marone, Federica; Wood, Vanessa

2016-02-24

Since the commercialization of lithium ion batteries (LIBs), layered transition metal oxides (LiMO2, where M = Co, Mn, Ni, or mixtures thereof) have been materials of choice for LIB cathodes. During cycling, the transition metals change their oxidation states, an effect that can be tracked by detecting energy shifts in the X-ray absorption near edge structure (XANES) spectrum. X-ray absorption spectroscopy (XAS) can therefore be used to visualize and quantify lithiation kinetics in transition metal oxide cathodes; however, in-situ measurements are often constrained by temporal resolution and X-ray dose, necessitating compromises in the electrochemistry cycling conditions used or the materials examined. We report a combined approach to reduce measurement time and X-ray exposure for operando XAS studies of lithium ion batteries. A highly discretized energy resolution coupled with advanced post-processing enables rapid yet reliable identification of the oxidation state. A full-field microscopy setup provides sub-particle resolution over a large area of battery electrode, enabling the oxidation state within many transition metal oxide particles to be tracked simultaneously. Here, we apply this approach to gain insights into the lithiation kinetics of a commercial, mixed-metal oxide cathode material, nickel cobalt aluminium oxide (NCA), during (dis)charge and its degradation during overcharge.

Rapid Mapping of Lithiation Dynamics in Transition Metal Oxide Particles with Operando X-ray Absorption Spectroscopy

PubMed Central

Nowack, Lea; Grolimund, Daniel; Samson, Vallerie; Marone, Federica; Wood, Vanessa

2016-01-01

Since the commercialization of lithium ion batteries (LIBs), layered transition metal oxides (LiMO2, where M = Co, Mn, Ni, or mixtures thereof) have been materials of choice for LIB cathodes. During cycling, the transition metals change their oxidation states, an effect that can be tracked by detecting energy shifts in the X-ray absorption near edge structure (XANES) spectrum. X-ray absorption spectroscopy (XAS) can therefore be used to visualize and quantify lithiation kinetics in transition metal oxide cathodes; however, in-situ measurements are often constrained by temporal resolution and X-ray dose, necessitating compromises in the electrochemistry cycling conditions used or the materials examined. We report a combined approach to reduce measurement time and X-ray exposure for operando XAS studies of lithium ion batteries. A highly discretized energy resolution coupled with advanced post-processing enables rapid yet reliable identification of the oxidation state. A full-field microscopy setup provides sub-particle resolution over a large area of battery electrode, enabling the oxidation state within many transition metal oxide particles to be tracked simultaneously. Here, we apply this approach to gain insights into the lithiation kinetics of a commercial, mixed-metal oxide cathode material, nickel cobalt aluminium oxide (NCA), during (dis)charge and its degradation during overcharge. PMID:26908198

Rapid Mapping of Lithiation Dynamics in Transition Metal Oxide Particles with Operando X-ray Absorption Spectroscopy

NASA Astrophysics Data System (ADS)

Nowack, Lea; Grolimund, Daniel; Samson, Vallerie; Marone, Federica; Wood, Vanessa

2016-02-01

Since the commercialization of lithium ion batteries (LIBs), layered transition metal oxides (LiMO2, where M = Co, Mn, Ni, or mixtures thereof) have been materials of choice for LIB cathodes. During cycling, the transition metals change their oxidation states, an effect that can be tracked by detecting energy shifts in the X-ray absorption near edge structure (XANES) spectrum. X-ray absorption spectroscopy (XAS) can therefore be used to visualize and quantify lithiation kinetics in transition metal oxide cathodes; however, in-situ measurements are often constrained by temporal resolution and X-ray dose, necessitating compromises in the electrochemistry cycling conditions used or the materials examined. We report a combined approach to reduce measurement time and X-ray exposure for operando XAS studies of lithium ion batteries. A highly discretized energy resolution coupled with advanced post-processing enables rapid yet reliable identification of the oxidation state. A full-field microscopy setup provides sub-particle resolution over a large area of battery electrode, enabling the oxidation state within many transition metal oxide particles to be tracked simultaneously. Here, we apply this approach to gain insights into the lithiation kinetics of a commercial, mixed-metal oxide cathode material, nickel cobalt aluminium oxide (NCA), during (dis)charge and its degradation during overcharge.

Molecular structures and excited states of CpM(CO)(2) (Cp = eta(5)-C(5)H(5); M = Rh, Ir) and [Cl(2)Rh(CO)(2)](-). Theoretical evidence for a competitive charge transfer mechanism.

PubMed

Hu, Zhenming; Boyd, Russell J; Nakatsuji, Hiroshi

2002-03-20

Molecular structures and excited states of CpM(CO)(2) (Cp = eta(5)-C(5)H(5); M = Rh, Ir) and [Cl(2)Rh(CO)(2)](-) complexes have been investigated using the B3LYP and the symmetry-adapted cluster (SAC)/SAC-configuration interaction (SAC-CI) theoretical methods. All the dicarbonyl complexes have singlet ground electronic states with large singlet-triplet separations. Thermal dissociations of CO from the parent dicarbonyls are energetically unfavorable. CO thermal dissociation is an activation process for [Cl(2)Rh(CO)(2)](-) while it is a repulsive potential for CpM(CO)(2). The natures of the main excited states of CpM(CO)(2) and [Cl(2)Rh(CO)(2)](-) are found to be quite different. For [Cl(2)Rh(CO)(2)](-), all the strong transitions are identified to be metal to ligand CO charge transfer (MLCT) excitations. A significant feature of the excited states of CpM(CO)(2) is that both MLCT excitation and a ligand Cp to metal and CO charge transfer excitation are strongly mixed in the higher energy states with the latter having the largest oscillator strength. A competitive charge transfer excited state has therefore been identified theoretically for CpRh(CO)(2) and CpIr(CO)(2). The wavelength dependence of the quantum efficiencies for the photoreactions of CpM(CO)(2) reported by Lees et al. can be explained by the existence of two different types of excited states. The origin of the low quantum efficiencies for the C-H/S-H bond activations of CpM(CO)(2) can be attributed to the smaller proportion of the MLCT excitation in the higher energy states.

Nonadiabatic effects on the charge transfer rate constant: A numerical study of a simple model system

NASA Astrophysics Data System (ADS)

Shin, Seokmin; Metiu, Horia

1995-06-01

We use a minimal model to study the effects of the upper electronic states on the rate of a charge transfer reaction. The model consists of three ions and an electron, all strung on a line. The two ions at the ends of the structure are held fixed, but the middle ion and the electron are allowed to move in one dimension, along the line joining them. The system has two bound states, one in which the electron ties the movable ion to the fixed ion at the left, and the other in which the binding takes place to the fixed ion at the right. The transition between these bound states is a charge transfer reaction. We use the flux-flux correlation function theory to perform two calculations of the rate constant for this reaction. In one we obtain numerically the exact rate constant. In the other we calculate the exact rate constant for the case when the reaction proceeds exclusively on the ground adiabatic state. The difference between these calculations gives the magnitude of the nonadiabatic effects. We find that the nonadiabatic effects are fairly large even when the gap between the ground and the excited adiabatic state substantially exceeds the thermal energy. The rate in the nonadiabatic theory is always smaller than that of the adiabatic one. Both rate constants satisfy the Arrhenius formula. Their activation energies are very close but the nonadiabatic one is always higher. The nonadiabatic preexponential is smaller, due to the fact that the upper electronic state causes an early recrossing of the reactive flux. The description of this reaction in terms of two diabatic states, one for reactants and one for products, is not always adequate. In the limit when nonadiabaticity is small, we need to use a third diabatic state, in which the electron binds to the moving ion as the latter passes through the transition state; this is an atom transfer process. The reaction changes from an atom transfer to an electron transfer, as nonadiabaticity is increased.

Sodium dopants in helium clusters: Structure, equilibrium and submersion kinetics

DOE Office of Scientific and Technical Information (OSTI.GOV)

Calvo, F.

Alkali impurities bind to helium nanodroplets very differently depending on their size and charge state, large neutral or charged dopants being wetted by the droplet whereas small neutral impurities prefer to reside aside. Using various computational modeling tools such as quantum Monte Carlo and path-integral molecular dynamics simulations, we have revisited some aspects of the physical chemistry of helium droplets interacting with sodium impurities, including the onset of snowball formation in presence of many-body polarization forces, the transition from non-wetted to wetted behavior in larger sodium clusters, and the kinetics of submersion of small dopants after sudden ionization.

Spin-isospin excitation of 3He with three-proton final state

NASA Astrophysics Data System (ADS)

Ishikawa, Souichi

2018-01-01

Spin-isospin excitation of the {}^3He nucleus by a proton-induced charge exchange reaction, {}^3He(p,n)ppp, at forward neutron scattering angle is studied in a plane wave impulse approximation (PWIA). In PWIA, cross sections of the reaction are written in terms of proton-neutron scattering amplitudes and response functions of the transition from {}3He to the three-proton state by spin-isospin transition operators. The response functions are calculated with realistic nucleon-nucleon potential models using a Faddeev three-body method. Calculated cross sections agree with available experimental data in substance. Possible effects arising from the uncertainty of proton-neutron amplitudes and three-nucleon interactions in the three-proton system are examined.

Nuclear magnetic resonance in high magnetic field: Application to condensed matter physics

NASA Astrophysics Data System (ADS)

Berthier, Claude; Horvatić, Mladen; Julien, Marc-Henri; Mayaffre, Hadrien; Krämer, Steffen

2017-05-01

In this review, we describe the potentialities offered by the nuclear magnetic resonance (NMR) technique to explore at a microscopic level new quantum states of condensed matter induced by high magnetic fields. We focus on experiments realised in resistive (up to 34 T) or hybrid (up to 45 T) magnets, which open a large access to these quantum phase transitions. After an introduction on NMR observables, we consider several topics: quantum spin systems (spin-Peierls transition, spin ladders, spin nematic phases, magnetisation plateaus, and Bose-Einstein condensation of triplet excitations), the field-induced charge density wave (CDW) in high-Tc superconductors, and exotic superconductivity including the Fulde-Ferrel-Larkin-Ovchinnikov superconducting state and the field-induced superconductivity due to the Jaccarino-Peter mechanism.

Strong magneto-optical effects in A Cr2O4 (A =Fe,Co ) spinel oxides generated by tetrahedrally coordinated transition metal ions

NASA Astrophysics Data System (ADS)

Kocsis, V.; Bordács, S.; Deisenhofer, J.; Kiss, L. F.; Ohgushi, K.; Kaneko, Y.; Tokura, Y.; Kézsmárki, I.

2018-03-01

Magneto-optical effects have been investigated over the infrared visible spectral range in A Cr2O4 (A =Fe,Co ) spinel oxides with noncollinear spin orders in their ground states. We found large magneto-optical Kerr rotation and ellipticity at the on-site d -d transitions of the A2 + ions located within the charge gap. The magneto-optical Kerr rotation of ϑKerr≈12∘ observed in CoCr2O4 is unprecedentedly large among magnetic semiconductors and points toward the uniqueness of tetrahedrally coordinated Co2 + ions in generating strong magneto-optical response. Criteria of strong magneto-optical effects emerging at on-site d -d transitions of transition metal ions are discussed.

Large Fermi Surface of Heavy Electrons at the Border of Mott Insulating State in NiS 2

DOE PAGES

Friedemann, S.; Chang, H.; Gamża, M. B.; ...

2016-05-12

One early triumph of quantum physics is the explanation why some materials are metallic whereas others are insulating. While a treatment based on single electron states is correct for most materials this approach can fail spectacularly, when the electrostatic repulsion between electrons causes strong correlations. Not only can these favor new and subtle forms of matter, such as magnetism or superconductivity, they can even cause the electrons in a half-filled energy band to lock into position, producing a correlated, or Mott insulator. The transition into the Mott insulating state raises important fundamental questions. Foremost among these is the fate ofmore » the electronic Fermi surface and the associated charge carrier mass, as the Mott transition is approached. We report the first direct observation of the Fermi surface on the metallic side of a Mott insulating transition by high pressure quantum oscillatory measurements in NiS 2. We find our results point at a large Fermi surface consistent with Luttinger's theorem and a strongly enhanced quasiparticle effective mass. These two findings are in line with central tenets of the Brinkman-Rice picture of the correlated metal near the Mott insulating state and rule out alternative scenarios in which the carrier concentration vanishes continuously at the metal-insulator transition.« less

Spectroscopic fingerprints for charge localization in the organic semiconductor (DOEO)4[HgBr4]·TCE

NASA Astrophysics Data System (ADS)

Koplak, Oksana V.; Chernenkaya, Alisa; Medjanik, Katerina; Brambilla, Alberto; Gloskovskii, Andrei; Calloni, Alberto; Elmers, Hans-Joachim; Schönhense, Gerd; Ciccacci, Franco; Morgunov, Roman B.

2015-05-01

Changes of the electronic structure accompanied by charge localization and a transition to an antiferromagnetic ground state were observed in the organic semiconductor (DOEO)4[HgBr4]·TCE. Localization starts in the temperature region of about 150 K and the antiferromagnetic state occurs below 60 K. The magnetic moment of the crystal contains contributions of inclusions (droplets), and individual paramagnetic centers formed by localized holes and free charge carriers at 2 K. Two types of inclusions of 100-400 nm and 2-5 nm sizes were revealed by transmission electron microscopy. Studying the temperature- and angular dependence of electron spin resonance (ESR) spectra revealed fingerprints of antiferromagnetic contributions as well as paramagnetic resonance spectra of individual localized charge carriers. The results point on coexistence of antiferromagnetic long and short range order as evident from a second ESR line. Photoelectron spectroscopy in the VUV, soft and hard X-ray range shows temperature-dependent effects upon crossing the critical temperatures around 60 K and 150 K. The substantially different probing depths of soft and hard X-ray photoelectron spectroscopy yield information on the surface termination. The combined investigation using complementary methods at the same sample reveals the close relation of changes in the transport properties and in the energy distribution of electronic states.

Interacton-driven phenomena and Wigner transition in two-dimensional systems

NASA Astrophysics Data System (ADS)

Knighton, Talbot

The formation of a quantum Wigner Cyrstal (WC) is one of the most anticipated predictions of electron-electron interaction. This is expected to occur in zero magnetic field when the Coulomb energy EC dominates over the Fermi energy EF (at a ratio rs ≡ EC/ EF ˜ 37) for temperatures T << EF / kB. The extremely low T and ultra dilute carrier concentrations necessary to meet these requirements are difficult to achieve. Alternatively, a perpendicular magnetic B-field can be used to quench the kinetic energy. As B increases, various energies compete to produce the ground state. High purity systems with large interaction rs >1 tend to exhibit reentrant insulating phases (RIP) between the integer and fractional Hall states. These are suspected to be a form of WC, but the evidence is not yet conclusive. We use transport measurements to identify a conduction threshold in the RIP at filling factor nu = 0.37 (close to the 1/3 state) that is several orders of magnitude larger than the pinning observed in many other systems. We analyze the temperature and electric E-field dependence of this insulating phase and find them to be consistent with a second-order phase transition to WC. The measurements are performed on dilute holes p = 4 x 1010 cm-2 of mobility mu = 1/perho ˜ 2.5 x 106 cm 2/Vs in 20 nm GaAs/AlGaAs quantum square wells. We also discuss various other projects related to the study of topological states and strongly interacting charges: direct testing of the bulk conduction in a developing quantum Hall state using a corbino-disk-like geometry (or "anti-Hall bar"); preliminary results for ultra dilute charges in undoped heterojunction insulated gated field effect transistors; quantum capacitance measurement of the density of states across the vanadium dioxide metal insulator transition; progress towards a scanning capacitance measurement using the tip of an atomic force microscope; and graphene devices for optical detection.

Epitaxial strain effect on the physical properties of layered ruthenate and iridate thin films

NASA Astrophysics Data System (ADS)

Miao, Ludi

Transition metal oxides have attracted widespread attention due to their broad range of fascinating exotic phenomena such as multiferroicity, superconductivity, colossal magnetoresistance and metal-to-insulator transition. Due to the interplay between spin, charge, lattice and orbital degrees of freedom of strongly correlated d electrons, these physical properties are extremely sensitive to the external perturbations such as magnetic field, charge carrier doping and pressure, which provide a unique chance in search for novel exotic quantum states. Ruthenate systems are a typical strongly correlated system, with rich ordered states and their properties are extremely sensitive to external stimuli. Recently, the experimental observation of spin-orbit coupling induced Mott insulator in Sr2IrO4 as well as the theoretical prediction of topological insulating state in other iridates, have attracted tremendous interest in the physics of strong correlation and spin-orbit coupling in 4d/5d compounds. We observe an itinerant ferromagnetic ground state of Ca2 RuO4 film in stark contrast to the Mott-insulating state in bulk Ca2RuO4. We have also established the epitaxial strain effect on the transport and magnetic properties for the (Ca,Sr) 2RuO4 thin films. For Sr2IrO4 thin films, we will show that the Jeff = 1/2 moment orientation can be modulated by epitaxial strain. In addition, we discovered novel Ba 7Ir3O13+x thin films which exhibit colossal permittivity.

47 CFR 51.909 - Transition of rate-of-return carrier access charges.

Code of Federal Regulations, 2012 CFR

2012-10-01

... charges. 51.909 Section 51.909 Telecommunication FEDERAL COMMUNICATIONS COMMISSION (CONTINUED) COMMON CARRIER SERVICES (CONTINUED) INTERCONNECTION Transitional Access Service Pricing § 51.909 Transition of...; and (2) Cap, in accordance with § 51.505(b)(2), the rates for rate all elements in its intrastate...

47 CFR 51.909 - Transition of rate-of-return carrier access charges.

Code of Federal Regulations, 2013 CFR

2013-10-01

... charges. 51.909 Section 51.909 Telecommunication FEDERAL COMMUNICATIONS COMMISSION (CONTINUED) COMMON CARRIER SERVICES (CONTINUED) INTERCONNECTION Transitional Access Service Pricing § 51.909 Transition of...; and (2) Cap, in accordance with § 51.505(b)(2), the rates for rate all elements in its intrastate...

47 CFR 51.909 - Transition of rate-of-return carrier access charges.

Code of Federal Regulations, 2014 CFR

2014-10-01

... charges. 51.909 Section 51.909 Telecommunication FEDERAL COMMUNICATIONS COMMISSION (CONTINUED) COMMON CARRIER SERVICES (CONTINUED) INTERCONNECTION Transitional Access Service Pricing § 51.909 Transition of...; and (2) Cap, in accordance with § 51.505(b)(2), the rates for rate all elements in its intrastate...

High field charge order across the phase diagram of YBa2Cu3Oy

NASA Astrophysics Data System (ADS)

Laliberté, Francis; Frachet, Mehdi; Benhabib, Siham; Borgnic, Benjamin; Loew, Toshinao; Porras, Juan; Le Tacon, Mathieu; Keimer, Bernhard; Wiedmann, Steffen; Proust, Cyril; LeBoeuf, David

2018-03-01

In hole-doped cuprates there is now compelling evidence that inside the pseudogap phase, charge order breaks translational symmetry. In YBa2Cu3Oy charge order emerges in two steps: a 2D order found at zero field and at high temperature inside the pseudogap phase, and a 3D order that is superimposed below the superconducting transition Tc when superconductivity is weakened by a magnetic field. Several issues still need to be addressed such as the effect of disorder, the relationship between those charge orders and their respective impact on the Fermi surface. Here, we report high magnetic field sound velocity measurements of the 3D charge order in underdoped YBa2Cu3Oy in a large doping range. We found that the 3D charge order exists over the same doping range as its 2D counterpart, indicating an intimate connection between the two distinct orders. Moreover, our data suggest that 3D charge order has only a limited impact on low-lying electronic states of YBa2Cu3Oy.

Critical Role of the Exchange Interaction for the Electronic Structure and Charge-Density-Wave Formation in TiSe2

NASA Astrophysics Data System (ADS)

Hellgren, Maria; Baima, Jacopo; Bianco, Raffaello; Calandra, Matteo; Mauri, Francesco; Wirtz, Ludger

2017-10-01

We show that the inclusion of screened exchange via hybrid functionals provides a unified description of the electronic and vibrational properties of TiSe2 . In contrast to local approximations in density functional theory, the explicit inclusion of exact, nonlocal exchange captures the effects of the electron-electron interaction needed to both separate the Ti -d states from the Se -p states and stabilize the charge-density-wave (CDW) (or low-T ) phase through the formation of a p -d hybridized state. We further show that this leads to an enhanced electron-phonon coupling that can drive the transition even if a small gap opens in the high-T phase. Finally, we demonstrate that the hybrid functionals can generate a CDW phase where the electronic bands, the geometry, and the phonon frequencies are in agreement with experiments.

First-Principle Characterization for Singlet Fission Couplings.

PubMed

Yang, Chou-Hsun; Hsu, Chao-Ping

2015-05-21

The electronic coupling for singlet fission, an important parameter for determining the rate, has been found to be too small unless charge-transfer (CT) components were introduced in the diabatic states, mostly through perturbation or a model Hamiltonian. In the present work, the fragment spin difference (FSD) scheme was generalized to calculate the singlet fission coupling. The largest coupling strength obtained was 14.8 meV for two pentacenes in a crystal structure, or 33.7 meV for a transition-state structure, which yielded a singlet fission lifetime of 239 or 37 fs, generally consistent with experimental results (80 fs). Test results with other polyacene molecules are similar. We found that the charge on one fragment in the S1 diabatic state correlates well with FSD coupling, indicating the importance of the CT component. The FSD approach is a useful first-principle method for singlet fission coupling, without the need to include the CT component explicitly.

Revisiting Cu 63 NMR evidence for charge order in superconducting La 1.885 Sr 0.115 CuO 4

DOE Office of Scientific and Technical Information (OSTI.GOV)

Imai, T.; Takahashi, S. K.; Arsenault, A.

Here, the presence of charge and spin stripe order in the La 2CuO 4-based family of superconductors continues to lead to new insight on the unusual ground-state properties of high- T c cuprates. Soon after the discovery of charge stripe order at T charge≃65 K in Nd 3+ co-doped La 1.48Nd 0.4Sr 0.12CuO 4( Tc≃6 K), Hunt et al. demonstrated that La 1.48Nd 0.4Sr 0.12CuO 4 and superconducting La 2–xSr xCuO 4 with x~1/8( Tc≃30 K) share nearly identical NMR anomalies near Tcharge of the former. Their inevitable conclusion that La 1.885Sr 0.115CuO 4 also undergoes charge order at amore » comparable temperature became controversial, because diffraction measurements at the time were unable to detect Bragg peaks associated with charge order. Recent advances in x-ray diffraction techniques finally led to definitive confirmations of the charge order Bragg peaks in La 1.885Sr 0.115CuO 4 with an onset at as high as Tcharge≃80 K. Meanwhile, improved instrumental technology has enabled routine NMR measurements that were not feasible two decades ago. Motivated by these new developments, we revisit the charge order transition of a La 1.885Sr 0.115CuO 4 single crystal based on 63Cu NMR techniques. We demonstrate that 63Cu NMR properties of the nuclear spin I z=–1/2 to +1/2 central transition below Tcharge exhibit unprecedentedly strong dependence on the measurement time scale set by the separation time τ between the 90° and 180° radio-frequency pulses; a new kind of anomalous, very broad winglike 63Cu NMR signals gradually emerge below Tcharge only for extremely short τ≲4μs, while the spectral weight I Normal of the normal NMR signals is progressively wiped out. The NMR linewidth and relaxation rates depend strongly on τ below Tcharge, and their enhancement in the charge ordered state indicates that charge order turns on strong but inhomogeneous growth of Cu spin-spin correlations.« less

Revisiting Cu 63 NMR evidence for charge order in superconducting La 1.885 Sr 0.115 CuO 4

DOE PAGES

Imai, T.; Takahashi, S. K.; Arsenault, A.; ...

2017-12-26

Here, the presence of charge and spin stripe order in the La 2CuO 4-based family of superconductors continues to lead to new insight on the unusual ground-state properties of high- T c cuprates. Soon after the discovery of charge stripe order at T charge≃65 K in Nd 3+ co-doped La 1.48Nd 0.4Sr 0.12CuO 4( Tc≃6 K), Hunt et al. demonstrated that La 1.48Nd 0.4Sr 0.12CuO 4 and superconducting La 2–xSr xCuO 4 with x~1/8( Tc≃30 K) share nearly identical NMR anomalies near Tcharge of the former. Their inevitable conclusion that La 1.885Sr 0.115CuO 4 also undergoes charge order at amore » comparable temperature became controversial, because diffraction measurements at the time were unable to detect Bragg peaks associated with charge order. Recent advances in x-ray diffraction techniques finally led to definitive confirmations of the charge order Bragg peaks in La 1.885Sr 0.115CuO 4 with an onset at as high as Tcharge≃80 K. Meanwhile, improved instrumental technology has enabled routine NMR measurements that were not feasible two decades ago. Motivated by these new developments, we revisit the charge order transition of a La 1.885Sr 0.115CuO 4 single crystal based on 63Cu NMR techniques. We demonstrate that 63Cu NMR properties of the nuclear spin I z=–1/2 to +1/2 central transition below Tcharge exhibit unprecedentedly strong dependence on the measurement time scale set by the separation time τ between the 90° and 180° radio-frequency pulses; a new kind of anomalous, very broad winglike 63Cu NMR signals gradually emerge below Tcharge only for extremely short τ≲4μs, while the spectral weight I Normal of the normal NMR signals is progressively wiped out. The NMR linewidth and relaxation rates depend strongly on τ below Tcharge, and their enhancement in the charge ordered state indicates that charge order turns on strong but inhomogeneous growth of Cu spin-spin correlations.« less

Revisiting 63Cu NMR evidence for charge order in superconducting La1.885Sr0.115CuO4

NASA Astrophysics Data System (ADS)

Imai, T.; Takahashi, S. K.; Arsenault, A.; Acton, A. W.; Lee, D.; He, W.; Lee, Y. S.; Fujita, M.

2017-12-01

The presence of charge and spin stripe order in the La2CuO4 -based family of superconductors continues to lead to new insight on the unusual ground-state properties of high-Tc cuprates. Soon after the discovery of charge stripe order at Tcharge≃65 K in Nd3 + co-doped La1.48Nd0.4Sr0.12CuO4 (Tc≃6 K) [Tranquada et al., Nature (London) 375, 561 (1995), 10.1038/375561a0], Hunt et al. demonstrated that La1.48Nd0.4Sr0.12CuO4 and superconducting La2 -xSrxCuO4 with x ˜1 /8 (Tc≃30 K) share nearly identical NMR anomalies near Tcharge of the former [Phys. Rev. Lett. 82, 4300 (1999), 10.1103/PhysRevLett.82.4300]. Their inevitable conclusion that La1.885Sr0.115CuO4 also undergoes charge order at a comparable temperature became controversial, because diffraction measurements at the time were unable to detect Bragg peaks associated with charge order. Recent advances in x-ray diffraction techniques finally led to definitive confirmations of the charge order Bragg peaks in La1.885Sr0.115CuO4 with an onset at as high as Tcharge≃80 K. Meanwhile, improved instrumental technology has enabled routine NMR measurements that were not feasible two decades ago. Motivated by these new developments, we revisit the charge order transition of a La1.885Sr0.115CuO4 single crystal based on 63Cu NMR techniques. We demonstrate that 63Cu NMR properties of the nuclear spin Iz=-1/2 to +1/2 central transition below Tcharge exhibit unprecedentedly strong dependence on the measurement time scale set by the separation time τ between the 90∘ and 180∘ radio-frequency pulses; a new kind of anomalous, very broad winglike 63Cu NMR signals gradually emerge below Tcharge only for extremely short τ ≲4 μ s , while the spectral weight INormal of the normal NMR signals is progressively wiped out. The NMR linewidth and relaxation rates depend strongly on τ below Tcharge, and their enhancement in the charge ordered state indicates that charge order turns on strong but inhomogeneous growth of Cu spin-spin correlations.

The perspectives of femtosecond imaging and spectroscopy of complex materials using electrons

NASA Astrophysics Data System (ADS)

Ruan, Chong-Yu; Duxbury, Phiilp M.; Berz, Martin

2014-09-01

The coexistence of various electronic and structural phases that are close in free-energy is a hallmark in strongly correlated electron systems with emergent properties, such as metal-insulator transition, colossal magnetoresistance, and high-temperature superconductivity. The cooperative phase transitions from one functional state to another can involve entanglements between the electronically and structurally ordered states, hence deciphering the fundamental mechanisms is generally difficult and remains very active in condensed matter physics and functional materials research. We outline the recent ultrafast characterizations of 2D charge-density wave materials, including the nonequilibrium electron dynamics unveiled by ultrafast optical spectroscopy-based techniques sensitive to the electronic order parameter. We also describe the most recent findings from ultrafast electron crystallography, which provide structural aspects to correlate lattice dynamics with electronic evolutions to address the two sides of a coin in the ultrafast switching of a cooperative state. Combining these results brings forth new perspectives and a fuller picture in understanding lightmatter interactions and various switching mechanisms in cooperative systems with many potential applications. We also discuss the prospects of implementing new ultrafast electron imaging as a local probe incorporated with femtosecond select-area diffraction, imaging and spectroscopy to provide a full scope of resolution to tackle the more challenging complex phase transitions on the femtosecond-nanometer scale all at once based on a recent understanding of the spacespace- charge-driven emittance limitation on the ultimate performance of these devices. The projection shows promising parameter space for conducting ultrafast electron micordiffraction at close to single-shot level, which is supported by the latest experimental characterization of such a system.

Nonadiabatic excited-state molecular dynamics modeling of photoinduced dynamics in conjugated molecules.

PubMed

Nelson, Tammie; Fernandez-Alberti, Sebastian; Chernyak, Vladimir; Roitberg, Adrian E; Tretiak, Sergei

2011-05-12

Nonadiabatic dynamics generally defines the entire evolution of electronic excitations in optically active molecular materials. It is commonly associated with a number of fundamental and complex processes such as intraband relaxation, energy transfer, and light harvesting influenced by the spatial evolution of excitations and transformation of photoexcitation energy into electrical energy via charge separation (e.g., charge injection at interfaces). To treat ultrafast excited-state dynamics and exciton/charge transport we have developed a nonadiabatic excited-state molecular dynamics (NA-ESMD) framework incorporating quantum transitions. Our calculations rely on the use of the Collective Electronic Oscillator (CEO) package accounting for many-body effects and actual potential energy surfaces of the excited states combined with Tully's fewest switches algorithm for surface hopping for probing nonadiabatic processes. This method is applied to model the photoinduced dynamics of distyrylbenzene (a small oligomer of polyphenylene vinylene, PPV). Our analysis shows intricate details of photoinduced vibronic relaxation and identifies specific slow and fast nuclear motions that are strongly coupled to the electronic degrees of freedom, namely, torsion and bond length alternation, respectively. Nonadiabatic relaxation of the highly excited mA(g) state is predicted to occur on a femtosecond time scale at room temperature and on a picosecond time scale at low temperature.

Radiative loss and charge exchange in low energy Na - Ca+ collisions

NASA Astrophysics Data System (ADS)

McLaughlin, B. M.; McAlpine, K.; McCann, J. F.; Pattillo, R.; Stancil, P. C.; Forrey, R. C.; Babb, J. F.

2016-05-01

Experiments on radiative loss and capture are currently being performed at the University of Connecticut. In response to this experimental effort we have performed detailed calculations for a variety of loss and capture processes. Several low lying states of the NaCa+ cation are used with the accurate potentials energy curves, transition dipole moments and non-adiabatic coupling matrix elements between the states, obtained at the MRCI+Q level of approximation with the MOLPRO suite of quantum chemistry codes. Cross sections and rate coefficients are calculated for radiative charge transfer (RCX), radiative association (RA) and charge exchange in a fully quantum molecular close-coupling (MOCC) approximation at the higher energies. We use a variety of approaches, the optical potential method, semi-classical and MOCC methods to compare and contrast approximations. In addition a kinetic theory recently applied to SiO is utilized which illustrates the dramatic impact resonances have on the radiative association rates. Supported by NASA and HLRS at Stuttgart University.

Possibility of transforming the electronic structure of one species of graphene adatoms into that of another by application of gate voltage: First-principles calculations

NASA Astrophysics Data System (ADS)

Chan, Kevin T.; Lee, Hoonkyung; Cohen, Marvin L.

2011-10-01

Graphene provides many advantages for controlling the electronic structure of adatoms and other adsorbates via gating. Using the projected density of states and charge density obtained from first-principles density-functional periodic supercell calculations, we investigate the possibility of performing “alchemy” of adatoms on graphene, i.e., transforming the electronic structure of one species of adatom into that of another species by application of a gate voltage. Gating is modeled as a change in the number of electrons in the unit cell, with the inclusion of a compensating uniform background charge. Within this model and the generalized gradient approximation to the exchange-correlation functional, we find that such transformations are possible for K, Ca, and several transition-metal adatoms. Gate control of the occupation of the p states of In on graphene is also investigated. The validity of the supercell approximation with uniform compensating charge and the model for exchange and correlation is also discussed.

Emergent order in the kagome Ising magnet Dy3Mg2Sb3O14

PubMed Central

Paddison, Joseph A. M.; Ong, Harapan S.; Hamp, James O.; Mukherjee, Paromita; Bai, Xiaojian; Tucker, Matthew G.; Butch, Nicholas P.; Castelnovo, Claudio; Mourigal, Martin; Dutton, S. E.

2016-01-01

The Ising model—in which degrees of freedom (spins) are binary valued (up/down)—is a cornerstone of statistical physics that shows rich behaviour when spins occupy a highly frustrated lattice such as kagome. Here we show that the layered Ising magnet Dy3Mg2Sb3O14 hosts an emergent order predicted theoretically for individual kagome layers of in-plane Ising spins. Neutron-scattering and bulk thermomagnetic measurements reveal a phase transition at ∼0.3 K from a disordered spin-ice-like regime to an emergent charge ordered state, in which emergent magnetic charge degrees of freedom exhibit three-dimensional order while spins remain partially disordered. Monte Carlo simulations show that an interplay of inter-layer interactions, spin canting and chemical disorder stabilizes this state. Our results establish Dy3Mg2Sb3O14 as a tuneable system to study interacting emergent charges arising from kagome Ising frustration. PMID:27996012

Digital modulation of the nickel valence state in a cuprate-nickelate heterostructure

NASA Astrophysics Data System (ADS)

Wrobel, F.; Geisler, B.; Wang, Y.; Christiani, G.; Logvenov, G.; Bluschke, M.; Schierle, E.; van Aken, P. A.; Keimer, B.; Pentcheva, R.; Benckiser, E.

2018-03-01

Layer-by-layer oxide molecular-beam epitaxy has been used to synthesize cuprate-nickelate multilayer structures of composition (La2CuO4)m/LaO /(LaNiO3)n . In a combined experimental and theoretical study, we show that these structures allow a clean separation of dopant and doped layers. Specifically, the LaO layer separating cuprate and nickelate blocks provides an additional charge that, according to density-functional theory calculations, is predominantly accommodated in the interfacial nickelate layers. This is reflected in an elongation of bond distances and changes in valence state, as observed by scanning transmission electron microscopy and x-ray absorption spectroscopy. Moreover, the predicted charge disproportionation in the nickelate interface layers leads to a metal-to-insulator transition when the thickness is reduced to n =2 , as observed in electrical transport measurements. The results exemplify the perspectives of charge transfer in metal-oxide multilayers to induce doping without introducing chemical and structural disorder.

The human peripheral subunit-binding domain folds rapidly while overcoming repulsive Coulomb forces

PubMed Central

Arbely, Eyal; Neuweiler, Hannes; Sharpe, Timothy D; Johnson, Christopher M; Fersht, Alan R

2010-01-01

Peripheral subunit binding domains (PSBDs) are integral parts of large multienzyme complexes involved in carbohydrate metabolism. PSBDs facilitate shuttling of prosthetic groups between different catalytic subunits. Their protein surface is characterized by a high density of positive charges required for binding to subunits within the complex. Here, we investigated folding thermodynamics and kinetics of the human PSBD (HSBD) using circular dichroism and tryptophan fluorescence experiments. HSBD was only marginally stable under physiological solvent conditions but folded within microseconds via a barrier-limited apparent two-state transition, analogous to its bacterial homologues. The high positive surface-charge density of HSBD leads to repulsive Coulomb forces that modulate protein stability and folding kinetics, and appear to even induce native-state movement. The electrostatic strain was alleviated at high solution-ionic-strength by Debye-Hückel screening. Differences in ionic-strength dependent characteristics among PSBD homologues could be explained by differences in their surface charge distributions. The findings highlight the trade-off between protein function and stability during protein evolution. PMID:20662005

Photonic crystals possessing multiple Weyl points and the experimental observation of robust surface states

PubMed Central

Chen, Wen-Jie; Xiao, Meng; Chan, C. T.

2016-01-01

Weyl points, as monopoles of Berry curvature in momentum space, have captured much attention recently in various branches of physics. Realizing topological materials that exhibit such nodal points is challenging and indeed, Weyl points have been found experimentally in transition metal arsenide and phosphide and gyroid photonic crystal whose structure is complex. If realizing even the simplest type of single Weyl nodes with a topological charge of 1 is difficult, then making a real crystal carrying higher topological charges may seem more challenging. Here we design, and fabricate using planar fabrication technology, a photonic crystal possessing single Weyl points (including type-II nodes) and multiple Weyl points with topological charges of 2 and 3. We characterize this photonic crystal and find nontrivial 2D bulk band gaps for a fixed kz and the associated surface modes. The robustness of these surface states against kz-preserving scattering is experimentally observed for the first time. PMID:27703140

Systematics of nuclear ground state properties in 78-100Sr by laser spectroscopy

NASA Astrophysics Data System (ADS)

Buchinger, F.; Ramsay, E. B.; Arnold, E.; Neu, W.; Neugart, R.; Wendt, K.; Silverans, R. E.; Lievens, P.; Vermeeren, L.; Berdichevsky, D.; Fleming, R.; Sprung, D. W. L.; Ulm, G.

1990-06-01

Hyperfine structures and isotope shifts of strontium isotopes with A=78 to A=98 and A=100 were measured by collinear fast beam laser spectroscopy. Nuclear spins, moments and changes in mean square charge radii are extracted from the data. The spins and moments of most of the odd isotopes are explained in the framework of the single particle model. The changes in mean square charge radii are compared with predictions of the droplet model and of Hartree-Fock-plus-BCS calculations. For the isotopes in the transitional regions below and above the N=50 shell closure, the inclusion of quadrupole zero point motion in the Droplet model describes part of the observed shell effect. An additional change in the surface region of the charge distribution at spherical shape is suggested by the microscopic model. Furthermore, we propose that the isotopes 78Sr and 80Sr may show an unusual shape-sharing structure, with different mean deformations in the ground and 2+1 excited states.

Coherent Electron Transfer at the Ag / Graphite Heterojunction Interface

NASA Astrophysics Data System (ADS)

Tan, Shijing; Dai, Yanan; Zhang, Shengmin; Liu, Liming; Zhao, Jin; Petek, Hrvoje

2018-03-01

Charge transfer in transduction of light to electrical or chemical energy at heterojunctions of metals with semiconductors or semimetals is believed to occur by photogenerated hot electrons in metal undergoing incoherent internal photoemission through the heterojunction interface. Charge transfer, however, can also occur coherently by dipole coupling of electronic bands at the heterojunction interface. Microscopic physical insights into how transfer occurs can be elucidated by following the coherent polarization of the donor and acceptor states on the time scale of electronic dephasing. By time-resolved multiphoton photoemission spectroscopy (MPP), we investigate the coherent electron transfer from an interface state that forms upon chemisorption of Ag nanoclusters onto graphite to a σ symmetry interlayer band of graphite. Multidimensional MPP spectroscopy reveals a resonant two-photon transition, which dephases within 10 fs completing the coherent transfer.

Criticality in a non-equilibrium, driven system: charged colloidal rods (fd-viruses) in electric fields.

PubMed

Kang, K; Dhont, J K G

2009-11-01

Experiments on suspensions of charged colloidal rods (fd-virus particles) in external electric fields are performed, which show that a non-equilibrium critical point can be identified. Several transition lines of field-induced phases and states meet at this point and it is shown that there is a length- and time-scale which diverge at the non-equilibrium critical point. The off-critical and critical behavior is characterized, with both power law and logarithmic divergencies. These experiments show that analogous features of the classical, critical divergence of correlation lengths and relaxation times in equilibrium systems are also exhibited by driven systems that are far out of equilibrium, related to phases/states that do not exist in the absence of the external field.

Control of the Speed of a Light-Induced Spin Transition through Mesoscale Core-Shell Architecture.

PubMed

Felts, Ashley C; Slimani, Ahmed; Cain, John M; Andrus, Matthew J; Ahir, Akhil R; Abboud, Khalil A; Meisel, Mark W; Boukheddaden, Kamel; Talham, Daniel R

2018-05-02

The rate of the light-induced spin transition in a coordination polymer network solid dramatically increases when included as the core in mesoscale core-shell particles. A series of photomagnetic coordination polymer core-shell heterostructures, based on the light-switchable Rb a Co b [Fe(CN) 6 ] c · mH 2 O (RbCoFe-PBA) as core with the isostructural K j Ni k [Cr(CN) 6 ] l · nH 2 O (KNiCr-PBA) as shell, are studied using temperature-dependent powder X-ray diffraction and SQUID magnetometry. The core RbCoFe-PBA exhibits a charge transfer-induced spin transition (CTIST), which can be thermally and optically induced. When coupled to the shell, the rate of the optically induced transition from low spin to high spin increases. Isothermal relaxation from the optically induced high spin state of the core back to the low spin state and activation energies associated with the transition between these states were measured. The presence of a shell decreases the activation energy, which is associated with the elastic properties of the core. Numerical simulations using an electro-elastic model for the spin transition in core-shell particles supports the findings, demonstrating how coupling of the core to the shell changes the elastic properties of the system. The ability to tune the rate of optically induced magnetic and structural phase transitions through control of mesoscale architecture presents a new approach to the development of photoswitchable materials with tailored properties.

Coexistence of charge order and antiferromagnetism in (TMTTF)2SbF6: NMR study

NASA Astrophysics Data System (ADS)

Nomura, K.; Yamamoto, M.; Matsunaga, N.; Hirose, S.; Shimohara, N.; Satoh, T.; Isome, T.; Liu, Y.; Kawamoto, A.

2015-03-01

The electronic state of (TMTTF)2SbF6 was investigated by the 1H and 13C NMR measurements. The temperature dependence of T1-1 in 1H NMR shows a sharp peak associated with the antiferromagnetic transition at TAF=6 K. The temperature dependence of T1-1 is described by the power law T2.4 below TAF. This suggests the nodal gapless spin wave excitation in antiferromagnetic phase. In 13C NMR, two sharp peaks at high temperature region, associated with the inner and the outer carbon sites in TMTTF dimer, split into four peaks below 150 K. It indicates that the charge disproportionation occurs. The degree of charge disproportionation Δρ is estimated as (0.25±0.09)e from the chemical shift difference. This value of Δρ is consistent with that obtained from the infrared spectroscopy. In the antiferromagnetic state (AFI), the observed line shape is well fitted by eight Lorentzian peaks. This suggests that the charge order with the same degree still remains in the AF state. From the line assignment, the AF staggered spin amplitude is obtained as 0.70 μB and 0.24 μB at the charge rich and the poor sites, respectively. These values corresponding to almost 1 μB per dimer are quite different from 0.11 μB of another AF (AFII) state in (TMTTF)2Br with effective higher pressure. As a result, it is understood that the antiferromagnetic staggered spin order is stabilized on the CO state in the AFI phase of (TMTTF)2SbF6.

Probing the catalytic roles of n2-site glutamate residues in Escherichia coli glutamine synthetase by mutagenesis.

PubMed Central

Witmer, M. R.; Palmieri-Young, D.; Villafranca, J. J.

1994-01-01

The contribution of metal ion ligand type and charge to catalysis and regulation at the lower affinity metal ion site (n2 site) of Escherichia coli glutamine synthetase (GS) was tested by mutagenesis and kinetic analysis. The 2 glutamate residues at the n2 site, E129 and E357, were changed to E129D, E129H, E357H, E357Q, and E357D, representing conservative and nonconservative alterations. Unadenylylated and fully adenylylated enzyme forms were studied. The Mn(2+)-KD values, UV-cis and fluorescence emission properties were similar for all mutants versus WTGS, except E129H. For kinetic determinations with both Mn2+ and Mg2+, nonconservative mutants (E357H, E129H, E357Q) showed lower biosynthetic activities than conservative mutants (E129D, E357D). Relative to WTGS, all the unadenylylated Mn(2+)-activated enzymes showed reduced kcat/Km values for ATP (> 7-fold) and for glutamate (> 10-fold). Of the unadenylylated Mg(2+)-activated enzymes, only E129D showed kinetic parameters competitive with WTGS, and adenylylated E129D was a 20-fold better catalyst than WTGS. We propose the n2-site metal ion activates ADP for departure in the phosphorylation of glutamate by ATP to generate gamma-glutamyl phosphate. Alteration of the charge density at this metal ion alters the transition-state energy for phosphoryl group transfer and may affect ATP binding and/or ADP release. Thus, the steady-state kinetic data suggest that modifying the charge density increases the transition-state energies for chemical steps. Importantly, the data demonstrate that each ligand position has a specialized spatial environment and the charge of the ligand modulates the catalytic steps occurring at the metal ion. The data are discussed in the context of the known X-ray structures of GS. PMID:7849593

Computer simulations of the solvatochromism of betaine-30

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mente, S.R.; Maroncelli, M.

1999-09-09

Monte Carlo simulations of the pyridinium N-phenolate dye betaine-30 in 12 solvents (20 solvent representations) were performed in order to explore the molecular basis of the E{sub T}(30) scale of solvent polarity. Ab initio (HF/6-31G{sup *}) and semiempirical (AM1 and INDO/S) electronic structure calculations were used to determine the geometry and charge distribution of betaine-30 in its S{sub 0} and S{sub 1} states. The solvent effect on the betaine absorption spectrum was assumed to derive from electrostatic interactions between the effective charge distributions of solvent molecules and the charge shift brought about by the S{sub 0} {r_arrow} S{sub 1} transition.more » Two models for this charge shift, one obtained from INDO/S calculations and the other an idealized two-site model, were used for the spectral calculations. Good agreement between simulated and observed {Delta}E{sub T} shifts (E{sub T}(30) values measured relative to the nonpolar standard tetramethylsilane) was found for both charge-shift models. In water and other hydroxylic solvents, the O atom of the betaine solute was observed to form moderately strong hydrogen bonds to between one and two solvent molecules. The contribution of these specifically coordinated molecules to the {Delta}E{sub T} shift was found to be large, (30--60%) and comparable to experimental estimates. Additional simulations of acetonitrile and methanol in equilibrium with the S{sub 1} state of betaine-30 were used to determine reorganization energies in these solvents and to decide the extent to which the solvent response to the S{sub 0} {leftrightarrow} S{sub 1} transition conforms to linear response predictions. In both solvents, the spectral distributions observed in the S{sub 0} state simulations were {approximately} 15% narrower than those in the S{sub 1} simulations, indicating only a relatively small departure from linear behavior. Reorganization energies were also estimated for a number of other solvents and compared to values reported in previous experimental and theoretical studies.« less

Superconducting and charge density wave transition in single crystalline LaPt2Si2

NASA Astrophysics Data System (ADS)

Gupta, Ritu; Dhar, S. K.; Thamizhavel, A.; Rajeev, K. P.; Hossain, Z.

2017-06-01

We present results of our comprehensive studies on single crystalline LaPt2Si2. Pronounced anomaly in electrical resistivity and heat capacity confirms the bulk nature of superconductivity (SC) and charge density wave (CDW) transition in the single crystals. While the charge density wave transition temperature is lower, the superconducting transition temperature is higher in single crystal compared to the polycrystalline sample. This result confirms the competing nature of CDW and SC. Another important finding is the anomalous temperature dependence of upper critical field H C2(T). We also report the anisotropy in the transport and magnetic measurements of the single crystal.

Solvable four-state Landau-Zener model of two interacting qubits with path interference

DOE PAGES

Sinitsyn, Nikolai A.

2015-11-30

In this paper, I identify a nontrivial four-state Landau-Zener model for which transition probabilities between any pair of diabatic states can be determined analytically and exactly. The model describes an experimentally accessible system of two interacting qubits, such as a localized state in a Dirac material with both valley and spin degrees of freedom or a singly charged quantum dot (QD) molecule with spin orbit coupling. Application of the linearly time-dependent magnetic field induces a sequence of quantum level crossings with possibility of interference of different trajectories in a semiclassical picture. I argue that this system satisfies the criteria ofmore » integrability in the multistate Landau-Zener theory, which allows one to derive explicit exact analytical expressions for the transition probability matrix. Finally, I also argue that this model is likely a special case of a larger class of solvable systems, and present a six-state generalization as an example.« less

Polarization effects on quantum levels in InN/GaN quantum wells.

PubMed

Lin, Wei; Li, Shuping; Kang, Junyong

2009-12-02

Polarization effects on quantum states in InN/GaN quantum wells have been investigated by means of ab initio calculation and spectroscopic ellipsometry. Through the position-dependent partial densities of states, our results show that the polarization modified by the strain with different well thickness leads to an asymmetry band bending of the quantum well. The quantum levels are identified via the band structures and their square wave function distributions are analyzed by the partial charge densities. Further theoretical and experimental comparison of the imaginary part of the dielectric function show that the overall transition probability increases under larger polarization fields, which can be attributable to the fact that the excited quantum states of 2h have a greater overlap with 1e states and enhance other hole quantum states in the well by a hybridization. These results would provide a new approach to improve the transition probability and light emission by enhancing the polarization fields in a proper way.

A Philosophical Case for OPCON Transition on the Korean Peninsula

DTIC Science & Technology

2011-01-01

Korean state was the fault of external meddling and the first step toward civil war. It is a perception that to this day is a source of distrust for...North Korean press statement intoned this message: “It is the unchanging strategic design of the United States to cling more tightly to South Korea...a collapse or jus post bellum situation, the perception that South Korea is in charge will be vital to any reasonable prospect for success

Pressure-induced amorphization of charge ordered spinel AlV{sub 2}O{sub 4} at low temperature

DOE Office of Scientific and Technical Information (OSTI.GOV)

Malavi, Pallavi S., E-mail: malavips@barc.gov.in; Karmakar, S., E-mail: malavips@barc.gov.in; Sharma, S. M.

2014-04-24

Structural properties of charge ordered spinel AlV{sub 2}O{sub 4} have been investigated under high pressure at low temperature (80K) by synchrotron based x-ray diffraction measurements. It is observed that upon increasing pressure the structure becomes progressively disordered due to the distortion of the AlO{sub 4} tetrahedral unit and undergoes amorphization above ∼12 GPa. While releasing pressure, the rhombohedral phase is only partially recovered at a much lower pressure (below 5 GPa). Within the stability of the rhombohedral phase, the distortion in the vanadium heptamer increases monotonically with pressure, suggesting enhanced charge ordering. This result is in sharp contrast with themore » recent observation of pressure-induced frustration in the charge ordered state leading to structural transition to the cubic phase at room temperature [JPCM 25, 292201, 2013].« less

Alternative route to charge density wave formation in multiband systems

PubMed Central

Eiter, Hans-Martin; Lavagnini, Michela; Hackl, Rudi; Nowadnick, Elizabeth A.; Kemper, Alexander F.; Devereaux, Thomas P.; Chu, Jiun-Haw; Analytis, James G.; Fisher, Ian R.; Degiorgi, Leonardo

2013-01-01

Charge and spin density waves, periodic modulations of the electron, and magnetization densities, respectively, are among the most abundant and nontrivial low-temperature ordered phases in condensed matter. The ordering direction is widely believed to result from the Fermi surface topology. However, several recent studies indicate that this common view needs to be supplemented. Here, we show how an enhanced electron–lattice interaction can contribute to or even determine the selection of the ordering vector in the model charge density wave system ErTe3. Our joint experimental and theoretical study allows us to establish a relation between the selection rules of the electronic light scattering spectra and the enhanced electron–phonon coupling in the vicinity of band degeneracy points. This alternative proposal for charge density wave formation may be of general relevance for driving phase transitions into other broken-symmetry ground states, particularly in multiband systems, such as the iron-based superconductors. PMID:23248317

Alternative route to charge density wave formation in multiband systems.

PubMed

Eiter, Hans-Martin; Lavagnini, Michela; Hackl, Rudi; Nowadnick, Elizabeth A; Kemper, Alexander F; Devereaux, Thomas P; Chu, Jiun-Haw; Analytis, James G; Fisher, Ian R; Degiorgi, Leonardo

2013-01-02

Charge and spin density waves, periodic modulations of the electron, and magnetization densities, respectively, are among the most abundant and nontrivial low-temperature ordered phases in condensed matter. The ordering direction is widely believed to result from the Fermi surface topology. However, several recent studies indicate that this common view needs to be supplemented. Here, we show how an enhanced electron-lattice interaction can contribute to or even determine the selection of the ordering vector in the model charge density wave system ErTe(3). Our joint experimental and theoretical study allows us to establish a relation between the selection rules of the electronic light scattering spectra and the enhanced electron-phonon coupling in the vicinity of band degeneracy points. This alternative proposal for charge density wave formation may be of general relevance for driving phase transitions into other broken-symmetry ground states, particularly in multiband systems, such as the iron-based superconductors.

Molecular orbital (SCF-Xα-SW) theory of metal-metal charge transfer processes in minerals - II. Application to Fe2+ --> Ti4+ charge transfer transitions in oxides and silicates

USGS Publications Warehouse

Sherman, David M.

1987-01-01

A molecular orbital description, based on Xα-Scattered wave calculations on a (FeTiO10)14− cluster, is given for Fe2+ → Ti4+ charge transfer transitions in minerals. The calculated energy for the lowest Fe2+ → Ti4+ metal-metal charge transfer transition is 18040 cm−1 in reasonable agreement with energies observed in the optical spectra of Fe-Ti oxides and silicates. As in the case of Fe2+ → Fe3+ charge transfer in mixed-valence iron oxides and silicates, Fe2+ → Ti4+ charge transfer is associated with Fe-Ti bonding across shared polyhedral edges. Such bonding results from the overlap of the Fe(t 2g ) and Ti(t 2g ) 3d orbitals.

Charge compensation mechanisms in favor of the incorporation of the Eu3+ ion into the ZnO host lattice

NASA Astrophysics Data System (ADS)

Baira, M.; Bekhti-Siad, A.; Hebali, K.; Bouhani-Benziane, H.; Sahnoun, M.

2018-05-01

Eu3+ doped phosphors with charge compensation are potential candidates of red emitting phosphors for lamp applications. Charge compensation improves the luminescence performance of the material. The charge compensation can most probably be achieved by three possible mechanisms: (a) two Zn2+ ions are replaced by one Eu3+ ions and one monovalent cation, 2Zn2+ →Eu3++ Li+, where Li+ is acting as a charge compensator; (b) the charge compensation is provided by a zinc vacancy (VZn) defects, 3Zn2+ → 2Eu3++ VZn, the subscript Zn denotes an ion in a normal zinc site in the lattice; (c) two Zn2+ ions are replaced by one Eu3+ ions with the presence of interstitial oxygen (Oi), 2Zn2+ → 2Eu3++ Oi. Electronic structures of the crystals corresponding to the three models are evaluated by the first-principles quantum mechanical calculations based on the density functional theory. It is found that the charge compensator defects make Eu3+ doping in ZnO energetically more favorable. They break the local symmetry around the Eu3+ ion and lead to deep states below the empty upper band, the conduction band that could facilitate intra-4f shell transitions, which can obviously improve the emission intensity of Eu3+-doped ZnO. Therefore, the effect of these defects on the host crystals electronic band states relative to the Eu3+ states is reported, since both electron transfer and electronically energy transfer processes enhance the performance of optoelectronic devices based on this material. These theoretical insights are helpful for designing rare-earth doped oxide materials with high photoluminescence (PL) performance.

The Broken Ring: Reduced Aromaticity in Lys-Trp Cations and High pH Tautomer Correlates with Lower Quantum Yield and Shorter Lifetimes

PubMed Central

2015-01-01

Several nonradiative processes compete with tryptophan fluorescence emission. The difficulty in spectral interpretation lies in associating specific molecular environmental features with these processes and thereby utilizing the fluorescence spectral data to identify the local environment of tryptophan. Here, spectroscopic and molecular modeling study of Lys-Trp dipeptide charged species shows that backbone-ring interactions are undistinguished. Instead, quantum mechanical ground state isosurfaces reveal variations in indole π electron distribution and density that parallel charge (as a function of pK1, pK2, and pKR) on the backbone and residues. A pattern of aromaticity-associated quantum yield and fluorescence lifetime changes emerges. Where quantum yield is high, isosurfaces have a charge distribution similar to the highest occupied molecular orbital (HOMO) of indole, which is the dominant fluorescent ground state of the 1La transition dipole moment. Where quantum yield is low, isosurface charge distribution over the ring is uneven, diminished, and even found off ring. At pH 13, the indole amine is deprotonated, and Lys-Trp quantum yield is extremely low due to tautomer structure that concentrates charge on the indole amine; the isosurface charge distribution bears scant resemblance to the indole HOMO. Such greatly diminished fluorescence has been observed for proteins where the indole nitrogen is hydrogen bonded, lending credence to the association of aromaticity changes with diminished quantum yield in proteins as well. Thus tryptophan ground state isosurfaces are an indicator of indole aromaticity, signaling the partition of excitation energy between radiative and nonradiative processes. PMID:24882092

Comparative studies of the spectroscopy of CuCl2: DFT versus standard ab initio approaches

NASA Astrophysics Data System (ADS)

Ramírez-Solís, A.; Poteau, R.; Vela, A.; Daudey, J. P.

2005-04-01

The XΠg2-Σg +2, XΠg2-Δg2, XΠg2-Σu +2, XΠg2-Πu2 transitions on CuCl2 have been studied using several exchange-correlation functionals from the various types of density functional theory (DFT) approaches like local density approximation (LDA), generalized gradient approximation (GGA), hybrid and meta-GGA. The results are compared with the experience and with those coming from the most sophisticated nondynamic and dynamic electronic correlation treatments using the same relativistic effective core potentials and especially developed basis sets to study the electronic structure of the five lowest states and the corresponding vertical and adiabatic transition energies. The calculated transition energies for three of the hybrid functionals (B3LYP, B97-2, and PBE0) are in very good agreement with the benchmark ab initio results and experimental figures. All of the other functionals largely overestimate the XΠg2-Σg +2 and XΠg2-Δg2 transition energies, many of them even placing the Δg2 ligand field state above the charge transfer Πu2 and Σu +2 states. The relative weight of the Hartree-Fock exchange in the definition of the functional used appears to play a key role in the accurate description of the ΛSΣ density defined by the orientation of the 3d hole (σ, π, or δ) on Cu in the field of both chlorine atoms, but no simple connection of this weight with the quality of the spectra has been found. Mulliken charges and spin densities are carefully analyzed; a possible link between the extent of spin density on the metal for the XΠg2 state and the performance of the various functionals was observed, suggesting that those that lead to the largest values (close to 0.65) are the ones that best reproduce these four transitions. Most functionals lead to a remarkably low ionicity for the three ligand field states even for the best performing functionals, compared to the complete active space (SCF) (21, 14) ab initio values. These findings show that not only large variational ab initio calculations can produce reliable spectroscopic results for extremely complex systems where delicate electronic correlation effects have to be carefully dealt with. However, those functionals that were recently shown to perform best for a series of molecular properties [J. Chem. Phys. 121 3405 (2004)] are not the ones that produce the best transition energies for this complex case.

Isospin symmetry of Tz =±3/2→±1/2 Gamow-Teller transitions in A=41 nuclei

NASA Astrophysics Data System (ADS)

Fujita, Y.; Shimbara, Y.; Adachi, T.; Berg, G. P.; Brown, B. A.; Fujita, H.; Hatanaka, K.; Kamiya, J.; Nakanishi, K.; Sakemi, Y.; Sasaki, S.; Shimizu, Y.; Tameshige, Y.; Uchida, M.; Wakasa, T.; Yosoi, M.

2004-11-01

Under the assumption that isospin T is a good quantum number, isobaric analog states and various analogous transitions are expected in isobars with mass number A . The strengths of Tz =±3/2→±1/2 analogous Gamow-Teller (GT) transitions and analogous M1 transitions within the A=41 isobar quartet are compared in detail. The Tz =+3/2→+1/2 GT transitions from the Jπ = 3/2+ ground state of 41K leading to excited Jπ = 1/2+ , 3/2+ , and 5/2+ states in 41Ca were measured using the ( 3He ,t) charge-exchange reaction. With a high energy resolution of 35 keV , many fragmented states were observed, and the GT strength distribution was determined up to 10 MeV excitation energy ( Ex ) . The main part of the strength was concentrated in the Ex =4 6 MeV region. A shell-model calculation could reproduce the concentration, but not so well details of the strength distribution. The obtained distribution was further compared with two results of 41Ti β decay studying the analogous Tz =-3/2→-1/2 GT strengths. They reported contradicting distributions. One-to-one correspondences of analogous transitions and analog states were assigned up to Ex =6 MeV in the comparison with one of these 41Ti β -decay results. Combining the spectroscopic information of the analog states in 41Ca and 41Sc , the most probable Jπ values were deduced for each pair of analog states. It was found that 5/2+ states carry the main part of the observed GT strength, while much less GT strength was carried by 1/2+ and 3/2+ states. The gross features of the GT strength distributions for each J were similar for the isospin analogous Tz =±3/2→±1/2 transitions, but the details were somewhat different. From the difference of the distributions, isospin-asymmetry matrix elements of ≈8 keV were deduced. The Coulomb displacement energy, which is sensitive to the configuration of states, showed a sudden increase of about 50 keV at the excitation energy of 3.8 MeV . The strengths of several M1 transitions to the IAS in 41Ca were compared with the strengths of analogous GT transitions. It was found that ratios of the M1 and GT transition strengths were similar, suggesting that the contributions of the ℓτ term in M1 transitions are small.

Resonant Coherent Excitation of Hydrogen-Like Ar Ions to the n =: 3 States

NASA Astrophysics Data System (ADS)

Azuma, T.; Ito, T.; Takabayashi, Y.; Komaki, K.; Yamazaki, Y.; Yamazaki, Y.; Takada, E.; Murakami, T.

We have succeeded in observing resonant coherent excitaion (RCE) of 1s electrons to the n = 3 states in 390 MeV/u hydrogen-like Ar17+ ions planar channeled in a silicon crystal through measurements of the charge-state distribution of ions transmitting the crystal. Furthermore, we directly confirmed RCE to the n = 3 states by observing the enhancement of the de-excitation X-rays, i.e., Kβ X-rays under the resonance condition. The resonance profiles of the charge-state distribution as functions of the incident angle to the crystal, which uniquely relates with the transition energy, have a characteristic structure consisting of several peaks. Compared with the profile of RCE to the n = 2 states, the present profiles show a large peak shift from the j = 1/2 and 3/2 levels in vacuum, and the profiles are much wider than those expected from the Stark-split level structure of the n = 3 manifolds due to the position- (distance from the channel center in the planar channel) dependent strong static field in the crystal.

Radio frequency reflectometry and charge sensing of a precision placed donor in silicon

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hile, Samuel J., E-mail: samhile@gmail.com; House, Matthew G.; Peretz, Eldad

2015-08-31

We compare charge transitions on a deterministic single P donor in silicon using radio frequency reflectometry measurements with a tunnel coupled reservoir and DC charge sensing using a capacitively coupled single electron transistor (SET). By measuring the conductance through the SET and comparing this with the phase shift of the reflected radio frequency (RF) excitation from the reservoir, we can discriminate between charge transfer within the SET channel and tunneling between the donor and reservoir. The RF measurement allows observation of donor electron transitions at every charge degeneracy point in contrast to the SET conductance signal where charge transitions aremore » only observed at triple points. The tunnel coupled reservoir has the advantage of a large effective lever arm (∼35%), allowing us to independently extract a neutral donor charging energy ∼62 ± 17 meV. These results demonstrate that we can replace three terminal transistors by a single terminal dispersive reservoir, promising for high bandwidth scalable donor control and readout.« less

Alternative Fuels Data Center: Delaware Transit Corporation Adds Propane

Science.gov Websites

. Television's Original Automotive Magazine Provided by Maryland Public Television Related Videos Photo of a car Electric Vehicles Charge up at State Parks in West Virginia Dec. 9, 2017 Photo of a car Hydrogen Powers Fuel Cell Vehicles in California Nov. 18, 2017 Photo of a car Smart Car Shopping Nov. 4, 2017 Photo of

Hybridization-controlled charge transfer and induced magnetism at correlated oxide interfaces

PubMed Central

Grisolia, M.N.; Arora, A.; Valencia, S.; Varela, M.; Abrudan, R.; Weschke, E.; Schierle, E.; Rault, J.E.; Rueff, J.-P.; Barthélémy, A.; Santamaria, J.; Bibes, M.

2015-01-01

At interfaces between conventional materials, band bending and alignment are classically controlled by differences in electrochemical potential. Applying this concept to oxides in which interfaces can be polar and cations may adopt a mixed valence has led to the discovery of novel two-dimensional states between simple band insulators such as LaAlO3 and SrTiO3. However, many oxides have a more complex electronic structure, with charge, orbital and/or spin orders arising from strong Coulomb interactions between transition metal and oxygen ions. Such electronic correlations offer a rich playground to engineer functional interfaces but their compatibility with the classical band alignment picture remains an open question. Here we show that beyond differences in electron affinities and polar effects, a key parameter determining charge transfer at correlated oxide interfaces is the energy required to alter the covalence of the metal-oxygen bond. Using the perovskite nickelate (RNiO3) family as a template, we probe charge reconstruction at interfaces with gadolinium titanate GdTiO3. X-ray absorption spectroscopy shows that the charge transfer is thwarted by hybridization effects tuned by the rare-earth (R) size. Charge transfer results in an induced ferromagnetic-like state in the nickelate, exemplifying the potential of correlated interfaces to design novel phases. Further, our work clarifies strategies to engineer two-dimensional systems through the control of both doping and covalence. PMID:27158255

Hybridization-controlled charge transfer and induced magnetism at correlated oxide interfaces

NASA Astrophysics Data System (ADS)

Grisolia, M. N.; Varignon, J.; Sanchez-Santolino, G.; Arora, A.; Valencia, S.; Varela, M.; Abrudan, R.; Weschke, E.; Schierle, E.; Rault, J. E.; Rueff, J.-P.; Barthélémy, A.; Santamaria, J.; Bibes, M.

2016-05-01

At interfaces between conventional materials, band bending and alignment are classically controlled by differences in electrochemical potential. Applying this concept to oxides in which interfaces can be polar and cations may adopt a mixed valence has led to the discovery of novel two-dimensional states between simple band insulators such as LaAlO3 and SrTiO3. However, many oxides have a more complex electronic structure, with charge, orbital and/or spin orders arising from strong Coulomb interactions at and between transition metal and oxygen ions. Such electronic correlations offer a rich playground to engineer functional interfaces but their compatibility with the classical band alignment picture remains an open question. Here we show that beyond differences in electron affinities and polar effects, a key parameter determining charge transfer at correlated oxide interfaces is the energy required to alter the covalence of the metal-oxygen bond. Using the perovskite nickelate (RNiO3) family as a template, we probe charge reconstruction at interfaces with gadolinium titanate GdTiO3. X-ray absorption spectroscopy shows that the charge transfer is thwarted by hybridization effects tuned by the rare-earth (R) size. Charge transfer results in an induced ferromagnetic-like state in the nickelate, exemplifying the potential of correlated interfaces to design novel phases. Further, our work clarifies strategies to engineer two-dimensional systems through the control of both doping and covalence.

Ligand-hole localization in oxides with unusual valence Fe

PubMed Central

Chen, Wei-Tin; Saito, Takashi; Hayashi, Naoaki; Takano, Mikio; Shimakawa, Yuichi

2012-01-01

Unusual high-valence states of iron are stabilized in a few oxides. A-site-ordered perovskite-structure oxides contain such iron cations and exhibit distinct electronic behaviors at low temperatures, e.g. charge disproportionation (4Fe4+ → 2Fe3+ + 2Fe5+) in CaCu3Fe4O12 and intersite charge transfer (3Cu2+ + 4Fe3.75+ → 3Cu3+ + 4Fe3+) in LaCu3Fe4O12. Here we report the synthesis of solid solutions of CaCu3Fe4O12 and LaCu3Fe4O12 and explain how the instabilities of their unusual valence states of iron are relieved. Although these behaviors look completely different from each other in simple ionic models, they can both be explained by the localization of ligand holes, which are produced by the strong hybridization of iron d and oxygen p orbitals in oxides. The localization behavior in the charge disproportionation of CaCu3Fe4O12 is regarded as charge ordering of the ligand holes, and that in the intersite charge transfer of LaCu3Fe4O12 is regarded as a Mott transition of the ligand holes. PMID:22690318

Role of electrostatic fluctuations in doped semiconductors upon the transition from band to hopping conduction (by the example of p-Ge:Ga)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Poklonski, N. A., E-mail: poklonski@bsu.by; Vyrko, S. A.; Poklonskaya, O. N.

The electrostatic model of ionization equilibrium between hydrogen-like acceptors and v-band holes in crystalline covalent p-type semiconductors is developed. The range of applicability of the model is the entire insulator side of the insulator–metal (Mott) phase transition. The density of the spatial distribution of acceptor- and donor-impurity atoms and holes over a crystal was assumed to be Poissonian and the fluctuations of their electrostatic potential energy, to be Gaussian. The model takes into account the effect of a decrease in the energy of affinity of an ionized acceptor to a v-band hole due to Debye–Hückel ion screening by both freemore » v-band holes and localized holes hopping over charge states (0) and (–1) of acceptors in the acceptor band. All donors are in charge state (+1) and are not directly involved in the screening, but ensure the total electroneutrality of a sample. In the quasiclassical approximation, analytical expressions for the root-mean-square fluctuation of the v-band hole energy W{sub p} and effective acceptor bandwidth W{sub a} are obtained. In calculating W{sub a}, only fluctuations caused by the Coulomb interaction between two nearest point charges (impurity ions and holes) are taken into account. It is shown that W{sub p} is lower than W{sub a}, since electrostatic fluctuations do not manifest themselves on scales smaller than the average de Broglie wavelength of a free hole. The delocalization threshold for v-band holes is determined as the sum of the diffusive-percolation threshold and exchange energy of holes. The concentration of free v-band holes is calculated at the temperature T{sub j} of the transition from dc band conductivity to conductivity implemented via hopping over acceptor states, which is determined from the virial theorem. The dependence of the differential energy of the thermal ionization of acceptors at the temperature 3T{sub j}/2 on their concentration N and degree of compensation K (the ratio between the donor and acceptor concentrations) is determined. Good quantitative agreement between the results of the calculation and data on the series of neutron transmutation doped p-Ge samples is obtained up to the Mott transition without using any fitting parameters.« less

Optical studies of the charge localization and delocalization in conducting polymers

NASA Astrophysics Data System (ADS)

Kim, Youngmin

A systematic charge transport study on the thermochromism of polyaniline (PAN) doped with a plasticizing dopant, and on a field effect device using conducting poly (3,4-ethylenedioxythiophene) (PEDOT) as its active material, was made at optical (20--45,000 cm-1) frequencies to probe the charge localization and delocalization phenomena and the insulator to metal transition (IMT) in the inhomogeneous conducting polymer system. Temperature dependent reflectance [20--8000 cm -1 (2.5 meV--1eV)] of the PAN sample, together with absorbance and do transport study done by Dr. Pron at the Laboratoire de Physique des Metaux Synthetiques in Grenoble, France, shows spectral weight loss in the infrared region but the reflectance in the very low frequency (below 100 cm-1) remains unaffected. There are two localization transitions. The origin of the 200 K localization transition that affect >˜15% of the electrons is the glass transition emanating from the dopants. The transition principally affects the IR response in the range of 200--8000 cm -1. The low temperature (<75K) localization transition affects the few electrons that provide the high conductivity. It is suggested that these electrons are localized by disorder at the lowest temperature and become delocalized through phonon induced delocalization as the temperature increases to 75K. It is noted that this temperature is typical of a Debye temperature in many organic materials. The thermocromism is attributed to the weak localization to strong localization transition through the glass transition temperature. Below the glass transition temperature (Tg), the lattice is "frozen" in configuration that reduces the charge delocalization and lead to cause increase of strongly localized polarons. Time variation of source-drain current, real-time IR reflectance [20--8000 cm-1 (2.5 meV--1eV)] modulation, and real-time UV/VIS/NIR absorbance [380--2400 nm (0.5--3.3 eV)] modulation were measured to investigate the field induced charge localization of PEDOT field effect device. Layer by layer thin film analysis showed strong localization of free carriers. The temperature dependence of the do conductivity changes with application of the gate voltage demonstrating that the electric field effect has changed bulk charge transport in the active channel despite the expected screening due to mobile charge carriers. Mid IR (500--8000 cm-1) reflectance showed little change in the vibrational modes, which distinguish this phenomenon from the doping-dedoping induced electrochemical MIT. UV/Vis/NIR absorbance modulation clearly showed that the increase of the strong localization of charges with the pi-pi* bandgap transition unchanged. It is proposed that conducting polymer is near the metal to insulator transition and that the applied gate voltage leads to this transition through field induced ion motion.

High-Rate Charging Induced Intermediate Phases and Structural Changes of Layer-Structured Cathode for Lithium-Ion Batteries

DOE PAGES

Zhou, Yong-Ning; Yue, Ji-Li; Hu, Enyuan; ...

2016-08-08

Using fast time-resolved in situ X-ray diffraction, charge-rate dependent phase transition processes of layer structured cathode material LiNi 1/3Mn 1/3Co 1/3O 2 for lithium-ion batteries are studied. During first charge, intermediate phases emerge at high rates of 10C, 30C, and 60C, but not at low rates of 0.1C and 1C. These intermediate phases can be continuously observed during relaxation after the charging current is switched off. After half-way charging at high rate, sample studied by scanning transmission electron microscopy shows Li-rich and Li-poor phases' coexistence with tetrahedral occupation of Li in Li-poor phase. Also, the high rate induced overpotential ismore » thought to be the driving force for the formation of this intermediate Li-poor phase. The in situ quick X-ray absorption results show that the oxidation of Ni accelerates with increasing charging rate and the Ni 4+ state can be reached at the end of charge with 30C rate. Finally, these results give new insights in the understanding of the layered cathodes during high-rate charging.« less

Depinning and nonequilibrium dynamic phases of particle assemblies driven over random and ordered substrates: A review

DOE PAGES

Reichhardt, Charles; Olson Reichhardt, Cynthia Jane

2016-12-20

Here, we review the depinning and nonequilibrium phases of collectively interacting particle systems driven over random or periodic substrates. This type of system is relevant to vortices in type-II superconductors, sliding charge density waves, electron crystals, colloids, stripe and pattern forming systems, and skyrmions, and could also have connections to jamming, glassy behaviors, and active matter. These systems are also ideal for exploring the broader issues of characterizing transient and steady state nonequilibrium flow phases as well as nonequilibrium phase transitions between distinct dynamical phases, analogous to phase transitions between different equilibrium states. We discuss the differences between elastic andmore » plastic depinning on random substrates and the different types of nonequilibrium phases which are associated with specific features in the velocity-force curves, fluctuation spectra, scaling relations, and local or global particle ordering. We describe how these quantities can change depending on the dimension, anisotropy, disorder strength, and the presence of hysteresis. Within the moving phase we discuss how there can be a transition from a liquid-like state to dynamically ordered moving crystal, smectic, or nematic states. Systems with periodic or quasiperiodic substrates can have multiple nonequilibrium second or first order transitions in the moving state between chaotic and coherent phases, and can exhibit hysteresis. We also discuss systems with competing repulsive and attractive interactions, which undergo dynamical transitions into stripes and other complex morphologies when driven over random substrates. Throughout this work we highlight open issues and future directions such as absorbing phase transitions, nonequilibrium work relations, inertia, the role of non-dissipative dynamics such as Magnus effects, and how these results could be extended to the broader issues of plasticity in crystals, amorphous solids, and jamming phenomena.« less

Depinning and nonequilibrium dynamic phases of particle assemblies driven over random and ordered substrates: a review

NASA Astrophysics Data System (ADS)

Reichhardt, C.; Olson Reichhardt, C. J.

2017-02-01

We review the depinning and nonequilibrium phases of collectively interacting particle systems driven over random or periodic substrates. This type of system is relevant to vortices in type-II superconductors, sliding charge density waves, electron crystals, colloids, stripe and pattern forming systems, and skyrmions, and could also have connections to jamming, glassy behaviors, and active matter. These systems are also ideal for exploring the broader issues of characterizing transient and steady state nonequilibrium flow phases as well as nonequilibrium phase transitions between distinct dynamical phases, analogous to phase transitions between different equilibrium states. We discuss the differences between elastic and plastic depinning on random substrates and the different types of nonequilibrium phases which are associated with specific features in the velocity-force curves, fluctuation spectra, scaling relations, and local or global particle ordering. We describe how these quantities can change depending on the dimension, anisotropy, disorder strength, and the presence of hysteresis. Within the moving phase we discuss how there can be a transition from a liquid-like state to dynamically ordered moving crystal, smectic, or nematic states. Systems with periodic or quasiperiodic substrates can have multiple nonequilibrium second or first order transitions in the moving state between chaotic and coherent phases, and can exhibit hysteresis. We also discuss systems with competing repulsive and attractive interactions, which undergo dynamical transitions into stripes and other complex morphologies when driven over random substrates. Throughout this work we highlight open issues and future directions such as absorbing phase transitions, nonequilibrium work relations, inertia, the role of non-dissipative dynamics such as Magnus effects, and how these results could be extended to the broader issues of plasticity in crystals, amorphous solids, and jamming phenomena.

SYMBMAT: Symbolic computation of quantum transition matrix elements

NASA Astrophysics Data System (ADS)

Ciappina, M. F.; Kirchner, T.

2012-08-01

We have developed a set of Mathematica notebooks to compute symbolically quantum transition matrices relevant for atomic ionization processes. The utilization of a symbolic language allows us to obtain analytical expressions for the transition matrix elements required in charged-particle and laser induced ionization of atoms. Additionally, by using a few simple commands, it is possible to export these symbolic expressions to standard programming languages, such as Fortran or C, for the subsequent computation of differential cross sections or other observables. One of the main drawbacks in the calculation of transition matrices is the tedious algebraic work required when initial states other than the simple hydrogenic 1s state need to be considered. Using these notebooks the work is dramatically reduced and it is possible to generate exact expressions for a large set of bound states. We present explicit examples of atomic collisions (in First Born Approximation and Distorted Wave Theory) and laser-matter interactions (within the Dipole and Strong Field Approximations and different gauges) using both hydrogenic wavefunctions and Slater-Type Orbitals with arbitrary nlm quantum numbers as initial states. Catalogue identifier: AEMI_v1_0 Program summary URL:http://cpc.cs.qub.ac.uk/summaries/AEMI_v1_0.html Program obtainable from: CPC Program Library, Queen's University, Belfast, N. Ireland Licensing provisions: Standard CPC license, http://cpc.cs.qub.ac.uk/licence/licence.html No. of lines in distributed program, including test data, etc.: 71 628 No. of bytes in distributed program, including test data, etc.: 444 195 Distribution format: tar.gz Programming language: Mathematica Computer: Single machines using Linux or Windows (with cores with any clock speed, cache memory and bits in a word) Operating system: Any OS that supports Mathematica. The notebooks have been tested under Windows and Linux and with versions 6.x, 7.x and 8.x Classification: 2.6 Nature of problem: The notebooks generate analytical expressions for quantum transition matrix elements required in diverse atomic processes: ionization by ion, electron, or photon impact and ionization within the framework of strong field physics. In charged-particle collisions approaches based on perturbation theory enjoy widespread utilization. Accordingly, we have chosen the First Born Approximation and Distorted Wave theories as examples. In light-matter interactions, the main ingredient for many types of calculations is the dipole transition matrix in its different formulations, i.e. length, velocity, and acceleration gauges. In all these cases the transitions of interest occur between a bound state and a continuum state which can be described in different ways. With the notebooks developed in the present work it is possible to calculate transition matrix elements analytically for any set of quantum numbers nlm of initial hydrogenic states or Slater-Type Orbitals and for plane waves or Coulomb waves as final continuum states. Solution method: The notebooks employ symbolic computation to generate analytical expressions for transition matrix elements used in both collision and light-matter interaction physics. fba_hyd.nb - This notebook computes analytical expressions for the transition matrix of collision-induced ionization in the First Born Approximation (FBA). The transitions considered are from a bound hydrogenic state with arbitrary quantum numbers nlm to a continuum state represented by a plane wave (PW) or a Coulomb wave (CW). distorted_hyd.nb - This notebook computes analytical expressions for the transition matrix of collision-induced ionization in Distorted Wave (DW) theories. The transitions considered are from a (distorted) bound hydrogenic state with arbitrary quantum numbers nlm to a distorted-wave continuum state. The computations are based on scalar and vectorial integrals (see the text for details). dipoleLength_hyd.nb - This notebook computes analytical expressions for the dipole transition matrix in length gauge. The transitions considered are from a bound hydrogenic state with arbitrary quantum numbers nlm to a continuum state represented by a PW (the Strong Field Approximation (SFA)) or a CW (the Coulomb-Volkov Approximation (CVA)). dipoleVelocity_hyd.nb - This notebook computes analytical expressions for the dipole transition matrix in velocity gauge. The transitions considered are from a bound hydrogenic state with arbitrary quantum numbers nlm to a continuum state represented by a PW (the SFA) or a CW (the CVA). dipoleAcceleration_hyd.nb - This notebook computes analytical expressions for the dipole transition matrix in acceleration gauge. The transitions considered are from a bound hydrogenic state with arbitrary quantum numbers nlm to a continuum state represented by a PW (the SFA). For the case of the CVA we only include the transition from the 1s state to a continuum state represented by a CW. fba_STO.nb - This notebook computes analytical expressions for the transition matrix of collision-induced ionization in the FBA. The transitions considered are from a Slater-Type Orbital (STO) with arbitrary quantum numbers nlm to a continuum state represented by a PW or a CW. distorted_STO.nb - This notebook computes analytical expressions for the transition matrix of collision-induced ionization in DW theories. The transitions considered are from a (distorted) STO with arbitrary quantum numbers nlm to a distorted-wave continuum state. The computations are based on scalar and vectorial integrals (see the text for details). dipoleLength_STO.nb - This notebook computes analytical expressions for the dipole transition matrix in length gauge. The transitions considered are from an STO with arbitrary quantum numbers nlm to a continuum state represented by a PW (the SFA) or a CW (the CVA). dipoleVelocity_STO.nb - This notebook computes analytical expressions for the dipole transition matrix in velocity gauge. The transitions considered are from an STO with arbitrary quantum numbers nlm to a continuum state represented by a PW (the SFA) or a CW (the CVA). dipoleAcceleration_STO.nb - This notebook computes analytical expressions for the dipole transition matrix in acceleration gauge. The transitions considered are from an STO with arbitrary quantum numbers nlm to a continuum state represented by a PW (the SFA). The symbolic expressions obtained within each notebook can be exported to standard programming languages such as Fortran or C using the Format.m package (see the text and Ref. Sofroniou (1993) [16] for details). Running time: Computational times vary according to the transition matrix selected and quantum numbers nlm of the initial state used. The typical running time is several minutes, but it will take longer for large values of nlm.

Correlation, Breit and Quantum Electrodynamics effects on energy level and transition properties of W54+ ion

NASA Astrophysics Data System (ADS)

Ding, Xiaobin; Sun, Rui; Koike, Fumihiro; Kato, Daiji; Murakami, Izumi; Sakaue, Hiroyuki A.; Dong, Chenzhong

2017-03-01

The electron correlation effects and Breit interaction as well as Quantum Electro-Dynamics (QED) effects were expected to have important contribution to the energy level and transition properties of heavy highly charged ions. The ground states [Ne]3s23p63d2 and first excited states [Ne]3s23p53d3 of W54+ ion have been studied by using Multi-Configuration Dirac-Fock method with the implementation of Grasp2K package. A restricted active space method was employed to investigate the correlation contribution from different models. The Breit interaction and QED effects were taken into account in the relativistic configuration interaction calculation with the converged wavefunction. It is found that the correlation contribution from 3s and 3p orbital have important contribution to the energy level, transition wavelength and probability of the ground and the first excited state of W54+ ion. Contribution to the Topical Issue "Atomic and Molecular Data and their Applications", edited by Gordon W.F. Drake, Jung-Sik Yoon, Daiji Kato, Grzegorz Karwasz.

Ionic effects on the temperature-force phase diagram of DNA.

PubMed

Amnuanpol, Sitichoke

2017-12-01

Double-stranded DNA (dsDNA) undergoes a structural transition to single-stranded DNA (ssDNA) in many biologically important processes such as replication and transcription. This strand separation arises in response either to thermal fluctuations or to external forces. The roles of ions are twofold, shortening the range of the interstrand potential and renormalizing the DNA elastic modulus. The dsDNA-to-ssDNA transition is studied on the basis that dsDNA is regarded as a bound state while ssDNA is regarded as an unbound state. The ground state energy of DNA is obtained by mapping the statistical mechanics problem to the imaginary time quantum mechanics problem. In the temperature-force phase diagram the critical force F c (T) increases logarithmically with the Na + concentration in the range from 32 to 110 mM. Discussing this logarithmic dependence of F c (T) within the framework of polyelectrolyte theory, it inevitably suggests a constraint on the difference between the interstrand separation and the length per unit charge during the dsDNA-to-ssDNA transition.

Charge modulation in two-dimensional compounds

NASA Astrophysics Data System (ADS)

Monceau, Pierre

2015-03-01

Although the first measurements demonstrating charge modulation were performed forty years ago, many open questions are now the matter of intense research. In the first part of this short review, some recent results obtained on transition metal dichalcogenides (MX2) compounds will be presented such as: mechanism of the Peierls transition, effect of strong electron-phonon coupling, soft mode in the phonon dispersion, chirality effects,....Charge order, ferroelectricity, frustration, glassiness in organic 2D systems will be the subject of the second part. The third part will be devoted to describe the properties of a new family of 2D compounds, namely rare earth tritellurides, in which the size of the rare earth determine the charge density wave transition temperature.

Experimental challenges for the measurement of the 116Cd(20Ne,20O)116Sn double charge exchange reaction at 15 AMeV

NASA Astrophysics Data System (ADS)

Carbone, D.; Cappuzzello, F.; Agodi, C.; Cavallaro, M.; Acosta, L.; Bonanno, D.; Bongiovanni, D.; Borello, T.; Boztosun, I.; Calabrese, S.; Calvo, D.; Chávez Lomelí, E. R.; Deshmukh, N.; de Faria, P. N.; Finocchiaro, P.; Fisichella, M.; Foti, A.; Gallo, G.; Hacisalihoglu, A.; Iazzi, F.; Introzzi, R.; Lanzalone, G.; Linares, R.; Longhitano, F.; Lo Presti, D.; Medina, N.; Muoio, A.; Oliveira, J. R. B.; Pakou, A.; Pandola, L.; Pinna, F.; Reito, S.; Russo, G.; Santagati, G.; Sgouros, O.; Solakcı, S. O.; Soukeras, V.; Souliotis, G.; Spatafora, A.; Torresi, D.; Tudisco, S.; Yildirim, A.; Zagatto, V. A. B.;

2018-05-01

The knowledge of the nuclear matrix elements (NME) entering in the expression of the half-life of the neutrinoless double beta decay is fundamental for neutrino physics. Information on the nuclear matrix elements can be obtained by measuring the absolute cross section of double charge exchange nuclear reactions. The two processes present some similarities, the initial and final-state wave functions are the same and the transition operators are similar. The experimental measurements of double charge exchange reactions induced by heavy ions present a number of challenging aspects, since such reactions are characterized by very low cross sections. Such difficulties are discussed for the measurement of the 116Cd(20Ne,20O)116Sn reaction at 15 AMeV.

Non-resonant inelastic x-ray scattering spectra of lithiated titanium oxides for battery applications

NASA Astrophysics Data System (ADS)

Nagle, Kenneth; Balasubramanian, Mali; Johnson, Christopher; Seidler, Gerald; Belharouak, Ilias

2008-03-01

Although lithium-ion batteries now see widespread use, there remain considerable questions concerning the basic solid state chemistry of both electrodes. Improved understanding of the local electronic structure, particularly the mechanism of charge transfer upon insertion and removal of lithium, could lead to innovation in battery design and improved performance. We present non-resonant inelastic x-ray scattering (NRIXS) spectra from 2p initial states in titanium; these spectra are among the first recorded for such states in a transition metal. These spectra were obtained using the lower energy resolution inelastic x-ray scattering (LERIX) spectrometer, which is capable of making simultaneous measurements at nineteen values of momentum transfer. We demonstrate the ability to obtain soft x-ray absorption-like information using a bulk-sensitive, hard x-ray technique. In addition, at high momentum transfer NRIXS provides information about non-dipole transitions that are inaccessible by soft x-ray spectroscopic methods.

Charge migration and charge transfer in molecular systems

PubMed Central

Wörner, Hans Jakob; Arrell, Christopher A.; Banerji, Natalie; Cannizzo, Andrea; Chergui, Majed; Das, Akshaya K.; Hamm, Peter; Keller, Ursula; Kraus, Peter M.; Liberatore, Elisa; Lopez-Tarifa, Pablo; Lucchini, Matteo; Meuwly, Markus; Milne, Chris; Moser, Jacques-E.; Rothlisberger, Ursula; Smolentsev, Grigory; Teuscher, Joël; van Bokhoven, Jeroen A.; Wenger, Oliver

2017-01-01

The transfer of charge at the molecular level plays a fundamental role in many areas of chemistry, physics, biology and materials science. Today, more than 60 years after the seminal work of R. A. Marcus, charge transfer is still a very active field of research. An important recent impetus comes from the ability to resolve ever faster temporal events, down to the attosecond time scale. Such a high temporal resolution now offers the possibility to unravel the most elementary quantum dynamics of both electrons and nuclei that participate in the complex process of charge transfer. This review covers recent research that addresses the following questions. Can we reconstruct the migration of charge across a molecule on the atomic length and electronic time scales? Can we use strong laser fields to control charge migration? Can we temporally resolve and understand intramolecular charge transfer in dissociative ionization of small molecules, in transition-metal complexes and in conjugated polymers? Can we tailor molecular systems towards specific charge-transfer processes? What are the time scales of the elementary steps of charge transfer in liquids and nanoparticles? Important new insights into each of these topics, obtained from state-of-the-art ultrafast spectroscopy and/or theoretical methods, are summarized in this review. PMID:29333473

Precision spectroscopy of the 2S-4P transition in atomic hydrogen

NASA Astrophysics Data System (ADS)

Maisenbacher, Lothar; Beyer, Axel; Matveev, Arthur; Grinin, Alexey; Pohl, Randolf; Khabarova, Ksenia; Kolachevsky, Nikolai; Hänsch, Theodor W.; Udem, Thomas

2017-04-01

Precision measurements of atomic hydrogen have long been successfully used to extract fundamental constants and to test bound-state QED. However, both these applications are limited by measurements of hydrogen lines other than the very precisely known 1S-2S transition. Moreover, the proton r.m.s.charge radius rp extracted from electronic hydrogen measurements currently disagrees by 4 σ with the much more precise value extracted from muonic hydrogen spectroscopy. We have measured the 2S-4P transition in atomic hydrogen using a cryogenic beam of hydrogen atoms optically excited to the initial 2S state. The first order Doppler shift of the one-photon 2S-4P transition is suppressed by actively stabilized counter-propagating laser beams and time-of-flight resolved detection. Quantum interference between excitation paths can lead to significant line distortions in our system. We use an experimentally verified, simple line shape model to take these distortions into account. With this, we can extract a new value for rp and the Rydberg constant R∞ with comparable accuracy as the combined previous H world data.

Study of dipion transitions among Υ(3S), Υ(2S), and Υ(1S) states

NASA Astrophysics Data System (ADS)

Cronin-Hennessy, D.; Gao, K. Y.; Hietala, J.; Kubota, Y.; Klein, T.; Lang, B. W.; Poling, R.; Scott, A. W.; Smith, A.; Zweber, P.; Dobbs, S.; Metreveli, Z.; Seth, K. K.; Tomaradze, A.; Ernst, J.; Ecklund, K. M.; Severini, H.; Love, W.; Savinov, V.; Lopez, A.; Mehrabyan, S.; Mendez, H.; Ramirez, J.; Huang, G. S.; Miller, D. H.; Pavlunin, V.; Sanghi, B.; Shipsey, I. P. J.; Xin, B.; Adams, G. S.; Anderson, M.; Cummings, J. P.; Danko, I.; Hu, D.; Moziak, B.; Napolitano, J.; He, Q.; Insler, J.; Muramatsu, H.; Park, C. S.; Thorndike, E. H.; Yang, F.; Artuso, M.; Blusk, S.; Khalil, S.; Li, J.; Menaa, N.; Mountain, R.; Nisar, S.; Randrianarivony, K.; Sia, R.; Skwarnicki, T.; Stone, S.; Wang, J. C.; Bonvicini, G.; Cinabro, D.; Dubrovin, M.; Lincoln, A.; Pappas, S. P.; Weinstein, A. J.; Asner, D. M.; Edwards, K. W.; Naik, P.; Briere, R. A.; Ferguson, T.; Tatishvili, G.; Vogel, H.; Watkins, M. E.; Rosner, J. L.; Adam, N. E.; Alexander, J. P.; Cassel, D. G.; Duboscq, J. E.; Ehrlich, R.; Fields, L.; Galik, R. S.; Gibbons, L.; Gray, R.; Gray, S. W.; Hartill, D. L.; Heltsley, B. K.; Hertz, D.; Jones, C. D.; Kandaswamy, J.; Kreinick, D. L.; Kuznetsov, V. E.; Mahlke-Krüger, H.; Mohapatra, D.; Onyisi, P. U. E.; Patterson, J. R.; Peterson, D.; Pivarski, J.; Riley, D.; Ryd, A.; Sadoff, A. J.; Schwarthoff, H.; Shi, X.; Stroiney, S.; Sun, W. M.; Wilksen, T.; Athar, S. B.; Patel, R.; Yelton, J.; Rubin, P.; Cawlfield, C.; Eisenstein, B. I.; Karliner, I.; Kim, D.; Lowrey, N.; Selen, M.; White, E. J.; Wiss, J.; Mitchell, R. E.; Shepherd, M. R.; Besson, D.; Pedlar, T. K.

2007-10-01

We present measurements of decay matrix elements for hadronic transitions of the form Υ(nS)→Υ(mS)ππ, where (n,m)=(3,1),(2,1),(3,2). We reconstruct charged and neutral pion modes with the final state Upsilon decaying to either μ+μ- or e+e-. Dalitz plot distributions for the 12 decay modes are fit individually as well as jointly assuming isospin symmetry, thereby measuring the matrix elements of the decay amplitude. We observe and account for the anomaly previously noted in the dipion invariant mass distribution for the Υ(3S)→Υ(1S)ππ transition and obtain good descriptions of the dynamics of the decay using the most general decay amplitude allowed by partial conservation of the axial-vector current considerations. The fits further indicate that the Υ(2S)→Υ(1S)ππ and Υ(3S)→Υ(2S)ππ transitions also show the presence of terms in the decay amplitude that were previously ignored, although at a relatively suppressed level.

Evidence for a Peierls phase-transition in a three-dimensional multiple charge-density waves solid

PubMed Central

Mansart, Barbara; Cottet, Mathieu J. G.; Penfold, Thomas J.; Dugdale, Stephen B.; Tediosi, Riccardo; Chergui, Majed; Carbone, Fabrizio

2012-01-01

The effect of dimensionality on materials properties has become strikingly evident with the recent discovery of graphene. Charge ordering phenomena can be induced in one dimension by periodic distortions of a material’s crystal structure, termed Peierls ordering transition. Charge-density waves can also be induced in solids by strong coulomb repulsion between carriers, and at the extreme limit, Wigner predicted that crystallization itself can be induced in an electrons gas in free space close to the absolute zero of temperature. Similar phenomena are observed also in higher dimensions, but the microscopic description of the corresponding phase transition is often controversial, and remains an open field of research for fundamental physics. Here, we photoinduce the melting of the charge ordering in a complex three-dimensional solid and monitor the consequent charge redistribution by probing the optical response over a broad spectral range with ultrashort laser pulses. Although the photoinduced electronic temperature far exceeds the critical value, the charge-density wave is preserved until the lattice is sufficiently distorted to induce the phase transition. Combining this result with ab initio electronic structure calculations, we identified the Peierls origin of multiple charge-density waves in a three-dimensional system for the first time. PMID:22451898

Canonical Schottky barrier heights of transition metal dichalcogenide monolayers in contact with a metal

NASA Astrophysics Data System (ADS)

Szcześniak, Dominik; Hoehn, Ross D.; Kais, Sabre

2018-05-01

The transition metal dichalcogenide (M X2 , where M =Mo , W and X =S , Se, Te) monolayers are of high interest for semiconducting applications at the nanoscale level; this interest is due to both their direct band gaps and high charge mobilities. In this regard, an in-depth understating of the related Schottky barrier heights, associated with the incorporation of M X2 sheets into novel low-dimensional metal-semiconductor junctions, is of crucial importance. Herein, we generate and provide analysis of the Schottky barrier heights behavior to account for the metal-induced gap states concept as its explanation. In particular, the present investigations concentrate on the estimation of the charge neutrality levels directly by employing the primary theoretical model, i.e., the cell-averaged Green's function formalism combined with the complex band structure technique. The results presented herein place charge neutrality levels in the vicinity of the midgap; this is in agreement with previous reports and analogous to the behavior of three-dimensional semiconductors. The calculated canonical Schottky barrier heights are also found to be in agreement with other computational and experimental values in cases where the difference between electronegativities of the semiconductor and metal contact is small. Moreover, the influence of the spin-orbit effects is herein considered and supports that Schottky barrier heights have metal-induced gap state-derived character, regardless whether spin-orbit coupling interactions are considered. The results presented within this report constitute a direct and vital verification of the importance of metal-induced gap states in explaining the behavior of observed Schottky barrier heights at M X2 -metal junctions.

Lattice instability and enhancement of superconductivity in YB6

NASA Astrophysics Data System (ADS)

Sluchanko, N.; Glushkov, V.; Demishev, S.; Azarevich, A.; Anisimov, M.; Bogach, A.; Voronov, V.; Gavrilkin, S.; Mitsen, K.; Kuznetsov, A.; Sannikov, I.; Shitsevalova, N.; Filipov, V.; Kondrin, M.; Gabáni, S.; Flachbart, K.

2017-10-01

The superconducting and normal state characteristics of yttrium hexaboride (YB6) have been investigated for the single crystals with a transition temperatures Tc ranging between 4.2 K and 7.6 K. The extracted set of microscopic parameters [the coherence length ξ (0 )˜320 -340 Å , the penetration depth λ (0 )˜1100 -3250 Å and the mean free path of charge carriers l =11 -58 Å , the Ginzburg-Landau-Maki parameters κ1 ,2(0 ) ˜3.3 -9.5, and the superconducting gap Δ (0 )˜6.2 -14.8 K] confirms the type II superconductivity in "dirty limit" (ξ ≫l ) with a medium to strong electron-phonon interaction (the electron-phonon interaction constant λe -ph=0.32 -0.96 ) and s -type pairing of charge carriers in this compound [2 Δ (0 ) /kBTc≈3 -4]. The comparative analysis of charge transport (resistivity, Hall and Seebeck coefficients) and thermodynamic (heat capacity, magnetization) properties in the normal state in YB6 allowed to assume a transition into the cage-glass state at T*˜50 K with a static disorder in the arrangement of the Y3 + ions. We argue that the significant Tc variations in YB6 single crystals are determined by two main factors: (i) the superconductivity enhancement is related with the increase of the number of vacancies, both at yttrium and boron sites, leading to nonstoichiometric composition, which is accompanied by the enhancement of electron-phonon interaction in the hexaboride lattice; (ii) stronger Tc depression is observed in near stoichiometric and more dense crystals and it is induced by the development of bcc lattice instability producing strong distortion, disordering, and formation of defect complexes in the matrix of YB6.

High-capacity electrode materials for rechargeable lithium batteries: Li3NbO4-based system with cation-disordered rocksalt structure.

PubMed

Yabuuchi, Naoaki; Takeuchi, Mitsue; Nakayama, Masanobu; Shiiba, Hiromasa; Ogawa, Masahiro; Nakayama, Keisuke; Ohta, Toshiaki; Endo, Daisuke; Ozaki, Tetsuya; Inamasu, Tokuo; Sato, Kei; Komaba, Shinichi

2015-06-23

Rechargeable lithium batteries have rapidly risen to prominence as fundamental devices for green and sustainable energy development. Lithium batteries are now used as power sources for electric vehicles. However, materials innovations are still needed to satisfy the growing demand for increasing energy density of lithium batteries. In the past decade, lithium-excess compounds, Li2MeO3 (Me = Mn(4+), Ru(4+), etc.), have been extensively studied as high-capacity positive electrode materials. Although the origin as the high reversible capacity has been a debatable subject for a long time, recently it has been confirmed that charge compensation is partly achieved by solid-state redox of nonmetal anions (i.e., oxide ions), coupled with solid-state redox of transition metals, which is the basic theory used for classic lithium insertion materials, such as LiMeO2 (Me = Co(3+), Ni(3+), etc.). Herein, as a compound with further excess lithium contents, a cation-ordered rocksalt phase with lithium and pentavalent niobium ions, Li3NbO4, is first examined as the host structure of a new series of high-capacity positive electrode materials for rechargeable lithium batteries. Approximately 300 mAh ⋅ g(-1) of high-reversible capacity at 50 °C is experimentally observed, which partly originates from charge compensation by solid-state redox of oxide ions. It is proposed that such a charge compensation process by oxide ions is effectively stabilized by the presence of electrochemically inactive niobium ions. These results will contribute to the development of a new class of high-capacity electrode materials, potentially with further lithium enrichment (and fewer transition metals) in the close-packed framework structure with oxide ions.

Excited state intramolecular charge transfer reaction in binary mixtures of water and tertiary butanol (TBA): alcohol mole fraction dependence.

PubMed

Pradhan, Tuhin; Ghoshal, Piue; Biswas, Ranjit

2008-02-07

The excited state intramolecular charge transfer reaction of 4-(1-azetidinyl)benzonitrile (P4C) has been studied in water-tertiary butanol (TBA) mixtures at different alcohol mole fractions by using steady state and time-resolved fluorescence spectroscopy. The ratio between the areas under the locally excited (LE) and charge transferred (CT) emission bands is found to exhibit a sharp rise at alcohol mole fraction approximately 0.04, a value at which several thermodynamic properties of this mixture is known to show anomalous change due to the enhancement of H-bonding network. The radiative rate associated with the LE emission also shows a maximum at this TBA mole fraction. Although the structural transition from the water-like tetrahedral network to the alcohol-like chain is reflected in the red shift of the absorption spectrum up to TBA mole fraction approximately 0.10, the emission bands (both LE and CT) show the typical nonideal alcohol mole fraction dependence at all TBA mole fractions. Quantum yield, CT radiative rate as well as transition moments also exhibit a nonideal alcohol mole fraction dependence. The time-resolved emission decay of P4C has been found to be biexponential at all TBA mole fractions, regardless of emission collection around either the LE or the CT bands. The time constant associated with the slow component (tau(slow)) shows a minimum at TBA mole fraction approximately 0.04, whereas such a minimum for the fast time constant, tau(fast) (representing the rate of LE --> CT conversion reaction) is not observed. The nonobservation of the minimum in tau(fast) might be due to the limited time resolution employed in our experiments.