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Sample records for excitation spectra spin

  1. Excitation spectra of generalized antiferromagnetic Heisenberg spin chains (abstract)

    NASA Astrophysics Data System (ADS)

    Parkinson, J. B.; Bonner, J. C.

    1988-04-01

    We compare the excitation spectra in the presence of a magnetic field of a number of integrable (exactly solvable) and nonintegrable quantum spin chains of various spin value s. The archetypal Bethe-ansatz integrable model is the s= 1/2 Heisenberg antiferromagnet (HB AFM). The excitation spectra are characterized by a soft mode which tracks across the Brillouin zone as the field increases to its saturation value. A class of Bethe-ansatz integrable models with SU(2) symmetry and the general spin s display excitation spectra qualitatively similar to the spin- 1/2 model above, for all s. A second class of Bethe-ansatz integrable models has SU(n) symmetry, where n=2s+1. Like the SU(2) integrable chains, these models have gapless excitation spectra, but the basic Brillouin zone changes from k=±2π/(2s+1)a. Studies show that periodicity of the SU(3) member of the class changes (increases) as the field increases to saturation. For both classes of integrable models, there is a single type of excitation pattern which is generically similar for all s. In the case of the other models, on the other hand, numerical studies show that the excitations divide into at least two distinct classes. In the case of the s=1 HB AFM, at high fields (corresponding to SzT=N,N-1, . . .,N/2) the excitations map approximately onto the complete set of excitations for s= 1/2 , whereas at low fields (SzT=N/2,N/2-1,. . .,0) the excitations have notable classical character. In the case of the s=1 model with pure biquadratic exchange, one set of excitations, corresponding to SzT even (SzT=N,N-2,. . .,2,0), again shows an approximate mapping to the complete excitation set for s= 1/2 . The second class of excitations, corresponding to SzT odd, are very different. They are symmetric about k=±π/2a for all SzT, i.e., correspond to a basic Brillouin zone of ±π/2a.

  2. Excitation spectra and spin gap of the half-filled Holstein-Hubbard model

    NASA Astrophysics Data System (ADS)

    Hohenadler, Martin; Assaad, Fakher F.

    2013-02-01

    Single- and two-particle excitation spectra of the one-dimensional, half-filled Holstein-Hubbard model are calculated using the continuous-time quantum Monte Carlo method. In the metallic phase, the results are consistent with a Luther-Emery liquid that has gapped spin and single-particle excitations but a gapless charge mode. However, given the initially exponential dependence of the spin gap on the backscattering matrix element, the numerical excitation spectra appear gapless in the weak-coupling regime, and therefore resemble those of a Luttinger liquid. The Mott phase has the expected charge gap and gapless spin excitations. The Peierls state shows a charge, spin, and single-particle gap, a soft phonon mode, backfolded shadow bands, and soliton excitations. Arguments and numerical evidence for the existence of a nonzero spin gap throughout the metallic phase are provided in terms of equal-time spin and charge correlation functions.

  3. Excitation spectra of a Bose-Einstein condensate with an angular spin-orbit coupling

    NASA Astrophysics Data System (ADS)

    Vasić, Ivana; Balaž, Antun

    2016-09-01

    A theoretical model of a Bose-Einstein condensate with angular spin-orbit coupling has recently been proposed and it has been established that a half-skyrmion represents the ground state in a certain regime of spin-orbit coupling and interaction. Here we investigate low-lying excitations of this phase by using the Bogoliubov method and numerical simulations of the time-dependent Gross-Pitaevskii equation. We find that a sudden shift of the trap bottom results in a complex two-dimensional motion of the system's center of mass that is markedly different from the response of a competing phase, and comprises two dominant frequencies. Moreover, the breathing mode frequency of the half-skyrmion is set by both the spin-orbit coupling and the interaction strength, while in the competing state it takes a universal value. Effects of interactions are especially pronounced at the transition between the two phases.

  4. Effect of frustration on spin-wave excitation spectra and ground-state properties of the quasi-one-dimensional antiferromagnetic chain with asymmetrical sublattices

    NASA Astrophysics Data System (ADS)

    Jiang, Jian-Jun; Liu, Yong-Jun; Zhang, Song-Jun; Yang, Cui-Hong

    2009-10-01

    We investigate the effect of frustration on spin-wave excitation spectra and the properties of the quasi-one-dimensional Heisenberg chain using a spin-wave-wave analysis, the exact diagonalization method and the density matrix renormalization group method. The results show that frustration can cause the softening of the acoustic excitation spectrum ω3, as well as the hardening of the optical excitation spectrum ω1. As a function of the frustration parameter α, the phase diagram exhibits a ferromagnetic phase, a narrow canted phase and a singlet phase. The results obtained from numerical methods show that the spin gap obviously opens and the tetramer-dimer state dominates the properties of the ground state in the singlet phase.

  5. Spin waves and magnetic excitations

    SciTech Connect

    Borovik-Romanov, A.S.; Sinha, S.K.

    1988-01-01

    This book describes both simple spin waves (magnons) and complicated excitations in magnetic systems. The following subjects are covered: - various methods of magnetic excitation investigations such as neutron scattering on magnetic excitations, spin-wave excitation by radio-frequency, power light scattering on magnons and magnetic excitation observation within the light-absorption spectrum; - oscillations of magnetic electron systems coupled with phonons, nuclear spin systems and localized impurity modes: - low-dimensional magnetics, amorphous magnetics and spin glasses.

  6. Magnetic excitations in a bond-centered stripe phase: spin waves far from the semiclassical limit.

    PubMed

    Vojta, Matthias; Ulbricht, Tobias

    2004-09-17

    Using a spin-only model, we compute spin excitation spectra in a bond-centered stripe state with long-range magnetic order. We employ a bond operator formalism, which naturally captures both dimerization and broken spin symmetry in a unified framework. At low energies, the spin excitations resemble spin waves, but at higher energies they are very similar to spin-one excitations of isolated spin ladders. Our theory does well describe neutron scattering data [Nature (London) 429, 534 (2004)

  7. Angular dependent study on ferromagnetic resonance and spin excitations by spin rectification

    SciTech Connect

    Zhang, Yichao; Fan, Xiaolong Zhao, Xiaobing; Rao, Jinwei; Zhou, Hengan; Guo, Dangwei; Xue, Desheng; Gui, Y. S.; Hu, C.-M.

    2015-01-14

    We report angular dependent spin rectification spectra which are applied to studying spin excitations in single permalloy stripe. Based on planar Hall effect, those spin excitations generate special resonant dc Hall voltages, which have been characterized as functions of the amplitude and direction of applied magnetic field. Through high angular resolution 2D mappings, the evolutions of different spin excitation can be directly presented, and the dynamic magnetic parameters such as the gyromagnetic ratio, effective exchange field, as well as the quantized numbers of standing spin waves can be accurately determined through fitting the angular evolution of each resonance.

  8. Room-temperature spin photocurrent spectra at interband excitation and comparison with reflectance-difference spectroscopy in InGaAs/AlGaAs quantum wells

    NASA Astrophysics Data System (ADS)

    Yu, J. L.; Chen, Y. H.; Jiang, C. Y.; Liu, Y.; Ma, H.

    2011-03-01

    Spectra of the interband spin photocurrent due to Rashba and Dresselhaus spin splittings have been experimentally investigated in InGaAs/AlGaAs quantum wells at room temperature. The Rashba- and Dresselhaus-induced circular photogalvanic effect (CPGE) spectra are found to be quite similar in the spectral regions corresponding to the transitions 1e1hh (the first conduction to the first valence sub-band of heavy hole) and 1e2hh. The ratio of Rashba- and Dresselhaus-induced CPGE currents for the transition 1e1hh is estimated to be 4.95. The magnitude of the Rashba-induced CPGE current is up to several tens of nA/W for the transition 1e1hh, which is 1 order of magnitude larger than that obtained in GaN/AlGaN superlattices. Comparing the CPGE spectrum with reflectance-difference and photoreflectance spectra, we find that the large Rashba spin splitting is mainly induced by a large indium atom segregation effect and by the internal field in the quantum wells.

  9. Spin photocurrent spectra induced by Rashba- and Dresselhaus-type circular photogalvanic effect at inter-band excitation in InGaAs/GaAs/AlGaAs step quantum wells

    NASA Astrophysics Data System (ADS)

    Yu, Jinling; Cheng, Shuying; Lai, Yunfeng; Zheng, Qiao; Chen, Yonghai

    2014-03-01

    Spin photocurrent spectra induced by Rashba- and Dresselhaus-type circular photogalvanic effect (CPGE) at inter-band excitation have been experimentally investigated in InGaAs/GaAs/AlGaAs step quantum wells (QWs) at room temperature. The Rashba- and Dresselhaus-induced CPGE spectra are quite similar with each other during the spectral region corresponding to the transition of the excitonic state 1H1E (the first valence subband of heavy hole to the first conduction subband of electrons). The ratio of Rashba- and Dresselhaus-induced CPGE current for the transition 1H1E is estimated to be 8.8±0.1, much larger than that obtained in symmetric QWs (4.95). Compared to symmetric QWs, the reduced well width enhances the Dresselhaus-type spin splitting, but the Rashba-type spin splitting increases more rapidly in the step QWs. Since the degree of the segregation effect of indium atoms and the intensity of build-in field in the step QWs are comparable to those in symmetric QWs, as proved by reflectance difference and photoreflectance spectra, respectively, the larger Rashba-type spin splitting is mainly induced by the additional interface introduced by step structures.

  10. Spin photocurrent spectra induced by Rashba- and Dresselhaus-type circular photogalvanic effect at inter-band excitation in InGaAs/GaAs/AlGaAs step quantum wells

    PubMed Central

    2014-01-01

    Spin photocurrent spectra induced by Rashba- and Dresselhaus-type circular photogalvanic effect (CPGE) at inter-band excitation have been experimentally investigated in InGaAs/GaAs/AlGaAs step quantum wells (QWs) at room temperature. The Rashba- and Dresselhaus-induced CPGE spectra are quite similar with each other during the spectral region corresponding to the transition of the excitonic state 1H1E (the first valence subband of heavy hole to the first conduction subband of electrons). The ratio of Rashba- and Dresselhaus-induced CPGE current for the transition 1H1E is estimated to be 8.8±0.1, much larger than that obtained in symmetric QWs (4.95). Compared to symmetric QWs, the reduced well width enhances the Dresselhaus-type spin splitting, but the Rashba-type spin splitting increases more rapidly in the step QWs. Since the degree of the segregation effect of indium atoms and the intensity of build-in field in the step QWs are comparable to those in symmetric QWs, as proved by reflectance difference and photoreflectance spectra, respectively, the larger Rashba-type spin splitting is mainly induced by the additional interface introduced by step structures. PMID:24646286

  11. Spin photocurrent spectra induced by Rashba- and Dresselhaus-type circular photogalvanic effect at inter-band excitation in InGaAs/GaAs/AlGaAs step quantum wells.

    PubMed

    Yu, Jinling; Cheng, Shuying; Lai, Yunfeng; Zheng, Qiao; Chen, Yonghai

    2014-03-19

    : Spin photocurrent spectra induced by Rashba- and Dresselhaus-type circular photogalvanic effect (CPGE) at inter-band excitation have been experimentally investigated in InGaAs/GaAs/AlGaAs step quantum wells (QWs) at room temperature. The Rashba- and Dresselhaus-induced CPGE spectra are quite similar with each other during the spectral region corresponding to the transition of the excitonic state 1H1E (the first valence subband of heavy hole to the first conduction subband of electrons). The ratio of Rashba- and Dresselhaus-induced CPGE current for the transition 1H1E is estimated to be 8.8±0.1, much larger than that obtained in symmetric QWs (4.95). Compared to symmetric QWs, the reduced well width enhances the Dresselhaus-type spin splitting, but the Rashba-type spin splitting increases more rapidly in the step QWs. Since the degree of the segregation effect of indium atoms and the intensity of build-in field in the step QWs are comparable to those in symmetric QWs, as proved by reflectance difference and photoreflectance spectra, respectively, the larger Rashba-type spin splitting is mainly induced by the additional interface introduced by step structures.

  12. Excitation spectra of circular, few-electron quantum dots

    PubMed

    Kouwenhoven; Oosterkamp; Danoesastro; Eto; Austing; Honda; Tarucha

    1997-12-05

    Studies of the ground and excited states in semiconductor quantum dots containing 1 to 12 electrons showed that the quantum numbers of the states in the excitation spectra can be identified and compared with exact calculations. A magnetic field induces transitions between the ground and excited states. These transitions were analyzed in terms of crossings between single-particle states, singlet-triplet transitions, spin polarization, and Hund's rule. These impurity-free quantum dots allow "atomic physics" experiments to be performed in magnetic field regimes not accessible for atoms.

  13. Excitation Spectra of Plane Site Cu Spins of Y0.52Pr0.48Ba2Cu3O7 (T_c≃ 20 K)

    NASA Astrophysics Data System (ADS)

    Kodama, Katsuaki; Shamoto, Shin-ichi; Harashina, Hiroshi; Sato, Masatoshi; Nishi, Masakazu; Kakurai, Kazuhisa

    1994-12-01

    Neutron inelastic scattering measurements have been carried out on Y0.52Pr0.48Ba2Cu3O7 with the superconducting transition temperature T_c≃ 20 K. From the spectral weight function χ''(q, ω) of the Cu-spin excitations in the CuO2 planes, the reduction of the hole-carrier concentration and the degree of the randomness induced by the substitution of Pr for Y are estimated. These results present evidences that the model of a hole-trapping by the hybridized states of the Pr4f and O2pπ orbitals proposed by Fehrenbacher and Rice [Phys. Rev. Lett. 70 (1993) 3471] provides an appropriate explanation of the experimental results associated with the well-known T c-suppression of R1-xPrxBa2Cu3O7 (R=Y or various lanthanide elements) by the Pr-doping.

  14. Temperature dependence of spin photocurrent spectra induced by Rashba- and Dresselhaus-type circular photogalvanic effect at inter-band excitation in InGaAs/AlGaAs quantum wells.

    PubMed

    Yu, Jinling; Cheng, Shuying; Lai, Yunfeng; Zheng, Qiao; Zhu, Laipan; Chen, Yonghai; Ren, Jun

    2015-10-19

    Spin photocurrent spectra induced by Rashba- and Dresselhaus-type circular photogalvanic effect (CPGE) at inter-band excitation have been experimentally investigated in InGaAs/AlGaAs quantum wells at a temperature range of 80 to 290 K. It is found that, the sign of Rashba-type current reverses at low temperatures, while that of Dresselhaus-type remains unchanged. The temperature dependence of ratio of Rashba and Dresselhaus spin-orbit coupling parameters, increasing from -6.7 to 17.9, is obtained, and the possible reasons are discussed. We also develop a model to extract the Rashba-type effective electric field at different temperatures. It is demonstrated that excitonic effect will significantly influence the Rashba-type CPGE, while it has little effect on Dresselhaus-type CPGE.

  15. Excitation of coherent propagating spin waves by pure spin currents

    PubMed Central

    Demidov, Vladislav E.; Urazhdin, Sergei; Liu, Ronghua; Divinskiy, Boris; Telegin, Andrey; Demokritov, Sergej O.

    2016-01-01

    Utilization of pure spin currents not accompanied by the flow of electrical charge provides unprecedented opportunities for the emerging technologies based on the electron's spin degree of freedom, such as spintronics and magnonics. It was recently shown that pure spin currents can be used to excite coherent magnetization dynamics in magnetic nanostructures. However, because of the intrinsic nonlinear self-localization effects, magnetic auto-oscillations in the demonstrated devices were spatially confined, preventing their applications as sources of propagating spin waves in magnonic circuits using these waves as signal carriers. Here, we experimentally demonstrate efficient excitation and directional propagation of coherent spin waves generated by pure spin current. We show that this can be achieved by using the nonlocal spin injection mechanism, which enables flexible design of magnetic nanosystems and allows one to efficiently control their dynamic characteristics. PMID:26818232

  16. Dynamical analysis of highly excited molecular spectra

    SciTech Connect

    Kellman, M.E.

    1993-12-01

    The goal of this program is new methods for analysis of spectra and dynamics of highly excited vibrational states of molecules. In these systems, strong mode coupling and anharmonicity give rise to complicated classical dynamics, and make the simple normal modes analysis unsatisfactory. New methods of spectral analysis, pattern recognition, and assignment are sought using techniques of nonlinear dynamics including bifurcation theory, phase space classification, and quantization of phase space structures. The emphasis is chaotic systems and systems with many degrees of freedom.

  17. Elementary spin excitations in ultrathin itinerant magnets

    NASA Astrophysics Data System (ADS)

    Zakeri, Khalil

    2014-12-01

    Elementary spin excitations (magnons) play a fundamental role in condensed matter physics, since many phenomena e.g. magnetic ordering, electrical (as well as heat) transport properties, ultrafast magnetization processes, and most importantly electron/spin dynamics can only be understood when these quasi-particles are taken into consideration. In addition to their fundamental importance, magnons may also be used for information processing in modern spintronics. Here the concept of spin excitations in ultrathin itinerant magnets is discussed and reviewed. Starting with a historical introduction, different classes of magnons are introduced. Different theoretical treatments of spin excitations in solids are outlined. Interaction of spin-polarized electrons with a magnetic surface is discussed. It is shown that, based on the quantum mechanical conservation rules, a magnon can only be excited when a minority electron is injected into the system. While the magnon creation process is forbidden by majority electrons, the magnon annihilation process is allowed instead. These fundamental quantum mechanical selection rules, together with the strong interaction of electrons with matter, make the spin-polarized electron spectroscopies as appropriate tools to excite and probe the elementary spin excitations in low-dimensional magnets e.g ultrathin films and nanostructures. The focus is put on the experimental results obtained by spin-polarized electron energy loss spectroscopy and spin-polarized inelastic tunneling spectroscopy. The magnon dispersion relation, lifetime, group and phase velocity measured using these approaches in various ultrathin magnets are discussed in detail. The differences and similarities with respect to the bulk excitations are addressed. The role of the temperature, atomic structure, number of atomic layers, lattice strain, electronic complexes and hybridization at the interfaces are outlined. A possibility of simultaneous probing of magnons and phonons

  18. Green's function formalism for calculating spin-wave spectra

    NASA Astrophysics Data System (ADS)

    Aryasetiawan, F.; Karlsson, K.

    1999-09-01

    We propose a formalism for calculating ab initio spin-wave spectra which is based on the many-body temperature Green's function. The main quantity to be calculated is the linear magnetic susceptibility from which all magnetic excitations involving the creation of an additional spin in the system can formally be obtained. The Schwinger functional derivative technique is employed in calculating the self-energy. The approach avoids both the assumption of local spins (Heisenberg model) and the use of a local exchange and correlation interaction (local-density approximation). Starting from the GW approximation we obtain a Bethe-Salpeter equation for the kernel describing the interaction between electrons in both spin channels. However, this kernel exhibits a nonlocal screened interaction.

  19. Confined spin wave spectra of Kagome artificial spin ice arrays

    NASA Astrophysics Data System (ADS)

    Panagiotopoulos, I.

    2017-01-01

    The spin wave modes of elongated magnetic islands arranged in Kagome artificial spin-ice arrays are micromagnetically simulated in the frequency regime between 3 and 16 GHz. The edge modes are more suitable in order to detect the signatures of various types of local order of the spin-ice lattice as they are much more sensitive to the magnetic configurations of neighboring elements. The spectra of arrays consisting up to 30 elements can be decomposed to those originating from local magnetic states of their vertices.

  20. Magnetic Excitation for Spin Vibration Testing

    NASA Technical Reports Server (NTRS)

    Johnson, Dexter; Mehmed, Oral; Brown, Gerald V.

    1997-01-01

    The Dynamic Spin Rig Laboratory (DSRL) at the NASA Lewis Research Center is a facility used for vibration testing of structures under spinning conditions. The current actuators used for excitation are electromagnetic shakers which are configured to apply torque to the rig's vertical rotor. The rotor is supported radially and axially by conventional bearings. Current operation is limited in rotational speed, excitation capability, and test duration. In an effort to enhance its capabilities, the rig has been initially equipped with a radial magnetic bearing which provides complementary excitation and shaft support. The new magnetic feature has been used in actual blade vibration tests and its performance has been favorable. Due to the success of this initial modification further enhancements are planned which include making the system fully magnetically supported. This paper reports on this comprehensive effort to upgrade the DSRL with an emphasis on the new magnetic excitation capability.

  1. Spin voltage generation through optical excitation of complementary spin populations

    NASA Astrophysics Data System (ADS)

    Bottegoni, Federico; Celebrano, Michele; Bollani, Monica; Biagioni, Paolo; Isella, Giovanni; Ciccacci, Franco; Finazzi, Marco

    2014-08-01

    By exploiting the spin degree of freedom of carriers inside electronic devices, spintronics has a huge potential for quantum computation and dissipationless interconnects. Pure spin currents in spintronic devices should be driven by a spin voltage generator, able to drive the spin distribution out of equilibrium without inducing charge currents. Ideally, such a generator should operate at room temperature, be highly integrable with existing semiconductor technology, and not interfere with other spintronic building blocks that make use of ferromagnetic materials. Here we demonstrate a device that matches these requirements by realizing the spintronic equivalent of a photovoltaic generator. Whereas a photovoltaic generator spatially separates photoexcited electrons and holes, our device exploits circularly polarized light to produce two spatially well-defined electron populations with opposite in-plane spin projections. This is achieved by modulating the phase and amplitude of the light wavefronts entering a semiconductor (germanium) with a patterned metal overlayer (platinum). The resulting light diffraction pattern features a spatially modulated chirality inside the semiconductor, which locally excites spin-polarized electrons thanks to electric dipole selection rules.

  2. Spin voltage generation through optical excitation of complementary spin populations.

    PubMed

    Bottegoni, Federico; Celebrano, Michele; Bollani, Monica; Biagioni, Paolo; Isella, Giovanni; Ciccacci, Franco; Finazzi, Marco

    2014-08-01

    By exploiting the spin degree of freedom of carriers inside electronic devices, spintronics has a huge potential for quantum computation and dissipationless interconnects. Pure spin currents in spintronic devices should be driven by a spin voltage generator, able to drive the spin distribution out of equilibrium without inducing charge currents. Ideally, such a generator should operate at room temperature, be highly integrable with existing semiconductor technology, and not interfere with other spintronic building blocks that make use of ferromagnetic materials. Here we demonstrate a device that matches these requirements by realizing the spintronic equivalent of a photovoltaic generator. Whereas a photovoltaic generator spatially separates photoexcited electrons and holes, our device exploits circularly polarized light to produce two spatially well-defined electron populations with opposite in-plane spin projections. This is achieved by modulating the phase and amplitude of the light wavefronts entering a semiconductor (germanium) with a patterned metal overlayer (platinum). The resulting light diffraction pattern features a spatially modulated chirality inside the semiconductor, which locally excites spin-polarized electrons thanks to electric dipole selection rules.

  3. Spin-flavor composition of excited baryons

    NASA Astrophysics Data System (ADS)

    Fernando, Ishara; Goity, Jose

    2015-10-01

    The excited baryon masses are analyzed in the framework of the 1 /Nc expansion using the available physical masses and also the masses obtained in lattice QCD for different quark masses. The baryon states are organized into irreducible representations of SU (6) × O (3) , where the [ 56 ,lP =0+ ] ground state and excited baryons, and the [ 56 ,2+ ] and [ 70 ,1- ] excited states are analyzed. The analyses are carried out to O 1 /Nc and first order in the quark masses. The issue of state identifications is discussed. Numerous parameter independent mass relations result at those orders, among them the well known Gell-Mann-Okubo and Equal Spacing relations, as well as additional relations involving baryons with different spins. It is observed that such relations are satisfied at the expected level of precision. Predictions for physically unknown states for each multiplet are obtained. From the quark-mass dependence of the coefficients in the baryon mass formulas an increasingly simpler picture of the spin-flavor composition of the baryons is observed with increasing pion mass (equivalently, increasing mu , d masses), as measured by the number of significant mass operators. This work was supported in part by DOE Contract No. DE-AC05-06OR23177 under which JSA operates the Thomas Jefferson National Accelerator Facility (J. L. G.), and by the NSF (USA) through Grant PHY-0855789 and PHY-1307413 (I. P. F and J. L. G).

  4. Spin excitations in fluctuating stripe phases of doped cuprate superconductors.

    PubMed

    Vojta, Matthias; Vojta, Thomas; Kaul, Ribhu K

    2006-09-01

    Using a phenomenological lattice model of coupled spin and charge modes, we determine the spin susceptibility in the presence of fluctuating stripe charge order. We assume the charge fluctuations to be slow compared to those of the spins, and combine Monte Carlo simulations for the charge order parameter with exact diagonalization of the spin sector. Our calculations unify the spin dynamics of both static and fluctuating stripe phases and support the notion of a universal spin excitation spectrum in doped cuprate superconductors.

  5. Excited state absorption spectra and intersystem crossing kinetics in diazanaphthalenes

    NASA Astrophysics Data System (ADS)

    Scott, Gary W.; Talley, Larry D.; Anderson, Robert W.

    1980-05-01

    Picosecond time-resolved, excited state absorption spectra in the visible following excitation at 355 nm are discussed for room temperature solutions of four diazanaphthalenes (DN)—quinoxaline (1,4-DN), quinazoline (1,3-DN), cinnoline (1,2-DN), and phthalazine (2,3-DN). Kinetics of singlet state decay are obtained by monitoring the decay of Sn←S1 bands. The intersystem crossing rate constant (kisc) is found to vary as kisc(1,4-DN)≳kisc(1,3-DN)≳kisc(1,2-DN). The kisc in phthalazine could not be determined from the weak, visible Sn←S1 absorption. Assuming rapid singlet vibrational relaxation and only minor effects due to energy gap variations, these experimental results agree with statistical limit predictions for the relative nonradiative rate. Calculations of the spin-orbit coupling matrix element βel= , using INDO wave functions, give the ordering βel(1,4-DN)≳βel(2,3-DN)≳βel(1,3-DN) ≳βel(1,2-DN).

  6. Spin excitations in hole-overdoped iron-based superconductors

    PubMed Central

    Horigane, K.; Kihou, K.; Fujita, K.; Kajimoto, R.; Ikeuchi, K.; Ji, S.; Akimitsu, J.; Lee, C. H.

    2016-01-01

    Understanding the overall features of magnetic excitation is essential for clarifying the mechanism of Cooper pair formation in iron-based superconductors. In particular, clarifying the relationship between magnetism and superconductivity is a central challenge because magnetism may play a key role in their exotic superconductivity. BaFe2As2 is one of ideal systems for such investigation because its superconductivity can be induced in several ways, allowing a comparative examination. Here we report a study on the spin fluctuations of the hole-overdoped iron-based superconductors Ba1-xKxFe2As2 (x = 0.5 and 1.0; Tc = 36 K and 3.4 K, respectively) over the entire Brillouin zone using inelastic neutron scattering. We find that their spin spectra consist of spin wave and chimney-like dispersions. The chimney-like dispersion can be attributed to the itinerant character of magnetism. The band width of the spin wave-like dispersion is almost constant from the non-doped to optimum-doped region, which is followed by a large reduction in the overdoped region. This suggests that the superconductivity is suppressed by the reduction of magnetic exchange couplings, indicating a strong relationship between magnetism and superconductivity in iron-based superconductors. PMID:27615691

  7. Spin excitations in hole-overdoped iron-based superconductors.

    PubMed

    Horigane, K; Kihou, K; Fujita, K; Kajimoto, R; Ikeuchi, K; Ji, S; Akimitsu, J; Lee, C H

    2016-09-12

    Understanding the overall features of magnetic excitation is essential for clarifying the mechanism of Cooper pair formation in iron-based superconductors. In particular, clarifying the relationship between magnetism and superconductivity is a central challenge because magnetism may play a key role in their exotic superconductivity. BaFe2As2 is one of ideal systems for such investigation because its superconductivity can be induced in several ways, allowing a comparative examination. Here we report a study on the spin fluctuations of the hole-overdoped iron-based superconductors Ba1-xKxFe2As2 (x = 0.5 and 1.0; Tc = 36 K and 3.4 K, respectively) over the entire Brillouin zone using inelastic neutron scattering. We find that their spin spectra consist of spin wave and chimney-like dispersions. The chimney-like dispersion can be attributed to the itinerant character of magnetism. The band width of the spin wave-like dispersion is almost constant from the non-doped to optimum-doped region, which is followed by a large reduction in the overdoped region. This suggests that the superconductivity is suppressed by the reduction of magnetic exchange couplings, indicating a strong relationship between magnetism and superconductivity in iron-based superconductors.

  8. Disorder, cluster spin glass, and hourglass spectra in striped magnetic insulators.

    PubMed

    Andrade, Eric C; Vojta, Matthias

    2012-10-05

    Hourglass-shaped magnetic excitation spectra have been detected in a variety of doped transition-metal oxides with stripelike charge order. Compared to the predictions of spin-wave theory for perfect stripes, these spectra display a different intensity distribution and anomalous broadening. Here we show, based on a comprehensive modeling for La5/3Sr1/3CoO4, how quenched disorder in the charge sector causes frustration, and consequently cluster-glass behavior at low temperatures, in the spin sector. This spin-glass physics, which is insensitive to the detailed nature of the charge disorder, but sensitive to the relative strength of the magnetic interstripe coupling, ultimately determines the distribution of magnetic spectral weight: The excitation spectrum, calculated using spin waves in finite disordered systems, is found to match in detail the observed hour-glass spectrum.

  9. On the particle excitations in the XXZ spin chain

    NASA Astrophysics Data System (ADS)

    Ovchinnikov, A. A.

    2013-12-01

    We continue to study the excited states for the XXZ spin chain corresponding to the complex roots of the Bethe Ansatz equations with the imaginary part equal to π/2. We propose the particle-hole symmetry which relates the eigenstates build up from the two different pseudovacuum states. We find the XXX spin chain limit for the eigenstates with the complex roots. We also comment on the low-energy excited states for the XXZ spin chain.

  10. Excitation of plasmons in Ag/Fe/W structure by spin-polarized electrons

    SciTech Connect

    Samarin, Sergey N.; Kostylev, Mikhail; Williams, J. F.; Artamonov, Oleg M.; Baraban, Alexander P.; Guagliardo, Paul

    2015-09-07

    Using Spin-polarized Electron-Energy Loss Spectroscopy (SPEELS), the plasmon excitations were probed in a few atomic layers thick Ag film deposited on an Fe layer or on a single crystal of W(110). The measurements were performed at two specular geometries with either a 25° or 72° angle of incidence. On a clean Fe layer (10 atomic layers thick), Stoner excitation asymmetry was observed, as expected. Deposition of a silver film on top of the Fe layer dramatically changed the asymmetry of the SPEELS spectra. The spin-effect depends on the kinematics of the scattering: angles of incidence and detection. The spin-dependence of the plasmon excitations in the silver film on the W(110) surface and on the ferromagnetic Fe film is suggested to arise from the spin-active Ag/W or Ag/Fe interfaces.

  11. Low-Energy Excitation Spectra in the Excitonic Phase of Cobalt Oxides

    NASA Astrophysics Data System (ADS)

    Yamaguchi, Tomoki; Sugimoto, Koudai; Ohta, Yukinori

    2017-04-01

    We study the excitonic phase and low-energy excitation spectra of perovskite cobalt oxides. Constructing the five-orbital Hubbard model defined on the three-dimensional cubic lattice for the 3d bands of Pr0.5Ca0.5CoO3, we calculate the excitonic susceptibility in the normal state in the random-phase approximation (RPA) to show the presence of the instability toward excitonic condensation. On the basis of the excitonic ground state with a magnetic multipole obtained in the mean-field approximation, we calculate the dynamical susceptibility of the excitonic phase in the RPA and find that there appear a gapless collective excitation in the spin-transverse mode (Goldstone mode) and a gapful collective excitation in the spin-longitudinal mode (Higgs mode). The experimental relevance of our results is discussed.

  12. Nonlinear spin-wave excitations at low magnetic bias fields

    PubMed Central

    Bauer, Hans G.; Majchrak, Peter; Kachel, Torsten; Back, Christian H.; Woltersdorf, Georg

    2015-01-01

    Nonlinear magnetization dynamics is essential for the operation of numerous spintronic devices ranging from magnetic memory to spin torque microwave generators. Examples are microwave-assisted switching of magnetic structures and the generation of spin currents at low bias fields by high-amplitude ferromagnetic resonance. Here we use X-ray magnetic circular dichroism to determine the number density of excited magnons in magnetically soft Ni80Fe20 thin films. Our data show that the common model of nonlinear ferromagnetic resonance is not adequate for the description of the nonlinear behaviour in the low magnetic field limit. Here we derive a model of parametric spin-wave excitation, which correctly predicts nonlinear threshold amplitudes and decay rates at high and at low magnetic bias fields. In fact, a series of critical spin-wave modes with fast oscillations of the amplitude and phase is found, generalizing the theory of parametric spin-wave excitation to large modulation amplitudes. PMID:26374256

  13. Excitations from a chiral magnetized state of a frustrated quantum spin liquid

    SciTech Connect

    Garlea, Vasile O; Zheludev, Andrey I; Tsvelik, A.; Regnault, L.-P.; Habicht, Klaus; Kiefer, K.; Roessli, Bertrand

    2009-01-01

    We study excitations in weakly interacting pairs of quantum spin ladders coupled through geometrically frustrated bonds. The ground state is a disordered spin liquid, at high fields replaced by an ordered chiral helimagnetic phase. The spectra observed by high-field inelastic neutron scattering experiments on the prototype compound Sul Cu2Cl4 are qualitatively different from those in the previously studied frustration-free spin liquids. Beyond the critical field Hc = 3.7 T, the soft mode that drives the quantum phase transition spawns two separate excitations: a gapless Goldstone mode and a massive magnon. Additional massive quasiparticles are clearly visible below Hc, but are destroyed in the ordered phase. In their place one observes a sharply bound excitation continuum.

  14. Excitations from a Chiral Magnetized State of a Frustrated Quantum Spin Liquid

    SciTech Connect

    Zheludev, A.; Tsvelik, A.; Garlea, V.O.; Regnault, L.-P.; Habicht, K.; Kiefer, K.; Roessli, B.

    2009-12-15

    We study excitations in weakly interacting pairs of quantum spin ladders coupled through geometrically frustrated bonds. The ground state is a disordered spin liquid that at high fields is replaced by an ordered chiral helimagnetic phase. The spectra observed by high-field inelastic neutron scattering experiments on the prototype compound Sul-Cu{sub 2}Cl{sub 4} are qualitatively different from those in the previously studied frustration-free spin liquids. Beyond the critical field H{sub c} = 3.7 T, the soft mode that drives the quantum phase transition spawns two separate excitations: a gapless Goldstone mode and a massive magnon. Additional massive quasiparticles are clearly visible below H{sub c}, but are destroyed in the ordered phase. In their place one observes a sharply bound excitation continuum.

  15. Hybrid excitations due to crystal field, spin-orbit coupling, and spin waves in LiFePO4

    NASA Astrophysics Data System (ADS)

    Yiu, Yuen; Le, Manh Duc; Toft-Peterson, Rasmus; Ehlers, Georg; McQueeney, Robert J.; Vaknin, David

    2017-03-01

    We report on the spin waves and crystal field excitations in single crystal LiFePO4 by inelastic neutron scattering over a wide range of temperatures, below and above the antiferromagnetic transition of this system. In particular, we find extra excitations below TN=50 K that are nearly dispersionless and are most intense around magnetic zone centers. We show that these excitations correspond to transitions between thermally occupied excited states of Fe2 + due to splitting of the S =2 levels that arise from the crystal field and spin-orbit interactions. These excitations are further amplified by the highly distorted nature of the oxygen octahedron surrounding the iron atoms. Above TN, magnetic fluctuations are observed up to at least 720 K, with an additional inelastic excitation around 4 meV, which we attribute to single-ion effects, as its intensity weakens slightly at 720 K compared to 100 K, which is consistent with the calculated cross sections using a single-ion model. Our theoretical analysis, using the MF-RPA model, provides both detailed spectra of the Fe d shell and estimates of the average ordered magnetic moment and TN. By applying the MF-RPA model to a number of existing spin-wave results from other Li M PO4 (M =Mn , Co, and Ni), we are able to obtain reasonable predictions for the moment sizes and transition temperatures.

  16. Non-compact local excitations in spin-glasses

    NASA Astrophysics Data System (ADS)

    Lamarcq, J.; Bouchaud, J.-P.; Martin, O. C.; Mézard, M.

    2002-05-01

    We study numerically the local low-energy excitations in the 3d Edwards-Anderson model for spin-glasses. Given the ground state, we determine the lowest-lying connected cluster of flipped spins with a fixed volume containing one given spin. These excitations are not compact, having a fractal dimension close to two, suggesting an analogy with lattice animals. Also, their energy does not grow with their size; the associated exponent is slightly negative whereas the one for compact clusters is positive. These findings call for a modification of the basic hypotheses underlying the droplet model.

  17. Excitations in a four-leg antiferromagnetic Heisenberg spin tube

    SciTech Connect

    Garlea, Vasile O; Zheludev, Andrey I; Regnault, L.-P.; Chung, J.-H.; Qiu, Y.; Boehm, Martin; Habicht, Klaus; Meissner, Michael

    2008-01-01

    Inelastic neutron scattering is used to investigate magnetic excitations in the quasi-one-dimensional quantum spin-liquid system Cu$_2$Cl$_{4}\\cdot$ D$_8$C$_4$SO$_2$. Contrary to previously conjectured models that relied on bond-alternating nearest neighbor interactions in the spin chains, the dominant interactions are actually next-nearest-neighbor in-chain antiferromagnetic couplings. The appropriate Heisenberg Hamiltonian is equivalent to that of a $S=1/2$ 4-leg spin-tube with almost perfect one dimensionality and no bond alternation. A partial geometric frustration of rung interactions induces a small incommensurability of short-range spin correlations.

  18. Excitations in a Four-Leg Antiferromagnetic Heisenberg Spin Tube,

    SciTech Connect

    Garlea, Vasile O; Zheludev, Andrey I; Regnault, L.-P.; Chung, J.-H.; Qiu, Y.; Boehm, Martin; Habicht, Klaus; Meissner, Michael; Fernandez-Baca, Jaime A

    2008-01-01

    Inelastic neutron scattering is used to investigate magnetic excitations in the quasi-one-dimensional quantum spin-liquid system Cu2Cl4 D8C4SO2. Contrary to previously conjectured models that relied on bond-alternating nearest-neighbor interactions in the spin chains, the dominant interactions are actually next-nearest-neighbor in-chain antiferromagnetic couplings. The appropriate Heisenberg Hamiltonian is equivalent to that of a S 1=2 4-leg spin-tube with almost perfect one dimensionality and no bond alternation. A partial geometric frustration of rung interactions induces a small incommensurability of short-range spin correlations.

  19. Excitations in a four-leg antiferromagnetic Heisenberg spin tube.

    PubMed

    Garlea, V O; Zheludev, A; Regnault, L-P; Chung, J-H; Qiu, Y; Boehm, M; Habicht, K; Meissner, M

    2008-01-25

    Inelastic neutron scattering is used to investigate magnetic excitations in the quasi-one-dimensional quantum spin-liquid system Cu(2)Cl(4).D(8)C(4)SO(2). Contrary to previously conjectured models that relied on bond-alternating nearest-neighbor interactions in the spin chains, the dominant interactions are actually next-nearest-neighbor in-chain antiferromagnetic couplings. The appropriate Heisenberg Hamiltonian is equivalent to that of a S=1/2 4-leg spin-tube with almost perfect one dimensionality and no bond alternation. A partial geometric frustration of rung interactions induces a small incommensurability of short-range spin correlations.

  20. First-principles Calculation of Excited State Spectra in QCD

    SciTech Connect

    Jozef Dudek,Robert Edwards,Michael Peardon,David Richards,Christopher Thomas

    2011-05-01

    Recent progress at understanding the excited state spectra of mesons and baryons is described. I begin by outlining the application of the variational method to compute the spectrum of QCD, and then present results for the excited meson spectrum, with continuum quantum numbers of the states clearly delineated. I emphasise the need to extend the calculation to encompass multi-hadron contributions, and describe a recent calculation of the I=2 pion-pion energy-dependent phase shifts as a precursor to the study of channels with resonant behavior. I conclude with recent results for the low lying baryon spectrum, and the prospects for future calculations.

  1. Analysis of the broadband chaotic spin-wave excitations in an active ring oscillator based on a metalized ferrite film

    NASA Astrophysics Data System (ADS)

    Kondrashov, A. V.; Ustinov, A. B.; Kalinikos, B. A.; Demokritov, S. O.

    2016-11-01

    This paper reports the first experimental study of broadband chaotic nonlinear spin- wave excitations which is formed through development of four-wave parametric processes in active ring oscillator based on metallized ferrite film. We find that an increase in the oscillation power leads to Hopf bifurcations sequence. Monochromatic, periodic quasi-periodic and chaotic excitations are observed. Spectra of the chaotic excitations consist of series of chaotic bands separated well in frequency. Parameters of the chaotic attractors are discussed.

  2. Electron-hole excitations and optical spectra from first principles

    SciTech Connect

    Rohlfing, Michael; Louie, Steven G.

    2000-08-15

    We present a recently developed approach to calculate electron-hole excitations and the optical spectra of condensed matter from first principles. The key concept is to describe the excitations of the electronic system by the corresponding one- and two-particle Green's function. The method combines three computational techniques. First, the electronic ground state is treated within density-functional theory. Second, the single-particle spectrum of the electrons and holes is obtained within the GW approximation to the electron self-energy operator. Finally, the electron-hole interaction is calculated and a Bethe-Salpeter equation is solved, yielding the coupled electron-hole excitations. The resulting solutions allow the calculation of the entire optical spectrum. This holds both for bound excitonic states below the band gap, as well as for the resonant spectrum above the band gap. We discuss a number of technical developments needed for the application of the method to real systems. To illustrate the approach, we discuss the excitations and optical spectra of spatially isolated systems (atoms, molecules, and semiconductor clusters) and of extended, periodic crystals (semiconductors and insulators). (c) 2000 The American Physical Society.

  3. Sensitivity enhancement of MQMAS NMR spectra of spin 3/2 nuclei using hyperbolic secant pulses

    NASA Astrophysics Data System (ADS)

    Siegel, Renée; Nakashima, Thomas T.; Wasylishen, Roderick E.

    2005-02-01

    The use of hyperbolic secant (HS) pulses to enhance the intensity of the central transition in MQMAS experiments for spin 3/2 quadrupolar nuclei is investigated by examining 87Rb NMR spectra of a powder sample of RbNO 3. The application of HS pulses prior to the triple-quantum (3Q) excitation provides sensitivity enhancements in MQMAS spectra that are superior to those previously reported. For the conversion of 3Q to single-quantum (1Q) observables, the HS pulses have an efficiency similar to that reported for double frequency sweeps (DFS) but greater than that of the fast amplitude modulation (FAM) technique.

  4. Magnetoluminescence spectra from quantum wells under high intensity pulsed excitation

    NASA Astrophysics Data System (ADS)

    Kioseoglou, G.; Haetty, J.; Cheong, H. D.; Chang, H. C.; Luo, H.; Petrou, A.; Dutta, M.; Pamulapati, J.

    1998-03-01

    Luminescence spectra from GaAs/AlAs and ZnCdSe/ZnSe quantum wells have been studied in magnetic fields up to 30 Tesla. The spectra were excited using a pulsed nitrogen laser pumping a dye module with a peak output power of 6 kW. The luminescence spectra exhibit a large number (up to 17) of distinct features due to interband transitions associated with the lowest confinement subbands e1 and h_1. The slopes dE/dB of these features indicate that they are associated with conduction band Landau levels. The value of these slopes is approximately 20% (12%) lower for the GaAs/AlAs (ZnCdSe/ZnSe) structures, assuming radiative recombinations with only the lowest valence band Landau level. If this assumption is relaxed, the observed reduction of the values of dE/dB would be even larger.

  5. Spin textures and spin-wave excitations in doped Dirac-Weyl semimetals

    NASA Astrophysics Data System (ADS)

    Araki, Yasufumi; Nomura, Kentaro

    2016-03-01

    We study correlations and magnetic textures of localized spins, doped in three-dimensional Dirac semimetals. An effective field theory for magnetic moments is constructed by integrating out the fermionic degrees of freedom. The spin correlation shows a strong anisotropy, originating from spin-momentum locking of Dirac electrons, in addition to the conventional Heisenberg-like ferromagnetic correlation. The anisotropic spin correlation allows topologically nontrivial magnetic excitation textures such as a transient hedgehog state, as well as the ferromagnetic ground state. The spin-wave dispersion in ferromagnetic Weyl semimetal also becomes anisotropic, being less dispersed perpendicular to the magnetization.

  6. Thermally excited proton spin-flip laser emission in tokamaks

    SciTech Connect

    Arunasalam, V.; Greene, G.J.

    1993-07-01

    Based on statistical thermodynamic fluctuation arguments, it is shown here for the first time that thermally excited spin-flip laser emission from the fusion product protons can occur in large tokamak devices that are entering the reactor regime of operation. Existing experimental data from TFTR supports this conjecture, in the sense that these measurements are in complete agreement with the predictions of the quasilinear theory of the spin-flip laser.

  7. Localized excitation of magnetostatic surface spin waves in yttrium iron garnet by shorted coaxial probe detected via spin pumping and rectification effect

    SciTech Connect

    Soh, Wee Tee Ong, C. K.; Peng, Bin

    2015-04-21

    We demonstrate the localized excitation and dc electrical detection of magnetostatic surface spin waves (MSSWs) in yttrium iron garnet (YIG) by a shorted coaxial probe. Thin films of NiFe and Pt are patterned at different regions onto a common bulk YIG substrate. A shorted coaxial probe is used to excite spin precession locally near various patterned regions. The dc voltages across the corresponding regions are recorded. For excitation of the Pt regions, the dc voltage spectra are dominated by the spin pumping of MSSWs from YIG, where various modes can be clearly distinguished. For the NiFe region, it is also found that spin pumping from MSSWs generated in YIG dominated the spectra, indicating that the spin pumped currents are dissipated into charge currents via the inverse Spin Hall effect (ISHE) in NiFe. For all regions, dc signals from YIG MSSWs are observed to be much stronger than the ferromagnetic resonance (FMR) uniform mode, likely due to the nature of the microwave excitation. The results indicate the potential of this probe for microwave imaging via dc detection of spin dynamics in continuous and patterned films.

  8. Efficient Spin-Flip Excitation of a Nickelocene Molecule.

    PubMed

    Ormaza, Maider; Bachellier, Nicolas; Faraggi, Marisa N; Verlhac, Benjamin; Abufager, Paula; Ohresser, Philippe; Joly, Loïc; Romeo, Michelangelo; Scheurer, Fabrice; Bocquet, Marie-Laure; Lorente, Nicolás; Limot, Laurent

    2017-02-22

    Inelastic electron tunneling spectroscopy (IETS) within the junction of a scanning tunneling microscope (STM) uses current-driven spin-flip excitations for an all-electrical characterization of the spin state of a single object. Usually decoupling layers between the single object, atom or molecule, and the supporting surface are needed to observe these excitations. Here we study the surface magnetism of a sandwich nickelocene molecule (Nc) adsorbed directly on Cu(100) by means of X-ray magnetic circular dichroism (XMCD) and density functional theory (DFT) calculations and show with IETS that it exhibits an exceptionally efficient spin-flip excitation. The molecule preserves its magnetic moment and magnetic anisotropy not only on Cu(100), but also in different metallic environments including the tip apex. By taking advantage of this robusteness, we are able to functionalize the microscope tip with a Nc, which can be employed as a portable source of inelastic excitations as exemplified by a double spin-flip excitation process.

  9. Spin excitations in the antiferromagnet NaNiO2

    NASA Astrophysics Data System (ADS)

    de Brion, S.; Darie, C.; Holzapfel, M.; Talbayev, D.; Mihály, L.; Simon, F.; Jánossy, A.; Chouteau, G.

    2007-03-01

    In NaNiO2 , Ni3+ ions form a quasi-two-dimensional triangular lattice of S=1/2 spins. The magnetic order observed below 20K has been described as an A type antiferromagnet with ferromagnetic layers weakly coupled antiferromagnetically. We studied the magnetic excitations with the electron spin resonance for frequencies 1-20cm-1 , in magnetic fields up to 14T . The bulk of the results are interpreted in terms of a phenomenological model involving biaxial anisotropy for the spins: a strong easy-plane term, and a weaker anisotropy within the plane.

  10. Spin Excitations in the Antiferromagnet NaNiO2

    SciTech Connect

    de Brion,S.; Darie, C.; Holzapfel, M.; Talbayev, D.; Mihaly, L.; Simon, F.; Janossy, A.; Chouteau, G.

    2007-01-01

    In NaNiO2 , Ni3+ ions form a quasi-two-dimensional triangular lattice of S=1/2 spins. The magnetic order observed below 20K has been described as an A type antiferromagnet with ferromagnetic layers weakly coupled antiferromagnetically. We studied the magnetic excitations with the electron spin resonance for frequencies 1 20cm-1 , in magnetic fields up to 14T . The bulk of the results are interpreted in terms of a phenomenological model involving biaxial anisotropy for the spins: a strong easy-plane term, and a weaker anisotropy within the plane

  11. Ground and Excited State Spectra of a Quantum Dot

    NASA Astrophysics Data System (ADS)

    Stewart, D. R.; Sprinzak, D.; Patel, S. R.; Marcus, C. M.; Duruoz, C. I.; Harris, J. S.

    1998-03-01

    We present linear and nonlinear magnetoconductance measurements of the ground and excited state spectra for successive electron occupancy in a gate defined lateral quantum dot. Previous measurementsfootnote D.R. Stewart, D. Sprinzak, C.M. Marcus, C.I. Duruoz and J.S. Harris Jr., Science 278, (1997). showed a direct correlation between the mth excited state of the N-electron system and the ground state of the (N+m)-electron system for m up to 4, consistent to a large degree with a single-particle picture. Here we report quantitative deviations of the excited state spectra from the spectrum of ground state magnetoconductances, attributed to many-body interactions in the finite system of N ~200 electrons. We also describe the behaviour of anticrossings in the ground state magnetoconductances. We acknowledge the support of JSEP (DAAH04-94-G-0058), ARO (DAAH04-95-1-0331), ONR-YIP (N00014-94-1-0622) and the NSF-PECASE program. D.S. acknowledges the support of MINERVA grant.

  12. Rotational Spectra in 29 Vibrationally Excited States of Interstellar Aminoacetonitrile

    NASA Astrophysics Data System (ADS)

    Kolesniková, L.; Alonso, E. R.; Mata, S.; Alonso, J. L.

    2017-04-01

    We report a detailed spectroscopic investigation of the interstellar aminoacetonitrile, a possible precursor molecule of glycine. Using a combination of Stark and frequency-modulation microwave and millimeter wave spectroscopies, we observed and analyzed the room-temperature rotational spectra of 29 excited states with energies up to 1000 cm‑1. We also observed the 13C isotopologues in the ground vibrational state in natural abundance (1.1%). The extensive data set of more than 2000 new rotational transitions will support further identifications of aminoacetonitrile in the interstellar medium.

  13. Excitations in a perfect magnetized quantum spin ladder

    NASA Astrophysics Data System (ADS)

    Zheludev, Andrey; Schmidiger, David; Muehlbauer, Sebastian; Severian, Gvasaliya; Bouillot, Pierre; Kollath, Corinna; Giamarchi, Thierry; Guidi, Tatiana; Bewley, Robert; Ehlers, Georg

    2013-03-01

    The strong-leg S = 1 / 2 Heisenberg spin ladder system C7(D10N)2CuBr4 is investigated in applied magnetic fields using inelastic neutron scattering anf DMRG calculations. The spectrum in the high-field Tomonaga-Luttinger spin liquid phase is found to be qualitatively different from that in the low-field spin gap phase. In the former, numerous spectral featrures, including incommensurate excitations and multi-spinon continua are identified. In contrast, the latter is dominated by long-lived magnon excitations and two-magnon bound states. An unprecedented quantitive agreement between experiment and numerical claculations is achieved. Supported by the Swiss National Fund through MANEP.

  14. On the spin wave multifractal spectra in magnetic multilayers

    NASA Astrophysics Data System (ADS)

    Bezerra, C. G.; Albuquerque, E. L.; , E. Nogueira, Jr.

    The multifractal properties of spin wave bandwidths in quasiperiodic magnetic multilayers are studied. The profiles of the bandwidths are analyzed and the f( α) function is calculated for different values of the dimensionless in-plane wave vector kxa and for four different sequences: Fibonacci, double-period, Thue-Morse and Rudin-Shapiro. We note that the f( α) spectra is qualitatively the same for different values of kxa.

  15. Correlations between ground and excited state spectra of a quantum Dot

    PubMed

    Stewart; Sprinzak; Marcus; Duruoz; Harris

    1997-12-05

    The ground and excited state spectra of a semiconductor quantum dot with successive electron occupancy were studied with linear and nonlinear magnetoconductance measurements. A direct correlation was observed between the mth excited state of the N-electron system and the ground state of the (N + m)-electron system for m up to 4. The results are consistent with a single-particle picture in which a fixed spectrum of energy levels is successively filled, except for a notable absence of spin degeneracy. Further departures from the single-particle picture due to electron-electron interaction were also observed. Magnetoconductance fluctuations of ground states show anticrossings where wave function characteristics are exchanged between adjacent levels.

  16. Fluorescence Emission and Excitation Spectra of Photo-Fragmented Nitrobenzene.

    NASA Astrophysics Data System (ADS)

    Lue, Christopher J.; Tanjaroon, Chakree; Johnson, J. Bruce; Allen, Susan D.; Reeve, Scott W.

    2012-06-01

    Upon absorption of a UV photon, nitrobenzene readily dissociates into C_6H_5, NO_2, C_6H_5NO, O, C_6H_5O, and NO through three different channels. We have recorded high resolution emission and excitation spectra of the NO resulting from photo-fragmented nitrobenzene using a pulsed picosecond tunable laser and a nanosecond dye laser. Specifically, the lasers probed the A^2Σ^+→ X^2π(1/2,3/2) NO band system between 225-260 nm using an one or two color process. In a one color process, the same energy (wavelength) photon is used to dissociate nitrobenzene and excite NO. In a two color process, photons of a particular energy are used to dissociate the nitrobenzene while photons of a different energy are used to probe the resultant NO. We have determined the rotational and vibrational temperatures of the nascent NO. And, we have examined the effect of the relative timing of the two photons on the fluorescence spectra to extract information about the photodissociation dynamics. Lin, M.-F.; Lee, Y. T.; Ni, C.-K.; Xu, S. and Lin, M. C. J. Chem. Phys., AIP, 2007, 126.

  17. Direct excitation of microwave-spin dressed states using a laser-excited resonance Raman interaction

    NASA Astrophysics Data System (ADS)

    Shahriar, M. S.; Hemmer, P. R.

    1990-10-01

    We have used a laser-induced resonance Raman transition between the ground-state hyperfine sublevels in a sodium atomic beam to excite individual dressed states of the microwave-spin hyperfine transition. In addition, we have used the microwave interaction to excite the Raman trapped state. Extension of this technique to mm waves or to the far infrared may lead to applications such as mm-wave-beam steering and holographic image conversion.

  18. The spin-flip extended single excitation configuration interaction method

    NASA Astrophysics Data System (ADS)

    Casanova, David; Head-Gordon, Martin

    2008-08-01

    An extension of the spin-flip single excitation configuration interaction (SF-CIS) method is introduced. The extension, abbreviated as SF-XCIS, includes all configurations in which no more than one virtual level of the high spin triplet reference becomes occupied and no more than one doubly occupied level becomes vacant. The number of such configurations is quadratic with molecule size, and the method is implemented in a direct algorithm whose cost scales in the same way with molecule size as CIS itself, thus permitting applications to large systems. Starting from a spin restricted triplet determinant, SF-XCIS yields spin-pure singlet, triplet, and quintet states, and treats both half-occupied reference orbitals in a fully balanced way to allow application to strongly correlated problems. Tests on bond dissociation in the HF molecule, the torsional potential of ethylene, and excited states of polyenes show encouraging improvements using SF-XCIS compared to SF-CIS and a previously suggested extension, the spin-complete CIS model.

  19. Excited state mass spectra of doubly heavy Ξ baryons

    NASA Astrophysics Data System (ADS)

    Shah, Zalak; Rai, Ajay Kumar

    2017-02-01

    In this paper, the mass spectra are obtained for doubly heavy Ξ baryons, namely, Ξ _{cc}+, Ξ _{cc}^{++}, Ξ _{bb}-, Ξ _{bb}0, Ξ _{bc}0 and Ξ _{bc}+. These baryons consist of two heavy quarks ( cc, bb, and bc) with a light ( d or u) quark. The ground, radial, and orbital states are calculated in the framework of the hypercentral constituent quark model with Coulomb plus linear potential. Our results are also compared with other predictions, thus, the average possible range of excited states masses of these Ξ baryons can be determined. The study of the Regge trajectories is performed in ( n, M2) and ( J, M2) planes and their slopes and intercepts are also determined. Lastly, the ground state magnetic moments of these doubly heavy baryons are also calculated.

  20. Optimization of excitation transfer in a spin chain

    NASA Astrophysics Data System (ADS)

    Gurman, Vladimir I.; Guseva, Irina S.; Fesko, Oles V.

    2016-06-01

    A revised formulation of the problem of fastest transfer of the excitation in a spin chain is considered on the base of Shrödinger equation which Hamiltonian depends linearly on control. It is taken into account that the excitation of the first or last spin means that it has greatest amplitude equal to the chain invariant whereas its phase is undefined and can be considered as an additional control variable. The role of this additional control is analyzed via transformation of the original problem with unbounded linear control to the regular derived problem known from the theory of degenerate problems [1, 2], in the same way as in [2]. The overall procedure is demonstrated in computational experiments with the use of visual examples.

  1. Quantum gates controlled by spin chain soliton excitations

    SciTech Connect

    Cuccoli, Alessandro; Nuzzi, Davide; Vaia, Ruggero; Verrucchi, Paola

    2014-05-07

    Propagation of soliton-like excitations along spin chains has been proposed as a possible way for transmitting both classical and quantum information between two distant parties with negligible dispersion and dissipation. In this work, a somewhat different use of solitons is considered. Solitons propagating along a spin chain realize an effective magnetic field, well localized in space and time, which can be exploited as a means to manipulate the state of an external spin (i.e., a qubit) that is weakly coupled to the chain. We have investigated different couplings between the qubit and the chain, as well as different soliton shapes, according to a Heisenberg chain model. It is found that symmetry properties strongly affect the effectiveness of the proposed scheme, and the most suitable setups for implementing single qubit quantum gates are singled out.

  2. Tuning Charge and Spin Excitations in Zigzag Edge Nanographene Ribbons

    PubMed Central

    Dutta, Sudipta; Wakabayashi, Katsunori

    2012-01-01

    Graphene and its quasi-one-dimensional counterpart, graphene nanoribbons, present an ideal platform for tweaking their unique electronic, magnetic and mechanical properties by various means for potential next-generation device applications. However, such tweaking requires knowledge of the electron-electron interactions that play a crucial role in these confined geometries. Here, we have investigated the magnetic and conducting properties of zigzag edge graphene nanoribbons (ZGNRs) using the many-body configuration interaction (CI) method on the basis of the Hubbard Hamiltonian. For the half-filled case, the many-body ground state shows a ferromagnetic spin-spin correlation along the zigzag edge, which supports the picture obtained from one-electron theory. However, hole doping reduces the spin and charge excitation gap, making the ground state conducting and magnetic. We also provide a two-state model that explains the low-lying charge and spin excitation spectrum of ZGNRs. An experimental setup to confirm the hole-mediated conducting and magnetic states is discussed. PMID:22816042

  3. User-friendly software for modeling collective spin wave excitations

    NASA Astrophysics Data System (ADS)

    Hahn, Steven; Peterson, Peter; Fishman, Randy; Ehlers, Georg

    There exists a great need for user-friendly, integrated software that assists in the scientific analysis of collective spin wave excitations measured with inelastic neutron scattering. SpinWaveGenie is a C + + software library that simplifies the modeling of collective spin wave excitations, allowing scientists to analyze neutron scattering data with sophisticated models fast and efficiently. Furthermore, one can calculate the four-dimensional scattering function S(Q,E) to directly compare and fit calculations to experimental measurements. Its generality has been both enhanced and verified through successful modeling of a wide array of magnetic materials. Recently, we have spent considerable effort transforming SpinWaveGenie from an early prototype to a high quality free open source software package for the scientific community. S.E.H. acknowledges support by the Laboratory's Director's fund, ORNL. Work was sponsored by the Division of Scientific User Facilities, Office of Basic Energy Sciences, US Department of Energy, under Contract No. DE-AC05-00OR22725 with UT-Battelle, LLC.

  4. Spin wave spectra in perpendicularly magnetized permalloy rings

    SciTech Connect

    Zhou, X.; Ding, J.; Adeyeye, A. O.; Kostylev, M.

    2015-03-16

    The dynamic behavior of perpendicularly magnetized permalloy circular rings is systematically investigated as a function of film thickness using broadband field modulated ferromagnetic resonance spectroscopy. We observed the splitting of one spin wave mode into a family of dense resonance peaks for the rings, which is markedly different from the single mode observed for continuous films of the same thickness. As the excitation frequency is increased, the mode family observed for the rings gradually converges into one mode. With the increase in the film thickness, a sparser spectrum of modes is observed. Our experimental results are in qualitative agreement with the dynamic micromagnetic simulations.

  5. Spin clusters and low-energy excitations in rare earth kagome systems

    NASA Astrophysics Data System (ADS)

    Hoch, M. J. R.

    2017-01-01

    The rare earth kagome systems R3Ga5SiO14 (R = Nd or Pr), which are weakly frustrated antiferromagnets, do not exhibit long-range order at temperatures down to 40 mK as revealed by neutron scattering. The neutron experiments provide evidence for the emergence at low temperatures of correlated spins in nanoscale cluster regions with magnetic field-dependent correlation lengths. A variety of techniques have been used to determine the magnetic and thermal properties of these systems. In particular, high-field electron spin resonance (ESR), nuclear magnetic resonance (NMR) and muon spin resonance (μSR) experiments have established that dynamic correlation of spins remains significant at temperatures well above 1 K. ESR provides evidence for spin wave excitations in spin clusters and the spectra have been interpreted using a Heisenberg model approach. While Nd3+ (J = 9/2) is a Kramers ion Pr3+ (J = 4) is not. This difference leads to contrasts in the magnetic properties of the two systems. This review surveys the information that has been obtained on the properties of these kagome materials over the past decade.

  6. Interaction between spin-wave excitations and pure spin currents in magnetic structures

    NASA Astrophysics Data System (ADS)

    Azevedo, Antonio

    2012-02-01

    The generation of pure spin current (PSC) in magnetic structures has attracted much attention not only for its fundamental importance in spintronics, but also because it opens up potential applications. One of the most exciting aspects of this area is the interplay between spin-waves (SW) and PSC. Here we report experimental results in which the PSC, generated by both spin pumping (SPE) [1] and spin Seebeck (SSE) [2] effects, can exert a spin-transfer torque sufficient to compensate the SW relaxation in yttrium iron garnet (YIG)/non-magnetic structures. By measuring the propagation of SW packets in single-crystal YIG films we were able to observe the amplification of volume and magnetostatic modes (MSW) by both SSE and SHE [3,4]. The excitation and detection of the SW packets is carried out by using a MSW delay line device. In both cases the amplification is attributed to the spin-transfer torque due to PSC generated by SSE as well as SHE. It will also be presented new results in which PSC are simultaneously excited by SSE and SPE effects in YIG films. While the spin current generated by SPE is obtained by exciting the ferromagnetic resonance (FMR) of the YIG film, the spin current due to SSE is created by applying a temperature gradient along the film plane. The effect of the superposition of both spin currents is characterized by measuring the spin Hall voltage (VH) along thin strips of Pt deposited on top of the YIG films. Whereas VH corresponding to the uniform FMR is amplified due the SSE the voltages corresponding to the other magnetostatic spin-wave modes are attenuated [5]. [4pt] [1] Y. Tserkovnyak, et al., Rev. Mod. Phys. 77, 1375 (2005).[0pt] [2] K. Uchida, et al., Nature 455, 778 (2008).[0pt] [3] E. Padr'on-Hern'andez, A. Azevedo, and S. M. Rezende, Phys. Rev. Letts., 107, 197203 (2011).[0pt] [4] E. Padr'on-Hern'andez, A. Azevedo, and S. M. Rezende, Appl. Phys. Letts., 99 (2011) in press.[0pt] [5] G.L. da Silva, L.H. Vilela-Leão, S. M. Rezende and A

  7. Excited and exotic charmonium, D s and D meson spectra for two light quark masses from lattice QCD

    NASA Astrophysics Data System (ADS)

    Cheung, Gavin K. C.; O'Hara, Cian; Moir, Graham; Peardon, Michael; Ryan, Sinéad M.; Thomas, Christopher E.; Tims, David

    2016-12-01

    We present highly-excited charmonium, D s and D meson spectra from dynamical lattice QCD calculations with light quarks corresponding to M π ˜ 240 MeV and compare these to previous results with M π ˜ 400 MeV. Utilising the distillation framework, large bases of carefully constructed interpolating operators and a variational procedure, we extract and reliably identify the continuum spin of an extensive set of excited mesons. These include states with exotic quantum numbers which, along with a number with non-exotic quantum numbers, we identify as having excited gluonic degrees of freedom and interpret as hybrid mesons. Comparing the spectra at the two different M π , we find only a mild light-quark mass dependence and no change in the overall pattern of states.

  8. Spin Excitation Under Electron Delocalization of Side Radicals in Quasi-One-Dimensional Organic Ferromagnet

    NASA Astrophysics Data System (ADS)

    Jiang, Hong; Hu, Xue-Ning; Zhao, Yin-chang; Zhang, Chao

    2017-02-01

    Spin excitation in poly(1,4-bis(2,2,6,6-tetramethyl-4-oxy-piperidyl-1-oxyl)-butadiin) (poly-BIPO), a quasi-one-dimensional organic ferromagnet, was investigated based on the extended Su-Schriffer-Heeger model by considering electron hopping and the spin correlation between the main chain and side radicals. The lattice, charge density, and spin density configurations of the single spin as well as spin domain excited states of the organic ferromagnet poly-BIPO were systematically studied. The side radical spin excitation gives rise to lattice distortion, charge density localization, and a spin density defect on the main chain. A peak induced by spin excitation is predicted to appear in the density of states of the organic ferromagnet poly-BIPO based on calculations for different spin electron states. These results expand knowledge on elementary excitation in organic materials and have significant implications for the design of spintronic devices.

  9. Low Lying Spin Excitation in the Spin Ice Ho2Ti2O7

    SciTech Connect

    Ehlers, Georg; Mamontov, Eugene; Zamponi, Michaela M; Gardner, Jason S

    2010-01-01

    The high flux and low background of the new backscattering spectrometer at the SNS combine to produce an excellent signal to noise ratio, allowing us to investigate a low lying weak excitation never seen before in the spin ice, Ho{sub 2}Ti{sub 2}O{sub 7}. This non-dispersive excitation has been observed at E = 26.3 {mu}eV below 100 K but is resolution limited only below {approx}65 K. It is indifferent to magnetic fields below {mu}{sub 0}H = 4.5 T, at 1.6 K. These characteristics help us to identify the excitation as due to the nuclear spin system.

  10. Excited-state Raman spectroscopy with and without actinic excitation: S{sub 1} Raman spectra of trans-azobenzene

    SciTech Connect

    Dobryakov, A. L.; Quick, M.; Ioffe, I. N.; Granovsky, A. A.; Ernsting, N. P.; Kovalenko, S. A.

    2014-05-14

    We show that femtosecond stimulated Raman spectroscopy can record excited-state spectra in the absence of actinic excitation, if the Raman pump is in resonance with an electronic transition. The approach is illustrated by recording S{sub 1} and S{sub 0} spectra of trans-azobenzene in n-hexane. The S{sub 1} spectra were also measured conventionally, upon nπ* (S{sub 0} → S{sub 1}) actinic excitation. The results are discussed and compared to earlier reports.

  11. Doping evolution of spin and charge excitations in the Hubbard model

    DOE PAGES

    Kung, Y. F.; Nowadnick, E. A.; Jia, C. J.; ...

    2015-11-05

    We shed light on how electronic correlations vary across the phase diagram of the cuprate superconductors, examining the doping evolution of spin and charge excitations in the single-band Hubbard model using determinant quantum Monte Carlo (DQMC). In the single-particle response, we observe that the effects of correlations weaken rapidly with doping, such that one may expect the random phase approximation (RPA) to provide an adequate description of the two-particle response. In contrast, when compared to RPA, we find that significant residual correlations in the two-particle excitations persist up to 40% hole and 15% electron doping (the range of dopings achievedmore » in the cuprates). Ultimately, these fundamental differences between the doping evolution of single- and multi-particle renormalizations show that conclusions drawn from single-particle processes cannot necessarily be applied to multi-particle excitations. Eventually, the system smoothly transitions via a momentum-dependent crossover into a weakly correlated metallic state where the spin and charge excitation spectra exhibit similar behavior and where RPA provides an adequate description.« less

  12. Doping evolution of spin and charge excitations in the Hubbard model

    SciTech Connect

    Kung, Y. F.; Nowadnick, E. A.; Jia, C. J.; Johnston, S.; Moritz, B.; Scalettar, R. T.; Devereaux, T. P.

    2015-11-05

    We shed light on how electronic correlations vary across the phase diagram of the cuprate superconductors, examining the doping evolution of spin and charge excitations in the single-band Hubbard model using determinant quantum Monte Carlo (DQMC). In the single-particle response, we observe that the effects of correlations weaken rapidly with doping, such that one may expect the random phase approximation (RPA) to provide an adequate description of the two-particle response. In contrast, when compared to RPA, we find that significant residual correlations in the two-particle excitations persist up to 40% hole and 15% electron doping (the range of dopings achieved in the cuprates). Ultimately, these fundamental differences between the doping evolution of single- and multi-particle renormalizations show that conclusions drawn from single-particle processes cannot necessarily be applied to multi-particle excitations. Eventually, the system smoothly transitions via a momentum-dependent crossover into a weakly correlated metallic state where the spin and charge excitation spectra exhibit similar behavior and where RPA provides an adequate description.

  13. Superconductivity and spin excitations in orbitally ordered FeSe

    NASA Astrophysics Data System (ADS)

    Kreisel, Andreas; Mukherjee, Shantanu; Hirschfeld, P. J.; Andersen, B. M.

    We provide a band-structure with low-energy properties consistent with recent photoemission and quantum oscillations measurements on the Fe-based superconductor FeSe, including a mean-field like orbital ordering in the dxz /dyz channel, and show that this model also accounts for the temperature dependence of the measured Knight shift and the spin-relaxation rate. An RPA calculation of the dynamical spin susceptibility yields spin excitations which are peaked at wave vector (π , 0) in the 1-Fe Brillouin zone, with a broad maximum at energies of order a few meV. Furthermore, the superconducting gap structure obtained from spin fluctuation theory exhibits nodes on the electron pockets, consistent with the 'V'-shaped density of states measured by tunneling spectroscopy on this material. The redistribution of spectral weight in the superconducting state creates a (π , 0) ''neutron resonance'' as seen in recent experiments. Comparing to various experimental results, we give predictions for further studies A.K. and B.M.A. acknowledge financial support from a Lundbeckfond fellowship (Grant No. A9318). P.J.H. was partially supported by the Department of Energy under Grant No. DE-FG02-05ER46236.

  14. Thermal Hall Effect of Spin Excitations in a Kagome Magnet.

    PubMed

    Hirschberger, Max; Chisnell, Robin; Lee, Young S; Ong, N P

    2015-09-04

    At low temperatures, the thermal conductivity of spin excitations in a magnetic insulator can exceed that of phonons. However, because they are charge neutral, the spin waves are not expected to display a thermal Hall effect. However, in the kagome lattice, theory predicts that the Berry curvature leads to a thermal Hall conductivity κ(xy). Here we report observation of a large κ(xy) in the kagome magnet Cu(1-3, bdc) which orders magnetically at 1.8 K. The observed κ(xy) undergoes a remarkable sign reversal with changes in temperature or magnetic field, associated with sign alternation of the Chern flux between magnon bands. The close correlation between κ(xy) and κ(xx) firmly precludes a phonon origin for the thermal Hall effect.

  15. Resonant excitation of coupled skyrmions by spin-transfer torque

    NASA Astrophysics Data System (ADS)

    Dai, Y. Y.; Wang, H.; Yang, T.; Zhang, Z. D.

    2016-12-01

    Resonant excitations of coupled skyrmions in Co/Ru/Co nanodisks activated by spin-transfer torque (STT) have been studied by micromagnetic simulations. It is found that STT is an effective method to manipulate skyrmion dynamics. Unlike the dynamics driven by a microwave field, two skyrmions with opposite chiralities move synchronously in the same direction when they are driven by STT, which makes it easier to observe the dynamics of coupled skyrmions in experiments. Resonant excitations of coupled skyrmions can be controlled by changing the frequency or amplitude ratio of a dual-frequency alternating current (AC). In addition, the magnetostatic interaction between the two skyrmions plays an important role in the dynamics of coupled skyrmions.

  16. Hydrodynamic study of edge spin-vortex excitations of fractional quantum Hall fluid

    NASA Astrophysics Data System (ADS)

    Rabiu, M.; Mensah, S. Y.; Seini, I. Y.; Abukari, S. S.

    2016-07-01

    We undertake a theoretical study of edge spin-vortex excitations in fractional quantum Hall fluid. This is done in view of quantised Euler hydrodynamics theory. The dispersions of true excitations for fractions within 0 ≤ ν ≤ 1 are simulated which exhibit universal similarities and differences in behaviour. The differences arise from different edge smoothness and spin (pseudo-spin) polarisations, in addition to spin-charge competition. In particular, tuning the spin-charge factor causes coherent spin flipping associated with partial and total polarisations of edge spin-vortices. This observation is tipped as an ideal mechanism for realisation of functional spintronic devices.

  17. Entanglement and corner Hamiltonian spectra of integrable open spin chains

    NASA Astrophysics Data System (ADS)

    Kim, Panjin; Katsura, Hosho; Trivedi, Nandini; Han, Jung Hoon

    2016-11-01

    We investigate the entanglement entropy (EE) and entanglement spectra (ES) of critical SU (N ) (2 ≤N ≤4 ) spin chains and other integrable models of finite length with the density matrix renormalization group method. For all models under investigation, we find a remarkable agreement of the level spacings and the degeneracy structure of the ES with the spectrum of the corner Hamiltonian (CS), defined as the generator of the associated corner transfer matrix. The correspondence holds between ES(n ) at the n th cut position from the edge of the spin model, and the spectrum CS(n ) of the corner Hamiltonian of length n , for all values of n that we have checked. The cut position dependence of the ES shows a period-N oscillatory behavior for a given SU (N ) chain, reminiscent of the oscillatory part of the entanglement entropy observed in the past for the same models. However, the oscillations of the ES do not die out in the bulk of the chain, in contrast to the asymptotically vanishing oscillation of the entanglement entropy. We present a heuristic argument based on Young tableaux construction that can explain the period-N structure of the ES qualitatively.

  18. Spin-torque-driven excitations in magnetic thin films

    NASA Astrophysics Data System (ADS)

    Wang, C.; Seinige, H.; Staudacher, T.; Tsoi, M.

    2011-03-01

    Spin transfer torque (STT) refers to a novel method to control and manipulate magnetic moments using an electrical current. For the past decade it has proven to be a fascinating domain of research with a number of manifestations in various systems interesting both from fundamental science's point of view as well as for technological applications. In ferromagnetic/nonmagnetic (F/N) multilayers a dc electrical current can switch and/or drive its constituent F parts into high-frequency precession which is of interest for microwave and magnetic recording technologies. Interestingly, application of high-frequency currents can also drive the multilayer, e.g., into ferromagnetic resonance (STT-FMR) precession. In our experiments we use point contacts to inject high microwave currents into a variety of magnetic thin films including NiFe/Cu/NiFe/IrMn and NiFe/Cu/Co spin valves, and single ferromagnetic (NiFe or Co) films. The resulting magnetodynamics are detected electrically when a small rectified dc voltage appears across the contact at resonance. We find that in addition to a standard FMR, the microwave currents can excite other resonance modes in our point contacts. We study the behavior of the excitations as a function of applied magnetic field, dc bias current, and microwave frequency. Supported in part by NSF grants DMR-06-45377.

  19. Using RIXS to Uncover Elementary Charge and Spin Excitations

    NASA Astrophysics Data System (ADS)

    Jia, Chunjing; Wohlfeld, Krzysztof; Wang, Yao; Moritz, Brian; Devereaux, Thomas P.

    2016-04-01

    Despite significant progress in resonant inelastic x-ray scattering (RIXS) experiments on cuprates at the Cu L -edge, a theoretical understanding of the cross section remains incomplete in terms of elementary excitations and the connection to both charge and spin structure factors. Here, we use state-of-the-art, unbiased numerical calculations to study the low-energy excitations probed by RIXS in the Hubbard model, relevant to the cuprates. The results highlight the importance of scattering geometry, in particular, both the incident and scattered x-ray photon polarization, and they demonstrate that on a qualitative level the RIXS spectral shape in the cross-polarized channel approximates that of the spin dynamical structure factor. However, in the parallel-polarized channel, the complexity of the RIXS process beyond a simple two-particle response complicates the analysis and demonstrates that approximations and expansions that attempt to relate RIXS to less complex correlation functions cannot reproduce the full diversity of RIXS spectral features.

  20. Energy spectra of a spin-½ XY spin molecule interacting with a single mode field cavity: Numerical study

    NASA Astrophysics Data System (ADS)

    Tonchev, H.; Donkov, A. A.; Chamati, H.

    2016-10-01

    In a previous paper [J.Phys.: Conf. Ser. 682 (2016) 012032] we studied analytically the energy spectra of a finite-size spin ½ XY chain (molecule) coupled at an arbitrary spin site to a single mode of an electromagnetic field via the Jaynes-Cummings model. We considered spin rings and open spin molecules with up to 4 spins and an interaction restricted to nearest-neighbours. Here we extend our investigation, addressing numerically the energy spectra of molecules of up to 10 spins with nearest-neighbour or long- range interaction. Furthermore we analyze the behaviour of an invariant operator, constructed by combining the magnetization of the spin-chain and the total number of photons in the system. We found a strong dependence on the number (even or odd) of sites in the molecules. This study is aimed at finding the appropriate combination of the physical parameters that could make the system suitable for use in quantum computations.

  1. The excited spin state of Comet 2P/Encke

    NASA Astrophysics Data System (ADS)

    Belton, Michael J. S.; Samarasinha, Nalin H.; Fernández, Yan R.; Meech, Karen J.

    2005-05-01

    Ways to rationalize the different periods (e.g., 15.08 h, Luu and Jewitt, 1990, Icarus 86, 69-81; 11.01 h, Fernández et al., 2004, Icarus, in this issue; Lowry et al., 2003, Lunar Planet. Sci. XXXIV, Abstract 2056) seen in near aphelion R-band light curves of Comet 2P/Encke are explored. We show that the comet is usually active at aphelion and it's observed light curves contain signal from both the nucleus and an unresolved coma. The coma contribution to the observed brightness is generally found to dominate with the nucleus providing from 28 to 87% of the total brightness. The amplitude of the observed variations cannot be explained by the nucleus alone and are due to coma activity. We show that some seven periodicities exist in the observed light curves at various times and that this is likely the result of an active nucleus spinning in an excited spin state. The changing periodicities are probably due to changes in the relative strengths of the active areas. We work out possible excited states based on experience with model light curves and by using an analogy to light curve observations of Comet 1P/Halley for which the spin state has been separately determined from spacecraft observations. There is a possibility of a fully relaxed principal axis spin state (0.538 d -1; P=44.6 h) but, because it provides a poorer fit to the observed periodicities than the best fit excited state together with the absence of a peak near 1.08 d -1 ( 2f) in the frequency spectrum of the Fernández et al. (2000, Icarus 147, 145-160) thermal IR lightcurve, we consider it unlikely. Both SAM and LAM excited states are allowed by the underlying periodicities and additional information is needed to choose between these. Our choice of a low excitation SAM state, i.e., one in which the instantaneous spin axis nutates around the total angular momentum vector in a motion that is characterized by limited angular oscillations around the long axis, is based on Sekanina's (1988, Astron J. 95

  2. Spin-wave excitations induced by spin current in spin-valve structures

    NASA Astrophysics Data System (ADS)

    Liu, Haoliang; Sun, Dali; Zhang, Chuang; Groesbeck, Matthew; Vardeny, Zeev Valy; Department of Physics; Astronomy, University of Utah, Salt Lake City, Utah 84112, USA Team

    2016-03-01

    We have investigated the magnetization dynamics of NiFe/Pt/Co spin-valve structures with different Pt layer thickness, using a broadband ferromagnetic resonance (FMR) and Brillouin light scattering (BLS) at ambient temperature. We found that the Gilbert damping factor, α of the two ferromagnetic (FM) layer films in the spin-valve structure are significantly larger than α of each individual FM layer. We interpret the increase in α in the spin-valve configuration as due to an interaction between the FM layers mediated by the induced spin current through the Pt interlayer when FMR conditions are met for one of the FM. This was verified by BLS of the spin-valve structure, in which the magnons density in the adjacent FM layer is enhanced upon FMR of the other FM layer. We have studied this spin-current-mediated interaction as a function of the Pt interlayer. Work supported by the MURI-AFOSR Grant FA9550-14-1-0037, and the UofU facility center supported by NSF-MRSEC Grant DMR-1121252.

  3. Multiple quantum magic-angle spinning using rotary resonance excitation

    NASA Astrophysics Data System (ADS)

    Vosegaard, Thomas; Florian, Pierre; Massiot, Dominique; Grandinetti, Philip J.

    2001-03-01

    We have discovered rotary resonances between rf field strength, ω1, and magic-angle spinning (MAS) frequency, ωR, which dramatically enhance the sensitivity of triple quantum preparation and mixing in the multiple-quantum MAS experiment, particularly for quadrupolar nuclei having low gyromagnetic ratios or experiencing strong quadrupole couplings. Triple quantum excitation efficiency minima occur when 2ω1=nωR, where n is an integer, with significant maxima occurring between these minima. For triple quantum mixing we observe maxima when ω1=nωR. In both preparation and mixing the pulse lengths required to reach maxima exceed one rotor period. We have combined these rotary resonance conditions into a new experiment called FASTER MQ-MAS, and have experimentally demonstrated a factor of 3 enhancement in sensitivity in comparison to conventional MQ-MAS.

  4. Excitation spectra of disordered dimer magnets near quantum criticality.

    PubMed

    Vojta, Matthias

    2013-08-30

    For coupled-dimer magnets with quenched disorder, we introduce a generalization of the bond-operator method, appropriate to describe both singlet and magnetically ordered phases. This allows for a numerical calculation of the magnetic excitations at all energies across the phase diagram, including the strongly inhomogeneous Griffiths regime near quantum criticality. We apply the method to the bilayer Heisenberg model with bond randomness and characterize both the broadening of excitations and the transfer of spectral weight induced by disorder. Inside the antiferromagnetic phase this model features the remarkable combination of sharp magnetic Bragg peaks and broad magnons, the latter arising from the tendency to localization of low-energy excitations.

  5. Excited State Mass Spectra of Ω0 c Baryon

    NASA Astrophysics Data System (ADS)

    Shah, Z.; Thakkar, K.; Rai, A. K.; Vinodkumar, P. C.

    2016-10-01

    We have calculated the radial and orbital excited states of singly charmed baryon Oc using the Hypercentral Constituent Quark Model (hCQM). The confinement potential is assumed as coulomb plus power potential (CPP V ). The ground state and excited state masses are determined with and with out first order correction to the potential. Furthermore, we plot graph between Mass(M) → Potential Index(v). Our calculated results are in good agreement with experimental and other theoretical predictions.

  6. Distance Dependence of Electron Spin Polarization during Photophysical Quenching of Excited Naphthalene by TEMPO Radical.

    PubMed

    Rane, Vinayak; Das, Ranjan

    2015-06-04

    Quenching of excited states by a free radical is generally studied in systems where these two are separate entities freely moving in a liquid solution. Random diffusive encounters bring them together to cause the quenching and leave the spins of the radical polarized. In the dynamics of the radical-triplet pair mechanism of the generation of electron spin polarization (ESP), the distance-dependent exchange interaction plays a crucial role. To investigate how the distance between the excited molecule and the radical influences the ESP, we have covalently linked a naphthalene moiety to a TEMPO free radical through a spacer group of three different lengths. We compared the ESP process of these linked compounds with that of the usual "unlinked system" of naphthalene and TEMPO through time-resolved EPR experiments at low temperature in n-hexane solution. The time evolution of both the linked and the "unlinked system" was treated on a similar footing. The time-dependent EPR signal was analyzed by combining photophysical kinetics and time-dependent Bloch equations incorporating spin dynamics. Sequential quenching of the singlet state and the triplet state of naphthalene was seen in all the systems, as revealed through the spin-polarized TREPR spectra of opposite phase. The magnitudes of the ESP in the linked molecules were higher than those of the "unlinked system," showing that when the two moieties are held together greater mixing of quartet-doublet states takes place. The magnitudes of ESP steadily decrease with increasing the length of the spacer group. The polarization magnitudes due to triplet quenching and singlet quenching are very similar, differing by a factor of only ∼2. These characteristics show that for all the linked molecules the quenching takes place in the "weak exchange" regime and at almost the same distance of separation between the two moieties. Our results also showed that observation of small absorptive TREPR signals does not necessarily imply

  7. Spin excitations of CoCO 3 in a longitudinal magnetic field

    NASA Astrophysics Data System (ADS)

    Loktev, V. M.

    1981-01-01

    The magnetization and the spectrum of spin excitations of CoCO 3 in an external magnetic field parallel to a third-order crystal axis are calculated using the model of an easy plane antiferrodielectric with spin 3/2. It is shown that with increasing field the spin projection on its quantization axis contracts due to the large single-ion anisotropy of cobalt carbonate. The dependence on the external field of the crystal absorption frequencies with excitation of spin waves and low-frequency excitations is analyzed.

  8. Spin observables for the isovector spin-dipole giant resonance excited in (p,n) reactions at medium energies.

    NASA Astrophysics Data System (ADS)

    Watson, J. W.

    1996-10-01

    For charge-exchange reactions at medium energies, one of the dominant features of small-angle spectra is the excitation of the ΔT = 1, ΔL = 1, ΔS = 1 isovector "spin-dipole" resonance (SDR). We describe how polarization-transfer measurements can be used to identify the overlapping J^π = 0^-, 1^-, and 2^- components of the SDR. Results for ^16O(p,n) and ^40Ca(p,n) using data (J. W. Watson et al.), Nucl. Phys. A577, 79c (1994). (J. W. Watson et al.), Nucl. Phys. A599, 211c (1996). for the transverse polarization-transfer coefficient D_NN' are presented and compared with distorted-wave impulse approximation (DWIA) calculations with theory of finite Fermi systems (TFFS) wavefunctions. (F. A. Gareev et al.), Sov. J. Part. Nucl. 19, 373 (1988). Future experiments will utilize complete sets of polarization-transfer data to extract the longitudinal and transverse spin responses,(M. Ichimura and K. Kawahigashi, Phys. Rev. C45), 1822 (1992). which will provide a more definitive separation of the different J^πs in the SDR. footnote Supported by NSF PHY 94-09265

  9. Persistent spin excitations in doped antiferromagnets revealed by resonant inelastic light scattering

    NASA Astrophysics Data System (ADS)

    Jia, C. J.; Nowadnick, E. A.; Wohlfeld, K.; Kung, Y. F.; Chen, C.-C.; Johnston, S.; Tohyama, T.; Moritz, B.; Devereaux, T. P.

    2014-02-01

    How coherent quasiparticles emerge by doping quantum antiferromagnets is a key question in correlated electron systems, whose resolution is needed to elucidate the phase diagram of copper oxides. Recent resonant inelastic X-ray scattering (RIXS) experiments in hole-doped cuprates have purported to measure high-energy collective spin excitations that persist well into the overdoped regime and bear a striking resemblance to those found in the parent compound, challenging the perception that spin excitations should weaken with doping and have a diminishing effect on superconductivity. Here we show that RIXS at the Cu L3-edge indeed provides access to the spin dynamical structure factor once one considers the full influence of light polarization. Further we demonstrate that high-energy spin excitations do not correlate with the doping dependence of Tc, while low-energy excitations depend sensitively on doping and show ferromagnetic correlations. This suggests that high-energy spin excitations are marginal to pairing in cuprate superconductors.

  10. Stratification effects and IUE spectra of high excitation planetaries

    NASA Technical Reports Server (NTRS)

    Feibelman, W.; Aller, L. H.

    1982-01-01

    Individual strips across IUE low resolution images of a number of high excitation planetaries with appreciable angular disks (including NGC 2452, 3242, 6818, and IC 1297) are analyzed to assess stratification effects. The familiar enhancement of high excitation lines toward the center is well exhibited, but some unexpected structural features are found in NGC 2452 where C IV shows a single central maximum, but C III, Ne IV, and He II seem to have a central dip. The new IUE data permit improved chemical composition estimates for several planetaries previously analyzed by Aller and Czyzak.

  11. Theoretical formalism for collective spin-wave edge excitations in arrays of dipolarly interacting magnetic nanodots

    NASA Astrophysics Data System (ADS)

    Lisenkov, Ivan; Tyberkevych, Vasyl; Nikitov, Sergey; Slavin, Andrei

    2016-06-01

    A general theory of collective spin-wave edge modes in semi-infinite and finite periodic arrays of magnetic nanodots having uniform dynamic magnetization (macrospin approximation) is developed. The theory is formulated using a formalism of multivectors of magnetization dynamics, which allows one to study edge modes in arrays having arbitrarily complex primitive cells and lattice structure. The developed formalism can describe spin-wave edge modes localized both at the physical edges of the array and at the internal "domain walls" separating the array regions existing in different static magnetization states. Using a perturbation theory, in the framework of the developed formalism, it is possible to calculate damping of the edge modes and to describe their excitation by external variable magnetic fields. The theory is illustrated on the following practically important examples: (i) calculation of the FMR absorption in a finite nanodot array having the shape of a right triangle; (ii) calculation of the spectra of nonreciprocal spin-wave edge modes, including the modes at the physical edges of an array and modes at the domain walls inside the array; and (iii) study of the influence of the domain wall modes on the FMR spectrum of an array existing in a nonideal chessboard antiferromagnetic ground state.

  12. Generating Coherent Phonons and Spin Excitations with Ultrafast Light Pulses

    NASA Astrophysics Data System (ADS)

    Merlin, Roberto

    2006-03-01

    Recent work on the generation of coherent low-lying excitations by ultrafast laser pulses will be reviewed, emphasizing the microscopic mechanisms of light-matter interaction. The topics covered include long-lived phonons in ZnO [C. Aku-Leh, J. Zhao, R. Merlin, J. Men'endez and M. Cardona, Phys. Rev.B 71, 205211 (2005)], squeezed magnons [J. Zhao, A. V. Bragas, D. J. Lockwood and R. Merlin, Phys. Rev. Lett. 93, 107203 (2004)], spin- and charge-density fluctuations [J. M. Bao et al., Phys. Rev. Lett. 92, 236601 (2004)] and cyclotron resonance [J. K. Wahlstrand, D. M. Wang, P. Jacobs, J. M. Bao, R. Merlin, K. W. West and L. N. Pfeiffer, AIP Conference Proceedings 772 (2005), p. 1313] in GaAs quantum wells. In addition, unpublished results on surface -avoiding phonons in GaAs-AlAs superlattices [M. Trigo et al., unpublished] and magnons in ferromagnetic Ga1-xMnxAs [D. M. Wang et al., unpublished] will be discussed. It will also be shown that frequencies can be measured using pump-probe techniques with a precision comparable to that of Brillouin scattering. It is now widely accepted that stimulated Raman scattering (SRS) is (often but not always) the mechanism responsible for the coherent coupling. Results will be presented showing that SRS is described by two separate tensors, one of which accounts for the excitation-induced modulation of the susceptibility, and the other one for the dependence of the amplitude of the oscillation on the light intensity [T. E. Stevens, J. Kuhl and R. Merlin, Phys. Rev. B 65, 144304 (2002)]. These tensors have the same real component, associated with impulsive coherent generation, but different imaginary parts. If the imaginary term dominates, that is, for strongly absorbing substances, the mechanism for two-band processes becomes displacive in nature, as in the DECP (displacive excitation of coherent phonons) model. It will be argued that DECP is not a separate mechanism, but a particular case of SRS. In the final part of the talk, an

  13. On the nature of excited electronic states in cyanine dyes: implications for visual pigment spectra

    NASA Astrophysics Data System (ADS)

    Dinur, Uri; Honig, Barry; Schulten, Klaus

    1980-06-01

    CNDO/S CI calculations are carried out on polyenes and on cyanine dyes. In contrast to polyenes, doubly excited configurations have a strong effect on the first optically allowed excited state in cyanines. Protonated Schiff bases of retinal are closely related to cyanine dyes, with important consequences for models of visual pigment spectra and photochemistry.

  14. Excitation Spectra of Carbon Nuclei near η ' Emission Threshold

    NASA Astrophysics Data System (ADS)

    Itahashi, Kenta; Ayyad, Yassid; Benlliure, Jose; Brinkmann, Kai-Thomas; Friedrich, Stefan; Fujioka, Hiroyuki; Geissel, Hans; Gellanki, Jnaneswari; Guo, Chenlei; Gutz, Eric; Haettner, Emma; Harakeh, Muhsin N.; Hayano, Ryugo S.; Higashi, Yuko; Hirenzaki, Satoru; Hornung, Christine; Igarashi, Yoichi; Ikeno, Natsumi; Iwasaki, Masahiko; Jido, Daisuke; Kalantar-Nayestanaki, Nasser; Kanungo, Rituparna; Knoebel, Ronja; Kurz, Nikolaus; Metag, Volker; Mukha, Ivan; Nagae, Tomofumi; Nagahiro, Hideko; Nanova, Mariana; Nishi, Takahiro; Ong, Hooi Jin; Pietri, Stephane; Prochazka, Andrej; Rappold, Christophe; Reiter, Moritz P.; Rodríguez-Sánchez, José L.; Scheidenberger, Christoph; Simon, Haik; Sitar, Branislav; Strmen, Peter; Sun, Baohua; Suzuki, Ken; Szarka, Imrich; Takechi, Maya; Tanaka, Yoshiki K.; Tanihata, Isao; Terashima, Satoru; Watanabe, Yuni N.; Weick, Helmut; Widmann, Eberhard; Winfield, John S.; Xu, Xiaodong; Yamakami, Hiroki; Zhao, Jianwei

    We measured an excitation spectrum of 12C(p, d) reaction near the η' emission threshold using a 2.5 GeV proton beam. The measured spectrum shows no peak structures which are associated to formation of η'-mesic nuclei. Further analysis is ongoing to deduce upper limits of the formation cross section and to set constraints in the η'-nucleus interaction.

  15. Magnetostatic spin wave modes excitation in yttrium-iron-garnet film under various temperatures

    NASA Astrophysics Data System (ADS)

    Kaack, M.; Jun, S.; Nikitov, S. A.; Pelzl, J.

    1999-09-01

    Temperature-dependent magnetostatic spin wave modes spectra in a ferromagnetic thin film of yttrium-iron-garnet are investigated by means of conventional and photothermally modulated ferromagnetic resonance techniques. Values for the anisotropy field are derived from the evaluation of resonance spectra. In the wide range of temperature the resonance characteristics of spin wave modes spectra are consistent with the Damon-Eshbach theory. Close to the Curie temperature they, however, strongly deviate from the theoretical predictions.

  16. Stripe phase and double-roton excitations in interacting spin-orbit-coupled spin-1 Bose-Einstein condensates

    NASA Astrophysics Data System (ADS)

    Sun, Kuei; Qu, Chunlei; Xu, Yong; Zhang, Yongping; Zhang, Chuanwei

    Spin-orbit (SO) coupling plays a major role in many important phenomena in condensed matter physics. However, the SO coupling physics in high-spin systems, especially with superfluids, has not been well explored because of the spin half of electrons in solids. In this context, the recent experimental realization of spin-orbit coupling in spin-1 Bose-Einstein condensates (BECs) has opened a completely new avenue for exploring SO-coupled high-spin superfluids. Nevertheless, the experiment has only revealed the single-particle physics of the system. Here, we study the effects of interactions between atoms on the ground states and collective excitations of SO-coupled spin-1 BECs in the presence of a spin-tensor potential. We find that ferromagnetic interaction between atoms can induce a stripe phase exhibiting two modulating patterns. We characterize the phase transitions between different phases using the spin-tensor density as well as the collective dipole motion of the BEC. We show that there exists a new type of double maxon-roton structure in the Bogoliubov-excitation spectrum, attributing to the three band minima of the SO-coupled spin-1 BEC. Our work could motivate further theoretical and experimental study along this direction.

  17. Solid-state proton NMR of paramagnetic metal complexes: DANTE spin echoes for selective excitation in inhomogeneously broadened lines

    NASA Astrophysics Data System (ADS)

    Carnevale, Diego; Perez Linde, A. J.; Bauer, Gerald; Bodenhausen, Geoffrey

    2013-08-01

    The paramagnetic complex bis(oxazolinylphenyl)amine-Fe(III)Cl2 is investigated by means of solid-state proton NMR at 18.8 T (800 MHz) using magic-angle spinning at 65 kHz. Spin echoes that are excited and refocused by combs of rotor-synchronized pulses in the manner of 'Delays Alternating with Nutation for Tailored Excitation' (DANTE) allow one to characterize different chemical environments that severely overlap in conventional MAS spectra. Such sequences combine two apparently contradictory features: an overall bandwidth exceeding several MHz, and very selective irradiation of a few kHz within inhomogeneously broadened sidebands. The experimental hyperfine interactions correlate well with DFT calculations.

  18. [Selective excitation spectra and energy level structure of Dy3+:ThO2 crystal].

    PubMed

    Yin, M; Krupa, J C

    2001-08-01

    Dy3+:ThO2 crystal was grown by the flux technique for the first time. The emission spectra, excitation spectra and fluorescence decay curves were measured and discussed. By using emission spectra obtained under selective dye laser excitation at 12 K, together with the crystal-field theory, the site symmetry of Dy3+ ions in ThO2 was determined as C3 nu and its energy level structure was tabulated. The lifetime of radiative level 4F9/2 was also determined as 0.40 ms.

  19. Fractionalization, entanglement, and separation: Understanding the collective excitations in a spin-orbital chain

    NASA Astrophysics Data System (ADS)

    Chen, Cheng-Chien; van Veenendaal, Michel; Devereaux, Thomas P.; Wohlfeld, Krzysztof

    2015-04-01

    Using a combined analytical and numerical approach, we study the collective spin and orbital excitations in a spin-orbital chain under a crystal field. Irrespective of the crystal-field strength, these excitations can be universally described by fractionalized fermions. The fractionalization phenomenon persists and contrasts strikingly with the case of a spin chain, where fractionalized spinons cannot be individually observed but confined to form magnons in a strong magnetic field. In the spin-orbital chain, each of the fractional quasiparticles carries both spin and orbital quantum numbers, and the two variables are always entangled in the collective excitations. Our result further shows that the recently reported separation phenomenon occurs when crystal fields fully polarize the orbital degrees of freedom. In this case, however, the spinon and orbiton dynamics are decoupled solely because of a redefinition of the spin and orbital quantum numbers.

  20. Equilibrium excited state and emission spectra of molecular aggregates from the hierarchical equations of motion approach.

    PubMed

    Jing, Yuanyuan; Chen, Liping; Bai, Shuming; Shi, Qiang

    2013-01-28

    The hierarchical equations of motion (HEOM) method was applied to calculate the emission spectra of molecular aggregates using the Frenkel exciton model. HEOM equations for the one-exciton excited state were first propagated until equilibration. The reduced density operator and auxiliary density operators (ADOs) were used to characterize the coupled system-bath equilibrium. The dipole-dipole correlation functions were then calculated to obtain the emission spectra of model dimers, and the B850 band of light-harvesting complex II (LH2) in purple bacteria. The effect of static disorder on equilibrium excited state and the emission spectra of LH2 was also explicitly considered. Several approximation schemes, including the high temperature approximation (HTA) of the HEOM, a modified version of the HTA, the stochastic Liouville equation approach, the perturbative time-local and time-nonlocal generalized quantum master equations, were assessed in the calculation of the equilibrium excited state and emission spectra.

  1. Single production of excited spin-3/2 neutrinos at linear colliders

    SciTech Connect

    Cakir, O.; Ozansoy, A.

    2009-03-01

    We study the potential of future high energy e{sup +}e{sup -} colliders to probe excited neutrino signals in different channels coming from the single production process via gauge interactions. We calculate the production cross section, decay widths, and branching ratios of excited spin-3/2 neutrinos according to their effective currents and we compare them with those of the spin-1/2 ones. The signals and corresponding backgrounds are examined in detail to get accessible limits on the masses and couplings of excited spin-3/2 neutrinos.

  2. Spin-wave excitation and propagation in microstructured waveguides of yttrium iron garnet/Pt bilayers

    SciTech Connect

    Pirro, P.; Chumak, A. V.; Lägel, B.; Leven, B.; Hillebrands, B.; Brächer, T.; Dubs, C.; Surzhenko, O.; Görnert, P.

    2014-01-06

    We present an experimental study of spin-wave excitation and propagation in microstructured waveguides consisting of a 100 nm thick yttrium iron garnet/platinum (Pt) bilayer. The life time of the spin waves is found to be more than an order of magnitude higher than in comparably sized metallic structures, despite the fact that the Pt capping enhances the Gilbert damping. Utilizing microfocus Brillouin light scattering spectroscopy, we reveal the spin-wave mode structure for different excitation frequencies. An exponential spin-wave amplitude decay length of 31 μm is observed which is a significant step towards low damping, insulator based micro-magnonics.

  3. Magnetic Field Dependence of Excitations Near Spin-Orbital Quantum Criticality

    NASA Astrophysics Data System (ADS)

    Biffin, A.; Rüegg, Ch.; Embs, J.; Guidi, T.; Cheptiakov, D.; Loidl, A.; Tsurkan, V.; Coldea, R.

    2017-02-01

    The spinel FeSc2 S4 has been proposed to realize a near-critical spin-orbital singlet (SOS) state, where entangled spin and orbital moments fluctuate in a global singlet state on the verge of spin and orbital order. Here we report powder inelastic neutron scattering measurements that observe the full bandwidth of magnetic excitations and we find that spin-orbital triplon excitations of an SOS state can capture well key aspects of the spectrum in both zero and applied magnetic fields up to 8.5 T. The observed shift of low-energy spectral weight to higher energies upon increasing applied field is naturally explained by the entangled spin-orbital character of the magnetic states, a behavior that is in strong contrast to spin-only singlet ground state systems, where the spin gap decreases upon increasing applied field.

  4. Angular dependences of spin-wave resonance spectra of inhomogeneous films with orthorhombic anisotropy

    NASA Astrophysics Data System (ADS)

    Zyuzin, A. M.; Bakulin, M. A.; Radaikin, V. V.; Yantsen, N. V.

    2017-02-01

    Zero spin-wave mode in inhomogeneous magnetic films with orthorhombic anisotropy has been found to exhibit a change of its localization region in two of three typical angular dependences of resonance fields of high-intensity modes. It has been shown that the anisotropy fields on both sides of the film can be determined from the resonance fields of the zero and uppermost high-intensity spin-wave modes of spin-wave resonance spectra.

  5. Doping dependence of spin excitations and its correlations with high-temperature superconductivity in iron pnictides.

    PubMed

    Wang, Meng; Zhang, Chenglin; Lu, Xingye; Tan, Guotai; Luo, Huiqian; Song, Yu; Wang, Miaoyin; Zhang, Xiaotian; Goremychkin, E A; Perring, T G; Maier, T A; Yin, Zhiping; Haule, Kristjan; Kotliar, Gabriel; Dai, Pengcheng

    2013-01-01

    High-temperature superconductivity in iron pnictides occurs when electrons and holes are doped into their antiferromagnetic parent compounds. Since spin excitations may be responsible for electron pairing and superconductivity, it is important to determine their electron/hole-doping evolution and connection with superconductivity. Here we use inelastic neutron scattering to show that while electron doping to the antiferromagnetic BaFe₂As₂ parent compound modifies the low-energy spin excitations and their correlation with superconductivity (<50 meV) without affecting the high-energy spin excitations (>100 meV), hole-doping suppresses the high-energy spin excitations and shifts the magnetic spectral weight to low-energies. In addition, our absolute spin susceptibility measurements for the optimally hole-doped iron pnictide reveal that the change in magnetic exchange energy below and above T(c) can account for the superconducting condensation energy. These results suggest that high-T(c) superconductivity in iron pnictides is associated with both the presence of high-energy spin excitations and a coupling between low-energy spin excitations and itinerant electrons.

  6. Doping dependence of spin excitations and its correlations with high-temperature superconductivity in iron pnictides

    PubMed Central

    Wang, Meng; Zhang, Chenglin; Lu, Xingye; Tan, Guotai; Luo, Huiqian; Song, Yu; Wang, Miaoyin; Zhang, Xiaotian; Goremychkin, E.A.; Perring, T.G.; Maier, T.A.; Yin, Zhiping; Haule, Kristjan; Kotliar, Gabriel; Dai, Pengcheng

    2013-01-01

    High-temperature superconductivity in iron pnictides occurs when electrons and holes are doped into their antiferromagnetic parent compounds. Since spin excitations may be responsible for electron pairing and superconductivity, it is important to determine their electron/hole-doping evolution and connection with superconductivity. Here we use inelastic neutron scattering to show that while electron doping to the antiferromagnetic BaFe2As2 parent compound modifies the low-energy spin excitations and their correlation with superconductivity (<50 meV) without affecting the high-energy spin excitations (>100 meV), hole-doping suppresses the high-energy spin excitations and shifts the magnetic spectral weight to low-energies. In addition, our absolute spin susceptibility measurements for the optimally hole-doped iron pnictide reveal that the change in magnetic exchange energy below and above Tc can account for the superconducting condensation energy. These results suggest that high-Tc superconductivity in iron pnictides is associated with both the presence of high-energy spin excitations and a coupling between low-energy spin excitations and itinerant electrons. PMID:24301219

  7. Spin exchange in the excitation of spin-polarized Na atoms by Ne/sup +/-ion impact

    SciTech Connect

    Jitschin, W.; Osimitsch, S.; Reihl, H.; Mueller, D.W.; Kleinpoppen, H.; Lutz, H.O.

    1986-11-01

    The 3s-3p excitation of spin-polarized Na atoms by Ne/sup +/ ions has been studied for impact energies E/sub lab/ = 200 eV to 6 keV, i.e., in the adiabatic regime. The total excitation cross section and the three Stokes polarization parameters of the fluorescence light have been measured. The linear polarization of the light shows a preferential excitation of the chemically bondm/sub l/chemically bond = 1 magnetic substates. The circular polarization probes the spin orientation of the excited 3p state. At the highest impact energies investigated the experimental data are compatible with conservation of spin orientation during the collision. With decreasing impact energy, the spin polarization of the final 3p state becomes smaller than the spin polarization of the initial 3s state. This apparent spin depolarization is attributed to the exchange interaction between the Na valence electron and the unfilled Ne/sup +/ 2p/sup 5/ core in the quasimolecule formed during the collision.

  8. Experimental investigation of shell-model excitations of 89Zr up to high spin

    NASA Astrophysics Data System (ADS)

    Saha, S.; Palit, R.; Sethi, J.; Trivedi, T.; Srivastava, P. C.; Kumar, S.; Naidu, B. S.; Donthi, R.; Jadhav, S.; Biswas, D. C.; Garg, U.; Goswami, A.; Jain, H. C.; Joshi, P. K.; Mukherjee, G.; Naik, Z.; Nag, S.; Nanal, V.; Pillay, R. G.; Saha, S.; Singh, A. K.

    2012-09-01

    Near yrast states in 89Zr were investigated up to high spin using the fusion evaporation reaction 80Se(13C, 4n) at an incident beam energy of 50 MeV. Excited levels of 89Zr have been observed up to ˜10 MeV excitation energy and spin ˜37/2ℏ using the prompt gamma spectroscopy technique with the Indian National Gamma Array (INGA). The angular distribution, directional correlation, and polarization measurements were carried out to assign the spin and parity of the newly reported states. The structures of both the positive and negative parity states up to highest spin observed in the present experiment have been compared with shell-model calculations using two recently developed residual interactions, JUN45 and jj44b. The role of proton excitations from p3/2 and f5/2 orbitals to the g9/2 orbital for the higher spin states has been discussed.

  9. Driving Spin Excitations by Hydrostatic Pressure in BiFeO(3).

    PubMed

    Buhot, J; Toulouse, C; Gallais, Y; Sacuto, A; de Sousa, R; Wang, D; Bellaiche, L; Bibes, M; Barthélémy, A; Forget, A; Colson, D; Cazayous, M; Measson, M-A

    2015-12-31

    Optical spectroscopy has been combined with computational and theoretical techniques to show how the spin dynamics in the model multiferroic BiFeO(3) responds to the application of hydrostatic pressure and its corresponding series of structural phase transitions from R3c to the Pnma phases. As pressure increases, multiple spin excitations associated with noncollinear cycloidal magnetism collapse into two excitations, which show jump discontinuities at some of the ensuing crystal phase transitions. The effective Hamiltonian approach provides information on the electrical polarization and structural changes of the oxygen octahedra through the successive structural phases. The extracted parameters are then used in a Ginzburg-Landau model to reproduce the evolution with pressure of the spin wave excitations observed at low energy, and we demonstrate that the structural phases and the magnetic anisotropy drive and control the spin excitations.

  10. Driving Spin Excitations by Hydrostatic Pressure in BiFeO3

    NASA Astrophysics Data System (ADS)

    Buhot, J.; Toulouse, C.; Gallais, Y.; Sacuto, A.; de Sousa, R.; Wang, D.; Bellaiche, L.; Bibes, M.; Barthélémy, A.; Forget, A.; Colson, D.; Cazayous, M.; Measson, M.-A.

    2015-12-01

    Optical spectroscopy has been combined with computational and theoretical techniques to show how the spin dynamics in the model multiferroic BiFeO3 responds to the application of hydrostatic pressure and its corresponding series of structural phase transitions from R 3 c to the P n m a phases. As pressure increases, multiple spin excitations associated with noncollinear cycloidal magnetism collapse into two excitations, which show jump discontinuities at some of the ensuing crystal phase transitions. The effective Hamiltonian approach provides information on the electrical polarization and structural changes of the oxygen octahedra through the successive structural phases. The extracted parameters are then used in a Ginzburg-Landau model to reproduce the evolution with pressure of the spin wave excitations observed at low energy, and we demonstrate that the structural phases and the magnetic anisotropy drive and control the spin excitations.

  11. Observations of thermally excited ferromagnetic resonance on spin torque oscillators having a perpendicularly magnetized free layer

    SciTech Connect

    Tamaru, S. Kubota, H.; Yakushiji, K.; Konoto, M.; Nozaki, T.; Fukushima, A.; Imamura, H.; Taniguchi, T.; Arai, H.; Tsunegi, S.; Yuasa, S.; Suzuki, Y.

    2014-05-07

    Measurements of thermally excited ferromagnetic resonance were performed on spin torque oscillators having a perpendicularly magnetized free layer and in-plane magnetized reference layer (abbreviated as PMF-STO in the following) for the purpose of obtaining magnetic properties in the PMF-STO structure. The measured spectra clearly showed a large main peak and multiple smaller peaks on the high frequency side. A Lorentzian fit on the main peak yielded Gilbert damping factor of 0.0041. The observed peaks moved in proportion to the out-of-plane bias field. From the slope of the main peak frequency as a function of the bias field, Lande g factor was estimated to be about 2.13. The mode intervals showed a clear dependence on the diameter of the PMF-STOs, i.e., intervals are larger for a smaller diameter. These results suggest that the observed peaks should correspond to eigenmodes of lateral spin wave resonance in the perpendicularly magnetized free layer.

  12. Simulation of optical excitation spectra of semiconductor nanowires within effective bond orbital model

    NASA Astrophysics Data System (ADS)

    Chang, Y. C.; Mahmoud, Waleed E.

    2015-11-01

    Systematic studies of optical excitation spectra of semiconductor nanowires (including group IV, III-V, and II-VI materials) obtained by using an eight-band effective bond-orbital model (EBOM) are presented. A new set of EBOM parameters are determined which produce good band structures of zincblende semiconductors for the entire Brillouin zone, suitable for modeling the excitation spectra from infrared to ultraviolet. The band structures and optical excitation spectra, including both the interband and intraband transitions (for doped cases) are calculated. The calculations were done with the use of a symmetrized basis functions which transform according to the irreducible representations of the underlying point group. This can improve the computation efficiency by about two orders of magnitude. Thus, the electronic and optical properties of a large class of materials can be simulated.

  13. Low-energy electrodynamics of novel spin excitations in the quantum spin ice Yb₂Ti₂O₇.

    PubMed

    Pan, LiDong; Kim, Se Kwon; Ghosh, A; Morris, Christopher M; Ross, Kate A; Kermarrec, Edwin; Gaulin, Bruce D; Koohpayeh, S M; Tchernyshyov, Oleg; Armitage, N P

    2014-09-18

    In condensed matter systems, formation of long-range order (LRO) is often accompanied by new excitations. However, in many geometrically frustrated magnetic systems, conventional LRO is suppressed, while non-trivial spin correlations are still observed. A natural question to ask is then what is the nature of the excitations in this highly correlated state without broken symmetry? Frequently, applying a symmetry breaking field stabilizes excitations whose properties reflect certain aspects of the anomalous state without LRO. Here we report a THz spectroscopy study of novel excitations in quantum spin ice Yb2Ti2O7 under a <001> directed magnetic field. At large positive fields, both right- and left-handed magnon and two-magnon-like excitations are observed. The g-factors of these excitations are dramatically enhanced in the low-field limit, showing a crossover of these states into features consistent with the quantum string-like excitations proposed to exist in quantum spin ice in small <001> fields.

  14. Ultrafast spin-transfer torque driven by femtosecond pulsed-laser excitation.

    PubMed

    Schellekens, A J; Kuiper, K C; de Wit, R R J C; Koopmans, B

    2014-07-10

    Spin currents have an important role in many proposed spintronic devices, as they govern the switching process of magnetic bits in random access memories or drive domain wall motion in magnetic shift registers. The generation of these spin currents has to be fast and energy efficient for realization of these envisioned devices. Recently it has been shown that femtosecond pulsed-laser excitation of thin magnetic films creates intense and ultrafast spin currents. Here we utilize this method to change the orientation of the magnetization in a magnetic bilayer by spin-transfer torque on sub-picosecond timescales. By analysing the dynamics of the magnetic bilayer after laser excitation, the rich physics governing ultrafast spin-transfer torque are elucidated opening up new pathways to ultrafast magnetization reversal, but also providing a new method to quantify optically induced spin currents generated on femtosecond timescales.

  15. Spin excitations and correlations in scanning tunneling spectroscopy

    NASA Astrophysics Data System (ADS)

    Ternes, Markus

    2015-06-01

    In recent years inelastic spin-flip spectroscopy using a low-temperature scanning tunneling microscope has been a very successful tool for studying not only individual spins but also complex coupled systems. When these systems interact with the electrons of the supporting substrate correlated many-particle states can emerge, making them ideal prototypical quantum systems. The spin systems, which can be constructed by arranging individual atoms on appropriate surfaces or embedded in synthesized molecular structures, can reveal very rich spectral features. Up to now the spectral complexity has only been partly described. This manuscript shows that perturbation theory enables one to describe the tunneling transport, reproducing the differential conductance with surprisingly high accuracy. Well established scattering models, which include Kondo-like spin-spin and potential interactions, are expanded to enable calculation of arbitrary complex spin systems in reasonable time scale and the extraction of important physical properties. The emergence of correlations between spins and, in particular, between the localized spins and the supporting bath electrons are discussed and related to experimentally tunable parameters. These results might stimulate new experiments by providing experimentalists with an easily applicable modeling tool.

  16. Spin-Wave Excitations in Finite Rectangular Elements

    NASA Astrophysics Data System (ADS)

    Bayer, Christian; Jorzick, Jörg; Demokritov, Sergej O.; Slavin, Andrei N.; Guslienko, Konstantin Y.; Berkov, Dmitry V.; Gorn, Natalia L.; Kostylev, Mikhail P.; Hillebrands, Burkard

    A review on recent Brillouin light scattering work on spin-wave modes in arrays of micrometer-size magnetic Ni80Fe20 stripes and rectangular elements is given. Several effects caused by the lateral confinement in the stripes are reviewed: 1. lateral quantization of dipole-dominated Damon-Eshbach spin-wave modes in a longitudinally magnetized stripe due to its finite width, 2. localization of exchange-dominated spin-wave modes near the edges and dipole-dominated spin-wave modes near the center of a transversely magnetized long magnetic stripe due to the inhomogeneity of its internal magnetic field, 3. combination of quantization and localization effects for the spin-wave modes in rectangular elements. The observed effects are analyzed using an analytical approach and numerical simulations.

  17. Study of two-photon excitation spectra of organic compounds absorbing in the UV region

    SciTech Connect

    Babenko, V A; Sychev, Andrei A

    2004-12-31

    A method is proposed for recording two-photon excitation (TPE) spectra of organic compounds with the help of picosecond pulses from a dye laser tunable in the range from 550 to 640 nm. The TPE spectra are obtained for organic scintillators and drugs: paraterphenyl in liquid and solid phases, stilbene single crystal and Streptocid powder, having a one-photon absorption band in the region from 270 to 350 nm. It is shown that the vibronic structure in the TPE spectra of these compounds is independent of their aggregate state and is an individual characteristic of each of the compounds. (active media)

  18. Numerical Simulation of Spin-Chirality Switching in Multiferroics via Intense Electromagnon Excitations

    NASA Astrophysics Data System (ADS)

    Mochizuki, Masahito; Nagaosa, Naoto

    2011-09-01

    Chirality, i.e., the right- and left-handedness of structure, is one of the key concepts in many fields of science including biology, chemistry and physics, and its manipulation is an issue of vital importance. The electron spins in solids can form chiral configurations. In perovskite manganites RMnO3 (R = Tb, Dy,...etc), the Mn-spins form a cycloidal structure, which induces ferroelectric polarization (P) through the relativistic spin-orbit interaction. This magnetism-induced ferroelectricity (multiferroics) and associated infrared-active spin waves (electromagnons) open a promising route to control the spins by purely electric means in a very short time. In this paper, we show theoretically with an accurate spin Hamiltonian for TbMnO3 that a picosecond optical pulse can switch the spin chirality by intensely exciting the electromagnons with a terahertz frequency.

  19. Momentum and Doping Dependence of Spin Excitations in Electron-Doped Cuprate Superconductors

    NASA Astrophysics Data System (ADS)

    Jing, Pengfei; Zhao, Huaisong; Kuang, Lülin; Lan, Yu; Feng, Shiping

    2017-01-01

    Superconductivity in copper oxides emerges on doping holes or electrons into their Mott-insulating parent compounds. The spin excitations are thought to be the mediating glue for the pairing in superconductivity. Here the momentum and doping dependence of the dynamical spin response in the electron-doped cuprate superconductors is studied based on the kinetic-energy-driven superconducting mechanism. It is shown that the dispersion of the low-energy spin excitations changes strongly upon electron doping; however, the hour-glass-shaped dispersion of the low-energy spin excitations appeared in the hole-doped case is absent on the electron-doped side due to the electron-hole asymmetry. In particular, the commensurate resonance appears in the superconducting state with the resonance energy that correlates with the dome-shaped doping dependence of the superconducting gap. Moreover, the spectral weight and dispersion of the high-energy spin excitations in the superconducting state are comparable with those in the corresponding normal state, indicating that the high-energy spin excitations do not play an important part in the pair formation.

  20. Simulating quantum spin models using Rydberg-excited atomic ensembles in magnetic microtrap arrays

    NASA Astrophysics Data System (ADS)

    Whitlock, Shannon; Glaetzle, Alexander W.; Hannaford, Peter

    2017-04-01

    We propose a scheme to simulate lattice spin models based on strong, long-range interacting Rydberg atoms stored in a large-spacing array of magnetic microtraps. Each spin is encoded in a collective spin state involving a single nS or (n+1)S Rydberg atom excited from an ensemble of ground-state alkali atoms prepared via Rydberg blockade. After the excitation laser is switched off, the Rydberg spin states on neighbouring lattice sites interact via general XXZ spin–spin interactions. To read out the collective spin states we propose a single Rydberg atom triggered avalanche scheme in which the presence of a single Rydberg atom conditionally transfers a large number of ground-state atoms in the trap to an untrapped state which can be readily detected by site-resolved absorption imaging. Such a quantum simulator should allow the study of quantum spin systems in almost arbitrary one-dimensional and two-dimensional configurations. This paves the way towards engineering exotic spin models, such as spin models based on triangular-symmetry lattices which can give rise to frustrated-spin magnetism.

  1. On the spin excitation energy of the nucleon in the Skyrme model

    NASA Astrophysics Data System (ADS)

    Adam, C.; Sanchez-Guillen, J.; Wereszczynski, A.

    2016-11-01

    In the Skyrme model of nucleons and nuclei, the spin excitation energy of the nucleon is traditionally calculated by a fit of the rigid rotor quantization of spin/isospin of the fundamental Skyrmion (the hedgehog) to the masses of the nucleon and the Delta resonance. The resulting, quite large spin excitation energy of the nucleon of about 73MeV is, however, rather difficult to reconcile with the small binding energies of physical nuclei, among other problems. Here, we argue that a more reliable interval of values for the spin excitation energy of the nucleon, compatible with many physical constraints is between 15MeV and 30MeV. The fit of the rigid rotor to the Delta, on the other hand, is problematic in any case, because it implies the use of a nonrelativistic method for a highly relativistic system.

  2. Direct Observation of a Nuclear Spin Excitation in Ho2Ti2O7

    SciTech Connect

    Ehlers, Georg; Mamontov, Eugene; Zamponi, Michaela M

    2009-01-01

    A single nondispersive excitation is observed by means of neutron backscattering, at E{sub 0} = 26.3 {micro}eV in the spin ice Ho{sub 2}Ti{sub 2}O{sub 7} but not in the isotopically enriched {sup 162}Dy{sub 2}Ti{sub 2}O{sub 7} analogue. The intensity of this excitation is rather small, {approx}< 0.2% of the elastic intensity. It is clearly observed below 80 K but resolution limited only below {approx}65 K. The application of a magnetic field up to {mu}{sub 0}H = 4.5 T, at 1.6 K, has no measurable effect on the energy or intensity. This nuclear excitation is believed to perturb the electronic, Ising spin system resulting in the persistent spin dynamics observed in spin ice compounds.

  3. Measurement of collective excitations in a spin-orbit-coupled Bose-Einstein condensate

    NASA Astrophysics Data System (ADS)

    Khamehchi, M. A.; Zhang, Yongping; Hamner, Chris; Busch, Thomas; Engels, Peter

    2014-12-01

    We measure the collective excitation spectrum of a spin-orbit-coupled Bose-Einstein condensate using Bragg spectroscopy. The spin-orbit coupling is generated by Raman dressing of atomic hyperfine states. When the Raman detuning is reduced, mode softening at a finite momentum is revealed, which provides insight into a supersolid-like phase transition. We find that for the parameters of our system, this softening stops at a finite excitation gap and is symmetric under a sign change of the Raman detuning. Finally, using a moving barrier that is swept through the BEC, we also show the effect of the collective excitation on the fluid dynamics.

  4. Manipulating charge transfer excited state relaxation and spin crossover in iron coordination complexes with ligand substitution

    DOE PAGES

    Zhang, Wenkai; Kjaer, Kasper S.; Alonso-Mori, Roberto; ...

    2016-08-25

    Developing light-harvesting and photocatalytic molecules made with iron could provide a cost effective, scalable, and environmentally benign path for solar energy conversion. To date these developments have been limited by the sub-picosecond metal-to-ligand charge transfer (MLCT) electronic excited state lifetime of iron based complexes due to spin crossover – the extremely fast intersystem crossing and internal conversion to high spin metal-centered excited states. We revitalize a 30 year old synthetic strategy for extending the MLCT excited state lifetimes of iron complexes by making mixed ligand iron complexes with four cyanide (CN–) ligands and one 2,2'-bipyridine (bpy) ligand. This enables MLCTmore » excited state and metal-centered excited state energies to be manipulated with partial independence and provides a path to suppressing spin crossover. We have combined X-ray Free-Electron Laser (XFEL) Kβ hard X-ray fluorescence spectroscopy with femtosecond time-resolved UV-visible absorption spectroscopy to characterize the electronic excited state dynamics initiated by MLCT excitation of [Fe(CN)4(bpy)]2–. The two experimental techniques are highly complementary; the time-resolved UV-visible measurement probes allowed electronic transitions between valence states making it sensitive to ligand-centered electronic states such as MLCT states, whereas the Kβ fluorescence spectroscopy provides a sensitive measure of changes in the Fe spin state characteristic of metal-centered excited states. Here, we conclude that the MLCT excited state of [Fe(CN)4(bpy)]2– decays with roughly a 20 ps lifetime without undergoing spin crossover, exceeding the MLCT excited state lifetime of [Fe(2,2'-bipyridine)3]2+ by more than two orders of magnitude.« less

  5. Manipulating charge transfer excited state relaxation and spin crossover in iron coordination complexes with ligand substitution

    SciTech Connect

    Zhang, Wenkai; Kjaer, Kasper S.; Alonso-Mori, Roberto; Bergmann, Uwe; Chollet, Matthieu; Fredin, Lisa A.; Hadt, Ryan G.; Hartsock, Robert W.; Harlang, Tobias; Kroll, Thomas; Kubicek, Katharina; Lemke, Henrik T.; Liang, Huiyang W.; Liu, Yizhu; Nielsen, Martin M.; Persson, Petter; Robinson, Joseph S.; Solomon, Edward I.; Sun, Zheng; Sokaras, Dimosthenis; van Driel, Tim B.; Weng, Tsu -Chien; Zhu, Diling; Warnmark, Kenneth; Sundstrom, Villy; Gaffney, Kelly J.

    2016-08-25

    Developing light-harvesting and photocatalytic molecules made with iron could provide a cost effective, scalable, and environmentally benign path for solar energy conversion. To date these developments have been limited by the sub-picosecond metal-to-ligand charge transfer (MLCT) electronic excited state lifetime of iron based complexes due to spin crossover – the extremely fast intersystem crossing and internal conversion to high spin metal-centered excited states. We revitalize a 30 year old synthetic strategy for extending the MLCT excited state lifetimes of iron complexes by making mixed ligand iron complexes with four cyanide (CN) ligands and one 2,2'-bipyridine (bpy) ligand. This enables MLCT excited state and metal-centered excited state energies to be manipulated with partial independence and provides a path to suppressing spin crossover. We have combined X-ray Free-Electron Laser (XFEL) Kβ hard X-ray fluorescence spectroscopy with femtosecond time-resolved UV-visible absorption spectroscopy to characterize the electronic excited state dynamics initiated by MLCT excitation of [Fe(CN)4(bpy)]2–. The two experimental techniques are highly complementary; the time-resolved UV-visible measurement probes allowed electronic transitions between valence states making it sensitive to ligand-centered electronic states such as MLCT states, whereas the Kβ fluorescence spectroscopy provides a sensitive measure of changes in the Fe spin state characteristic of metal-centered excited states. Here, we conclude that the MLCT excited state of [Fe(CN)4(bpy)]2– decays with roughly a 20 ps lifetime without undergoing spin crossover, exceeding the MLCT excited state lifetime of [Fe(2,2'-bipyridine)3]2+ by more than two orders of magnitude.

  6. Discernment of lint trash in raw cotton using multivariate analysis of excitation-emission luminescence spectra

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Excitation-Emission luminescence spectra of basic (pH 12.5) phosphate buffer solution extracts were used to distinguish among botanical components of trash within seed cotton. All components were separated from whole plants removed from a field in southern New Mexico. Unfolded Principal Component An...

  7. Fluorescence, Absorption, and Excitation Spectra of Polycyclic Aromatic Hydrocarbons as a Tool for Quantitative Analysis

    ERIC Educational Resources Information Center

    Rivera-Figueroa, A. M.; Ramazan, K. A.; Finlayson-Pitts, B. J.

    2004-01-01

    A quantitative and qualitative study of the interplay between absorption, fluorescence, and excitation spectra of pollutants called polycyclic aromatic hydrocarbons (PAHs) is conducted. The study of five PAH displays the correlation of the above-mentioned properties along with the associated molecular changes.

  8. Emission spectra of YAG:Er3+ under pulse laser-thermal excitation

    NASA Astrophysics Data System (ADS)

    Marchenko, V. M.; Shakir, Yu. A.

    2016-12-01

    Spectra and kinetics of emission of YAG:0.5% Er3+ monocrystal in visible and NIR ranges were investigated under laser-thermal excitation by the pulses of CO2 laser of 100 ns duration at wavelength λ = 10,6 μμm. Kinetics of integral emission was interpreted.

  9. Microwave excitation of spin wave beams in thin ferromagnetic films

    PubMed Central

    Gruszecki, P.; Kasprzak, M.; Serebryannikov, A. E.; Krawczyk, M.; Śmigaj, W.

    2016-01-01

    An inherent element of research and applications in photonics is a beam of light. In magnonics, which is the magnetic counterpart of photonics, where spin waves are used instead of electromagnetic waves to transmit and process information, the lack of a beam source limits exploration. Here, we present an approach enabling generation of narrow spin wave beams in thin homogeneous nanosized ferromagnetic films by microwave current. We show that the desired beam-type behavior can be achieved with the aid of a properly designed coplanar waveguide transducer generating a nonuniform microwave magnetic field. We test this idea using micromagnetic simulations, confirming numerically that the resulting spin wave beams propagate over distances of several micrometers. The proposed approach requires neither inhomogeneity of the ferromagnetic film nor nonuniformity of the biasing magnetic field. It can be generalized to different magnetization configurations and yield multiple spin wave beams of different width at the same frequency. PMID:26971711

  10. Phase reciprocity of spin-wave excitation by a microstrip antenna

    NASA Astrophysics Data System (ADS)

    Schneider, T.; Serga, A. A.; Neumann, T.; Hillebrands, B.; Kostylev, M. P.

    2008-06-01

    Using space-, time-, and phase-resolved Brillouin light-scattering spectroscopy we investigate the difference in phase of the two counterpropagating spin waves excited by the same microwave microstrip transducer. These studies are performed both for backward volume magnetostatic waves and magnetostatic surface waves in an in-plane magnetized yttrium iron garnet film. The experiments show that for the backward volume magnetostatic spin waves (which are reciprocal and excited symmetrically in amplitude) there is a phase difference of π associated with the excitation process and thus the phase symmetry is distorted. On the contrary, for the magnetostatic surface spin waves (which are nonreciprocal and unsymmetrical in amplitude) the phase symmetry is preserved (there is no phase difference between the two waves associated with the excitation). Theoretical analysis confirms this effect.

  11. Collective Nature of Spin Excitations in Superconducting Cuprates Probed by Resonant Inelastic X-Ray Scattering

    NASA Astrophysics Data System (ADS)

    Minola, M.; Dellea, G.; Gretarsson, H.; Peng, Y. Y.; Lu, Y.; Porras, J.; Loew, T.; Yakhou, F.; Brookes, N. B.; Huang, Y. B.; Pelliciari, J.; Schmitt, T.; Ghiringhelli, G.; Keimer, B.; Braicovich, L.; Le Tacon, M.

    2015-05-01

    We used resonant inelastic x-ray scattering (RIXS) with and without analysis of the scattered photon polarization, to study dispersive spin excitations in the high temperature superconductor YBa2Cu3O6 +x over a wide range of doping levels (0.1 ≤x ≤1 ). The excitation profiles were carefully monitored as the incident photon energy was detuned from the resonant condition, and the spin excitation energy was found to be independent of detuning for all x . These findings demonstrate that the largest fraction of the spin-flip RIXS profiles in doped cuprates arises from magnetic collective modes, rather than from incoherent particle-hole excitations as recently suggested theoretically [Benjamin et al. Phys. Rev. Lett. 112, 247002 (2014)]. Implications for the theoretical description of the electron system in the cuprates are discussed.

  12. Collective excitation of a trapped Bose-Einstein condensate with spin-orbit coupling

    NASA Astrophysics Data System (ADS)

    Chen, Li; Pu, Han; Yu, Zeng-Qiang; Zhang, Yunbo

    2017-03-01

    We investigate the collective excitations of a Raman-induced spin-orbit coupled Bose-Einstein condensate confined in a quasi-one-dimensional harmonic trap using the Bogoliubov method. By tuning the Raman coupling strength, three phases of the system can be identified. By calculating the transition strength, we are able to classify various excitation modes that are experimentally relevant. We show that the three quantum phases possess distinct features in their collective excitation properties. In particular, the spin dipole and the spin breathing modes can be used to clearly map out the phase boundaries. We confirm these predictions by direct numerical simulations of the quench dynamics that excites the relevant collective modes.

  13. Spectrometer calibration protocol for Raman spectra recorded with different excitation wavelengths.

    PubMed

    Bocklitz, T W; Dörfer, T; Heinke, R; Schmitt, M; Popp, J

    2015-01-01

    The combination of Raman spectroscopy with chemometrics has gained significant importance within the last years to address a broad variety of biomedical and life science questions. However, the routine application of chemometric models to analyze Raman spectra recorded with Raman devices different from the device used to establish the model is extremely challenging due to Raman device specific influences on the recorded Raman spectra. Here we report on the influence of different non-resonant excitation wavelengths on Raman spectra and propose a calibration routine, which corrects for the main part of the spectral differences between Raman spectra recorded with different (non-resonant) excitation wavelengths. The calibration routine introduced within this contribution is an improvement to the known 'standard' calibration routines and is a starting point for the development of a calibration protocol to generate spectrometer independent Raman spectra. The presented routine ensures that a chemometric model utilizes only Raman information of the sample and not artifacts from small shifts in the excitation wavelength. This is crucial for the application of Raman-spectroscopy in real-world-settings, such as diagnostics of diseases or identification of bacteria.

  14. Modification of Optical Properties of Seawater Exposed to Oil Contaminants Based on Excitation-Emission Spectra

    NASA Astrophysics Data System (ADS)

    Baszanowska, E.; Otremba, Z.

    2015-10-01

    The optical behaviour of seawater exposed to a residual amount of oil pollution is presented and a comparison of the fluorescence spectra of oil dissolved in both n-hexane and seawater is discussed based on excitation-emission spectra. Crude oil extracted from the southern part of the Baltic Sea was used to characterise petroleum properties after contact with seawater. The wavelength-independent fluorescence maximum for natural seawater and seawater artificially polluted with oil were determined. Moreover, the specific excitation-emission peaks for natural seawater and polluted water were analysed to identify the natural organic matter composition. It was found that fluorescence spectra identification is a promising method to detect even an extremely low concentration of petroleum residues directly in the seawater. In addition, alien substances disturbing the fluorescence signatures of natural organic substances in a marine environment is also discussed.

  15. Spin-vibronic quantum dynamics for ultrafast excited-state processes.

    PubMed

    Eng, Julien; Gourlaouen, Christophe; Gindensperger, Etienne; Daniel, Chantal

    2015-03-17

    Ultrafast intersystem crossing (ISC) processes coupled to nuclear relaxation and solvation dynamics play a central role in the photophysics and photochemistry of a wide range of transition metal complexes. These phenomena occurring within a few hundred femtoseconds are investigated experimentally by ultrafast picosecond and femtosecond transient absorption or luminescence spectroscopies, and optical laser pump-X-ray probe techniques using picosecond and femtosecond X-ray pulses. The interpretation of ultrafast structural changes, time-resolved spectra, quantum yields, and time scales of elementary processes or transient lifetimes needs robust theoretical tools combining state-of-the-art quantum chemistry and developments in quantum dynamics for solving the electronic and nuclear problems. Multimode molecular dynamics beyond the Born-Oppenheimer approximation has been successfully applied to many small polyatomic systems. Its application to large molecules containing a transition metal atom is still a challenge because of the nuclear dimensionality of the problem, the high density of electronic excited states, and the spin-orbit coupling effects. Rhenium(I) α-diimine carbonyl complexes, [Re(L)(CO)3(N,N)](n+) are thermally and photochemically robust and highly flexible synthetically. Structural variations of the N,N and L ligands affect the spectroscopy, the photophysics, and the photochemistry of these chromophores easily incorporated into a complex environment. Visible light absorption opens the route to a wide range of applications such as sensors, probes, or emissive labels for imaging biomolecules. Halide complexes [Re(X)(CO)3(bpy)] (X = Cl, Br, or I; bpy = 2,2'-bipyridine) exhibit complex electronic structure and large spin-orbit effects that do not correlate with the heavy atom effects. Indeed, the (1)MLCT → (3)MLCT intersystem crossing (ISC) kinetics is slower than in [Ru(bpy)3](2+) or [Fe(bpy)3](2+) despite the presence of a third-row transition metal

  16. Lifetime-vibrational interference effects in resonantly excited x-ray emission spectra of CO

    SciTech Connect

    Skytt, P.; Glans, P.; Gunnelin, K.

    1997-04-01

    The parity selection rule for resonant X-ray emission as demonstrated for O{sub 2} and N{sub 2} can be seen as an effect of interference between coherently excited degenerate localized core states. One system where the core state degeneracy is not exact but somewhat lifted was previously studied at ALS, namely the resonant X-ray emission of amino-substituted benzene (aniline). It was shown that the X-ray fluorescence spectrum resulting from excitation of the C1s at the site of the {open_quotes}aminocarbon{close_quotes} could be described in a picture separating the excitation and the emission processes, whereas the spectrum corresponding to the quasi-degenerate carbons could not. Thus, in this case it was necessary to take interference effects between the quasi-degenerate intermediate core excited states into account in order to obtain agreement between calculations and experiment. The different vibrational levels of core excited states in molecules have energy splittings which are of the same order of magnitude as the natural lifetime broadening of core excitations in the soft X-ray range. Therefore, lifetime-vibrational interference effects are likely to appear and influence the band shapes in resonant X-ray emission spectra. Lifetime-vibrational interference has been studied in non-resonant X-ray emission, and in Auger spectra. In this report the authors discuss results of selectively excited soft X-ray fluorescence spectra of molecules, where they focus on lifetime-interference effects appearing in the band shapes.

  17. Tunable short-wavelength spin wave excitation from pinned magnetic domain walls

    PubMed Central

    Van de Wiele, Ben; Hämäläinen, Sampo J.; Baláž, Pavel; Montoncello, Federico; van Dijken, Sebastiaan

    2016-01-01

    Miniaturization of magnonic devices for wave-like computing requires emission of short-wavelength spin waves, a key feature that cannot be achieved with microwave antennas. In this paper, we propose a tunable source of short-wavelength spin waves based on highly localized and strongly pinned magnetic domain walls in ferroelectric-ferromagnetic bilayers. When driven into oscillation by a microwave spin-polarized current, the magnetic domain walls emit spin waves with the same frequency as the excitation current. The amplitude of the emitted spin waves and the range of attainable excitation frequencies depend on the availability of domain wall resonance modes. In this respect, pinned domain walls in magnetic nanowires are particularly attractive. In this geometry, spin wave confinement perpendicular to the nanowire axis produces a multitude of domain wall resonances enabling efficient spin wave emission at frequencies up to 100 GHz and wavelengths down to 20 nm. At high frequency, the emission of spin waves in magnetic nanowires becomes monochromatic. Moreover, pinning of magnetic domain wall oscillators onto the same ferroelectric domain boundary in parallel nanowires guarantees good coherency between spin wave sources, which opens perspectives towards the realization of Mach-Zehnder type logic devices and sensors. PMID:26883893

  18. Tunable short-wavelength spin wave excitation from pinned magnetic domain walls.

    PubMed

    Van de Wiele, Ben; Hämäläinen, Sampo J; Baláž, Pavel; Montoncello, Federico; van Dijken, Sebastiaan

    2016-02-17

    Miniaturization of magnonic devices for wave-like computing requires emission of short-wavelength spin waves, a key feature that cannot be achieved with microwave antennas. In this paper, we propose a tunable source of short-wavelength spin waves based on highly localized and strongly pinned magnetic domain walls in ferroelectric-ferromagnetic bilayers. When driven into oscillation by a microwave spin-polarized current, the magnetic domain walls emit spin waves with the same frequency as the excitation current. The amplitude of the emitted spin waves and the range of attainable excitation frequencies depend on the availability of domain wall resonance modes. In this respect, pinned domain walls in magnetic nanowires are particularly attractive. In this geometry, spin wave confinement perpendicular to the nanowire axis produces a multitude of domain wall resonances enabling efficient spin wave emission at frequencies up to 100 GHz and wavelengths down to 20 nm. At high frequency, the emission of spin waves in magnetic nanowires becomes monochromatic. Moreover, pinning of magnetic domain wall oscillators onto the same ferroelectric domain boundary in parallel nanowires guarantees good coherency between spin wave sources, which opens perspectives towards the realization of Mach-Zehnder type logic devices and sensors.

  19. Distribution of tempo-dichlorotriazine spin label on immunoglobulin molecule. Interpretation of ESR spectra

    SciTech Connect

    Nezlin, R.

    1986-03-05

    Spin label TEMPO-dichlorotriazine (DT) has been used previously for determination of the rotational relaxation times of immunoglobulin (Ig) molecules and evaluation of their flexibility. Well defined outer wide extrema as well as sharp inner extrema are characteristic for ESR spectra of spin labeled Ig molecules. Such patterns of the spectrum can be accounted for either by the existence of the spin label in two states, one corresponding to its rapid and another to its restricted rotation or by varying environments of the spin label located in different areas of the Ig molecule. To choose between these possibilities, the distribution of /sup 14/C-TEMPO-DT on human IgG1(k) was studied. The same amount of the label per mg of protein was found in H and L chains as well as in the Fab fragment, and a smaller amount in the pFc'. The label was detected in most of the L chain tryptic peptides. Thus, the spin label is distributed nearly uniformly on IgG molecule, which is due to the regular distribution of amino acid residues reacted with the spin label. ESR spectra can be interpreted as a sum of individual spectra.

  20. Crossover from spin waves to diffusive spin excitations in underdoped Ba(Fe1-xCox)2 As2

    SciTech Connect

    Tucker, G S; Fernandes, R M; Pratt, D K; Thaler, A; Ni, N; Marty, K; Christianson, A D; Lumsden, M D; Sales, B C; Sefat, A S; Bud'ko, S L; Canfield, P C; Kreyssig, A; Goldman, A I; McQueeney, R J

    2014-05-01

    Using inelastic neutron scattering, we show that the onset of superconductivity in underdoped Ba(Fe1-xCox)2As2 coincides with a crossover from well-defined spin waves to overdamped and diffusive spin excitations. This crossover occurs despite the presence of long-range stripe antiferromagnetic order for samples in a compositional range from x=0.04 to 0.055, and is a consequence of the shrinking spin-density wave gap and a corresponding increase in the particle-hole (Landau) damping. The latter effect is captured by a simple itinerant model relating Co doping to changes in the hot spots of the Fermi surface. We argue that the overdamped spin fluctuations provide a pairing mechanism for superconductivity in these materials.

  1. Mass-number and excitation-energy dependence of the spin cutoff parameter

    SciTech Connect

    Grimes, S. M.; Voinov, A. V.; Massey, T. N.

    2016-07-12

    Here, the spin cutoff parameter determining the nuclear level density spin distribution ρ(J) is defined through the spin projection as < J2z > 1/2 or equivalently for spherical nuclei, (< J(J+1) >/3)1/2. It is needed to divide the total level density into levels as a function of J. To obtain the total level density at the neutron binding energy from the s-wave resonance count, the spin cutoff parameter is also needed. The spin cutoff parameter has been calculated as a function of excitation energy and mass with a super-conducting Hamiltonian. Calculations have been compared with two commonly used semiempirical formulas. A need for further measurements is also observed. Some complications for deformed nuclei are discussed. The quality of spin cut off parameter data derived from isomeric ratio measurement is examined.

  2. Mass-number and excitation-energy dependence of the spin cutoff parameter

    DOE PAGES

    Grimes, S. M.; Voinov, A. V.; Massey, T. N.

    2016-07-12

    Here, the spin cutoff parameter determining the nuclear level density spin distribution ρ(J) is defined through the spin projection as < J2z > 1/2 or equivalently for spherical nuclei, (< J(J+1) >/3)1/2. It is needed to divide the total level density into levels as a function of J. To obtain the total level density at the neutron binding energy from the s-wave resonance count, the spin cutoff parameter is also needed. The spin cutoff parameter has been calculated as a function of excitation energy and mass with a super-conducting Hamiltonian. Calculations have been compared with two commonly used semiempirical formulas.more » A need for further measurements is also observed. Some complications for deformed nuclei are discussed. The quality of spin cut off parameter data derived from isomeric ratio measurement is examined.« less

  3. Cotunneling spectroscopy and the properties of excited-state spin manifolds of Mn12 single molecule magnets

    NASA Astrophysics Data System (ADS)

    Rostamzadeh Renani, Fatemeh; Kirczenow, George

    2014-10-01

    We study charge transport through single molecule magnet (SMM) junctions in the cotunneling regime as a tool for investigating the properties of the excited-state manifolds of neutral Mn12 SMs. This study is motivated by a recent transport experiment [S. Kahle et al., Nano Lett. 12, 518 (2012), 10.1021/nl204141z] that probed the details of the magnetic and electronic structure of Mn12 SMMs beyond the ground-state spin manifold. A giant spin Hamiltonian and master equation approach is used to explore theoretically the cotunneling transport through Mn12-Ac SMM junctions. We identify SMM transitions that can account for both the strong and weak features of the experimental differential conductance spectra. We find the experimental results to imply that the excited spin-state manifolds of the neutral SMM have either different anisotropy constants or different g factors in comparison with its ground-state manifold. However, the latter scenario accounts best for the experimental data.

  4. Emergence of nontrivial magnetic excitations in a spin-liquid state of kagomé volborthite

    PubMed Central

    Watanabe, Daiki; Sugii, Kaori; Shimozawa, Masaaki; Suzuki, Yoshitaka; Yajima, Takeshi; Ishikawa, Hajime; Hiroi, Zenji; Shibauchi, Takasada; Matsuda, Yuji; Yamashita, Minoru

    2016-01-01

    When quantum fluctuations destroy underlying long-range ordered states, novel quantum states emerge. Spin-liquid (SL) states of frustrated quantum antiferromagnets, in which highly correlated spins fluctuate down to very low temperatures, are prominent examples of such quantum states. SL states often exhibit exotic physical properties, but the precise nature of the elementary excitations behind such phenomena remains entirely elusive. Here, we use thermal Hall measurements that can capture the unexplored property of the elementary excitations in SL states, and report the observation of anomalous excitations that may unveil the unique features of the SL state. Our principal finding is a negative thermal Hall conductivity κxy which the charge-neutral spin excitations in a gapless SL state of the 2D kagomé insulator volborthite Cu3V2O7(OH)2⋅2H2O exhibit, in much the same way in which charged electrons show the conventional electric Hall effect. We find that κxy is absent in the high-temperature paramagnetic state and develops upon entering the SL state in accordance with the growth of the short-range spin correlations, demonstrating that κxy is a key signature of the elementary excitation formed in the SL state. These results suggest the emergence of nontrivial elementary excitations in the gapless SL state which feel the presence of fictitious magnetic flux, whose effective Lorentz force is found to be less than 1/100 of the force experienced by free electrons. PMID:27439874

  5. Emergence of nontrivial magnetic excitations in a spin-liquid state of kagomé volborthite.

    PubMed

    Watanabe, Daiki; Sugii, Kaori; Shimozawa, Masaaki; Suzuki, Yoshitaka; Yajima, Takeshi; Ishikawa, Hajime; Hiroi, Zenji; Shibauchi, Takasada; Matsuda, Yuji; Yamashita, Minoru

    2016-08-02

    When quantum fluctuations destroy underlying long-range ordered states, novel quantum states emerge. Spin-liquid (SL) states of frustrated quantum antiferromagnets, in which highly correlated spins fluctuate down to very low temperatures, are prominent examples of such quantum states. SL states often exhibit exotic physical properties, but the precise nature of the elementary excitations behind such phenomena remains entirely elusive. Here, we use thermal Hall measurements that can capture the unexplored property of the elementary excitations in SL states, and report the observation of anomalous excitations that may unveil the unique features of the SL state. Our principal finding is a negative thermal Hall conductivity [Formula: see text] which the charge-neutral spin excitations in a gapless SL state of the 2D kagomé insulator volborthite Cu3V2O7(OH)2[Formula: see text]2H2O exhibit, in much the same way in which charged electrons show the conventional electric Hall effect. We find that [Formula: see text] is absent in the high-temperature paramagnetic state and develops upon entering the SL state in accordance with the growth of the short-range spin correlations, demonstrating that [Formula: see text] is a key signature of the elementary excitation formed in the SL state. These results suggest the emergence of nontrivial elementary excitations in the gapless SL state which feel the presence of fictitious magnetic flux, whose effective Lorentz force is found to be less than 1/100 of the force experienced by free electrons.

  6. "Parallel factor analysis of multi-excitation ultraviolet resonance Raman spectra for protein secondary structure determination".

    PubMed

    Oshokoya, Olayinka O; JiJi, Renee D

    2015-09-10

    Protein secondary structural analysis is important for understanding the relationship between protein structure and function, or more importantly how changes in structure relate to loss of function. The structurally sensitive protein vibrational modes (amide I, II, III and S) in deep-ultraviolet resonance Raman (DUVRR) spectra resulting from the backbone C-O and N-H vibrations make DUVRR a potentially powerful tool for studying secondary structure changes. Experimental studies reveal that the position and intensity of the four amide modes in DUVRR spectra of proteins are largely correlated with the varying fractions of α-helix, β-sheet and disordered structural content of proteins. Employing multivariate calibration methods and DUVRR spectra of globular proteins with varying structural compositions, the secondary structure of a protein with unknown structure can be predicted. A disadvantage of multivariate calibration methods is the requirement of known concentration or spectral profiles. Second-order curve resolution methods, such as parallel factor analysis (PARAFAC), do not have such a requirement due to the "second-order advantage." An exceptional feature of DUVRR spectroscopy is that DUVRR spectra are linearly dependent on both excitation wavelength and secondary structure composition. Thus, higher order data can be created by combining protein DUVRR spectra of several proteins collected at multiple excitation wavelengths to give multi-excitation ultraviolet resonance Raman data (ME-UVRR). PARAFAC has been used to analyze ME-UVRR data of nine proteins to resolve the pure spectral, excitation and compositional profiles. A three factor model with non-negativity constraints produced three unique factors that were correlated with the relative abundance of helical, β-sheet and poly-proline II dihedral angles. This is the first empirical evidence that the typically resolved "disordered" spectrum represents the better defined poly-proline II type structure.

  7. Excitation-emission spectra and fluorescence quantum yields for fresh and aged biogenic secondary organic aerosols

    SciTech Connect

    Lee, Hyun Ji; Laskin, Alexander; Laskin, Julia; Nizkorodov, Sergey A.

    2013-05-10

    Certain biogenic secondary organic aerosols (SOA) become absorbent and fluorescent when exposed to reduced nitrogen compounds such as ammonia, amines and their salts. Fluorescent SOA may potentially be mistaken for biological particles by detection methods relying on fluorescence. This work quantifies the spectral distribution and effective quantum yields of fluorescence of SOA generated from two monoterpenes, limonene and a-pinene, and two different oxidants, ozone (O3) and hydroxyl radical (OH). The SOA was generated in a smog chamber, collected on substrates, and aged by exposure to ~100 ppb ammonia vapor in air saturated with water vapor. Absorption and excitation-emission matrix (EEM) spectra of aqueous extracts of aged and control SOA samples were measured, and the effective absorption coefficients and fluorescence quantum yields (~0.005 for 349 nm excitation) were determined from the data. The strongest fluorescence for the limonene-derived SOA was observed for excitation = 420+- 50 nm and emission = 475 +- 38 nm. The window of the strongest fluorescence shifted to excitation = 320 +- 25 nm and emission = 425 +- 38 nm for the a-pinene-derived SOA. Both regions overlap with the excitation-emission matrix (EEM) spectra of some of the fluorophores found in primary biological aerosols. Our study suggests that, despite the low quantum yield, the aged SOA particles should have sufficient fluorescence intensities to interfere with the fluorescence detection of common bioaerosols.

  8. Excitation spectra of Ag3-DNA bases complexes: A benchmark study

    NASA Astrophysics Data System (ADS)

    Maksimov, D. A.; Pomogaev, V. A.; Kononov, A. I.

    2017-04-01

    Assessment of different ab initio and TDDFT methods was studied for calculation of the excitation energies of the complexes of pyrimidine bases with positively charged Ag3+ clusters. Performance of CIS, CIS(D), CC2, ADC(2), MP2, and TDDFT techniques with the use of different hybrid-GGA and meta-hybrid-GGA functionals and basis sets is studied. We found that M06-2X functional shows good accuracy in comparison with the ADC(2) ab initio method and that the geometry optimization approach can strongly affect the excitation spectra of the complexes. Our results may have important implications for further studies of ligand-stabilized silver nanoclusters.

  9. Cross-shell excitations in {sup 30}Al and {sup 30}Si at high spin.

    SciTech Connect

    Steppenbeck, D.; Deacon, A. N.; Freeman, S. J.; Janssens, R. V .F.; Carpenter, M. P.; Hoffman, C. R.; Kay, B. P.; Lauritsen, T.; Lister, C. J.; O'Donnell, D.; Ollier, J.; Seweryniak, D.; Smith, J. F.; Spohr, K.-M.; Tabor, S. L.; Tripathi, V.; Wady, P. T.; Zhu, S.

    2010-12-01

    Yrast and near-yrast states in {sup 30}Al and {sup 30}Si have been populated to high spin with the {sup 18}O + {sup 14}C fusion-evaporation reaction in inverse kinematics. The level schemes for these two isobars have been extended up to J {approx} 9 {h_bar} at 9.4 and 15.5 MeV, respectively. Their decay schemes indicate that cross-shell excitations dominate at high spin, where negative-parity structures exist. Positive-parity states are compared to the results of shell-model calculations using the USD, USDA, and USDB effective interactions. The negative-parity levels are compared to predictions of the WBP interaction and the recently-developed WBP-a Hamiltonian, by allowing 1p-1h excitations to fp-shell orbitals. The results suggest that single-neutron excitations to the 0f7/2 orbital play a significant role at high spin.

  10. Direct observation of dynamic modes excited in a magnetic insulator by pure spin current

    PubMed Central

    Demidov, V. E.; Evelt, M.; Bessonov, V.; Demokritov, S. O.; Prieto, J. L.; Muñoz, M.; Ben Youssef, J.; Naletov, V. V.; de Loubens, G.; Klein, O.; Collet, M.; Bortolotti, P.; Cros, V.; Anane, A.

    2016-01-01

    Excitation of magnetization dynamics by pure spin currents has been recently recognized as an enabling mechanism for spintronics and magnonics, which allows implementation of spin-torque devices based on low-damping insulating magnetic materials. Here we report the first spatially-resolved study of the dynamic modes excited by pure spin current in nanometer-thick microscopic insulating Yttrium Iron Garnet disks. We show that these modes exhibit nonlinear self-broadening preventing the formation of the self-localized magnetic bullet, which plays a crucial role in the stabilization of the single-mode magnetization oscillations in all-metallic systems. This peculiarity associated with the efficient nonlinear mode coupling in low-damping materials can be among the main factors governing the interaction of pure spin currents with the dynamic magnetization in high-quality magnetic insulators. PMID:27608533

  11. Spin wave excitation in yttrium iron garnet films with micron-sized antennas

    NASA Astrophysics Data System (ADS)

    Khivintsev, Y. V.; Filimonov, Y. A.; Nikitov, S. A.

    2015-02-01

    In this paper, we explore spin waves excitation in monolithic structures based on yttrium iron garnet (YIG) films with micro-sized antennas. Samples based on plain and patterned YIG film were fabricated and tested for tangential bias field geometries. We observed spin wave excitation and propagation with wave numbers up to 3.5 × 104 rad/cm. The corresponding wavelength is thus shorter more than by one order of magnitude compared to previous experiments with such films. For the sample with a periodic array of nanotrenches, we observed the effect of the shape anisotropy resulting in the shift of the spin wave propagation band in comparison to the unpatterned YIG film. Our results are very promising for the exploitation of short spin waves in YIG and provide great opportunity for significant miniaturization of YIG film based microwave devices.

  12. Spin wave excitation in yttrium iron garnet films with micron-sized antennas

    SciTech Connect

    Khivintsev, Y. V. Filimonov, Y. A.; Nikitov, S. A.

    2015-02-02

    In this paper, we explore spin waves excitation in monolithic structures based on yttrium iron garnet (YIG) films with micro-sized antennas. Samples based on plain and patterned YIG film were fabricated and tested for tangential bias field geometries. We observed spin wave excitation and propagation with wave numbers up to 3.5 × 10{sup 4} rad/cm. The corresponding wavelength is thus shorter more than by one order of magnitude compared to previous experiments with such films. For the sample with a periodic array of nanotrenches, we observed the effect of the shape anisotropy resulting in the shift of the spin wave propagation band in comparison to the unpatterned YIG film. Our results are very promising for the exploitation of short spin waves in YIG and provide great opportunity for significant miniaturization of YIG film based microwave devices.

  13. Kondo screening and spin excitation in few-layer CoPc molecular assembly stacking on Pb(111) surface: A DFT+HEOM study

    NASA Astrophysics Data System (ADS)

    Wang, Yu; Zheng, Xiao; Yang, Jinlong

    2016-10-01

    Transition metal phthalocyanine molecules adsorbed on a metal substrate exhibit rich spin-related phenomena such as magnetic anisotropy, spin excitation, and Kondo effect. In this work, we investigate theoretically few-layer cobalt phthalocyanine (CoPc) molecular assembly stacking on Pb(111) surface with the use of a combined density functional theory (DFT) and hierarchical equations of motion (HEOM) approach. Calculation results indicate that the local spin properties of CoPc/Pb(111) composites depend critically on the number of adsorption layers. The first layer of CoPc on the Pb(111) surface serves as a spin-insulating buffer, while the CoPc molecules in the second layer exhibit spin-1/2 Kondo effect with a Kondo temperature of about 22 K. In a triple-layer CoPc assembly stacking on Pb(111), the antiferromagnetic coupling between the second and third layers leads to local spin-flip excitations under finite bias voltages, which gives rise to characteristic signatures in the differential conductance spectra. The DFT+HEOM approach thus provides a practical means for investigating the local electronic and spin properties of two-dimensional molecular assemblies adsorbed on the metal surface. The insights obtained from the first-principles based simulations could be useful for experimental manipulation or design of magnetic composite systems.

  14. High-resolution fluorescence excitation spectra of jet-cooled benzyl and p-methylbenzyl radicals

    NASA Astrophysics Data System (ADS)

    Lin, Tai-Yuan David; Tan, Xue-Qing; Cerny, Timothy M.; Williamson, James M.; Cullin, David W.; Miller, Terry A.

    1992-11-01

    High-resolution, rotationally resolved, laser-induced, fluorescence excitation spectra of the A 1 and 6a 10 bands of benzyl and the 0 00 band of p-methylbenzyl radicals were obtained in supersonic expansions. All three spectra were assigned and fit, using the rigid rotor Hamiltonian as well as methyl group internal rotation theory. The results of the rotational analysis provide good rotation constants for benzyl and p-methylbenzyl and establish unambiguously that the symmetry of the excited electronic state in this transition of p-methylbenzyl is 2A 2 (in C 2v). The heights of torsional barriers that hinder the internal rotation of the methyl group in p-methylbenzyl also are determined. The torsional results are compared to those obtained previously for this radical in a vibrational analysis and to other open shell radicals.

  15. Controlling the Excited-State Dynamics of Nuclear Spin Isomers Using the Dynamic Stark Effect.

    PubMed

    Waldl, Maria; Oppel, Markus; González, Leticia

    2016-07-14

    Stark control of chemical reactions uses intense laser pulses to distort the potential energy surfaces of a molecule, thus opening new chemical pathways. We use the concept of Stark shifts to convert a local minimum into a local maximum of the potential energy surface, triggering constructive and destructive wave-packet interferences, which then induce different dynamics on nuclear spin isomers in the electronically excited state of a quinodimethane derivative. Model quantum-dynamical simulations on reduced dimensionality using optimized ultrashort laser pulses demonstrate a difference of the excited-state dynamics of two sets of nuclear spin isomers, which ultimately can be used to discriminate between these isomers.

  16. Singlet-to-Triplet Excitations in the Unconventional Spin-Peierls System TiOBr

    SciTech Connect

    Clancy, James P; Gaulin, Bruce D.; Adams, Carl P; Granroth, Garrett E; Kolesnikov, Alexander I; Sherline, Todd E; Chou, F. C.

    2011-01-01

    We have performed time-of-flight neutron scattering measurements on powder samples of the unconventional spin-Peierls compound TiOBr using the fine-resolution Fermi chopper spectrometer (SEQUOIA) at the SNS. These measurements reveal two branches of magnetic excitations within the commensurate and incommensurate spin-Peierls phases, which we associate with n = 1 and n = 2 triplet excitations out of the singlet ground state. These measurements represent the first direct measure of the singlet-triplet energy gap in TiOBr, which is found to have a value of Eg 21 meV.

  17. Singlet-Triplet Excitations in the Unconventional Spin-Peierls TiOBr Compound

    NASA Astrophysics Data System (ADS)

    Clancy, J. P.; Gaulin, B. D.; Adams, C. P.; Granroth, G. E.; Kolesnikov, A. I.; Sherline, T. E.; Chou, F. C.

    2011-03-01

    We have performed time-of-flight neutron scattering measurements on powder samples of the unconventional spin-Peierls compound TiOBr using the fine-resolution Fermi chopper spectrometer (SEQUOIA) at the Spallation Neutron Source at Oak Ridge National Laboratory. These measurements reveal two branches of magnetic excitations within the commensurate and incommensurate spin-Peierls phases, which we associate with n=1 and n=2 triplet excitations out of the singlet ground state. These results represent the first direct measurement of the singlet-triplet energy gap in TiOBr, which has a value of Eg=21.2±1.0meV.

  18. Localized and propagating excitations in gapped phases of spin systems with bond disorder

    NASA Astrophysics Data System (ADS)

    Utesov, O. I.; Sizanov, A. V.; Syromyatnikov, A. V.

    2014-10-01

    Using the conventional T-matrix approach, we discuss gapped phases in one-, two-, and three-dimensional (3D) spin systems (both with and without a long-range magnetic order) with bond disorder and with weakly interacting bosonic elementary excitations. This work is motivated by recent experimental and theoretical activity in spin-liquid-like systems with disorder and in the disordered interacting boson problem. In particular, we apply our theory to both paramagnetic low-field and fully polarized high-field phases in dimerized spin-1/2 systems and in integer-spin magnets with large single-ion easy-plane anisotropy D with disorder in exchange coupling constants (and/or D). The elementary excitation spectrum and the density of states are calculated in the first order in defects concentration c ≪1. In 2D and 3D systems, the scattering on defects leads to a finite damping of all propagating excitations in the band except for states lying near its edges. We demonstrate that the analytical approach is inapplicable for states near the band edges and our numerical calculations reveal their localized nature. We find that the damping of propagating excitations can be much more pronounced in considered systems than in magnetically ordered gapless magnets with impurities. In 1D systems, the disorder leads to localization of all states in the band, while those lying far from the band edges (short-wavelength excitations) can look like conventional wave packets.

  19. Lifetime measurement of excited low-spin states via the (p, p‧ γ) reaction

    NASA Astrophysics Data System (ADS)

    Hennig, A.; Derya, V.; Mineva, M. N.; Petkov, P.; Pickstone, S. G.; Spieker, M.; Zilges, A.

    2015-09-01

    In this paper a method for lifetime measurements in the sub-picosecond regime via the Doppler-shift attenuation method (DSAM) following the inelastic proton scattering reaction is presented. In a pioneering experiment we extracted the lifetimes of 30 excited low-spin states of 96Ru, taking advantage of the coincident detection of scattered protons and de-exciting γ-rays as well as the large number of particle and γ-ray detectors provided by the SONIC@HORUS setup at the University of Cologne. The large amount of new experimental data shows that this technique is suited for the measurement of lifetimes of excited low-spin states, especially for isotopes with a low isotopic abundance, where (n ,n‧ γ) or - in case of investigating dipole excitations - (γ ,γ‧) experiments are not feasible due to the lack of sufficient isotopically enriched target material.

  20. Excitation spectra and wave functions of quasiparticle bound states in bilayer Rashba superconductors

    NASA Astrophysics Data System (ADS)

    Higashi, Yoichi; Nagai, Yuki; Yoshida, Tomohiro; Kato, Masaru; Yanase, Youichi

    2015-11-01

    We study the excitation spectra and the wave functions of quasiparticle bound states at a vortex and an edge in bilayer Rashba superconductors under a magnetic field. In particular, we focus on the quasiparticle states at the zero energy in the pair-density wave state in a topologically non-trivial phase. We numerically demonstrate that the quasiparticle wave functions with zero energy are localized at both the edge and the vortex core if the magnetic field exceeds the critical value.

  1. Direct excitation of propagating spin waves by focused ultrashort optical pulses.

    PubMed

    Au, Y; Dvornik, M; Davison, T; Ahmad, E; Keatley, P S; Vansteenkiste, A; Van Waeyenberge, B; Kruglyak, V V

    2013-03-01

    An all-optical experiment long utilized to image phonons excited by ultrashort optical pulses has been applied to a magnetic sample. In addition to circular ripples due to surface acoustic waves, we observe an X-shaped pattern formed by propagating spin waves. The emission of spin waves from the optical pulse epicenter in the form of collimated beams is qualitatively reproduced by micromagnetic simulations. We explain the observed pattern in terms of the group velocity distribution of Damon-Eshbach magnetostatic spin waves in the reciprocal space and the wave vector spectrum of the focused ultrafast laser pulse.

  2. Direct Excitation of Propagating Spin Waves by Focused Ultrashort Optical Pulses

    NASA Astrophysics Data System (ADS)

    Au, Y.; Dvornik, M.; Davison, T.; Ahmad, E.; Keatley, P. S.; Vansteenkiste, A.; Van Waeyenberge, B.; Kruglyak, V. V.

    2013-03-01

    An all-optical experiment long utilized to image phonons excited by ultrashort optical pulses has been applied to a magnetic sample. In addition to circular ripples due to surface acoustic waves, we observe an X-shaped pattern formed by propagating spin waves. The emission of spin waves from the optical pulse epicenter in the form of collimated beams is qualitatively reproduced by micromagnetic simulations. We explain the observed pattern in terms of the group velocity distribution of Damon-Eshbach magnetostatic spin waves in the reciprocal space and the wave vector spectrum of the focused ultrafast laser pulse.

  3. Spin-wave population in nickel after femtosecond laser pulse excitation

    NASA Astrophysics Data System (ADS)

    Lenk, Benjamin; Eilers, Gerrit; Hamrle, Jaroslav; Münzenberg, Markus

    2010-10-01

    The spin-wave relaxation mechanisms after intense laser excitation in ferromagnetic nickel films are investigated with all-optical pump-probe experiments. Uniform precession (Kittel mode), Damon-Eshbach surface modes and perpendicular standing spin waves can be identified by their dispersion ω(Hext) . However, different to other ferromagnets ω(Hext) deviates from the expected behavior. Namely, a mode discontinuity is observed that can be attributed to a nonlinear process. Above a critical field the power spectrum reveals a redistribution of the energy within the spin-wave spectrum populated.

  4. Breathers and rogue waves excited by all-magnonic spin-transfer torque

    NASA Astrophysics Data System (ADS)

    Li, Zai-Dong; Li, Qiu-Yan; Xu, Tian-Fu; He, Peng-Bin

    2016-10-01

    In terms of Darboux transformation we investigate the dynamic process of spin wave passing through a magnetic soliton. It causes nonlinear excitations, such as Akhmediev breathers solution and Kuznetsov-Ma soliton. The former case demonstrates a spatial periodic process of a magnetic soliton forming the petal with four pieces. The spatial separation of adjacent magnetic petals increases rapidly, while one valley splits into two and the amplitude of valley increases gradually with the increasing amplitude of spin wave. The other case shows a localized process of the spin-wave background. In the limit case, we get rogue waves and clarify its formation mechanism.

  5. Breathers and rogue waves excited by all-magnonic spin-transfer torque.

    PubMed

    Li, Zai-Dong; Li, Qiu-Yan; Xu, Tian-Fu; He, Peng-Bin

    2016-10-01

    In terms of Darboux transformation we investigate the dynamic process of spin wave passing through a magnetic soliton. It causes nonlinear excitations, such as Akhmediev breathers solution and Kuznetsov-Ma soliton. The former case demonstrates a spatial periodic process of a magnetic soliton forming the petal with four pieces. The spatial separation of adjacent magnetic petals increases rapidly, while one valley splits into two and the amplitude of valley increases gradually with the increasing amplitude of spin wave. The other case shows a localized process of the spin-wave background. In the limit case, we get rogue waves and clarify its formation mechanism.

  6. Discrimination of nuclear spin isomers exploiting the excited state dynamics of a quinodimethane derivative

    SciTech Connect

    Obaid, Rana; Kinzel, Daniel; Oppel, Markus González, Leticia

    2014-10-28

    Despite the concept of nuclear spin isomers (NSIs) exists since the early days of quantum mechanics, only few approaches have been suggested to separate different NSIs. Here, a method is proposed to discriminate different NSIs of a quinodimethane derivative using its electronic excited state dynamics. After electronic excitation by a laser field with femtosecond time duration, a difference in the behavior of several quantum mechanical operators can be observed. A pump-probe experimental approach for separating these different NSIs is then proposed.

  7. Discrimination of nuclear spin isomers exploiting the excited state dynamics of a quinodimethane derivative.

    PubMed

    Obaid, Rana; Kinzel, Daniel; Oppel, Markus; González, Leticia

    2014-10-28

    Despite the concept of nuclear spin isomers (NSIs) exists since the early days of quantum mechanics, only few approaches have been suggested to separate different NSIs. Here, a method is proposed to discriminate different NSIs of a quinodimethane derivative using its electronic excited state dynamics. After electronic excitation by a laser field with femtosecond time duration, a difference in the behavior of several quantum mechanical operators can be observed. A pump-probe experimental approach for separating these different NSIs is then proposed.

  8. Spin excitations and thermodynamics of the antiferromagnetic Heisenberg model on the layered honeycomb lattice

    NASA Astrophysics Data System (ADS)

    Vladimirov, Artem A.; Ihle, Dieter; Plakida, Nikolay M.

    2017-03-01

    We present a spin-rotation-invariant Green-function theory for the dynamic spin susceptibility in the spin-1/2 antiferromagnetic Heisenberg model on a stacked honeycomb lattice. Employing a generalized mean-field approximation for arbitrary temperatures, the thermodynamic quantities (two-spin correlation functions, internal energy, magnetic susceptibility, staggered magnetization, Néel temperature, correlation length) and the spin-excitation spectrum are calculated by solving a coupled system of self-consistency equations for the correlation functions. The temperature dependence of the magnetic (uniform static) susceptibility is ascribed to antiferromagnetic short-range order. The Néel temperature is calculated for arbitrary interlayer couplings. Our results are in a good agreement with numerical computations for finite clusters and with available experimental data on the β-Cu2V2O2 compound.

  9. Resonance Raman spectra of organic molecules absorbed on inorganic semiconducting surfaces: Contribution from both localized intramolecular excitation and intermolecular charge transfer excitation

    NASA Astrophysics Data System (ADS)

    Ye, ChuanXiang; Zhao, Yi; Liang, WanZhen

    2015-10-01

    The time-dependent correlation function approach for the calculations of absorption and resonance Raman spectra (RRS) of organic molecules absorbed on semiconductor surfaces [Y. Zhao and W. Z. Liang, J. Chem. Phys. 135, 044108 (2011)] is extended to include the contribution of the intermolecular charge transfer (CT) excitation from the absorbers to the semiconducting nanoparticles. The results demonstrate that the bidirectionally interfacial CT significantly modifies the spectral line shapes. Although the intermolecular CT excitation makes the absorption spectra red shift slightly, it essentially changes the relative intensities of mode-specific RRS and causes the oscillation behavior of surface enhanced Raman spectra with respect to interfacial electronic couplings. Furthermore, the constructive and destructive interferences of RRS from the localized molecular excitation and CT excitation are observed with respect to the electronic coupling and the bottom position of conductor band. The interferences are determined by both excitation pathways and bidirectionally interfacial CT.

  10. Excitation-emission spectra and fluorescence quantum yields for fresh and aged biogenic secondary organic aerosols.

    PubMed

    Lee, Hyun Ji Julie; Laskin, Alexander; Laskin, Julia; Nizkorodov, Sergey A

    2013-06-04

    Certain biogenic secondary organic aerosols (SOA) become absorbent and fluorescent when exposed to reduced nitrogen compounds such as ammonia, amines, and their salts. Fluorescent SOA may potentially be mistaken for biological particles by detection methods relying on fluorescence. This work quantifies the spectral distribution and effective quantum yields of fluorescence of water-soluble SOA generated from two monoterpenes, limonene and α-pinene, and two different oxidants, ozone (O3) and hydroxyl radical (OH). The SOA was generated in a smog chamber, collected on substrates, and aged by exposure to ∼100 ppb ammonia in air saturated with water vapor. Absorption and excitation-emission matrix (EEM) spectra of aqueous extracts of aged and control SOA samples were measured, and the effective absorption coefficients and fluorescence quantum yields (∼0.005 for 349 nm excitation) were determined from the data. The strongest fluorescence for the limonene-derived SOA was observed for λexcitation = 420 ± 50 nm and λemission = 475 ± 38 nm. The window of the strongest fluorescence shifted to λexcitation = 320 ± 25 nm and λemission = 425 ± 38 nm for the α-pinene-derived SOA. Both regions overlap with the EEM spectra of some of the fluorophores found in primary biological aerosols. Despite the low quantum yield, the aged SOA particles may have sufficient fluorescence intensities to interfere with the fluorescence detection of common bioaerosols.

  11. Ultrafast spin exchange-coupling torque via photo-excited charge-transfer processes

    SciTech Connect

    Ma, X.; Fang, F.; Li, Q.; Zhu, J.; Yang, Y.; Wu, Y. Z.; Zhao, H. B.; Lüpke, G.

    2015-10-28

    In this study, optical control of spin is of central importance in the research of ultrafast spintronic devices utilizing spin dynamics at short time scales. Recently developed optical approaches such as ultrafast demagnetization, spin-transfer and spin-orbit torques open new pathways to manipulate spin through its interaction with photon, orbit, charge or phonon. However, these processes are limited by either the long thermal recovery time or the low-temperature requirement. Here we experimentally demonstrate ultrafast coherent spin precession via optical charge-transfer processes in the exchange-coupled Fe/CoO system at room temperature. The efficiency of spin precession excitation is significantly higher and the recovery time of the exchange-coupling torque is much shorter than for the demagnetization procedure, which is desirable for fast switching. The exchange coupling is a key issue in spin valves and tunnelling junctions, and hence our findings will help promote the development of exchange-coupled device concepts for ultrafast coherent spin manipulation.

  12. Ultrafast spin exchange-coupling torque via photo-excited charge-transfer processes

    DOE PAGES

    Ma, X.; Fang, F.; Li, Q.; ...

    2015-10-28

    In this study, optical control of spin is of central importance in the research of ultrafast spintronic devices utilizing spin dynamics at short time scales. Recently developed optical approaches such as ultrafast demagnetization, spin-transfer and spin-orbit torques open new pathways to manipulate spin through its interaction with photon, orbit, charge or phonon. However, these processes are limited by either the long thermal recovery time or the low-temperature requirement. Here we experimentally demonstrate ultrafast coherent spin precession via optical charge-transfer processes in the exchange-coupled Fe/CoO system at room temperature. The efficiency of spin precession excitation is significantly higher and the recoverymore » time of the exchange-coupling torque is much shorter than for the demagnetization procedure, which is desirable for fast switching. The exchange coupling is a key issue in spin valves and tunnelling junctions, and hence our findings will help promote the development of exchange-coupled device concepts for ultrafast coherent spin manipulation.« less

  13. Ultrafast spin exchange-coupling torque via photo-excited charge-transfer processes

    PubMed Central

    Ma, X.; Fang, F.; Li, Q.; Zhu, J.; Yang, Y.; Wu, Y. Z.; Zhao, H. B.; Lüpke, G.

    2015-01-01

    Optical control of spin is of central importance in the research of ultrafast spintronic devices utilizing spin dynamics at short time scales. Recently developed optical approaches such as ultrafast demagnetization, spin-transfer and spin-orbit torques open new pathways to manipulate spin through its interaction with photon, orbit, charge or phonon. However, these processes are limited by either the long thermal recovery time or the low-temperature requirement. Here we experimentally demonstrate ultrafast coherent spin precession via optical charge-transfer processes in the exchange-coupled Fe/CoO system at room temperature. The efficiency of spin precession excitation is significantly higher and the recovery time of the exchange-coupling torque is much shorter than for the demagnetization procedure, which is desirable for fast switching. The exchange coupling is a key issue in spin valves and tunnelling junctions, and hence our findings will help promote the development of exchange-coupled device concepts for ultrafast coherent spin manipulation. PMID:26508587

  14. Spin correlations and spin-wave excitations in Dirac-Weyl semimetals

    NASA Astrophysics Data System (ADS)

    Araki, Yasufumi; Nomura, Kentaro

    We study correlations among magnetic dopants in three-dimensional Dirac and Weyl semimetals. Effective field theory for localized magnetic moments is derived by integrating out the itinerant electron degrees of freedom. We find that spin correlation in the spatial direction parallel to local magnetization is more rigid than that in the perpendicular direction, reflecting spin-momentum locking nature of the Dirac Hamiltonian. Such an anisotropy becomes stronger for Fermi level close to the Dirac points, due to Van Vleck paramagnetism triggered by spin-orbit coupling. One can expect topologically nontrivial spin textures under this anisotropy, such as a hedgehog around a single point, or a radial vortex around an axis, as well as a uniform ferromagnetic order. We further investigate the characteristics of spin waves in the ferromagnetic state. Spin-wave dispersion also shows a spatial anisotropy, which is less dispersed in the direction transverse to the magnetization than that in the longitudinal direction. The spin-wave dispersion anisotropy can be traced back to the rigidity and flexibility of spin correlations discussed above. This work was supported by Grant-in-Aid for Scientific Research (Grants No.15H05854, No.26107505, and No.26400308) from the Ministry of Education, Culture, Sports, Science and Technology (MEXT), Japan.

  15. Detection of nanoscale electron spin resonance spectra demonstrated using nitrogen-vacancy centre probes in diamond

    PubMed Central

    Hall, L. T.; Kehayias, P.; Simpson, D. A.; Jarmola, A.; Stacey, A.; Budker, D.; Hollenberg, L. C. L.

    2016-01-01

    Electron spin resonance (ESR) describes a suite of techniques for characterizing electronic systems with applications in physics, chemistry, and biology. However, the requirement for large electron spin ensembles in conventional ESR techniques limits their spatial resolution. Here we present a method for measuring ESR spectra of nanoscale electronic environments by measuring the longitudinal relaxation time of a single-spin probe as it is systematically tuned into resonance with the target electronic system. As a proof of concept, we extracted the spectral distribution for the P1 electronic spin bath in diamond by using an ensemble of nitrogen-vacancy centres, and demonstrated excellent agreement with theoretical expectations. As the response of each nitrogen-vacancy spin in this experiment is dominated by a single P1 spin at a mean distance of 2.7 nm, the application of this technique to the single nitrogen-vacancy case will enable nanoscale ESR spectroscopy of atomic and molecular spin systems. PMID:26728001

  16. 14N overtone NMR spectra under magic angle spinning: Experiments and numerically exact simulations

    NASA Astrophysics Data System (ADS)

    O'Dell, Luke A.; Brinkmann, Andreas

    2013-02-01

    It was recently shown that high resolution 14N overtone NMR spectra can be obtained directly under magic angle spinning (MAS) conditions [L. A. O'Dell and C. I. Ratcliffe, Chem. Phys. Lett. 514, 168 (2011)], 10.1016/j.cplett.2011.08.030. Preliminary experimental results showed narrowed powder pattern widths, a frequency shift that is dependent on the MAS rate, and an apparent absence of spinning sidebands, observations which appeared to be inconsistent with previous theoretical treatments. Herein, we reproduce these effects using numerically exact simulations that take into account the full nuclear spin Hamiltonian. Under sample spinning, the 14N overtone signal is split into five (0, ±1, ±2) overtone sidebands separated by the spinning frequency. For a powder sample spinning at the magic angle, the +2ωr sideband is dominant while the others show significantly lower signal intensities. The resultant MAS powder patterns show characteristic quadrupolar lineshapes from which the 14N quadrupolar parameters and isotropic chemical shift can be determined. Spinning the sample at other angles is shown to alter both the shapes and relative intensities of the five overtone sidebands, with MAS providing the benefit of averaging dipolar couplings and shielding anisotropy. To demonstrate the advantages of this experimental approach, we present the 14N overtone MAS spectrum obtained from L-histidine, in which powder patterns from all three nitrogen sites are clearly resolved.

  17. Subpicosecond spin dynamics of excited states in the topological insulator Bi2Te3

    NASA Astrophysics Data System (ADS)

    Sánchez-Barriga, J.; Battiato, M.; Krivenkov, M.; Golias, E.; Varykhalov, A.; Romualdi, A.; Yashina, L. V.; Minár, J.; Kornilov, O.; Ebert, H.; Held, K.; Braun, J.

    2017-03-01

    Using time-, spin-, and angle-resolved photoemission, we investigate the ultrafast spin dynamics of hot electrons on the surface of the topological insulator Bi2Te3 following optical excitation by femtosecond-infrared pulses. We observe two surface-resonance states above the Fermi level coexisting with a transient population of Dirac fermions that relax in ˜2 ps. One state disperses up to ˜0.4 eV just above the bulk continuum, and the other one at ˜0.8 eV inside a projected bulk band gap. At the onset of the excitation, both states exhibit a reversed spin texture with respect to that of the transient Dirac bands, in agreement with our one-step photoemission calculations. Our data reveal that the high-energy state undergoes spin relaxation within ˜0.5 ps, a process that triggers the subsequent spin dynamics of both the Dirac cone and the low-energy state, which behave as two dynamically locked electron populations. We discuss the origin of this behavior by comparing the relaxation times observed for electrons with opposite spins to the ones obtained from a microscopic Boltzmann model of ultrafast band cooling introduced into the photoemission calculations. Our results demonstrate that the nonequilibrium surface dynamics is governed by electron-electron rather than electron-phonon scattering, with a characteristic time scale unambiguously determined by the complex spin texture of excited states above the Fermi level. Our findings reveal the critical importance of detecting momentum and energy-resolved spin textures with femtosecond resolution to fully understand the subpicosecond dynamics of transient electrons on the surface of topological insulators.

  18. Spin Chirality and Hall-Like Transport Phenomena of Spin Excitations

    NASA Astrophysics Data System (ADS)

    Han, Jung Hoon; Lee, Hyunyong

    2017-01-01

    Experimental and theoretical aspects of Hall-type transport of spins in magnetic insulators are reviewed. A general formalism for linear response theory of thermal Hall transport in the spin model is developed, which is general enough to be applicable to both the magnon and the paramagnetic, spin-liquid regimes. The expression of the energy current operator in the spin language is shown to be closely related to the spin chirality operator. Recent experiments on magnon-mediated thermal Hall transport in the two-dimensional kagome, and three-dimensional pyrochlore ferromagnetic insulators are reviewed in light of the multi-band magnon theory of Hall transport, and compared to the more mysterious thermal Hall transport found in the putative quantum spin ice material. As realizations of spin-chirality driven magnon transport in the real space, we review the general theory of emergent gauge fields governing the magnon dynamics in the textured magnet, and discuss its application to the magnon-Skyrmion scattering problem. Topological magnon Hall effect driven by the Skyrmion texture is discussed.

  19. Transient Exciton Spin Splitting in GaAs Quantum Wells under Near-Resonant Excitation

    NASA Astrophysics Data System (ADS)

    Zin Latt, Kyaw; Lai, Chih-Wei

    2010-03-01

    We investigated spin dependent exciton-exciton interaction and energy relaxation under near-resonant circularly polarized ps pulsed excitation in single, multiple, or double coupled GaAs/AlGaAs quantum wells. Transient exciton spin splitting and relaxation were determined from time-resolved photoluminescence (TRPL) spectroscopy and polarimetry with a streak camera system. In contrast to standard TRPL measurements based on up-conversion and pump-probe techniques, the streak-camera setup allows for speedy spectroscopy and Stokes polarimetry measurements as a function of the exciton density and magnetic/electric field under near -resonant excitation (˜3 to 10 meV from the exciton resonance). For 6-nm and 14-nm GaAs/AlGaAs quantum wells at intermediate density (a few 10^10 cm-2), a spin splitting of 2 and 1 meV appeared instantly within 10 ps after excitation and exhibited a decay time constant of ˜100 and 500 ps, respectively. In the presence of magnetic fields, the spin splitting and relaxation dynamics became non-exponential and exhibited asymmetric and nonlinear dependence on the direction and magnitude of the field up to 10 Tesla. We analyzed the spin splitting and relaxation dynamics in terms of inter-exciton and intra-exciton exchange interaction and exciton-carrier interaction.

  20. Exploring ground states and excited states of spin-1 Bose-Einstein condensates by continuation methods

    SciTech Connect

    Chen, Jen-Hao; Chern, I-Liang; Wang Weichung

    2011-03-20

    A pseudo-arclength continuation method (PACM) is employed to compute the ground state and excited state solutions of spin-1 Bose-Einstein condensates (BEC). The BEC is governed by the time-independent coupled Gross-Pitaevskii equations (GPE) under the conservations of the mass and magnetization. The coupling constants that characterize the spin-independent and spin-exchange interactions are chosen as the continuation parameters. The continuation curve starts from a ground state or an excited state with very small coupling parameters. The proposed numerical schemes allow us to investigate the effect of the coupling constants and study the bifurcation diagrams of the time-independent coupled GPE. Numerical results on the wave functions and their corresponding energies of spin-1 BEC with repulsive/attractive and ferromagnetic/antiferromagnetic interactions are presented. Furthermore, we reveal that the component separation and population transfer between the different hyperfine states can only occur in excited states due to the spin-exchange interactions.

  1. Excitation of propagating spin waves in ferromagnetic nanowires by microwave voltage-controlled magnetic anisotropy.

    PubMed

    Verba, Roman; Carpentieri, Mario; Finocchio, Giovanni; Tiberkevich, Vasil; Slavin, Andrei

    2016-04-26

    The voltage-controlled magnetic anisotropy (VCMA) effect, which manifests itself as variation of anisotropy of a thin layer of a conductive ferromagnet on a dielectric substrate under the influence of an external electric voltage, can be used for the development of novel information storage and signal processing devices with low power consumption. Here it is demonstrated by micromagnetic simulations that the application of a microwave voltage to a nanosized VCMA gate in an ultrathin ferromagnetic nanowire results in the parametric excitation of a propagating spin wave, which could serve as a carrier of information. The frequency of the excited spin wave is twice smaller than the frequency of the applied voltage while its amplitude is limited by 2 mechanisms: (i) the so-called "phase mechanism" described by the Zakharov-L'vov-Starobinets "S-theory" and (ii) the saturation mechanism associated with the nonlinear frequency shift of the excited spin wave. The developed extension of the "S-theory", which takes into account the second limitation mechanism, allowed us to estimate theoretically the efficiency of the parametric excitation of spin waves by the VCMA effect.

  2. Excitation energies and spins of the yrast superdeformed band in {sup 191}Hg

    SciTech Connect

    Siem, S.; Reiter, P.; Khoo, T.L.; Lauritsen, T.; Carpenter, M.P.; Ahmad, I.; Calderin, I.J.; Duguet, T.; Fischer, S.M.; Gassmann, D.; Hackman, G.; Janssens, R.V.F.; Nisius, D.; Heenen, P.-H.; Amro, H.; Moore, E.F.; Doessing, T.; Garg, U.; Kharraja, B.; Hannachi, F.

    2004-07-01

    The excitation energies and spins of the levels in the yrast superdeformed band of {sup 191}Hg have been determined from two single-step {gamma} transitions and the quasicontinuum spectrum connecting the superdeformed and normal-deformed states. The results are compared with those from theoretical mean-field calculations with different interactions. A discussion of pairing in superdeformed states is also included.

  3. Evolution of spin excitations into the superconducting state in FeTe1-xSex

    NASA Astrophysics Data System (ADS)

    Lumsden, M. D.; Christianson, A. D.; Goremychkin, E. A.; Nagler, S. E.; Mook, H. A.; Stone, M. B.; Abernathy, D. L.; Guidi, T.; MacDougall, G. J.; de La Cruz, C.; Sefat, A. S.; McGuire, M. A.; Sales, B. C.; Mandrus, D.

    2010-03-01

    The origin of the superconducting state in the recently discovered Fe-based materials is the subject of intense scrutiny. Neutron scattering and NMR (ref. 8) measurements have already demonstrated a strong correlation between magnetism and superconductivity. A central unanswered question concerns the nature of the normal-state spin fluctuations that may be responsible for the pairing. Here we present inelastic neutron scattering measurements from large single crystals of superconducting and non-superconducting Fe1+yTe1-xSex. These measurements indicate a spin fluctuation spectrum dominated by two-dimensional incommensurate excitations extending to energies greater than 250meV. Most importantly, the spin excitations in Fe1+yTe1-xSex have four-fold symmetry about the (1, 0) wavevector (square-lattice (π,π) point). Moreover, the excitations are described by the identical wavevector and can be characterized by the same model as the normal-state spin excitations in the high-TC cuprates. These results demonstrate commonality between the magnetism in these classes of materials, which perhaps extends to a common origin for superconductivity.

  4. Excitation of propagating spin waves in ferromagnetic nanowires by microwave voltage-controlled magnetic anisotropy

    PubMed Central

    Verba, Roman; Carpentieri, Mario; Finocchio, Giovanni; Tiberkevich, Vasil; Slavin, Andrei

    2016-01-01

    The voltage-controlled magnetic anisotropy (VCMA) effect, which manifests itself as variation of anisotropy of a thin layer of a conductive ferromagnet on a dielectric substrate under the influence of an external electric voltage, can be used for the development of novel information storage and signal processing devices with low power consumption. Here it is demonstrated by micromagnetic simulations that the application of a microwave voltage to a nanosized VCMA gate in an ultrathin ferromagnetic nanowire results in the parametric excitation of a propagating spin wave, which could serve as a carrier of information. The frequency of the excited spin wave is twice smaller than the frequency of the applied voltage while its amplitude is limited by 2 mechanisms: (i) the so-called “phase mechanism” described by the Zakharov-L’vov-Starobinets “S-theory” and (ii) the saturation mechanism associated with the nonlinear frequency shift of the excited spin wave. The developed extension of the “S-theory”, which takes into account the second limitation mechanism, allowed us to estimate theoretically the efficiency of the parametric excitation of spin waves by the VCMA effect. PMID:27113392

  5. Cumulant approach for electronic excitations in x-ray and electron spectra

    NASA Astrophysics Data System (ADS)

    Rehr, J. J.

    A quantitative treatment of electronic excitations and other many-body effects in x-ray and electron spectra has long been challenging. Physically, electronic correlations and atomic vibrations lead to inelastic losses and damping effects that are ignored in ground state methods or approximations such as TDDFT. Quasi-particle (QP) approaches such as the GW approximation yield significant improvements, as demonstrated in real-space Green's function and GW/Bethe-Salpeter equation calculations, but still ignore multi-electron excitations. Recently such excitations have been treated with considerable success using cumulant expansion techniques and the quasi-boson approximation. In this beyond QP approach, excitations such as plasmons and electron-hole excitations appear as satellites in the spectral function. The method naturally accounts for multiple-satellites and can be extended to include extrinsic losses and interference effects. Extensions for effects of vibrations and strong correlations including charge-transfer satellites may also be possible. These advances are illustrated with a number of applications. Supported by DOE Grant DE-FG02-97ER45623.

  6. Quantitative first-principles calculations of valence and core excitation spectra of solid C60

    NASA Astrophysics Data System (ADS)

    Fossard, F.; Hug, G.; Gilmore, K.; Kas, J. J.; Rehr, J. J.; Vila, F. D.; Shirley, E. L.

    2017-03-01

    We present calculated valence and C 1 s near-edge excitation spectra of solid C60 and experimental results measured with high-resolution electron energy-loss spectroscopy. The near-edge calculations are carried out using three different methods: solution of the Bethe-Salpeter equation (BSE) as implemented in the ocean suite (Obtaining Core Excitations with Ab Initio methods and the NIST BSE solver), the excited-electron core-hole approach, and the constrained-occupancy method using the Stockholm-Berlin core excitation code, StoBe. The three methods give similar results and are in good agreement with experiment, though the BSE results are the most accurate. The BSE formalism is also used to carry out valence level calculations using the NIST BSE solver. Theoretical results include self-energy corrections to the band gap and bandwidths, lifetime-damping effects, and Debye-Waller effects in the core excitation case. A comparison of spectral features to those observed experimentally illustrates the sensitivity of certain features to computational details, such as self-energy corrections to the band structure and core-hole screening.

  7. Spin excitations of ferronematic order in underdoped cuprate superconductors

    PubMed Central

    Seibold, G.; Di Castro, C.; Grilli, M.; Lorenzana, J.

    2014-01-01

    High-temperature superconductors exhibit a characteristic hourglass-shaped spectrum of magnetic fluctuations which most likely contribute to the pairing glue in the cuprates. Recent neutron scattering experiments in strongly underdoped compounds have revealed a significant low energy anisotropy of these fluctuations which we explain by a model in which topological defects of the antiferromagnet clump to producing domain wall segments with ferronematic order. This state does not invoke global charge order but breaks C4 rotational and inversion symmetry. The incommensurability of the low doping charge-disordered state is in good agreement with experiment and interpolates smoothly with the incommensurability of the stripe phase at higher doping. Within linear spin-wave theory the dynamic structure factor is in very good agreement with inelastic neutron scattering data and can account for the observed energy dependent anisotropy. PMID:24936723

  8. Excitation dynamics in Phycoerythrin 545: modeling of steady-state spectra and transient absorption with modified Redfield theory.

    PubMed

    Novoderezhkin, Vladimir I; Doust, Alexander B; Curutchet, Carles; Scholes, Gregory D; van Grondelle, Rienk

    2010-07-21

    We model the spectra and excitation dynamics in the phycobiliprotein antenna complex PE545 isolated from the unicellular photosynthetic cryptophyte algae Rhodomonas CS24. The excitonic couplings between the eight bilins are calculated using the CIS/6-31G method. The site energies are extracted from a simultaneous fit of the absorption, circular dichroism, fluorescence, and excitation anisotropy spectra together with the transient absorption kinetics using the modified Redfield approach. Quantitative fit of the data enables us to assign the eight exciton components of the spectra and build up the energy transfer picture including pathways and timescales of energy relaxation, thus allowing a visualization of excitation dynamics within the complex.

  9. Ultrafast spin-transfer torque driven by femtosecond pulsed-laser excitation

    NASA Astrophysics Data System (ADS)

    Koopmans, Bert

    A hot topic in the field of ultrafast laser-induced manipulation of the magnetic state is that of the role and exploitation of laser-induced spin currents. Intense debate has been triggered by claims that such a spin-transfer, e.g. in the form of super-diffusive spin currents over tens of nanometers, might be a main contributor to the demagnetization process in ferromagnetic thin films after femtosecond laser excitation. In this presentation the underlying concepts will be introduced and recent developments reviewed. Particularly we demonstrate the possibility to apply a laser-induced spin transfer torque on a free magnetic layer, using a non-collinear multilayer configuration consisting of a free in-plane layer on top of a perpendicularly magnetized injection layer, as separated by a nonmagnetic spacer. Interestingly, this approach allows for a quantitative measurement of the amount of spin transfer. Moreover, it might provide access to novel device architectures in which the magnetic state is controlled by fs laser pulses. Careful analysis of the resulting precession of the free layer allows us to quantify the applied torque, and distinguish between driving mechanisms based on laser-induced transfer of hot electrons versus a spin Seebeck effect due to the large thermal gradients. Further engineering of the layered structures in order to gain fundamental understanding and optimize efficiencies will be reported. A simple model that treats local non-equilibrium magnetization dynamics to spin transport effects via a spin-dependent chemical potential will be introduced.

  10. Experimental observation and computational study of the spin-gap excitation in Ba3BiRu2O9

    NASA Astrophysics Data System (ADS)

    Ling, C. D.; Huang, Z.; Kennedy, B. J.; Rols, S.; Johnson, M. R.; Zbiri, M.; Kimber, S. A. J.; Hudspeth, J.; Adroja, D. T.; Rule, K. C.; Avdeev, M.; Blanchard, P. E. R.

    2016-11-01

    Ba3BiRu2O9 is a 6H-type perovskite compound containing face-sharing octahedral M2O9 (M =Ir , Ru) dimers, which are magnetically frustrated at low temperatures. On cooling through T*=176 K, it undergoes a pronounced magnetostructural transition, which is not accompanied by any change in space group symmetry, long-range magnetic ordering, or charge ordering. Here, we report the first direct evidence from inelastic neutron scattering that this transition is due to an opening of a gap in the excitation spectra of dimers of low-spin Ru4 + (S =1 ) ions. X-ray absorption spectroscopy reveals a change in Ru-Ru orbital overlap at T*, linking the emergence of this spin-gap excitation to the magnetostructural transition. Ab initio calculations point to a geometrically frustrated magnetic ground state due to antiferromagnetic interdimer exchange on a triangular Ru2O9 dimer lattice. X-ray total-scattering data rule out long-range magnetic ordering at low temperatures, consistent with this geometrically frustrated model.

  11. Development of a microwave probe for the optical study of microwave-excited spin physics

    NASA Astrophysics Data System (ADS)

    Ou, Yu-Sheng; Chiu, Yi-Hsin; Adur, Rohan; Odenthal, Patrick; Kawakami, Roland; Hammel, P. Chris; Johnston-Halperin, Ezekiel

    2014-03-01

    We have developed an experimental probe that allows simultaneous broadband microwave excitation and optical excitation/detection at variable temperature and magnetic field. Specifically, we have designed a unique sample probe with a microwave stripline based sample mount that allows for direct optical access to the sample under study within a magneto- optical cryostat. This powerful combination enables optical studies of spintronic systems under microwave excitation using both CW (e.g. photo- and electro-luminescence) and time resolved (e.g. time resolved absorption/transmission and time resolved Kerr rotation, TRKR) techniques. To benchmark the capabilities of this probe we present data demonstrating simultaneous ferromagnetic resonance (FMR) and TRKR in a Fe/MgO/GaAs heterostructure. Such studies have potential applications in the study of FMR driven spin pumping and interaction of free carrier spins with native and engineered defects. MRSEC (DMR-0820414).

  12. Excitation and emission spectra of rubidium in rare-gas thin-films

    NASA Astrophysics Data System (ADS)

    Gerhardt, Ilja; Sin, Kyungseob; Momose, Takamasa

    2012-07-01

    To understand the optical properties of atoms in solid state matrices, the absorption, excitation, and emission spectra of rubidium doped thin-films of argon, krypton, and xenon were investigated in detail. A two-dimensional spectral analysis extends earlier reports on the excitation and emission properties of rubidium in rare-gas hosts. We found that the doped crystals of krypton and xenon exhibit a simple absorption-emission relation, whereas rubidium in argon showed more complicated spectral structures. Our sample preparation employed in the present work yielded different results for the Ar crystal, but our peak positions were consistent with the prediction based on the linear extrapolation of Xe and Kr data. We also observed a bleaching behavior in rubidium excitation spectra, which suggests a population transfer from one to another spectral feature due to hole-burning. The observed optical response implies that rubidium in rare-gas thin-films is detectable with extremely high sensitivity, possibly down to a single atom level, in low concentration samples.

  13. Excitation and emission spectra of rubidium in rare-gas thin-films.

    PubMed

    Gerhardt, Ilja; Sin, Kyungseob; Momose, Takamasa

    2012-07-07

    To understand the optical properties of atoms in solid state matrices, the absorption, excitation, and emission spectra of rubidium doped thin-films of argon, krypton, and xenon were investigated in detail. A two-dimensional spectral analysis extends earlier reports on the excitation and emission properties of rubidium in rare-gas hosts. We found that the doped crystals of krypton and xenon exhibit a simple absorption-emission relation, whereas rubidium in argon showed more complicated spectral structures. Our sample preparation employed in the present work yielded different results for the Ar crystal, but our peak positions were consistent with the prediction based on the linear extrapolation of Xe and Kr data. We also observed a bleaching behavior in rubidium excitation spectra, which suggests a population transfer from one to another spectral feature due to hole-burning. The observed optical response implies that rubidium in rare-gas thin-films is detectable with extremely high sensitivity, possibly down to a single atom level, in low concentration samples.

  14. Excitation and emission spectra of rubidium in rare-gas thin-films

    SciTech Connect

    Gerhardt, Ilja; Sin, Kyungseob; Momose, Takamasa

    2012-07-07

    To understand the optical properties of atoms in solid state matrices, the absorption, excitation, and emission spectra of rubidium doped thin-films of argon, krypton, and xenon were investigated in detail. A two-dimensional spectral analysis extends earlier reports on the excitation and emission properties of rubidium in rare-gas hosts. We found that the doped crystals of krypton and xenon exhibit a simple absorption-emission relation, whereas rubidium in argon showed more complicated spectral structures. Our sample preparation employed in the present work yielded different results for the Ar crystal, but our peak positions were consistent with the prediction based on the linear extrapolation of Xe and Kr data. We also observed a bleaching behavior in rubidium excitation spectra, which suggests a population transfer from one to another spectral feature due to hole-burning. The observed optical response implies that rubidium in rare-gas thin-films is detectable with extremely high sensitivity, possibly down to a single atom level, in low concentration samples.

  15. Quasidegenerate scaled opposite spin second order perturbation corrections to single excitation configuration interaction

    NASA Astrophysics Data System (ADS)

    Casanova, David; Rhee, Young Min; Head-Gordon, Martin

    2008-04-01

    Scaled opposite spin (SOS) second order perturbative corrections to single excitation configuration interaction (CIS) are extended to correctly treat quasidegeneracies between excited states. Two viable methods, termed as SOS-CIS(D0) and SOS-CIS(D1), are defined, implemented, and tested. Each involves one empirical parameter (plus a second for the SOS-MP2 ground state), has computational cost that scales with the fourth power of molecule size, and has storage requirements that are cubic, with only quantities of the rank of single excitations produced and stored during iterations. Tests on a set of low-lying adiabatic valence excitation energies and vertical Rydberg excitations of organic and inorganic molecules show that the empirical parameter can be acceptably transferred from the corresponding nondegenerate perturbation theories without any further fitting. Further tests on higher excited states show that the new methods correctly perform for surface crossings for which nondegenerate approaches fail. Numerical results show that SOS-CIS(D0) appears to treat Rydberg excitations in a more balanced way than SOS-CIS(D1) and is, therefore, likely to be the preferred approach. It should be useful for exploring excited state geometries, transition structures, and conical intersections for states of medium to large organic molecules that are dominated by single excitations.

  16. Magnetic phase transitions and monopole excitations in spin ice under uniaxial pressure: A Monte Carlo simulation

    SciTech Connect

    Xie, Y. L. Yan, Z. B.; Liu, J.-M.; Lin, L.

    2015-05-07

    In this work, we explore the spin ice model under uniaxial pressure using the Monte Carlo simulation method. For the known spin ices, the interaction correction (δ) introduced by the uniaxial pressure varies in quite a wide range from positive to negative. When δ is positive, the ground state characterized by the ferromagnetic spin chains is quite unstable, and in real materials it serves as intermediate state connecting the ice state and the long range ordered dipolar spin ice ground state. In the case of negative δ, the system relaxes from highly degenerate ice state to ordered ferromagnetic state via a first order phase transition. Furthermore, the domain walls in such ferromagnetic state are the hotbed of the excitations of magnetic monopoles, thus indicating that the uniaxial pressure can greatly increase the monopole density.

  17. Spin transport in undoped InGaAs/AlGaAs multiple quantum well studied via spin photocurrent excited by circularly polarized light.

    PubMed

    Zhu, Laipan; Liu, Yu; Huang, Wei; Qin, Xudong; Li, Yuan; Wu, Qing; Chen, Yonghai

    2016-12-01

    The spin diffusion and drift at different excitation wavelengths and different temperatures have been studied in undoped InGaAs/AlGaAs multiple quantum well (MQW). The spin polarization was created by optical spin orientation using circularly polarized light, and the reciprocal spin Hall effect was employed to measure the spin polarization current. We measured the ratio of the spin diffusion coefficient to the mobility of spin-polarized carriers. From the wavelength dependence of the ratio, we found that the spin diffusion and drift of holes became as important as electrons in this undoped MQW, and the ratio for light holes was much smaller than that for heavy holes at room temperature. From the temperature dependence of the ratio, the correction factors for the common Einstein relationship for spin-polarized electrons and heavy holes were firstly obtained to be 93 and 286, respectively.

  18. Observation of potassium-intercalated carbon nanotubes and their valence-band excitation spectra

    NASA Astrophysics Data System (ADS)

    Suzuki, S.; Tomita, M.

    1996-04-01

    Second-stage potassium-intercalated carbon nanotubes were synthesized in a specially designed ultrahigh vacuum analytical electron microscope and their valence-band excitation spectra in the region of the π+σ plasmon were measured by electron energy loss spectroscopy. The carbon nanostructures consisted of graphene sheets. Potassium was deposited in an ultrahigh vacuum at room temperature. As a result, a second stage of intercalated nanotubes was found to be formed close to the surface. The energy loss spectra of the intercalated nanotubes showed humps at about 16, 19, and 22 eV, in addition to those of unintercalated tubes. This suggests that intercalation modified the band structure of the interlayer bands and/or the σ(σ*) bands.

  19. Dipole moment of benzonitrile in its excited S 1 state from thermochromic shifts of fluorescence spectra

    NASA Astrophysics Data System (ADS)

    Kawski, A.; Kukliński, B.; Bojarski, P.

    2006-02-01

    The effect of temperature T ranging from 293 to 393 K on absorption and fluorescence spectra of benzonitrile (BN) in ethyl acetate is studied. The absorption spectra of BN remain unchanged with increasing T. The analysis of fluorescence band shift by the Bilot and Kawski theory [L. Bilot, A. Kawski, Z. Naturforsch. 17a (1962) 621], for the known dipole moment value in the ground state μg = 4.18 D and α/ a3 = 0.5 ( α is the polarizability and a is the Onsager interaction radius of the solute), yield the average value of excited state dipole moment μe = 4.42 D. This value is in satisfactory agreement with 4.45, 4.51 and 4.57 D obtained previously from the Stark shift of rotational lines.

  20. Effects of oxygen on EPR spectra of nitroxide spin-label probes of model membranes

    NASA Astrophysics Data System (ADS)

    Popp, Carol A.; Hyde, James S.

    The use of a methylpentene polymer, TPX, for construction of sample containers that allow easy equilibration of electron paramagnetic resonance samples with nitrogen is described. The effects of oxygen-dependent shortening of the electron spin relaxation times of nitroxide spin labels were studied in dispersions of dimyristoylphosphatidylcholine (DMPC) and dipalmitoylphosphatidylchohne (DPPC). First-harmonic, in-phase, absorption spectra of deoxygenated samples of 2-(14-carboxytetradecyl)-2-ethyl-4,4-dimethyl-3-oxazolidinyloxyl (16SASL) in DMPC display decreased linewidths and increased peak-to-peak heigths and resolution of 13C splittings. Continuous-wave (cw) saturation studies of 16SASL/DMPC and both lipid- and aqueous-phase components of 2,2,6,6-tetramethyl-piperidinooxyl (Tempo) partitioned into DPPC show that the rf field at which the signal intensity is maximized decreases when aerated samples are equilibrated with nitrogen. Second-harmonic, out-of-phase, absorption (saturation transfer) spectra of deoxygenated samples of 16SASUDMPC at -22°C and 2-(3-carboxypropyl)-4,4-dimethyl-2-tridecyl-3-oxazolidinyloxyl (5SASL) in DPPC at 35°C display increased signal intensity and lineshape changes. Electron-electron double resonance (ELDOR) spectra display much greater ELDOR reduction in signal intensity when a deoxygenated sample of 16SASL/DMPC is used. Our results indicate that the routine use of deoxygenated samples in biologically relevant studies using spin-label probes should be considered.

  1. Continuous excitations of the triangular-lattice quantum spin liquid YbMgGaO4

    NASA Astrophysics Data System (ADS)

    Paddison, Joseph A. M.; Daum, Marcus; Dun, Zhiling; Ehlers, Georg; Liu, Yaohua; Stone, Matthew B.; Zhou, Haidong; Mourigal, Martin

    2016-12-01

    A quantum spin liquid (QSL) is an exotic state of matter in which electrons’ spins are quantum entangled over long distances, but do not show magnetic order in the zero-temperature limit. The observation of QSL states is a central aim of experimental physics, because they host collective excitations that transcend our knowledge of quantum matter; however, examples in real materials are scarce. Here, we report neutron-scattering experiments on YbMgGaO4, a QSL candidate in which Yb3+ ions with effective spin-1/2 occupy a triangular lattice. Our measurements reveal a continuum of magnetic excitations--the essential experimental hallmark of a QSL--at very low temperature (0.06 K). The origin of this peculiar excitation spectrum is a crucial question, because isotropic nearest-neighbour interactions do not yield a QSL ground state on the triangular lattice. Using measurements in the field-polarized state, we identify antiferromagnetic next-nearest-neighbour interactions, spin-space anisotropies, and chemical disorder between the magnetic layers as key ingredients in YbMgGaO4.

  2. Wall-like spin excitations in A-type antiferromagnetic CaCo2As2

    NASA Astrophysics Data System (ADS)

    Sapkota, A.; Ueland, B. G.; Pandey, Abhishek; Johnston, D. C.; Kreyssig, A.; McQueeney, R. J.; Goldman, A. I.; Anand, V. K.; Niedziela, J. L.; Abernathy, D. L.

    The ACo2As2 (A = Ca, Sr, Ba) compounds are structurally and chemically similar to AFe2As2 and possess some interesting similarities and differences in their magnetism. We recently discovered that SrCo2As2 has stripe antiferromagnetic (AFM) spin correlations similar to stripe-ordered AFe2As2. On the other hand, CaCo2As2 orders in an A-type AFM structure with ferromagnetic correlation of the spins in the square-lattice Co-layer and AFM correlations between layers. Despite the A-type order, our recent inelastic neutron scattering measurements show that spin excitations in CaCo2As2 are not associated with either the A-type or stripe-type order. Instead, we observe broad excitations that extend longitudinally (along (1,1,0) in reciprocal space), but remain sharply defined in the transverse direction. These excitations seem to be best characterized as a ``wall'' of scattering and suggest that CaCo2As2 has quasi-one-dimensional spin dynamics very different than in AFe2As2 and SrCo2As2. Work at Ames Laboratory was supported by US DOE, Basic Energy Sciences, Division of Materials Sciences and Engineering, under Contract No. DE-AC02-07CH11358. Work at ORNL was supported by US DOE, Office of Basic Energy Sciences, Scientific User Facilities Division.

  3. Excited states and absorption spectra of β-diketonate complexes of boron difluoride with aromatic substituents

    NASA Astrophysics Data System (ADS)

    Vovna, V. I.; Kazachek, M. V.; L'vov, I. B.

    2012-04-01

    In the approximation of the time-dependent electron density functional theory, we have studied using the quantum-chemical method the nature of excited states of boron difluoride acetylacetonate F2BAA and its substituted derivatives that contain aromatic groups with one or two benzene cycles in the β-position. Optimization of the geometry of complexes show coplanar positions of cycles for all compounds, except for that with the substituent C6H3(CH3)2. Based on the calculated transition energies and oscillator strengths, we have simulated the absorption spectra in the prevacuum range. The calculated absorption spectra have been compared with the experimental spectra in the gas phase or in solutions. We show that, in the absorption spectra of complexes that contain substituents with one benzene cycle, the first three bands are caused by the transition of π electrons of the substituent to the LUMO of the chelate cycle. In complexes with two cycles in the substituent, the number of these transitions increases to five. As the π system becomes more extended, a bathochromic shift of the first absorption band and an increase in the transition probability are observed.

  4. Spinon excitations in the spin-1 XXZ chain and hidden supersymmetry

    NASA Astrophysics Data System (ADS)

    Matsui, Chihiro

    2016-12-01

    We study spinon excitations of the integrable spin-1 (Fateev-Zamolodchikov; FZ) chain and their relation to the hidden supersymmetry. Using the notion of the supercharges earlier introduced to the spin chains, which change the system length by one, we found that they nontrivially act on one of two kinds of the degrees of freedom for the FZ chain. Their actions were obtained to be the same as those of the supercharges defined on the supersymmetric sine-Gordon model, the low-energy effective field theory of the FZ chain. Moreover, we construct the eigenstates which are invariant under the supersymmetric Hamiltonian given as the anti-commutator of the supercharges.

  5. Non-thermal optical excitation of terahertz-spin precession in a magneto-optical insulator

    SciTech Connect

    Parchenko, Sergii; Maziewski, Andrzej; Stupakiewicz, Andrzej; Satoh, Takuya; Yoshimine, Isao; Stobiecki, Feliks

    2016-01-18

    We demonstrate non-thermal ultrafast laser excitation of spin precession with THz frequency in Gd-Bi-substituted iron garnet via the inverse Faraday effect. The modulation of THz precession by about 60 GHz below the compensation temperature of magnetic moment was observed. The THz frequency precession was caused by the exchange resonance between the Gd and Fe sublattices; we attributed the low-frequency modulation to dielectric resonance mode with a magnetic contribution. We demonstrate the possibility of polarization-sensitive control of spin precession under THz generation by laser pulses, helping to develop high-speed magneto-optical devices.

  6. Excitations from a Bose-Einstein condensate of magnons in coupled spin ladders.

    PubMed

    Garlea, V O; Zheludev, A; Masuda, T; Manaka, H; Regnault, L-P; Ressouche, E; Grenier, B; Chung, J-H; Qiu, Y; Habicht, K; Kiefer, K; Boehm, M

    2007-04-20

    The weakly coupled quasi-one-dimensional spin ladder compound (CH3)2CHNH3CuCl3 is studied by neutron scattering in magnetic fields exceeding the critical field of Bose-Einstein condensation of magnons. Commensurate long-range order and the associated Goldstone mode are detected and found to be similar to those in reference to spin-dimer materials. However, for the upper two massive magnon branches, the observed behavior is totally different, culminating in a drastic collapse of excitation bandwidth beyond the transition point.

  7. Excitations from a Bose-Einstein Condensate of Magnons in Coupled Spin Ladders

    SciTech Connect

    Garlea, Vasile O; Zheludev, Andrey I; Masuda, T.; Manaka, H.; Regnault, L.-P.; Ressouche, E.; Grenier, B.; Chung, J.-H.; Qiu, Y.; Habicht, Klaus; Kiefer, K.; Boehm, Martin

    2007-01-01

    The weakly coupled quasi-one-dimensional spin ladder compound CH32HHNH3CuCl3 is studied by neutron scattering in magnetic fields exceeding the critical field of Bose-Einstein condensation of magnons. Commensurate long-range order and the associated Goldstone mode are detected and found to be similar to those in reference to spin-dimer materials. However, for the upper two massive magnon branches, the observed behavior is totally different, culminating in a drastic collapse of excitation bandwidth beyond the transition point.

  8. Anomalous spin excitation spectrum of the Heisenberg model in a magnetic field.

    PubMed

    Syljuåsen, Olav F; Lee, Patrick A

    2002-05-20

    Making the assumption that high-energy fermions exist in the two dimensional spin- 1/2 Heisenberg antiferromagnet, we present predictions based on the pi-flux ansatz for the dynamic structure factor when the antiferromagnet is subject to a uniform magnetic field. The main result is the presence of gapped excitations in a momentum region near (pi,pi) with energy lower than that at (pi,pi). This is qualitatively different from spin-wave theory predictions and may be tested by experiments or by quantum Monte Carlo.

  9. Spins, Parity, Excitation Energies, and Octupole Structure of an Excited Superdeformed Band in {sup 194}Hg and Implications for Identical Bands

    SciTech Connect

    Hackman, G.; Khoo, T.L.; Carpenter, M.P.; Lauritsen, T.; Calderin, I.J.; Janssens, R.V.; Ackermann, D.; Ahmad, I.; Agarwala, S.; Blumenthal, D.J.; Fischer, S.M.; Nisius, D.; Reiter, P.; Young, J.; Amro, H.; Lopez-Martens, A.; Hannachi, F.; Korichi, A.; Amro, H.; Moore, E.F.; Lee, I.Y.; Macchiavelli, A.O.; Do Nakatsukasa, T.

    1997-11-01

    An excited superdeformed band in {sup 194}Hg , observed to decay directly to both normal-deformed and superdeformed yrast states, is proposed to be a K{sup {pi}}=2{sup {minus}} octupole vibrational band, based on its excitation energies, spins, and likely parity. The transition energies are identical to those of the yrast superdeformed band in {sup 192}Hg , but originate from levels with different spins and parities. The evolution of transition energies with spin suggests that cancellations between pairing and particle alignment are partly responsible for the identical transition energies. {copyright} {ital 1997} {ital The American Physical Society}

  10. Photoluminescence excitation spectra of lanthanide doped YAlO3 in vacuum ultraviolet region

    NASA Astrophysics Data System (ADS)

    Shimizu, Yuhei; Ueda, Kazushige; Inaguma, Yoshiyuki

    2017-04-01

    To understand luminescent mechanisms of lanthanide (Ln) doped phosphors, it is important to know the energy positions of unoccupied Ln2+ 4f and Ln3+ 5d states, as well as occupied Ln3+ 4f states, relative to the energy bands of host materials. Photoluminescence excitation (PLE) spectra of Ln doped YAlO3 were measured in a vacuum ultraviolet (VUV) region and the energy positions of Ln2+ 4f and Ln3+ 5d states in the wide-gap YAlO3 were elucidated. Peaks assignable to host lattice excitation were observed in all samples at approximately 8 eV in the PLE spectra. PLE peaks derived from charge transfer (CT) and 4f-5d transitions were observed at lower energy than the bandgap energy. Ln2+ 4f energy levels were obtained from the PLE peak energies for the CT transitions along with the valence band maximum. In contrast, Ln3+ 5d energy levels were evaluated from those for the 4f-5d transitions along with the Ln3+ 4f energy levels, which were obtained previously from X-ray photoelectron spectroscopy measurements. The elucidated Ln2+ 4f and Ln3+ 5d energy levels were exhibited in an energy diagram together with Ln3+ 4f energy levels and host energy bands. The experimental Ln2+ 4f and Ln3+ 5d energy levels were in good agreement with the reported theoretical data.

  11. Analysis of anisotropic spin-label motion in saturation-transfer ESR spectra of spin-labeled cowpea chlorotic mottle virus

    NASA Astrophysics Data System (ADS)

    Hemminga, M. A.; Faber, A. J.

    A saturation-transfer ESR study is carried out on maleimide spin-labeled cowpea chlorotic mottle virus dissolved in various glycerol-water systems. The saturation-transfer ESR spectra were analyzed by comparing them with reference spectra of isotropically reorienting spin labels. The results are interpreted in terms of the overall motion of the virus particle, described by an isotropic rotational correlation time τR, and a local anisotropic spin-label motion with rotational correlation times τ| and τ⊥.

  12. Stable oscillation in spin torque oscillator excited by a small in-plane magnetic field

    SciTech Connect

    Taniguchi, Tomohiro; Tsunegi, Sumito; Kubota, Hitoshi; Ito, Takahiro; Utsumi, Yasuhiro

    2015-08-07

    Theoretical conditions to excite self-oscillation in a spin torque oscillator consisting of a perpendicularly magnetized free layer and an in-plane magnetized pinned layer are investigated by analytically solving the Landau-Lifshitz-Gilbert equation. The analytical relation between the current and oscillation frequency is derived. It is found that a large amplitude oscillation can be excited by applying a small field pointing to the direction anti-parallel to the magnetization of the pinned layer. The validity of the analytical results is confirmed by comparing with numerical simulation, showing good agreement especially in a low current region.

  13. Strongly gapped spin-wave excitation in the insulating phase of NaOsO3

    NASA Astrophysics Data System (ADS)

    Calder, S.; Vale, J. G.; Bogdanov, N.; Donnerer, C.; Pincini, D.; Moretti Sala, M.; Liu, X.; Upton, M. H.; Casa, D.; Shi, Y. G.; Tsujimoto, Y.; Yamaura, K.; Hill, J. P.; van den Brink, J.; McMorrow, D. F.; Christianson, A. D.

    2017-01-01

    NaOsO3 hosts a rare manifestation of a metal-insulator transition driven by magnetic correlations, placing the magnetic exchange interactions in a central role. We use resonant inelastic x-ray scattering to directly probe these magnetic exchange interactions. A dispersive and strongly gapped (58 meV) excitation is observed, indicating appreciable spin-orbit coupling in this 5 d3 system. The excitation is well described within a minimal model Hamiltonian with strong anisotropy and Heisenberg exchange (J1=J2=13.9 meV ). The observed behavior places NaOsO3 on the boundary between localized and itinerant magnetism.

  14. Coherent storage of microwave excitations in rare-earth nuclear spins.

    PubMed

    Wolfowicz, Gary; Maier-Flaig, Hannes; Marino, Robert; Ferrier, Alban; Vezin, Hervé; Morton, John J L; Goldner, Philippe

    2015-05-01

    Interfacing between various elements of a computer--from memory to processors to long range communication--will be as critical for quantum computers as it is for classical computers today. Paramagnetic rare-earth doped crystals, such as Nd(3+):Y2SiO5(YSO), are excellent candidates for such a quantum interface: they are known to exhibit long optical coherence lifetimes (for communication via optical photons), possess a nuclear spin (memory), and have in addition an electron spin that can offer hybrid coupling with superconducting qubits (processing). Here we study two of these three elements, demonstrating coherent storage and retrieval between electron and (145)Nd nuclear spin states in Nd(3+):YSO. We find nuclear spin coherence times can reach 9 ms at ∼5  K, about 2 orders of magnitude longer than the electron spin coherence, while quantum state and process tomography of the storage or retrieval operation between the electron and nuclear spin reveal an average state fidelity of 0.86. The times and fidelities are expected to further improve at lower temperatures and with more homogeneous radio-frequency excitation.

  15. Thermal phase transition in artificial spin ice systems induces the formation and migration of monopole-like magnetic excitations

    NASA Astrophysics Data System (ADS)

    León, Alejandro

    2016-11-01

    Artificial spin ice systems exhibit monopole-like magnetic excitations. We develop here a theoretical study of the thermal phase transition of an artificial spin ice system, and we elucidate the role of the monopole excitations in the transition temperature. The dynamics of the spin ice is described by an efficient model based on cellular automata, which considers both thermal effects and dipolar interactions. We have established the critical temperature of the phase transition as function of the magnetic moment and the energy barrier of reversion. In addition, we predict that thermal gradients in the system induce the motion of elementary excitations, which could permit to manipulate monopole-like states.

  16. Theoretical probing of inelastic spin-excitations in adatoms on surfaces

    NASA Astrophysics Data System (ADS)

    Lounis, Samir; Schweflinghaus, Benedikt; Dias, Manuel dos Santos; Bouhassoune, Mohammed; Muniz, Roberto B.; Costa, Antonio T.

    2014-12-01

    We review our recent work on the simulation, description and prediction of spin-excitations in adatoms and dimers deposited on metallic surfaces. This work done together with Douglas L. Mills, is an extension of his seminal contribution (with Pascal Lederer) published 50 years ago on the spin-dynamics of transition metal impurities embedded in transition metal hosts [Lederer et al. (1967)]. The main predictions of his model were verified experimentally with state of the art inelastic scanning tunneling spectroscopy on adatoms. Our formalism, presented in this review, is based on time-dependent density functional theory, combined with the Korringa-Kohn-Rostoker Green function method. Comparison to experiments is shown and discussed in detail. Our scheme enables the description and prediction of the main characteristics of these excitations, i.e. their resonance frequency, their lifetime and their behavior upon application of external perturbations such as a magnetic field.

  17. Spin excitations in the two-dimensional strongly coupled dimer system malachite

    NASA Astrophysics Data System (ADS)

    Canévet, E.; Fâk, B.; Kremer, R. K.; Chun, J. H.; Enderle, M.; Gordon, E. E.; Bettis, J. L.; Whangbo, M.-H.; Taylor, J. W.; Adroja, D. T.

    2015-02-01

    The mineral malachite, Cu 2(OD )2CO 3, has a quantum spin-liquid ground state and no long-range magnetic order down to at least T =0.4 K. Inelastic neutron scattering measurements show that the excitation spectrum consists of dispersive gapped singlet-triplet excitations, characteristic of spin-1/2 dimer-forming Heisenberg antiferromagnets. We identify a distinct two-dimensional dimerized coupling scheme with strong interdimer coupling J'/J1≈0.3 that places malachite between strongly coupled alternating chains, square lattice antiferromagnets, and infinite-legged ladders. The geometry of the interaction scheme resembles the staggered dimer lattice, which may allow unconventional quantum criticality.

  18. High-resolution Valence and Core Excitation Spectra via First-Principles Calculations and Experiment

    NASA Astrophysics Data System (ADS)

    Shirley, Eric; Fossard, F.; Gilmore, K.; Hug, G.; Kas, J. J.; Rehr, J. J.; Vila, F.

    We calculate the optical and C K-edge near edge spectra of crystalline and molecular C60 measured with high-resolution electron energy-loss spectroscopy. The calculations are carried out using at least three different methods: Bethe-Salpeter calculations using the NIST Bethe-Salpeter Equation solver (NBSE) in the valence and OCEAN (Obtaining Core Excitation with Ab initio methods and NBSE) suite [Gilmore et al., Comp. Phys. Comm., (2015)]; excited-core-hole calculations using XCH [D. Prendergast and G. Galli, Phys. Rev. Lett. 96, 215502 (2006)]; and constrained occupancy using StoBe (Stockholm-Berlin core-excitation code) [StoBe-deMon version 3.0, K. Hermann et al. (2009)]. They include self-energy effects, lifetime-damping, and Debye-Waller effects. A comparison of spectral features to those observed illustrates the sensitivity of certain features to computation details (e.g., self-energy corrections and core-hole screening). This may point to limitations of various approximations, e.g. in conventional BSE paradigm and/or the incomplete treatment of vibrational effects. Supported in part by DOE BES Grant DE-FG03-97ER45623 (JJR, JJK, FV).

  19. Sensitivity of Raman spectra excited at 325 nm to surface treatments of undoped polycrystalline diamond films

    NASA Astrophysics Data System (ADS)

    Ghodbane, S.; Deneuville, A.; Tromson, D.; Bergonzo, P.; Bustarret, E.; Ballutaud, D.

    2006-08-01

    About 20 m thick films were deposited in the same run by MPCVD at 900 °C on Si substrates and then hydrogenated in situ during 30 min with a hydrogen plasma at the same temperature. Their surfaces were kept as prepared or more or less strongly oxidized by annealing at 600 °C under ambient atmosphere or by sulphochromic acid or aqua regia treatments. Raman spectra were excited at 325 and 632.8 nm. Spectra of the as-prepared sample exhibit structures around 2835 and 2895 cm-1 from monohydride carbon-hydrogen ascribed to the atomically flat (111) and (100) areas, respectively, on the facets of the sample surface crystallites. The decrease of these structures in the normalized spectra after the various oxidation treatments confirms these assignments. The decrease is smaller for the aqua regia treatment than for the two other treatments which give similar effects. Other Raman signals from sp2 C around 1589 cm-1 and CHx bonds around 2930, 2952, 3025 and 3050 cm-1 originate from species at the surface and within the films. Their variation with the oxidizing treatments indicates a significant contribution from the surface species.

  20. Edge physics of the quantum spin Hall insulator from a quantum dot excited by optical absorption.

    PubMed

    Vasseur, Romain; Moore, Joel E

    2014-04-11

    The gapless edge modes of the quantum spin Hall insulator form a helical liquid in which the direction of motion along the edge is determined by the spin orientation of the electrons. In order to probe the Luttinger liquid physics of these edge states and their interaction with a magnetic (Kondo) impurity, we consider a setup where the helical liquid is tunnel coupled to a semiconductor quantum dot that is excited by optical absorption, thereby inducing an effective quantum quench of the tunneling. At low energy, the absorption spectrum is dominated by a power-law singularity. The corresponding exponent is directly related to the interaction strength (Luttinger parameter) and can be computed exactly using boundary conformal field theory thanks to the unique nature of the quantum spin Hall edge.

  1. Magnetic structure and spin excitations in BaMn2Bi2

    DOE PAGES

    Calder, Stuart A.; Saparov, Bayrammurad I; Cao, H. B.; ...

    2014-02-19

    We present a single crystal neutron scattering study of BaMn2Bi2, a recently synthesized material with the same ThCr2Si2type structure found in several Fe-based unconventional superconducting materials. We show long range magnetic order, in the form of a G-type antiferromagnetic structure, to exist up to 390 K with an indication of a structural transition at 100 K. Utilizing inelastic neutron scattering we observe a spin-gap of 16 meV, with spin-waves extending up to 55 meV. We find these magnetic excitations are well fit to a J1-J2-Jc Heisenberg model and present values for the exchange interactions. The spin wave spectrum appears tomore » be unchanged by the 100 K structural phase transition.« less

  2. Fully Suspended, Five-Axis, Three-Magnetic-Bearing Dynamic Spin Rig With Forced Excitation

    NASA Technical Reports Server (NTRS)

    Morrison, Carlos R.; Provenza, Andrew; Kurkov, Anatole; Montague, Gerald; Duffy, Kirsten; Mehmed, Oral; Johnson, Dexter; Jansen, Ralph

    2004-01-01

    The Five-Axis, Three-Magnetic-Bearing Dynamic Spin Rig, a significant advancement in the Dynamic Spin Rig (DSR), is used to perform vibration tests of turbomachinery blades and components under rotating and nonrotating conditions in a vacuum. The rig has as its critical components three magnetic bearings: two heteropolar radial active magnetic bearings and a magnetic thrust bearing. The bearing configuration allows full vertical rotor magnetic suspension along with a feed-forward control feature, which will enable the excitation of various natural blade modes in bladed disk test articles. The theoretical, mechanical, electrical, and electronic aspects of the rig are discussed. Also presented are the forced-excitation results of a fully levitated, rotating and nonrotating, unbladed rotor and a fully levitated, rotating and nonrotating, bladed rotor in which a pair of blades was arranged 180 degrees apart from each other. These tests include the bounce mode excitation of the rotor in which the rotor was excited at the blade natural frequency of 144 Hz. The rotor natural mode frequency of 355 Hz was discerned from the plot of acceleration versus frequency. For nonrotating blades, a blade-tip excitation amplitude of approximately 100 g/A was achieved at the first-bending critical (approximately 144 Hz) and at the first-torsional and second-bending blade modes. A blade-tip displacement of 70 mils was achieved at the first-bending critical by exciting the blades at a forced-excitation phase angle of 908 relative to the vertical plane containing the blades while simultaneously rotating the shaft at 3000 rpm.

  3. Influence of spin-transfer torque on thermally activated ferromagnetic resonance excitations in magnetic tunnel junctions

    NASA Astrophysics Data System (ADS)

    Petit, S.; de Mestier, N.; Baraduc, C.; Thirion, C.; Liu, Y.; Li, M.; Wang, P.; Dieny, B.

    2008-11-01

    Voltage noise measurements on magnetic tunnel junctions show that thermal fluctuations of the magnetization are either amplified or quenched by subcritical spin-transfer torque depending on the current direction. We present an analytical model that describes the dependence of thermally activated ferromagnetic resonance on bias current. The evolution of the peak amplitude and linewidth with the applied current is directly related to the longitudinal torque, whereas the shift of the resonance frequency is sensitive to the transverse torque. Both spin torque terms are independently extracted from the measured noise spectra. Our results support the general idea that it is more pertinent to describe spin torque in terms of voltage rather than current in magnetic tunnel junctions.

  4. Spin Correlations and Excitations in the Quasi-2D Triangular Bilayer Spin Glass LuCoGaO4

    NASA Astrophysics Data System (ADS)

    Fritsch, K.; Granroth, G. E.; Savici, A. T.; Noad, H. M. L.; Dabkowska, H. A.; Gaulin, B. D.

    2012-02-01

    LuCoGaO4 is a layered magnetic-bilayer material wherein Co2+ magnetic moments and nonmagnetic Ga3+ ions are randomly distributed on planar triangular bilayers. This makes it an ideal case to study the interplay between geometric frustration, site disorder and low dimensionality and its influence on the magnetic ground of the system. This novel material has been grown for the first time in single crystal form at McMaster University. We have performed magnetization measurements, revealing a previously identified spin glass transition near Tf˜19K, and a Curie Weiss temperature of Tcw˜-96K, consistent with antiferromagnetic interactions[1]. We discuss time-of-flight neutron scattering measurements using SEQUOIA at SNS which elucidate the evolution of the static and dynamic spin correlations in LuCoGaO4 over a range of temperatures from T<< Tf to T>Tcw. We observe quasielastic scattering at (1/3,1/3,L) positions in reciprocal space and rods of scattering along the c*-direction, consistent with short range antiferromagnetic correlations within decoupled bilayers, and which comfirm the 2-dimensional character of this system. Inelastic scattering measurements show a gapped ˜ 12 meV spin excitation which softens and broadens in energy, filling in the gap on a temperature scale of ˜ Tcw/2. [1] Cava et al., J. Solid State Chem. 140, 337 (1998).

  5. A Magnetic Suspension and Excitation System for Spin Vibration Testing of Turbomachinery Blades

    NASA Technical Reports Server (NTRS)

    Johnson, Dexter; Brown, Gerald V.; Mehmed, Oral

    1998-01-01

    The Dynamic Spin Rig (DSR) is used to perform vibration tests of turbomachinery blades and components under spinning conditions in a vacuum. A heteropolar radial active magnetic bearing was integrated into the DSR to provide non-contact magnetic suspension and mechanical excitation of the rotor to induce turbomachinery blade vibrations. The magnetic bearing replaces one of the two existing conventional radial ball bearings. Prior operation of the DSR used two voice-coil type linear electromagnetic shakers which provided axial excitation of the rotor. The new magnetic suspension and excitation system has provided enhanced testing capabilities. Tests were performed at high rotational speeds for longer duration and higher vibration amplitudes. Some characteristics of the system include magnetic bearing stiffness values up to 60,000 lb./in., closed loop control bandwidth around 500 Hz, and multi-directional radial excitation of the rotor. This paper reports on the implementation and operation of this system and presents some test results using this system.

  6. Excitations for lattice ferromagnetic classical spin systems at high temperature: noneven single-spin distributions

    PubMed

    Schor; O'Carroll

    2000-06-01

    We consider general d-dimensional lattice ferromagnetic spin systems with nearest neighbor interactions in the high temperature region (beta<1). Each model is characterized by a single-site a priori spin probability distribution taken to be noneven. We state our results in terms of the parameter alpha=(<&smacr; (4)>-3<&smacr; (2)>(2)-<&smacr; (3)>(2)<&smacr; (2)>(-1))/(<&smacr; (4)>-<&smacr; (2)>(2)-<&smacr; (3)>(2)<&smacr; (2)>(-1)), where &smacr;=s-, and denotes the kth moment of the single-site distribution. Associated with the model is a lattice quantum field theory which is known to contain a particle of mass m approximately ln beta. Assuming <&smacr;(3)> not equal0 we show that for alpha>0, beta small, there exists a bound state with mass below the two-particle threshold 2m. For alpha<0 bound states do not exist. These results are obtained using a Bethe-Salpeter (BS) equation in the ladder approximation in conjunction with a representation for the inverse of the two-point function designed to analyze the spectrum below but close to 2m.

  7. Transient Loschmidt Echo and Orthogonality Catastrophe in highly excited Quantum Ising Spin Chains

    NASA Astrophysics Data System (ADS)

    Schiro, Marco; Lupo, Carla

    We study the response to sudden local perturbations of highly excited Quantum Ising Spin Chains. The key quantity encoding this response is the overlap between time-dependent wave functions, which we write as a transient Loschmidt echo. We compute the Echo perturbatively in the case of a weak local quench and study its asymptotics at long times, which contains crucial information about the structure of the highly excited non-equilibrium environment induced by the quench. Our results reveal that the Echo decays exponentially, rather than power law as in the low-energy Orthogonality Catastrophe, a further example of quench-induced decoherence. The emerging decoherence scale is set by the strenght of the local potential and the bulk excitation energy. In addition, the transient evolution features aging behavior at the Ising quantum critical point.

  8. Neutron scattering studies of spin excitations in superconducting Rb0.82Fe1.68Se2

    SciTech Connect

    Wang, Miaoyin; Li, Chunhong; Abernathy, Douglas L; Song, Yu; Carr, Scott V.; Lu, Xiangye; Li, Shiliang; Yamari, Zahra; Hu, Jiangping; Xiang, Tao; Dai, Pengcheng

    2012-01-01

    We use inelastic neutron scattering to show that superconducting (SC) rubidium iron selenide Rb0.82Fe1.68Se2 exhibits antiferromagnetic (AF) spin excitations near the in-plane wave vector Q = ( ,0) identical to that for iron arsenide superconductors. Moreover, we find that these excitations change from incommensurate to commensurate with increasing energy and occur at the expense of spin waves associated with the coexisting 5 5 block AF phase. Since these spin excitations cannot come from Fermi surface nesting based on angle resolved photoemission experiments, our results indicate the presence of local moments in SC Rb0.82Fe1.68Se2 that may have a similar origin as the hourglass-like spin excitations in copper oxide superconductors.

  9. Spin contamination-free N-electron wave functions in the excitation-based configuration interaction treatment.

    PubMed

    Alcoba, Diego R; Torre, Alicia; Lain, Luis; Massaccesi, Gustavo E; Oña, Ofelia B; Capuzzi, Pablo

    2016-07-07

    This work deals with the spin contamination in N-electron wave functions provided by the excitation-based configuration interaction methods. We propose a procedure to ensure a suitable selection of excited N-electron Slater determinants with respect to a given reference determinant, required in these schemes. The procedure guarantees the construction of N-electron wave functions which are eigenfunctions of the spin-squared operator Sˆ(2), avoiding any spin contamination. Our treatment is based on the evaluation of the excitation level of the determinants by means of the expectation value of an excitation operator formulated in terms of spin-free replacement operators. We report numerical determinations of energies and 〈Sˆ(2)〉 expectation values, arising from our proposal as well as from traditional configuration interaction methods, in selected open-shell systems, in order to compare the behavior of these procedures and their computational costs.

  10. A Bloch equation approach to intensity dependent optical spectra of light harvesting complex II: excitation dependence of light harvesting complex II pump-probe spectra.

    PubMed

    Richter, Marten; Renger, Thomas; Knorr, Andreas

    2008-01-01

    On the basis of the recent progress in the resolution of the structure of the antenna light harvesting complex II (LHC II) of the photosystem II, we propose a microscopically motivated theory to predict excitation intensity-dependent spectra. We show that optical Bloch equations provide the means to include all 2( N ) excited states of an oligomer complex of N coupled two-level systems and analyze the effects of Pauli Blocking and exciton-exciton annihilation on pump-probe spectra. We use LHC Bloch equations for 14 Coulomb coupled two-level systems, which describe the S (0) and S (1) level of every chlorophyll molecule. All parameter introduced into the Hamiltonian are based on microscopic structure and a quantum chemical model. The derived Bloch equations describe not only linear absorption but also the intensity dependence of optical spectra in a regime where the interplay of Pauli Blocking effects as well as exciton-exciton annihilation effects are important. As an example, pump-probe spectra are discussed. The observed saturation of the spectra for high intensities can be viewed as a relaxation channel blockade on short time scales due to Pauli blocking. The theoretical investigation is useful for the interpretation of the experimental data, if the experimental conditions exceed the low intensity pump limit and effects like strong Pauli Blocking and exciton-exciton annihilation need to be considered. These effects become important when multiple excitations are generated by the pump pulse in the complex.

  11. Ground state spin and excitation energies in half-filled Lieb lattices

    NASA Astrophysics Data System (ADS)

    Ţolea, M.; Niţǎ, M.

    2016-10-01

    We present detailed spectral calculations for small Lieb lattices having up to N =4 number of cells, in the regime of half-filling, an instance of particular relevance for the nanomagnetism of discrete systems such as quantum dot arrays, due to the degenerate levels at midspectrum. While for the Hubbard interaction model—and even number of sites—the ground state spin is given by the Lieb theorem, the inclusion of long-range interaction—or odd number of sites—makes the spin state not known a priori, which justifies our approach. We calculate also the excitation energies, which are of experimental importance, and find significant variation induced by the interaction potential. One obtains insights on the mechanisms involved that impose as ground state the Lieb state with lower spin rather than the Hund one with maximum spin for the degenerate levels, showing this in the first and second orders of the interaction potential for the smaller lattices. The analytical results agree with the numerical ones, which are performed by exact diagonalization calculations or by a combined mean-field and configuration interaction method. While the Lieb state is always lower in energy than the Hund state, for strong long-range interaction, when possible, another minimal spin state is imposed as ground state.

  12. Dynamic magnetization switching and spin wave excitations by voltage-induced torque

    NASA Astrophysics Data System (ADS)

    Shiota, Yoichi

    2013-03-01

    The effect of electric fields on ultrathin ferromagnetic metal layer is one of the promising approaches for manipulating the spin direction with low-energy consumption, localization, and coherent behavior. Several experimental approaches to realize it have been investigated using ferromagnetic semiconductors, magnetostriction together with piezo-electric materials, multiferroic materials, and ultrathin ferromagnetic layer. In this talk, we will present a dynamic control of spins by voltage-induced torque. We used the magnetic tunnel junctions with ultrathin ferromagnetic layer, which shows voltage-induced perpendicular magnetic anisotropy change. By applying the voltage to the junction, the magnetic easy-axis in the ultrathin ferromagnetic layer changes from in-plane to out-of-plane, which causes a precession of the spins. This precession resulted in a two-way toggle switching by determining an appropriate pulse length. On the other hand, an application of rf-voltage causes an excitation of a uniform spin-wave. Since the precession of spin associates with an oscillation in the resistance of the junction, the applied rf-signal is rectified and produces a dc-voltage. From the spectrum of the dc-voltage as a function of frequency, we could estimate the voltage-induced torque. This research was supported by CREST-JST, G-COE program, and JSPS for the fellowship. Collaborators include T. Nozaki, S. Miwa, F. Bonell, N. Mizuochi, T. Shinjo, and Y. Suzuki.

  13. Early excitation of spin-orbit misalignments in close-in planetary systems

    SciTech Connect

    Spalding, Christopher; Batygin, Konstantin

    2014-07-20

    Continued observational characterization of transiting planets that reside in close proximity to their host stars has shown that a substantial fraction of such objects possess orbits that are inclined with respect to the spin axes of their stars. Mounting evidence for the wide-spread nature of this phenomenon has challenged the conventional notion that large-scale orbital transport occurs during the early epochs of planet formation and is accomplished via planet-disk interactions. However, recent work has shown that the excitation of spin-orbit misalignment between protoplanetary nebulae and their host stars can naturally arise from gravitational perturbations in multi-stellar systems as well as magnetic disk-star coupling. In this work, we examine these processes in tandem. We begin with a thorough exploration of the gravitationally facilitated acquisition of spin-orbit misalignment and analytically show that the entire possible range of misalignments can be trivially reproduced. Moreover, we demonstrate that the observable spin-orbit misalignment only depends on the primordial disk-binary orbit inclination. Subsequently, we augment our treatment by accounting for magnetic torques and show that more exotic dynamical evolution is possible, provided favorable conditions for magnetic tilting. Cumulatively, our results suggest that observed spin-orbit misalignments are fully consistent with disk-driven migration as a dominant mechanism for the origin of close-in planets.

  14. Emergence of nontrivial magnetic excitations in a spin-liquid state of kagomé volborthite

    NASA Astrophysics Data System (ADS)

    Watanabe, Daiki; Sugii, Kaori; Shimozawa, Masaaki; Suzuki, Yoshitaka; Yajima, Takeshi; Ishikawa, Hajime; Hiroi, Zenji; Shibauchi, Takasada; Matsuda, Yuji; Yamashita, Minoru

    2016-08-01

    When quantum fluctuations destroy underlying long-range ordered states, novel quantum states emerge. Spin-liquid (SL) states of frustrated quantum antiferromagnets, in which highly correlated spins fluctuate down to very low temperatures, are prominent examples of such quantum states. SL states often exhibit exotic physical properties, but the precise nature of the elementary excitations behind such phenomena remains entirely elusive. Here, we use thermal Hall measurements that can capture the unexplored property of the elementary excitations in SL states, and report the observation of anomalous excitations that may unveil the unique features of the SL state. Our principal finding is a negative thermal Hall conductivity κxyκxy which the charge-neutral spin excitations in a gapless SL state of the 2D kagomé insulator volborthite Cu3V2O7(OH)2ṡ2H2O exhibit, in much the same way in which charged electrons show the conventional electric Hall effect. We find that κxyκxy is absent in the high-temperature paramagnetic state and develops upon entering the SL state in accordance with the growth of the short-range spin correlations, demonstrating that κxyκxy is a key signature of the elementary excitation formed in the SL state. These results suggest the emergence of nontrivial elementary excitations in the gapless SL state which feel the presence of fictitious magnetic flux, whose effective Lorentz force is found to be less than 1/100 of the force

  15. Dipole moment of aniline in the excited S 1 state from thermochromic effect on electronic spectra

    NASA Astrophysics Data System (ADS)

    Kawski, A.; Kukliński, B.; Bojarski, P.

    2005-11-01

    Using the thermochromic shift method of absorption and fluorescence spectra of aniline in ethyl acetate for temperature ranging from 213 to 393 K, the change of the dipole moment Δ μ = μe - μg = 0.84 D between the ground and first excited singlet state was determined based on the Bilot and Kawski theory. This is in agreement with the result obtained by Lombardi from optical Stark effect in the rotational fine structure. For the known dipole moment in the ground state μg = 1.53 D and for α/ a3 = 0.483 ( α is the polarizability and a is the Onsager interaction radius of the solute) the average value of μe = 2.37 D and a = 2.7 Å were determined. The values obtained for aniline are compared with the experimental values determined by other authors.

  16. Quantitative Förster resonance energy transfer efficiency measurements using simultaneous spectral unmixing of excitation and emission spectra.

    PubMed

    Mustafa, Sanam; Hannagan, John; Rigby, Paul; Pfleger, Kevin; Corry, Ben

    2013-02-01

    Accurate quantification of Förster resonance energy transfer (FRET) using intensity-based methods is difficult due to the overlap of fluorophore excitation and emission spectra. Consequently, mechanisms are required to remove bleedthrough of the donor emission into the acceptor channel and direct excitation of the acceptor when aiming to excite only the donor fluorophores. Methods to circumvent donor bleedthrough using the unmixing of emission spectra have been reported, but these require additional corrections to account for direct excitation of the acceptor. Here we present an alternative method for robust quantification of FRET efficiencies based upon the simultaneous spectral unmixing of both excitation and emission spectra. This has the benefit over existing methodologies in circumventing the issue of donor bleedthrough and acceptor cross excitation without the need for additional corrections. Furthermore, we show that it is applicable with as few as two excitation wavelengths and so can be used for quantifying FRET efficiency in microscope images as easily as for data collected on a spectrofluorometer. We demonstrate the accuracy of the approach by reproducing efficiency values in well characterized FRET standards: HEK cells expressing a variety of linked cerulean and venus fluorescent proteins. Finally we describe simple ImageJ plugins that can be used to calculate and create images of FRET efficiencies from microscope images.

  17. Analytic model for low energy excitation states and phase transitions in spin-ice systems

    NASA Astrophysics Data System (ADS)

    López-Bara, F. I.; López-Aguilar, F.

    2017-04-01

    Low energy excitation states in magnetic structures of the so-called spin-ices are produced via spin flips among contiguous tetrahedra of their crystal structure. These spin flips generate entities which mimic magnetic dipoles in every two tetrahedra according to the dumbbell model. When the temperature increases, the spin-flip processes are transmitted in the lattice, generating so-called Dirac strings, which constitute structural entities that can present mimetic behavior similar to that of magnetic monopoles. In recent studies of both specific heat and ac magnetic susceptibility, two (even possibly three) phases have been shown to vary the temperature. The first of these phases presents a sharp peak in the specific heat and another phase transition occurs for increasing temperature whose peak is broader than that of the former phase. The sharp peak occurs when there are no free individual magnetic charges and temperature of the second phase transition coincides with the maximum proliferation of free deconfined magnetic charges. In the present paper, we propose a model for analyzing the low energy excitation many-body states of these spin-ice systems. We give analytical formulas for the internal energy, specific heat, entropy and their temperature evolution. We study the description of the possible global states via the nature and structure of their one-body components by means of the thermodynamic functions. Below 0.37 K, the Coulomb-like magnetic charge interaction can generate a phase transition to a condensation of pole–antipole pairs, possibly having Bose–Einstein structure which is responsible for the sharp peak of the first phase transition. When there are sufficient free positive and negative charges, the system tends to behave as a magnetic plasma, which implies the broader peak in the specific heat appearing at higher temperature than the sharper experimental peak.

  18. Spin-flip resolution achieved with a one-proton self-excited oscillator

    NASA Astrophysics Data System (ADS)

    Guise, Nicholas Damien Sun-Wo

    In a Penning trap with an extremely large magnetic gradient, the axial frequency of a one-proton self-excited oscillator is resolved at the level of the shift from a proton spin flip. This sensitivity opens a possible path towards detection of single-proton spin flips, novel measurements of the proton and antiproton g-factors, and a stringent test of CPT invariance by comparing proton and antiproton magnetic moments at precision likely to be a million times higher than achieved to date. The central challenge of extending similar electron magnetic moment measurements to one proton is overcoming the substantially larger mass and weaker magnetic moment, which conspire to greatly reduce the frequency shift that signals a spin flip. Within a magnetic bottle gradient 50 times larger than used in the recent electron g-factor measurements, the proton spin-flip shift is still only 60 mHz out of a 553 kHz axial frequency. In such a large gradient, standard application of sideband cooling to reduce the magnetron radius changes the axial frequency by an amount greater than this spin-flip shift on average. Proton axial frequency resolution at the 60 mHz level is enabled by feedback techniques realized previously only with one electron. Self-excitation produces a narrow feature with large signal-to-noise, ideal for rapid frequency measurements at high precision. Unwanted effects of the strong magnetic gradient are minimized by axial and radial cooling. Feedback cooling is used to reduce the proton axial motion below the temperature of a damping resistor. Axial-magnetron sideband cooling of the undamped radial motion is then demonstrated to reach a 14 mK theoretical limit.

  19. Theoretical analysis of the optical excitation spectra of silver and gold nanowires.

    PubMed

    Guidez, Emilie B; Aikens, Christine M

    2012-07-21

    The excitation spectra of linear atomic chains of silver and gold with various sizes have been calculated using time-dependent density functional theory. Silver chains show longitudinal and transverse peaks as well as a low-intensity d-band. The longitudinal peak, corresponding to the HOMO-LUMO transition (along the main axis of the chain), shifts linearly to the red as the length of the system increases, consistent with the particle-in-a-box model. The transverse peak remains at approximately constant energy for all systems studied and corresponds to ∑(m)→Π(m) transitions in the xy plane perpendicular to the chain. As the chain grows, transitions arising from d orbitals contribute to the transverse peak, which affects its oscillator strength. Contrary to silver, gold chains display a strong d-band that converges to a distinct pattern at a chain length of about twelve atoms. The transitions involved in the d-band originate from localized d-orbitals with a d(z(2)) character since they have the right symmetry to give transitions into the LUMO, LUMO + 1, …, which have ∑ symmetry. Transitions arising from these localized d-orbitals also affect the position of the longitudinal peak and generate a wide transverse band. Although the majority of the transitions involved in the transverse band have a d∑→Π or dΠ→∑ character, they are hidden by much stronger excitations of dΠ→Π character in gold nanowires.

  20. Fluorescence Excitation-Emission Matrix Regional Integration to Quantify Spectra for Dissolved Organic Matter

    USGS Publications Warehouse

    Chen, W.; Westerhoff, P.; Leenheer, J.A.; Booksh, K.

    2003-01-01

    Excitation-emission matrix (EEM) fluorescence spectroscopy has been widely used to characterize dissolved organic matter (DOM) in water and soil. However, interpreting the >10,000 wavelength-dependent fluorescence intensity data points represented in EEMs has posed a significant challenge. Fluorescence regional integration, a quantitative technique that integrates the volume beneath an EEM, was developed to analyze EEMs. EEMs were delineated into five excitation-emission regions based on fluorescence of model compounds, DOM fractions, and marine waters or freshwaters. Volumetric integration under the EEM within each region, normalized to the projected excitation-emission area within that region and dissolved organic carbon concentration, resulted in a normalized region-specific EEM volume (??i,n). Solid-state carbon nuclear magnetic resonance (13C NMR), Fourier transform infrared (FTIR) analysis, ultraviolet-visible absorption spectra, and EEMs were obtained for standard Suwannee River fulvic acid and 15 hydrophobic or hydrophilic acid, neutral, and base DOM fractions plus nonfractionated DOM from wastewater effluents and rivers in the southwestern United States. DOM fractions fluoresced in one or more EEM regions. The highest cumulative EEM volume (??T,n = ????i,n) was observed for hydrophobic neutral DOM fractions, followed by lower ??T,n values for hydrophobic acid, base, and hydrophilic acid DOM fractions, respectively. An extracted wastewater biomass DOM sample contained aromatic protein- and humic-like material and was characteristic of bacterial-soluble microbial products. Aromatic carbon and the presence of specific aromatic compounds (as indicated by solid-state 13C NMR and FTIR data) resulted in EEMs that aided in differentiating wastewater effluent DOM from drinking water DOM.

  1. A comparative theoretical study on core-hole excitation spectra of azafullerene and its derivatives

    SciTech Connect

    Deng, Yunfeng; Gao, Bin; Deng, Mingsen; Luo, Yi

    2014-03-28

    The core-hole excitation spectra—near-edge x-ray absorption spectroscopy (NEXAFS), x-ray emission spectroscopy (XES), and x-ray photoelectron spectroscopy (XPS) shake-up satellites have been simulated at the level of density functional theory for the azafullerene C{sub 59}N and its derivatives (C{sub 59}N){sup +}, C{sub 59}HN, (C{sub 59}N){sub 2}, and C{sub 59}N–C{sub 60}, in which the XPS shake-up satellites were simulated using our developed equivalent core hole Kohn-Sham (ECH-KS) density functional theory approach [B. Gao, Z. Wu, and Y. Luo, J. Chem. Phys. 128, 234704 (2008)] which aims for the study of XPS shake-up satellites of large-scale molecules. Our calculated spectra are generally in good agreement with available experimental results that validates the use of the ECH-KS method in the present work. The nitrogen K-edge NEXAFS, XES, and XPS shake-up satellites spectra in general can be used as fingerprints to distinguish the azafullerene C{sub 59}N and its different derivatives. Meanwhile, different carbon K-edge spectra could also provide detailed information of (local) electronic structures of different molecules. In particular, a peak (at around 284.5 eV) in the carbon K-edge NEXAFS spectrum of the heterodimer C{sub 59}N–C{sub 60} is confirmed to be related to the electron transfer from the C{sub 59}N part to the C{sub 60} part in this charge-transfer complex.

  2. Progress in Neutron Scattering Studies of Spin Excitations in High-Tc Cuprates

    NASA Astrophysics Data System (ADS)

    Fujita, Masaki; Hiraka, Haruhiro; Matsuda, Masaaki; Matsuura, Masato; Tranquada, John M.; Wakimoto, Shuichi; Xu, Guangyong; Yamada, Kazuyoshi

    2012-01-01

    Neutron scattering experiments continue to improve our knowledge of spin fluctuations in layered cuprates, excitations that are symptomatic of the electronic correlations underlying high-temperature superconductivity. Time-of-flight spectrometers, together with new and varied single crystal samples, have provided a more complete characterization of the magnetic energy spectrum and its variation with carrier concentration. While the spin excitations appear anomalous in comparison with simple model systems, there is clear consistency among a variety of cuprate families. Focusing initially on hole-doped systems, we review the nature of the magnetic spectrum, and variations in magnetic spectral weight with doping. We consider connections with the phenomena of charge and spin stripe order, and the potential generality of such correlations as suggested by studies of magnetic-field and impurity induced order. We contrast the behavior of the hole-doped systems with the trends found in the electron-doped superconductors. Returning to hole-doped cuprates, studies of translation-symmetry-preserving magnetic order are discussed, along with efforts to explore new systems. We conclude with a discussion of future challenges.

  3. Multi-reference approach to the calculation of photoelectron spectra including spin-orbit coupling

    SciTech Connect

    Grell, Gilbert; Bokarev, Sergey I. Kühn, Oliver; Winter, Bernd; Seidel, Robert; Aziz, Emad F.; Aziz, Saadullah G.

    2015-08-21

    X-ray photoelectron spectra provide a wealth of information on the electronic structure. The extraction of molecular details requires adequate theoretical methods, which in case of transition metal complexes has to account for effects due to the multi-configurational and spin-mixed nature of the many-electron wave function. Here, the restricted active space self-consistent field method including spin-orbit coupling is used to cope with this challenge and to calculate valence- and core-level photoelectron spectra. The intensities are estimated within the frameworks of the Dyson orbital formalism and the sudden approximation. Thereby, we utilize an efficient computational algorithm that is based on a biorthonormal basis transformation. The approach is applied to the valence photoionization of the gas phase water molecule and to the core ionization spectrum of the [Fe(H{sub 2}O){sub 6}]{sup 2+} complex. The results show good agreement with the experimental data obtained in this work, whereas the sudden approximation demonstrates distinct deviations from experiments.

  4. Topological honeycomb magnon Hall effect: A calculation of thermal Hall conductivity of magnetic spin excitations

    NASA Astrophysics Data System (ADS)

    Owerre, S. A.

    2016-07-01

    Quite recently, the magnon Hall effect of spin excitations has been observed experimentally on the kagome and pyrochlore lattices. The thermal Hall conductivity κxy changes sign as a function of magnetic field or temperature on the kagome lattice, and κxy changes sign upon reversing the sign of the magnetic field on the pyrochlore lattice. Motivated by these recent exciting experimental observations, we theoretically propose a simple realization of the magnon Hall effect in a two-band model on the honeycomb lattice. The magnon Hall effect of spin excitations arises in the usual way via the breaking of inversion symmetry of the lattice, however, by a next-nearest-neighbour Dzyaloshinsky-Moriya interaction. We find that κxy has a fixed sign for all parameter regimes considered. These results are in contrast to the Lieb, kagome, and pyrochlore lattices. We further show that the low-temperature dependence on the magnon Hall conductivity follows a T2 law, as opposed to the kagome and pyrochlore lattices. These results suggest an experimental procedure to measure thermal Hall conductivity within a class of 2D honeycomb quantum magnets and ultracold atoms trapped in a honeycomb optical lattice.

  5. Comparative study of resonance Raman and surface-enhanced resonance Raman chlorophyll a spectra using soret and red excitation

    SciTech Connect

    Thomas, L.L.; Kim, Jaeho; Cotton, T.M. )

    1990-12-05

    Surface-enhanced resonance Raman scattering (SERRS) spectra are reported for chlorophyll a adsorbed on a silver electrode at 298 and 77 K with 406.7-, 457.9-, 514.5-, and 647.1-nm excitation. Submerging the electrode in degassed water at 298 K was found to improve the spectral quality by minimizing sample heating and photooxidation. Spectral intensities and peak resolutions were greater at all excitation wavelengths at liquid nitrogen temperature. Most significantly, roughened silver at the low temperature quenched the fluorescence accompanying red excitation and minimized sample photooxidation, resulting in richly detailed SERRS spectra of chlorophyll a. The close correspondence between chlorophyll a resonance Raman (RR) and SERRS spectra suggests that an electromagnetic mechanism is the major source of the surface enhancement, rather than a chemical mechanism (e.g. a charge-transfer complex between chlorophyll a and the metal). The spectral similarities, together with the presence of the MgN{sub 4} vibration band in the SERRS spectra, also provide evidence that structural alterations (e.g. cleavage of ring V or loss of Mg) do not occur in chlorophyll a after adsorption at the electrode surface. A distinctive SERRS spectrum was obtained for each excitation wavelength. Selective excitation within the various electronic transitions can thus be utilized to verify assignments of the vibrational modes of chlorophyll a and to monitor its interactions and photochemical behavior in biomimetic systems.

  6. Importance of cross-correlated relaxation in the spectra of simple organofluorine compounds: Spectral complexity of A3B3X spin systems compared to ABX spin systems

    NASA Astrophysics Data System (ADS)

    Alemany, Lawrence B.; Malloy, Thomas B.; Nunes, Megan M.; Zaibaq, Nicholas G.

    2012-09-01

    In a continuation of our initial investigation of the complex 13C and 19F spectra exhibited by two simple organofluorine compounds, additional organofluorine compounds expected to exhibit a wide range of spectral complexity were studied. Spectral simulations are critical for analyzing the more complex spin systems, in particular, A3B3X and A6B3X. Cross-correlated relaxation is commonly observed; examples of 13Csbnd 19F cross-correlated relaxation are shown with the signals for each nucleus exhibiting unequal relaxation rates. Higher order effects are particularly noticeable in the spectra of perfluoro-t-butyl alcohol because of a large 4JFF value in the (13CF3)(12CF3)212COH isotopomer. The many additional transitions in an A3B3X spin system compared to an ABX spin system result in much more complex 19F (A3 and B3) and 13C (X) spectra, even though only three types of nuclei are involved in each spin system. The corresponding protio compounds typically constitute a much simpler A3M3X spin system because the long-range nJHH coupling (n ⩾ 4) is much smaller than the corresponding long-range nJFF coupling. Spectra previously published for ethane-1-13C (A3B3X) and hexafluoroethane-1-13C (A3M3X) are notable exceptions and are discussed.

  7. Longitudinal spin excitations and magnetic anisotropy in antiferromagnetically ordered BaFe2As2

    NASA Astrophysics Data System (ADS)

    Li, Yuan; Wang, Chong; Zhang, Rui; Luo, Huiqian; Wang, Fa; Dai, Pengcheng; Regnault, Louis-Pierre

    2014-03-01

    In the iron-based superconductors, there is an outstanding debate on the microscopic origin of the magnetism, whether it arises from local moments or itinerant electrons with Fermi-surface nesting. To answer this question, we performed a spin-polarized inelastic neutron scattering study of spin waves in the antiferromagnetically ordered state of BaFe2As2. Three distinct excitation components are identified, with spins fluctuating along the c-axis, perpendicular to the ordering direction in the ab -plane, and parallel to the ordering direction. While the first two ``transverse'' components can be described by a linear spin-wave theory with magnetic anisotropy and inter-layer coupling, the third ``longitudinal'' component is generically incompatible with the local moment picture. It points towards a contribution of itinerant electrons to the magnetism already in the parent compound of this family of Fe-based superconductors. (arXiv:1309.7553) Supported by the National Basic Research Program of China, the National Science Foundation of China, and the US National Science Foundation.

  8. Visible and near-infrared excitation spectra from the neptunyl ion doped into a uranyl tetrachloride lattice

    NASA Astrophysics Data System (ADS)

    Barker, Beau J.; Berg, John M.; Kozimor, Stosh A.; Wozniak, Nicholas R.; Wilkerson, Marianne P.

    2016-03-01

    Visible and near-infrared illumination induces 5f-5f and ligand-to-metal charge-transfer (LMCT) transitions of the neptunyl tetrachloride anion in polycrystalline Cs2U(Np)O2Cl4, and results in near-infrared luminescence from the second electronically excited state to the ground state. This photoluminescence is used as a detection method to collect excitation spectra throughout the near-infrared and visible regions. The excitation spectra of LMCT transitions in excitation spectra were identified in previous work. Here the measurement and analysis is extended to include both LMCT and intra-5f transitions. The results manifest variation in structural properties of the neptunium-oxo bond among the low-lying electronic states. Vibronic intensity patterns and energy spacings are used to compare bond lengths and vibrational frequencies in the excited states, confirming significant characteristic differences between those excited by 5f-5f transitions from those due to LMCT transitions. Results are compared with recently published RASPT2/SO calculations of [NpO2Cl4]2-.

  9. Excited-state quantum phase transitions in the two-spin elliptic Gaudin model.

    PubMed

    Relaño, Armando; Esebbag, Carlos; Dukelsky, Jorge

    2016-11-01

    We study the integrability of the two-spin elliptic Gaudin model for arbitrary values of the Hamiltonian parameters. The limit of a very large spin coupled to a small one is well described by a semiclassical approximation with just one degree of freedom. Its spectrum is divided into bands that do not overlap if certain conditions are fulfilled. In spite of the fact that there are no quantum phase transitions in each of the band heads, the bands show excited-state quantum phase transitions separating a region in which the parity symmetry is broken from another region in which time-reversal symmetry is broken. We derive analytical expressions for the critical energies in the semiclassical approximation, and confirm the results by means of exact diagonalizations for large systems.

  10. Spin-Wave Excitations Evidencing the Kitaev Interaction in Single Crystalline α-RuCl_{3}.

    PubMed

    Ran, Kejing; Wang, Jinghui; Wang, Wei; Dong, Zhao-Yang; Ren, Xiao; Bao, Song; Li, Shichao; Ma, Zhen; Gan, Yuan; Zhang, Youtian; Park, J T; Deng, Guochu; Danilkin, S; Yu, Shun-Li; Li, Jian-Xin; Wen, Jinsheng

    2017-03-10

    Kitaev interactions underlying a quantum spin liquid have long been sought, but experimental data from which their strengths can be determined directly, are still lacking. Here, by carrying out inelastic neutron scattering measurements on high-quality single crystals of α-RuCl_{3}, we observe spin-wave spectra with a gap of ∼2  meV around the M point of the two-dimensional Brillouin zone. We derive an effective-spin model in the strong-coupling limit based on energy bands obtained from first-principles calculations, and find that the anisotropic Kitaev interaction K term and the isotropic antiferromagnetic off-diagonal exchange interaction Γ term are significantly larger than the Heisenberg exchange coupling J term. Our experimental data can be well fit using an effective-spin model with K=-6.8  meV and Γ=9.5  meV. These results demonstrate explicitly that Kitaev physics is realized in real materials.

  11. Spin-Wave Excitations Evidencing the Kitaev Interaction in Single Crystalline α -RuCl3

    NASA Astrophysics Data System (ADS)

    Ran, Kejing; Wang, Jinghui; Wang, Wei; Dong, Zhao-Yang; Ren, Xiao; Bao, Song; Li, Shichao; Ma, Zhen; Gan, Yuan; Zhang, Youtian; Park, J. T.; Deng, Guochu; Danilkin, S.; Yu, Shun-Li; Li, Jian-Xin; Wen, Jinsheng

    2017-03-01

    Kitaev interactions underlying a quantum spin liquid have long been sought, but experimental data from which their strengths can be determined directly, are still lacking. Here, by carrying out inelastic neutron scattering measurements on high-quality single crystals of α -RuCl3 , we observe spin-wave spectra with a gap of ˜2 meV around the M point of the two-dimensional Brillouin zone. We derive an effective-spin model in the strong-coupling limit based on energy bands obtained from first-principles calculations, and find that the anisotropic Kitaev interaction K term and the isotropic antiferromagnetic off-diagonal exchange interaction Γ term are significantly larger than the Heisenberg exchange coupling J term. Our experimental data can be well fit using an effective-spin model with K =-6.8 meV and Γ =9.5 meV . These results demonstrate explicitly that Kitaev physics is realized in real materials.

  12. Femtosecond switching of magnetism via strongly correlated spin-charge quantum excitations.

    PubMed

    Li, Tianqi; Patz, Aaron; Mouchliadis, Leonidas; Yan, Jiaqiang; Lograsso, Thomas A; Perakis, Ilias E; Wang, Jigang

    2013-04-04

    The technological demand to push the gigahertz (10(9) hertz) switching speed limit of today's magnetic memory and logic devices into the terahertz (10(12) hertz) regime underlies the entire field of spin-electronics and integrated multi-functional devices. This challenge is met by all-optical magnetic switching based on coherent spin manipulation. By analogy to femtosecond chemistry and photosynthetic dynamics--in which photoproducts of chemical and biochemical reactions can be influenced by creating suitable superpositions of molecular states--femtosecond-laser-excited coherence between electronic states can switch magnetic order by 'suddenly' breaking the delicate balance between competing phases of correlated materials: for example, manganites exhibiting colossal magneto-resistance suitable for applications. Here we show femtosecond (10(-15) seconds) photo-induced switching from antiferromagnetic to ferromagnetic ordering in Pr0.7Ca0.3MnO3, by observing the establishment (within about 120 femtoseconds) of a huge temperature-dependent magnetization with photo-excitation threshold behaviour absent in the optical reflectivity. The development of ferromagnetic correlations during the femtosecond laser pulse reveals an initial quantum coherent regime of magnetism, distinguished from the picosecond (10(-12) seconds) lattice-heating regime characterized by phase separation without threshold behaviour. Our simulations reproduce the nonlinear femtosecond spin generation and underpin fast quantum spin-flip fluctuations correlated with coherent superpositions of electronic states to initiate local ferromagnetic correlations. These results merge two fields, femtosecond magnetism in metals and band insulators, and non-equilibrium phase transitions of strongly correlated electrons, in which local interactions exceeding the kinetic energy produce a complex balance of competing orders.

  13. Quantum interference of stored dual-channel spin-wave excitations in a single tripod system

    SciTech Connect

    Wang Hai; Li Shujing; Xu Zhongxiao; Zhao Xingbo; Zhang Lijun; Li Jiahua; Wu Yuelong; Xie Changde; Peng Kunchi; Xiao Min

    2011-04-15

    We present an experimental demonstration of dual-channel memory in a single tripod atomic system. The total readout signal exhibits either constructive or destructive interference when the dual-channel spin-wave excitations (SWEs) are retrieved by two reading beams with a controllable relative phase. When the two reading beams have opposite phases, the SWEs will remain in the medium, which can be retrieved later with two in-phase reading beams. Such a phase-sensitive storage and retrieval scheme can be used to measure and control the relative phase between the two SWEs in the memory medium, which may find applications in quantum-information processing.

  14. Theoretical analysis of the optical excitation spectra of silver and gold nanowires

    NASA Astrophysics Data System (ADS)

    Guidez, Emilie B.; Aikens, Christine M.

    2012-06-01

    The excitation spectra of linear atomic chains of silver and gold with various sizes have been calculated using time-dependent density functional theory. Silver chains show longitudinal and transverse peaks as well as a low-intensity d-band. The longitudinal peak, corresponding to the HOMO-LUMO transition (along the main axis of the chain), shifts linearly to the red as the length of the system increases, consistent with the particle-in-a-box model. The transverse peak remains at approximately constant energy for all systems studied and corresponds to ∑m --> Πm transitions in the xy plane perpendicular to the chain. As the chain grows, transitions arising from d orbitals contribute to the transverse peak, which affects its oscillator strength. Contrary to silver, gold chains display a strong d-band that converges to a distinct pattern at a chain length of about twelve atoms. The transitions involved in the d-band originate from localized d-orbitals with a dz2 character since they have the right symmetry to give transitions into the LUMO, LUMO + 1, ..., which have ∑ symmetry. Transitions arising from these localized d-orbitals also affect the position of the longitudinal peak and generate a wide transverse band. Although the majority of the transitions involved in the transverse band have a d∑ --> Π or dΠ --> ∑ character, they are hidden by much stronger excitations of dΠ --> Π character in gold nanowires.The excitation spectra of linear atomic chains of silver and gold with various sizes have been calculated using time-dependent density functional theory. Silver chains show longitudinal and transverse peaks as well as a low-intensity d-band. The longitudinal peak, corresponding to the HOMO-LUMO transition (along the main axis of the chain), shifts linearly to the red as the length of the system increases, consistent with the particle-in-a-box model. The transverse peak remains at approximately constant energy for all systems studied and corresponds to

  15. CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES: A Green's function model for ferromagnetism and spin excitations of (Ga, Mn)As diluted magnetic semiconductors

    NASA Astrophysics Data System (ADS)

    Liu, Gui-Bin; Liu, Bang-Gui

    2009-11-01

    We study (Ga, Mn)As diluted magnetic semiconductors in terms of the Ruderman-Kittel-Kasuya-Yosida quantum spin model in Green's function approach. Random distributions of the magnetic atoms are treated by using an analytical average of magnetic configurations. Average magnetic moments and spin excitation spectra as functions of temperature can be obtained by solving self-consistent equations, and the Curie temperature TC is given explicitly. TC is proportional to magnetic atomic concentration, and there exists a maximum for TC as a function of carrier concentration. Applied to (Ga, Mn)As, the theoretical results are consistent with experiment and the experimental TC can be obtained with reasonable parameters. This modelling can also be applied to other diluted magnetic semiconductors.

  16. First glimpse of the soft x-ray induced excited spin-state trapping effect dynamics on spin cross-over molecules

    SciTech Connect

    Davesne, V.; Gruber, M.; Miyamachi, T.; Da Costa, V.; Boukari, S.; Scheurer, F.; Joly, L.; Bowen, M.; Beaurepaire, E.; Ohresser, P.; Otero, E.; Choueikani, F.; Gaspar, A. B.; Real, J. A.; Wulfhekel, W.

    2013-08-21

    The dynamics of the soft x-ray induced excited spin state trapping (SOXIESST) effect of Fe(phen){sub 2}(NCS){sub 2} (Fe-phen) powder have been investigated by x-ray absorption spectroscopy (XAS) using the total electron yield method, in a wide temperature range. The low-spin (LS) state is excited into the metastable high-spin (HS) state at a rate that depends on the intensity of the x-ray illumination it receives, and both the temperature and the intensity of the x-ray illumination will affect the maximum HS proportion that is reached. We find that the SOXIESST HS spin state transforms back to the LS state at a rate that is similar to that found for the light induced excited spin state trapping (LIESST) effect. We show that it is possible to use the SOXIESST effect in combination with the LIESST effect to investigate the influence of cooperative behavior on the dynamics of both effects. To investigate the impact of molecular cooperativity, we compare our results on Fe-phen with those obtained for Fe([Me{sub 2}Pyrz]{sub 3}BH){sub 2} (Fe-pyrz) powder, which exhibits a similar thermal transition temperature but with a hysteresis. We find that, while the time constant of the dynamic is identical for both molecules, the SOXIESST effect is less efficient at exciting the HS state in Fe-pyrz than in Fe-phen.

  17. Broadband excitation by chirped pulses: application to single electron spins in diamond

    NASA Astrophysics Data System (ADS)

    Niemeyer, I.; Shim, J. H.; Zhang, J.; Suter, D.; Taniguchi, T.; Teraji, T.; Abe, H.; Onoda, S.; Yamamoto, T.; Ohshima, T.; Isoya, J.; Jelezko, F.

    2013-03-01

    Pulsed excitation of broad spectra requires very high field strengths if monochromatic pulses are used. If the corresponding high power is not available or not desirable, the pulses can be replaced by suitable low-power pulses that distribute the power over a wider bandwidth. As a simple case, we use microwave pulses with a linear frequency chirp. We use these pulses to excite spectra of single nitrogen-vacancy centres in a Ramsey experiment. Compared to the conventional Ramsey experiment, our approach increases the bandwidth by at least an order of magnitude. Compared to the conventional continuous wave-ODMR experiment, the chirped Ramsey experiment does not suffer from power broadening and increases the resolution by at least an order of magnitude. As an additional benefit, the chirped Ramsey spectrum contains not only ‘allowed’ single quantum transitions, but also ‘forbidden’ zero- and double quantum transitions, which can be distinguished from the single quantum transitions by phase-shifting the readout pulse with respect to the excitation pulse or by variation of the external magnetic field strength.

  18. Excitation spectra of photoluminescence and its kinetics in structures with self-assembled Ge:Si nanoislands

    SciTech Connect

    Yablonskiy, A. N. Baidakova, N. A. Novikov, A. V.; Lobanov, D. N.; Shaleev, M. V.

    2015-11-15

    The spectral and time characteristics of photoluminescence associated with the radiative recombination of charge carriers in SiGe/Si(001) multilayer structures with self-assembled Ge:Si islands are investigated. The time dependences of the photoluminescence of Ge:Si islands in a wide range of delay times after the pump pulse are considered at various optical-excitation levels. The photoluminescence-excitation spectra from Ge(Si) islands in the SiGe/Si(001) structures are investigated in the region of band-to-band and subband optical pumping corresponding to various time components in the photoluminescence-relaxation kinetics. A significant difference in the shape of the excitation spectra is revealed for fast (0–100 μs) and slow (100 μs–50 ms) components of the photoluminescence signal from the islands. The significant dependence of the photoluminescence-excitation spectra of Ge(Si)/Si(001) islands on the optical-pump power is shown to be associated with the prolonged diffusion of nonequilibrium charge carriers from bulk-silicon layers to Ge:Si islands at high excitation levels.

  19. Velocity autocorrelation spectra in molten polymers measured by NMR modulated gradient spin-echo

    NASA Astrophysics Data System (ADS)

    Stepišnik, Janez; Mohorič, Aleš; Mattea, Carlos; Stapf, Siegfried; Serša, Igor

    2014-04-01

    The segmental dynamics in molten linear polymers is studied by the NMR method of modulated gradient spin-echo, which directly probes a spectrum of molecular velocity autocorrelation function. Diffusion spectra of mono-disperse poly(isoprene-1.4) with different molecular masses, measured in the frequency range 0.1-10 kHz at a temperature of 26\\ ^{\\circ}\\text{C} , have a form similar to the spectrum of Rouse chain dynamics, which implicates the tube-Rouse motion as the dominant dynamic process in this frequency range. The scaling of the center-of-mass diffusion coefficient, given from the fitting parameters, changes from N^{-1} into N^{-2.4} at around N \\approx 3\\text{-}5 Kuhn steps, which is less than predicted by theory and simulations, while the correlation times of the tube-Rouse mode do not follow the anticipated scaling.

  20. Dynamic nuclear spin polarization in the resonant laser excitation of an InGaAs quantum dot.

    PubMed

    Högele, A; Kroner, M; Latta, C; Claassen, M; Carusotto, I; Bulutay, C; Imamoglu, A

    2012-05-11

    Resonant optical excitation of lowest-energy excitonic transitions in self-assembled quantum dots leads to nuclear spin polarization that is qualitatively different from the well-known optical orientation phenomena. By carrying out a comprehensive set of experiments, we demonstrate that nuclear spin polarization manifests itself in quantum dots subjected to finite external magnetic field as locking of the higher energy Zeeman transition to the driving laser field, as well as the avoidance of the resonance condition for the lower energy Zeeman branch. We interpret our findings on the basis of dynamic nuclear spin polarization originating from noncollinear hyperfine interaction and find excellent agreement between experiment and theory. Our results provide evidence for the significance of noncollinear hyperfine processes not only for nuclear spin diffusion and decay, but also for buildup dynamics of nuclear spin polarization in a coupled electron-nuclear spin system.

  1. Spin wave excitations in the tetragonal double perovskite Sr2CuWO6

    NASA Astrophysics Data System (ADS)

    Walker, H. C.; Mustonen, O.; Vasala, S.; Voneshen, D. J.; Le, M. D.; Adroja, D. T.; Karppinen, M.

    2016-08-01

    Sr2CuWO6 is a double perovskite proposed to be at the border between two- and three-dimensional magnetism, with a square lattice of S =1/2 Cu2 + ions. We have used inelastic neutron scattering to investigate the spin wave excitations of the system, to find out how they evolve as a function of temperature, as well as to obtain information about the magnetic exchange interactions. We observed well defined dispersive spin wave modes at 6 K, which partially survive above the magnetic ordering temperature TN=24 K. Linear spin wave theory is used to determine the exchange interactions revealing them to be highly two dimensional in nature. Density functional theory calculations are presented supporting this experimental finding, which is in contrast to a previous ab initio study of the magnetic interactions. Our analysis confirms that not the nearest neighbor, but the next nearest neighbor interactions in the tetragonal a b plane are the strongest. Low incident energy measurements reveal the opening of a 0.6(1) meV gap below TN, which suggests the presence of a very weak single ion anisotropy term in the form of an easy axis along a ̂.

  2. Ultraviolet high-excitation Fe II fluorescence lines excited by O VI, C IV, and H I resonance emission as seen in IUE spectra

    NASA Technical Reports Server (NTRS)

    Feibelman, Walter A.; Bruhweiler, Frederick C.; Johansson, Sveneric

    1991-01-01

    Archival high-dispersion spectra from the IUE are used in a search for Bowen emission lines of Fe II excited by the stronger transition of the O VI resonance doublet. The possibility of using these Fe II emission lines as a diagnostic of the strength of the far-ultraviolet emission of O VI at 1032 A is explored. It is found that the Fe II emission lines are quite common and strong in symbiotic stars, particularly those of the type known as 'symbiotic novae', as well as in normal novae. The lines are observed in central stars of some planetary nebulae of the O VI sequence besides a few central stars of type WR. High density, high excitation, and high temperature are suggested to be requirements for the excitation of the Fe II fluorescence lines. It is pointed out that while these lines were observed in PG 1159-035 and K1-16, they were not observed in AGNs.

  3. Excited states of large open-shell molecules: an efficient, general, and spin-adapted approach based on a restricted open-shell ground state wave function.

    PubMed

    Roemelt, Michael; Neese, Frank

    2013-04-11

    A spin-adapted configuration interaction with singles method that is based on a restricted open-shell reference function (ROCIS) with general total spin S is presented. All excited configuration state functions (CSFs) are generated with the aid of a spin-free second quantization formalism that only leads to CSFs within the first order interacting space. By virtue of the CSF construction, the formalism involves higher than singly excited determinants but not higher than singly excited configurations. Matrix elements between CSFs are evaluated on the basis of commutator relationships using a symbolic algebra program. The final equations were, however, hand-coded in order to maximize performance. The method can be applied to fairly large systems with more than 100 atoms in reasonable wall-clock times and also parallelizes well. Test calculations demonstrate that the approach is far superior to UHF-based configuration interaction with single excitations but necessarily falls somewhat short of quantitative accuracy due to the lack of dynamic correlation contributions. In order to implicitly account for dynamic correlation in a crude way, the program optionally allows for the use of Kohn-Sham orbitals in combination with a modest downscaling of two-electron integrals (DFT/ROCIS). All two-electron integrals of Kohn-Sham orbitals that appear in the Hamiltonian matrix are reduced by a total of three scaling parameters that are suitable for a wide range of molecules. Test calculations on open-shell organic radicals as well as transition metal complexes demonstrate the wide applicability of the method and its ability to calculate the electronic spectra of large molecular systems.

  4. Spin-excitations of the quantum Hall ferromagnet of composite fermions

    NASA Astrophysics Data System (ADS)

    Doretto, R. L.; Goerbig, M. O.; Lederer, P.; Caldeira, A. O.; Smith, C. Morais

    2005-07-01

    The spin excitations of a fractional quantum Hall system are evaluated within a bosonization approach. In a first step, we generalize Murthy and Shankar’s Hamiltonian theory of the fractional quantum Hall effect to the case of composite fermions with an extra discrete degree of freedom. Here, we mainly investigate the spin degrees of freedom, but the proposed formalism may be useful also in the study of bilayer quantum-Hall systems, where the layer index may formally be treated as an isospin. In a second step, we apply a bosonization scheme, recently developed for the study of the two-dimensional electron gas, to the interacting composite-fermion Hamiltonian. The dispersion of the bosons, which represent quasiparticle-quasihole excitations, is analytically evaluated for fractional quantum Hall systems at ν=1/3 and ν=1/5 . The finite width of the two-dimensional electron gas is also taken into account explicitly. Furthermore, we consider the interacting bosonic model and calculate the lowest-energy state for two bosons. In addition to a continuum describing scattering states, we find a bound-state of two bosons. This state is interpreted as a pair excitation, which consists of a skyrmion of composite fermions and an antiskyrmion of composite fermions. The dispersion relation of the two-boson state is evaluated for ν=1/3 and ν=1/5 . Finally, we show that our theory provides the microscopic basis for a phenomenological nonlinear σ model for studying the skyrmion of composite fermions.

  5. Disappearance of antiferromagnetic spin excitations in overdoped La2-xSrxCuO4.

    PubMed

    Wakimoto, S; Yamada, K; Tranquada, J M; Frost, C D; Birgeneau, R J; Zhang, H

    2007-06-15

    Magnetic excitations for energies up to approximately 100 meV are studied for overdoped La(2-x)Sr(x)CuO(4) with x=0.25 and 0.30, using time-of-flight neutron spectroscopy. Comparison of spectra integrated over the width of an antiferromagnetic Brillouin zone demonstrates that the magnetic scattering at intermediate energies, 20

  6. Modeling of fluorescence line-narrowed spectra in weakly coupled dimers in the presence of excitation energy transfer

    SciTech Connect

    Lin, Chen; Reppert, Mike; Feng, Ximao; Jankowiak, Ryszard

    2014-07-21

    This work describes simple analytical formulas to describe the fluorescence line-narrowed (FLN) spectra of weakly coupled chromophores in the presence of excitation energy transfer (EET). Modeling studies for dimer systems (assuming low fluence and weak coupling) show that the FLN spectra (including absorption and emission spectra) calculated for various dimers using our model are in good agreement with spectra calculated by: (i) the simple convolution method and (ii) the more rigorous treatment using the Redfield approach [T. Renger and R. A. Marcus, J. Chem. Phys. 116, 9997 (2002)]. The calculated FLN spectra in the presence of EET of all three approaches are very similar. We argue that our approach provides a simplified and computationally more efficient description of FLN spectra in the presence of EET. This method also has been applied to FLN spectra obtained for the CP47 antenna complex of Photosystem II reported by Neupane et al. [J. Am. Chem. Soc. 132, 4214 (2010)], which indicated the presence of uncorrelated EET between pigments contributing to the two lowest energy (overlapping) exciton states, each mostly localized on a single chromophore. Calculated and experimental FLN spectra for CP47 complex show very good qualitative agreement.

  7. Magnonic band structure, complete bandgap, and collective spin wave excitation in nanoscale two-dimensional magnonic crystals

    SciTech Connect

    Kumar, D.; Barman, A.; Kłos, J. W.; Krawczyk, M.

    2014-01-28

    We present the observation of a complete bandgap and collective spin wave excitation in two-dimensional magnonic crystals comprised of arrays of nanoscale antidots and nanodots, respectively. Considering that the frequencies dealt with here fall in the microwave band, these findings can be used for the development of suitable magnonic metamaterials and spin wave based signal processing. We also present the application of a numerical procedure, to compute the dispersion relations of spin waves for any high symmetry direction in the first Brillouin zone. The results obtained from this procedure have been reproduced and verified by the well established plane wave method for an antidot lattice, when magnetization dynamics at antidot boundaries are pinned. The micromagnetic simulation based method can also be used to obtain iso–frequency contours of spin waves. Iso–frequency contours are analogous of the Fermi surfaces and hence, they have the potential to radicalize our understanding of spin wave dynamics. The physical origin of bands, partial and full magnonic bandgaps have been explained by plotting the spatial distribution of spin wave energy spectral density. Although, unfettered by rigid assumptions and approximations, which afflict most analytical methods used in the study of spin wave dynamics, micromagnetic simulations tend to be computationally demanding. Thus, the observation of collective spin wave excitation in the case of nanodot arrays, which can obviate the need to perform simulations, may also prove to be valuable.

  8. Fluorescence excitation and emission spectra of 1,5-dihydroxyanthraquinone-d2 in n-hexane at 10 K

    NASA Astrophysics Data System (ADS)

    Smulevich, Giulietta; Foggi, Paolo

    1987-11-01

    The fluorescence excitation, between 430 and 505 nm, and emission, between 505 and 725 nm, spectra in n-hexane of 1,5-dihydroxyanthraquinone-d0 and -d2 at 10 K have been measured. Dual excitation and emission associated to excited state proton transfer were observed. Apart from the long wavelength emission, well resolved vibrational structures were obtained. A remarkable spectral shift (684 cm-1) of the origin of the high frequency transition was observed upon deuteration. The energy gaps between the transition origins both in excitation and emission as well as the isotopic shifts of the origins, were interpreted in terms of Lippincott-Schroeder asymmetric double minimum potential functions along the OH coordinate. An extra fluorescence occurs in the low frequency range, vanishing upon deuteration. It was explained as due to the ν(OH) stretching mode of the high frequency emission enhanced via vibronic coupling between the two ground states.

  9. Excitation Emission Matrix Spectra (EEMS) of Chromophoric Dissolved Organic Matter Produced during Microbial Incubation

    NASA Astrophysics Data System (ADS)

    McDonald, N.; Nelson, N. B.; Parsons, R.

    2013-12-01

    The chromophoric or light-absorbing fraction of dissolved organic matter (CDOM) is present ubiquitously in natural waters and has a significant impact on ocean biogeochemistry, affecting photosynthesis and primary production as well direct and indirect photochemical reactions (Siegel et al., 2002; Nelson et al., 2007). It has been largely researched in the past few decades, however the exact chemical composition remains unknown. Instrumental methods of analysis including simultaneous excitation-emission fluorescence spectra have allowed for further insight into source and chemical composition. While certain excitation-emission peaks have been associated with ';marine' sources, they have not been exclusively linked to bacterial production of CDOM (Coble, 1996; Zepp et al., 2004). In this study, ';grazer diluted' seawater samples (70% 0.2μm filtered water; 30% whole water) were collected at the Bermuda Atlantic Time Series (BATS) site in the Sargasso Sea (31° 41' N; 64° 10' W) and incubated with an amendment of labile dissolved organic carbon (10μM C6H12O6), ammonium (1μM NH4Cl) and phosphate (0.1μM K2HPO4) to facilitate bacterial production. These substrates and concentrations have been previously shown to facilitate optimum bacterial and CDOM production (Nelson et al., 2004). Sample depths were chosen at 1m and 200m as water at these depths has been exposed to UV light (the Subtropical Mode Water at 200m has been subducted from the surface) and therefore has low initial concentrations of CDOM. After the samples were amended, they were incubated at in-situ temperatures in the dark for 72 hours, with bacteria counts, UV-Vis absorption and EEMS measurements taken at 6-8 hour intervals. Dissolved organic carbon (DOC) measurements were collected daily. For the surface water experiment specific bacteria populations were investigated using Fluorescence In-Situ Hybridization (FISH) analysis. Results showed a clear production of bacteria and production of CDOM, which

  10. Phase relaxed localized excitation pulses for inner volume fast spin echo imaging

    PubMed Central

    Hajnal, Joseph V.

    2015-01-01

    Purpose To design multidimensional spatially selective radiofrequency (RF) pulses for inner volume imaging (IVI) with three‐dimensional (3D) fast spin echo (FSE) sequences. Enhanced background suppression is achieved by exploiting particular signal properties of FSE sequences. Theory and Methods The CPMG condition dictates that echo amplitudes will rapidly decrease if a 90° phase difference between excitation and refocusing pulses is not present, and refocusing flip angles are not precisely 180°. This mechanism is proposed as a means for generating additional background suppression for spatially selective excitation, by biasing residual excitation errors toward violating the CPMG condition. 3D RF pulses were designed using this method with a 3D spherical spiral trajectory, under‐sampled by factor 5.6 for an eight‐channel PTx system, at 3 Tesla. Results 3D‐FSE IVI with pulse durations of approximately 12 ms was demonstrated in phantoms and for T2‐weighted brain imaging in vivo. Good image quality was obtained, with mean background suppression factors of 103 and 82 ± 6 in phantoms and in vivo, respectively. Conclusion Inner Volume Imaging with 3D‐FSE has been demonstrated in vivo with tailored 3D‐RF pulses. The proposed design methods are also applicable to 2D pulses. Magn Reson Med 76:848–861, 2016. © 2015 The Authors. Magnetic Resonance in Medicine published by Wiley Periodicals, Inc. on behalf of International Society for Magnetic Resonance in Medicine PMID:26451691

  11. The Excitation and Fano Resonance Spectra of Some Acceptors in Silicon and Germanium

    NASA Astrophysics Data System (ADS)

    Piao, Gejin

    Rich and well resolved p_{3/2 } and p_{1/2} optical absorption spectra have been observed for indium in silicon and p_{3/2}^ectra for singly ionised zinc, Zn^-, in germanium, revealing some new transitions and permitting re-examination in detail of the transition energies, level schemes and deformation potential constants. Ratios of about 4.2 and 4.1 for the binding energies of Zn ^- in germanium to those of group III impurities and neutral zinc in germanium, respectively, were determined. A comparison with theoretical energies was made, showing excellent agreement. A set of asymmetric and broad excitation features was observed in the spectra of Zn^- in germanium; these have a one-to-one correspondence with the p_{3/2} transitions and are separated from them by the zone centre optical phonon energy of bulk germanium. These new features have been identified as Fano resonances. The Fano resonance of the G line was found to be well defined, while the G line in the p_{3/2}^ectrum is almost undetectable. This is the first observation of Fano resonances associated with bound holes in germanium. A simple and accurate method has been developed to deduce the parameters q, Gamma and f of the resonances. The stress behaviour of the rm p _{3/2}, p_{1/2} and Fano series of indium in silicon for F| <111>, <100> and <110> and of the p_{3/2} and Fano series of Zn^- in germanium for F|<111> and <100> have been observed with linearly polarised radiation. The Fano resonances experience splitting under stress in a way similar to their counterparts in the p_{3/2} series. Their strengths, however, do not follow those of their p_{3/2} counterparts. The piezo-Fano selection rules have been derived using group theory. A striking phenomenon for Zn^- in germanium is the appearance of the some stress components of the Fano resonances for which their parents in the p_{3/2} series are strictly forbidden. This is consistent with the selection rules which show how the rules for the p_ {3

  12. Unusual magnetic excitations in the weakly ordered spin- 12 chain antiferromagnet Sr2CuO3: Possible evidence for Goldstone magnon coupled with the amplitude mode

    DOE PAGES

    Sergeicheva, E. G.; Sosin, S. S.; Prozorova, L. A.; ...

    2017-01-18

    We report on an electron spin resonance (ESR) study of a nearly one-dimensional (1D) spin-1/2 chain antiferromagnet, Sr2CuO3, with extremely weak magnetic ordering. The ESR spectra at T > TN, in the disordered Luttinger-spin-liquid phase, reveal nearly ideal Heisenberg-chain behavior with only a very small, field-independent linewidth, ~1/T. In the ordered state, below TN, we identify field-dependent antiferromagnetic resonance modes, which are well described by pseudo-Goldstone magnons in the model of a collinear biaxial antiferromagnet. Additionally, we observe a major resonant mode with unusual and strongly anisotropic properties, which is not anticipated by the conventional theory of Goldstone spin waves.more » Lastly, we propose that this unexpected magnetic excitation can be attributed to a field-independent magnon mode renormalized due to its interaction with the high-energy amplitude (Higgs) mode in the regime of weak spontaneous symmetry breaking.« less

  13. First-principles calculation of ground and excited-state absorption spectra of ruby and alexandrite considering lattice relaxation

    NASA Astrophysics Data System (ADS)

    Watanabe, Shinta; Sasaki, Tomomi; Taniguchi, Rie; Ishii, Takugo; Ogasawara, Kazuyoshi

    2009-02-01

    We performed first-principles calculations of multiplet structures and the corresponding ground-state absorption and excited-state absorption spectra for ruby (Cr3+:α-Al2O3) and alexandrite (Cr3+:BeAl2O4) which included lattice relaxation. The lattice relaxation was estimated using the first-principles total energy and molecular-dynamics method of the CASTEP code. The multiplet structure and absorption spectra were calculated using the configuration-interaction method based on density-functional calculations. For both ruby and alexandrite, the theoretical absorption spectra, which were already in reasonable agreement with experimental spectra, were further improved by consideration of lattice relaxation. In the case of ruby, the peak positions and peak intensities were improved through the use of models with relaxations of 11 or more atoms. For alexandrite, the polarization dependence of the U band was significantly improved, even by a model with a relaxation of only seven atoms.

  14. Time-domain excitation of quantized magnetostatic spin-wave modes in patterned NiFe thin film ensembles

    NASA Astrophysics Data System (ADS)

    Crawford, T. M.; Covington, M.; Parker, G. J.

    2003-01-01

    We measure quantized spin waves excited by a spatially inhomogeneous pulsed magnetic field in patterned NiFe thin films by inductive detection of the dynamic magnetization. When anisotropy and numerically calculated demagnetizing fields are included in the magnetostatic Damon Eshbach spin-wave dispersion relation, the predicted mode frequencies agree closely with measurements. Micromagnetic calculations predict the correct mode frequencies and agree remarkably well with time-domain measurements.

  15. A simplified Tamm-Dancoff density functional approach for the electronic excitation spectra of very large molecules

    NASA Astrophysics Data System (ADS)

    Grimme, Stefan

    2013-06-01

    Two approximations in the Tamm-Dancoff density functional theory approach (TDA-DFT) to electronically excited states are proposed which allow routine computations for electronic ultraviolet (UV)- or circular dichroism (CD) spectra of molecules with 500-1000 atoms. Speed-ups compared to conventional time-dependent DFT (TD-DFT) treatments of about two to three orders of magnitude in the excited state part at only minor loss of accuracy are obtained. The method termed sTDA ("s" for simplified) employs atom-centered Löwdin-monopole based two-electron repulsion integrals with the asymptotically correct 1/R behavior and perturbative single excitation configuration selection. It is formulated generally for any standard global hybrid density functional with given Fock-exchange mixing parameter ax. The method performs well for two standard benchmark sets of vertical singlet-singlet excitations for values of ax in the range 0.2-0.6. The mean absolute deviations from reference data are only 0.2-0.3 eV and similar to those from standard TD-DFT. In three cases (two dyes and one polypeptide), good mutual agreement between the electronic spectra (up to 10-11 eV excitation energy) from the sTDA method and those from TD(A)-DFT is obtained. The computed UV- and CD-spectra of a few typical systems (e.g., C60, two transition metal complexes, [7]helicene, polyalanine, a supramolecular aggregate with 483 atoms and about 7000 basis functions) compare well with corresponding experimental data. The method is proposed together with medium-sized double- or triple-zeta type atomic-orbital basis sets as a quantum chemical tool to investigate the spectra of huge molecular systems at a reliable DFT level.

  16. Magnetic excitations in the spin-1/2 triangular-lattice antiferromagnet Cs2CuBr4

    DOE PAGES

    Zvyagin, S. A.; Ozerov, M.; Kamenskyi, D.; ...

    2015-11-27

    We present on high- field electron spin resonance (ESR) studies of magnetic excitations in the spin- 1/2 triangular-lattice antiferromagnet Cs2CuBr4. Frequency- field diagrams of ESR excitations are measured for different orientations of magnetic fields up to 25 T. We show that the substantial zero- field energy gap, Δ ≈ 9.5 K, observed in the low-temperature excitation spectrum of Cs2CuBr4 [Zvyagin et al:, Phys. Rev. Lett. 112, 077206 (2014)], is present well above TN. Noticeably, the transition into the long-range magnetically ordered phase does not significantly affect the size of the gap, suggesting that even below TN the high-energy spin dynamicsmore » in Cs2CuBr4 is determined by short-range-order spin correlations. The experimental data are compared with results of model spin-wave-theory calculations for spin-1/2 triangle-lattice antiferromagnet.« less

  17. Hyperfine Sublevel Correlation (HYSCORE) Spectra for Paramagnetic Centers with Nuclear Spin I = 1 Having Isotropic Hyperfine Interactions

    SciTech Connect

    Maryasov, Alexander G.; Bowman, Michael K.

    2004-07-08

    It is shown that HYSCORE spectra of paramagnetic centers having nuclei of spin I=1 with isotropic hfi and arbitrary NQI consist of ridges having zero width. A parametric presentation of these ridges is found which shows the range of possible frequencies in the HYSCORE spectrum and aids in spectral assignments and rapid estimation of spin Hamiltonian parameters. An alternative approach for the spectral density calculation is presented that is based on spectral decomposition of the Hamiltonian. Only the eigenvalues of the Hamiltonian are needed in this approach. An atlas of HYSCORE spectra is given in the Supporting Information. This approach is applied to the estimation of the spin Hamiltonian parameters of the oxovanadium-EDTA complex.

  18. Ultrabright fluorescent silica particles with a large number of complex spectra excited with a single wavelength for multiplex applications.

    PubMed

    Palantavida, S; Peng, B; Sokolov, I

    2017-02-08

    We report on a novel approach to synthesize ultrabright fluorescent silica particles capable of producing a large number of complex spectra. The spectra can be excited using a single wavelength which is paramount in quantitative fluorescence imaging, flow cytometry and sensing applications. The approach employs the physical encapsulation of organic fluorescent molecules inside a nanoporous silica matrix with no dye leakage. As was recently demonstrated, such an encapsulation allowed for the encapsulation of very high concentrations of organic dyes without quenching their fluorescent efficiency. As a result, dye molecules are distanced within ∼5 nm from each other; it theoretically allows for efficient exchange of excitation energy via Förster resonance energy transfer (FRET). Here we present the first experimental demonstration of the encapsulation of fluorescent dyes in the FRET sequence. Attaining a FRET sequence of up to five different dyes is presented. The number of distinguishable spectra can be further increased by using different relative concentrations of encapsulated dyes. Combining these approaches allows for creating a large number of ultrabright fluorescent particles with substantially different fluorescence spectra. We also demonstrate the utilization of these particles for potential multiplexing applications. Though fluorescence spectra of the obtained multiplex probes are typically overlapping, they can be distinguished by using standard linear decomposition algorithms.

  19. Deformation increase of high-spin core-excited isomers in the astatine nuclei

    SciTech Connect

    Scheveneels, G.; Hardeman, F.; Neyens, G.; Coussement, R. )

    1991-06-01

    Quadrupole moments of six high-spin isomers in the At isotopes have been measured with the level-mixing-spectroscopy method: {sup 208}At(16{sup {minus}}), {sup 209}At(29/2{sup +}), {sup 210}At(19{sup +},15{sup {minus}}), {sup 211}At(39/2{sup {minus}},29/2{sup +}). The results show that level mixing spectroscopy is a promising technique to determine quadrupole moments of isomers that are difficult to measure by other in-beam hyperfine interaction methods. A large increase of the quadrupole moment is observed if neutrons are excited across or removed from the {ital N}=126 shell closure. This behavior is explained in terms of an enhanced core softness for fewer core neutrons; the aligned valence particles, moving in equatorial orbits, then easily polarize the core towards oblate deformation.

  20. Thermal Excitation of Gadolinium-Based Contrast Agents Using Spin Resonance

    PubMed Central

    Fridjhon, Peter; Rubin, David M.

    2016-01-01

    Theoretical and experimental investigations into the thermal excitation of liquid paramagnetic contrast agents using the spin resonance relaxation mechanism are presented. The electronic spin-lattice relaxation time τ1e of gadolinium-based contrast agents, which is estimated at 0.1 ns, is ten orders of magnitude faster than the relaxation time of protons in water. The shorter relaxation time is found to significantly increase the rate of thermal energy deposition. To the authors’ knowledge this is the first study of gadolinium based contrast agents in a liquid state used as thermal agents. Analysis shows that when τ1e and other experimental parameters are optimally selected, a maximum theoretical heating rate of 29.4 °C.s−1 could be achieved which would suffice for clinical thermal ablation of neoplasms. The experimental results show a statistically significant thermal response for two out of the four contrast agents tested. The results are compared to the simulated estimates via analysis of a detailed model of the system. While these experimentally determined temperature rises are small and thus of no clinical utility, their presence supports the theoretical analysis and strongly suggests that the chemical structure of the selected compounds plays an important role in this mechanism of heat deposition. There exists an opportunity for the development of alternative gadolinium-based compounds with an order of magnitude longer τ1e in a diluted form to be used as an efficient hyperthermia agent for clinical use. PMID:27341338

  1. Spin-lozenge thermodynamics and magnetic excitations in Na3RuO4

    SciTech Connect

    Haraldsen, Jason T; Stone, Matthew B; Lumsden, Mark D; Barnes, Ted {F E }; Jin, Rongying; Taylor, J. W.; Fernandez-Alonso, F

    2009-01-01

    We report inelastic and elastic neutron scattering, magnetic susceptibility, and heat capacity measurements of polycrystalline sodium ruthenate (Na3RuO4). Previous work suggests this material consists of isolated tetramers of S = 3/2 Ru5+ ions in a so-called lozenge configuration. Using a Heisenberg antiferromagnet Hamiltonian, we analytically determine the energy eigenstates for general spin S. From this model, the neutron scattering cross-sections for excitations associated with spin-3/2 tetramer configurations is determined. Comparison of magnetic susceptibility and inelastic neutron scattering results shows that the proposed lozenge model is not distinctly supported, but provides evidence that the system may be better described as a pair of non-interacting inequivalent dimers, i.e double dimers. However, the existence of long-range magnetic order below Tc ≈ 28 K immediately questions such a description. Although no evidence of the lozenge model is observed, future studies on single crystals may further clarify the appropriate magnetic Hamiltonian.

  2. Calculation of Vibrational and Electronic Excited-State Absorption Spectra of Arsenic-Water Complexes Using Density Functional Theory

    DTIC Science & Technology

    2016-06-03

    of Arsenic- Water Complexes Using Density Functional Theory June 3, 2016 Approved for public release; distribution is unlimited. L. Huang S.g...NUMBER OF PAGES 17. LIMITATION OF ABSTRACT Calculation of Vibrational and Electronic Excited-State Absorption Spectra of Arsenic- Water Complexes Using... water molecules should be associated with response features that are intermediate between that of isolated molecules and that of a bulk system. DFT and

  3. Singlet-Triplet Excitations in the Unconventional Spin-Peierls System TiOBr

    NASA Astrophysics Data System (ADS)

    Clancy, J. P.; Gaulin, B. D.; Adams, C. P.; Granroth, G. E.; Kolesnikov, A. I.; Sherline, T. E.; Chou, F. C.

    2011-03-01

    TiOBr belongs to a select group of quasi-one-dimensional materials which undergo a spin-Peierls (SP) phase transition and develop a dimerized singlet ground state at low temperatures. However, unlike conventional SP systems, TiOBr exhibits not one, but two successive phase transitions upon cooling: a continuous transition into an incommensurate SP state at TC 2 ~ 48 K, followed by a discontinuous transition into a commensurate SP state at TC 1 ~ 27 K. We have performed time-of-flight neutron scattering measurements on powder samples of TiOBr using the fine-resolution Fermi chopper spectrometer (SEQUOIA) at the Spallation Neutron Source. These measurements reveal two branches of magnetic excitations within the commensurate and incommensurate SP phases, which we associate with n = 1 and n = 2 triplet excitations out of the singlet ground state. This study represents the first direct measure of the singlet-triplet energy gap in TiOBr, which we have determined to be Eg = 21.2 +/- 1.0 meV.

  4. Orphan spin operators enable the acquisition of multiple 2D and 3D magic angle spinning solid-state NMR spectra

    NASA Astrophysics Data System (ADS)

    Gopinath, T.; Veglia, Gianluigi

    2013-05-01

    We propose a general method that enables the acquisition of multiple 2D and 3D solid-state NMR spectra for U-13C, 15N-labeled proteins. This method, called MEIOSIS (Multiple ExperIments via Orphan SpIn operatorS), makes it possible to detect four coherence transfer pathways simultaneously, utilizing orphan (i.e., neglected) spin operators of nuclear spin polarization generated during 15N-13C cross polarization (CP). In the MEIOSIS experiments, two phase-encoded free-induction decays are decoded into independent nuclear polarization pathways using Hadamard transformations. As a proof of principle, we show the acquisition of multiple 2D and 3D spectra of U-13C, 15N-labeled microcrystalline ubiquitin. Hadamard decoding of CP coherences into multiple independent spin operators is a new concept in solid-state NMR and is extendable to many other multidimensional experiments. The MEIOSIS method will increase the throughput of solid-state NMR techniques for microcrystalline proteins, membrane proteins, and protein fibrils.

  5. Characterization of photoluminescence spectra from poly allyl diglycol carbonate (CR-39) upon excitation with the ultraviolet radiation of various wavelengths

    NASA Astrophysics Data System (ADS)

    El Ghazaly, M.; Al-Thomali, Talal A.

    2013-04-01

    The induced photoluminescence (PL) from the π-conjugated polymer poly allyl diglycol carbonate (PADC) (CR-39) upon excitation with the ultraviolet radiation of different wavelengths was investigated. The absorption and attenuation coefficients of PADC (CR-39) were recorded using a UV-visible spectrometer. It was found that the absorption and attenuation coefficients of the PADC (CR-39) exhibit a strong dependence on the wavelength of ultraviolet radiation. The PL spectra were measured with a Flormax-4 spectrofluorometer (Horiba). PADC (CR-39) samples were excited by ultraviolet radiation with wavelengths in the range from 260 to 420 nm and the corresponding PL emission bands were recorded. The obtained results show a strong correlation between the PL and the excitation wavelength of ultraviolet radiation. The position of the fluorescence emission band peak was red shifted starting from 300 nm, which was increased with the increase in the excitation wavelength. The PL yield and its band peak height were increased with the increase in the excitation wavelength till 290 nm, thereafter they decreased exponentially with the increase in the ultraviolet radiation wavelength. These new findings should be considered carefully during the use of the PADC (CR-39) in the scientific applications and in using PADC (CR-39) in eyeglasses.

  6. Triplet excited state spectra and dynamics of carotenoids from the thermophilic purple photosynthetic bacterium Thermochromatium tepidum

    SciTech Connect

    Niedzwiedzki, Dariusz; Kobayashi, Masayuki; Blankenship, R. E.

    2011-01-13

    Light-harvesting complex 2 from the anoxygenic phototrophic purple bacterium Thermochromatium tepidum was purified and studied by steady-state absorption, fluorescence and flash photolysis spectroscopy. Steady-state absorption and fluorescence measurements show that carotenoids play a negligible role as supportive energy donors and transfer excitation to bacteriochlorophyll-a with low energy transfer efficiency of ~30%. HPLC analysis determined that the dominant carotenoids in the complex are rhodopin and spirilloxanthin. Carotenoid excited triplet state formation upon direct (carotenoid) or indirect (bacteriochlorophyll-a Q{sub x} band) excitation shows that carotenoid triplets are mostly localized on spirilloxanthin. In addition, no triplet excitation transfer between carotenoids was observed. Such specific carotenoid composition and spectroscopic results strongly suggest that this organism optimized carotenoid composition in the light-harvesting complex 2 in order to maximize photoprotective capabilities of carotenoids but subsequently drastically suppressed their supporting role in light-harvesting process.

  7. How to Collect National Institute of Standards and Technology (NIST) Traceable Fluorescence Excitation and Emission Spectra.

    PubMed

    Gilmore, Adam Matthew

    2014-01-01

    Contemporary spectrofluorimeters comprise exciting light sources, excitation and emission monochromators, and detectors that without correction yield data not conforming to an ideal spectral response. The correction of the spectral properties of the exciting and emission light paths first requires calibration of the wavelength and spectral accuracy. The exciting beam path can be corrected up to the sample position using a spectrally corrected reference detection system. The corrected reference response accounts for both the spectral intensity and drift of the exciting light source relative to emission and/or transmission detector responses. The emission detection path must also be corrected for the combined spectral bias of the sample compartment optics, emission monochromator, and detector. There are several crucial issues associated with both excitation and emission correction including the requirement to account for spectral band-pass and resolution, optical band-pass or neutral density filters, and the position and direction of polarizing elements in the light paths. In addition, secondary correction factors are described including (1) subtraction of the solvent's fluorescence background, (2) removal of Rayleigh and Raman scattering lines, as well as (3) correcting for sample concentration-dependent inner-filter effects. The importance of the National Institute of Standards and Technology (NIST) traceable calibration and correction protocols is explained in light of valid intra- and interlaboratory studies and effective spectral qualitative and quantitative analyses including multivariate spectral modeling.

  8. Investigation on the spectral properties of 2D asynchronous fluorescence spectra generated by using variable excitation wavelengths as a perturbation

    NASA Astrophysics Data System (ADS)

    Wang, Jingdan; He, Anqi; Guo, Ran; Wei, Yongju; Feng, Juan; Xu, Yizhuang; Noda, Isao; Wu, Jinguang

    2016-11-01

    Properties of 2D asynchronous spectra generated from a series of fluorescence emission spectra are investigated. Variable excitation wavelengths are utilized as an external perturbation. Based on the results of mathematical analysis and computer simulation, we find that no cross peak will be produced on the 2D asynchronous spectrum if the fluorescent solute under investigation occurs in a single micro-environment. The observation of cross peaks implies that the fluorescent molecule may occur in different micro-environments in a solution. Based on these results, we use 2D asynchronous spectra to investigate the emission spectra of anthracene dissolved in cyclohexane. When the concentration of anthracene is low, no cross peak is produced in the resultant 2D asynchronous spectrum, confirming that anthracene is dissolved as single molecule in the solution. As the concentration elevated, cross peaks appear in the corresponding 2D asynchronous spectra. A plausible explanation of this phenomenon is that anthracene may undergo aggregation via π-π interaction or π-C-H interaction.

  9. Excitation of Self-Localized Spin-Wave Bullets by Spin-Polarized Current in In-Plane Magnetized Magnetic Nano-Contacts: A Micromagnetic Study

    DTIC Science & Technology

    2007-10-08

    self- localized nonlinear bullet mode: large precession angle, strong spatial localization, and low frequency below the fer- romagnetic resonance FMR ...bullet mode with the fre- quency lower than the FMR frequency of the free layer is excited, in full agreement with the results of previous simulations...through it is varied. FORMULATION OF THE PROBLEM We studied current-induced spin-wave dynamics in a magnetic multilayered system consisting of a thick

  10. Calculations of the electronic levels, spin-Hamiltonian parameters and vibrational spectra for the CrCl3 layered crystals

    NASA Astrophysics Data System (ADS)

    Avram, C. N.; Gruia, A. S.; Brik, M. G.; Barb, A. M.

    2015-12-01

    Calculations of the Cr3+ energy levels, spin-Hamiltonian parameters and vibrational spectra for the layered CrCl3 crystals are reported for the first time. The crystal field parameters and the energy level scheme were calculated in the framework of the Exchange Charge Model of crystal field. The spin-Hamiltonian parameters (zero-field splitting parameter D and g-factors) for Cr3+ ion in CrCl3 crystals were obtained using two independent techniques: i) semi-empirical crystal field theory and ii) density functional theory (DFT)-based model. In the first approach, the spin-Hamiltonian parameters were calculated from the perturbation theory method and the complete diagonalization (of energy matrix) method. The infrared (IR) and Raman frequencies were calculated for both experimental and fully optimized geometry of the crystal structure, using CRYSTAL09 software. The obtained results are discussed and compared with the experimental available data.

  11. Raman electron spin-lattice relaxation with the Debye-type and with real phonon spectra in crystals

    NASA Astrophysics Data System (ADS)

    Hoffmann, Stanislaw K.; Lijewski, Stefan

    2013-02-01

    Electron spin-lattice relaxation temperature dependence was measured for Ti2+ (S = 1) and for Cu2+ (S = 1/2) ions in SrF2 single crystal by electron spin echo method in temperature range 4-109 K. The spin relaxation was governed by the two-phonon Raman processes. The relaxation theory is outlined and presented in a form suitable for applying with real phonon spectra. The experimental relaxation results were described using Debye-type phonon spectrum and the real phonon spectrum of SrF2 crystal. The Debye approximation does not fit well the results for SrF2 both at low and at high temperature. The relaxation rate is faster than that predicted by Debye-type phonon spectrum at low temperatures where excess of lattice vibrations over the Debye model exists but is slower at higher temperatures (above 50 K) where density of phonon states continuously decreases when approaching to the maximal acoustic phonon frequency. The expected deviation from Debye approximation was analyzed also for Cu2+ in NaCl and MgSiO3 crystals for which phonon spectra are available. The fitting with the real phonon spectrum allowed us to calculate spin-phonon coupling parameter as 267 cm-1 for Ti2+ and 1285 cm-1 for Cu2+ in SrF2.

  12. The mutable nature of particle-core excitations with spin in the one-valence-proton nucleus 133Sb

    NASA Astrophysics Data System (ADS)

    Bocchi, G.; Leoni, S.; Fornal, B.; Colò, G.; Bortignon, P. F.; Bottoni, S.; Bracco, A.; Michelagnoli, C.; Bazzacco, D.; Blanc, A.; de France, G.; Jentschel, M.; Köster, U.; Mutti, P.; Régis, J.-M.; Simpson, G.; Soldner, T.; Ur, C. A.; Urban, W.; Fraile, L. M.; Lozeva, R.; Belvito, B.; Benzoni, G.; Bruce, A.; Carroll, R.; Cieplicka-Oryǹczak, N.; Crespi, F. C. L.; Didierjean, F.; Jolie, J.; Korten, W.; Kröll, T.; Lalkovski, S.; Mach, H.; Mărginean, N.; Melon, B.; Mengoni, D.; Million, B.; Nannini, A.; Napoli, D.; Olaizola, B.; Paziy, V.; Podolyák, Zs.; Regan, P. H.; Saed-Samii, N.; Szpak, B.; Vedia, V.

    2016-09-01

    The γ-ray decay of excited states of the one-valence-proton nucleus 133Sb has been studied using cold-neutron induced fission of 235U and 241Pu targets, during the EXILL campaign at the ILL reactor in Grenoble. By using a highly efficient HPGe array, coincidences between γ-rays prompt with the fission event and those delayed up to several tens of microseconds were investigated, allowing to observe, for the first time, high-spin excited states above the 16.6 μs isomer. Lifetimes analysis, performed by fast-timing techniques with LaBr3(Ce) scintillators, revealed a difference of almost two orders of magnitude in B(M1) strength for transitions between positive-parity medium-spin yrast states. The data are interpreted by a newly developed microscopic model which takes into account couplings between core excitations (both collective and non-collective) of the doubly magic nucleus 132Sn and the valence proton, using the Skyrme effective interaction in a consistent way. The results point to a fast change in the nature of particle-core excitations with increasing spin.

  13. Cooling a mechanical resonator with nitrogen-vacancy centres using a room temperature excited state spin-strain interaction

    NASA Astrophysics Data System (ADS)

    Macquarrie, E. R.; Otten, M.; Gray, S. K.; Fuchs, G. D.

    2017-02-01

    Cooling a mechanical resonator mode to a sub-thermal state has been a long-standing challenge in physics. This pursuit has recently found traction in the field of optomechanics in which a mechanical mode is coupled to an optical cavity. An alternate method is to couple the resonator to a well-controlled two-level system. Here we propose a protocol to dissipatively cool a room temperature mechanical resonator using a nitrogen-vacancy centre ensemble. The spin ensemble is coupled to the resonator through its orbitally-averaged excited state, which has a spin-strain interaction that has not been previously studied. We experimentally demonstrate that the spin-strain coupling in the excited state is 13.5+/-0.5 times stronger than the ground state spin-strain coupling. We then theoretically show that this interaction, combined with a high-density spin ensemble, enables the cooling of a mechanical resonator from room temperature to a fraction of its thermal phonon occupancy.

  14. Excitation spectra of unconventional FQHE states in the SLL from Light Scattering Experiments

    NASA Astrophysics Data System (ADS)

    Wurstbauer, Ursula; Levy, Antonio; Pinczuk, Aron; Watson, John; Gardner, Geoff; Manfra, Michael; West, Ken; Pfeiffer, Loren

    The fascinating interaction physics in the second Landau level (SLL) supports the emergence of exotic quantum phases and unconventional possibly FQHE states such as e.g. at ν = 5/2 and 2 +1/3 and the weaker state at ν = 2 +3/8 and 2 +2/5. We observe clear signatures for gapped collective excitations in inelastic light scattering experiments just for these `magic' filling factors and only for low temperatures substantiating access to the physics of the incompressible quantum fluids. The lowest excitation feature in the spectrum at 2 +1/3 occurs at around 70 μeV. The analysis of spectral lineshapes suggests magnetoroton features that are characteristic of 2D neutral excitations in a perpendicular magnetic field. The striking polarization dependence observable in light scattering experiments in the SLL are consistent with nematic FQHE states. Supported by award NSF-DMR-1306976.

  15. Calculation of Nuclear Level Density Parameters of Some Light Deformed Medical Radionuclides Using Collective Excitation Modes of Observed Nuclear Spectra

    NASA Astrophysics Data System (ADS)

    Okuducu, Ş.; Akti, N. N.; Saraç, H.; Bölükdemir, M. H.; Tel, E.

    In this study the nuclear energy level density based on nuclear collective excitation mechanism has been identified in terms of the low-lying collective level bands near the neutron binding energy. Nuclear level density parameters of some light deformed medical radionuclides used widely in medical applications have been calculated by using different collective excitation modes of observed nuclear spectra. The calculated parameters have been used successfully in estimation of the neutron-capture cross section basic data for the production of new medical radionuclides. The investigated radionuclides have been considered in the region of mass number 40

  16. Electron-hole excitations and optical spectra of bulk SrO from many-body perturbation theory

    NASA Astrophysics Data System (ADS)

    Pan, Bo; Wang, Neng-Ping; Rohlfing, Michael

    2015-08-01

    This paper reports the quasiparticle band structure and the optical absorption spectrum of SrO, using many-body perturbation theory. The quasiparticle band structure is calculated within the GW approximation. Taking the electron-hole interaction into consideration, electron-hole pair states and optical excitations are obtained by solving the Bethe-Salpeter equation for the electron-hole two-particle Green function. The calculated band gap for SrO is 6.0 eV, which is in good agreement with the corresponding experimental results. The theoretical result of optical absorption spectrum for SrO is also in close agreement with the experimental data. In particular, the calculated excitation energy for the lowest exciton peak in the optical absorption spectra of SrO reproduces very well the corresponding experimental result.

  17. Nuclear response theory for spin-isospin excitations in a relativistic quasiparticle-phonon coupling framework

    NASA Astrophysics Data System (ADS)

    Robin, Caroline; Litvinova, Elena

    2016-07-01

    A new theoretical approach to spin-isospin excitations in open-shell nuclei is presented. The developed method is based on the relativistic meson-exchange nuclear Lagrangian of Quantum Hadrodynamics and extends the response theory for superfluid nuclear systems beyond relativistic quasiparticle random phase approximation in the proton-neutron channel (pn-RQRPA). The coupling between quasiparticle degrees of freedom and collective vibrations (phonons) introduces a time-dependent effective interaction, in addition to the exchange of pion and ρ -meson taken into account without retardation. The time-dependent contributions are treated in the resonant time-blocking approximation, in analogy to the previously developed relativistic quasiparticle time-blocking approximation (RQTBA) in the neutral (non-isospin-flip) channel. The new method is called proton-neutron RQTBA (pn-RQTBA) and is applied to the Gamow-Teller resonance in a chain of neutron-rich nickel isotopes 68-78Ni . A strong fragmentation of the resonance along with quenching of the strength, as compared to pn-RQRPA, is obtained. Based on the calculated strength distribution, beta-decay half-lives of the considered isotopes are computed and compared to pn-RQRPA half-lives and to experimental data. It is shown that a considerable improvement of the half-life description is obtained in pn-RQTBA because of the spreading effects, which bring the lifetimes to a very good quantitative agreement with data.

  18. Correlation between electron spin resonance spectra and oil yield in eastern oil shales

    USGS Publications Warehouse

    Choudhury, M.; Rheams, K.F.; Harrell, J.W.

    1986-01-01

    Organic free radical spin concentrations were measured in 60 raw oil shale samples from north Alabama and south Tennessee and compared with Fischer assays and uranium concentrations. No correlation was found between spin concentration and oil yield for the complete set of samples. However, for a 13 sample set taken from a single core hole, a linear correlation was obtained. No correlation between spin concentration and uranium concentration was found. ?? 1986.

  19. Measurement of Excitation Spectra in the 12/SUP>C 1(p ,d ) Reaction near the η' Emission Threshold

    NASA Astrophysics Data System (ADS)

    Tanaka, Y. K.; Itahashi, K.; Fujioka, H.; Ayyad, Y.; Benlliure, J.; Brinkmann, K.-T.; Friedrich, S.; Geissel, H.; Gellanki, J.; Guo, C.; Gutz, E.; Haettner, E.; Harakeh, M. N.; Hayano, R. S.; Higashi, Y.; Hirenzaki, S.; Hornung, C.; Igarashi, Y.; Ikeno, N.; Iwasaki, M.; Jido, D.; Kalantar-Nayestanaki, N.; Kanungo, R.; Knöbel, R.; Kurz, N.; Metag, V.; Mukha, I.; Nagae, T.; Nagahiro, H.; Nanova, M.; Nishi, T.; Ong, H. J.; Pietri, S.; Prochazka, A.; Rappold, C.; Reiter, M. P.; Rodríguez-Sánchez, J. L.; Scheidenberger, C.; Simon, H.; Sitar, B.; Strmen, P.; Sun, B.; Suzuki, K.; Szarka, I.; Takechi, M.; Tanihata, I.; Terashima, S.; Watanabe, Y. N.; Weick, H.; Widmann, E.; Winfield, J. S.; Xu, X.; Yamakami, H.; Zhao, J.; η-PRiME/Super-FRS Collaboration

    2016-11-01

    Excitation spectra of 11C are measured in the 12C (p ,d ) reaction near the η' emission threshold. A proton beam extracted from the synchrotron SIS-18 at GSI with an incident energy of 2.5 GeV impinges on a carbon target. The momenta of deuterons emitted at 0° are precisely measured with the fragment separator (FRS) operated as a spectrometer. In contrast to theoretical predictions on the possible existence of deeply bound η'-mesic states in carbon nuclei, no distinct structures are observed associated with the formation of bound states. The spectra are analyzed to set stringent constraints on the formation cross section and on the hitherto barely known η'-nucleus interaction.

  20. Effect of nearest-neighbor ions on excited ionic states, emission spectra, and line profiles in hot and dense plasmas

    NASA Technical Reports Server (NTRS)

    Salzmann, D.; Stein, J.; Goldberg, I. B.; Pratt, R. H.

    1991-01-01

    The effect of the cylindrical symmetry imposed by the nearest-neighbor ions on the ionic levels and the emission spectra of a Li-like Kr ion immersed in hot and dense plasmas is investigated using the Stein et al. (1989) two-centered model extended to include computations of the line profiles, shifts, and widths, as well as the energy-level mixing and the forbidden transition probabilities. It is shown that the cylindrical symmetry mixes states with different orbital quantum numbers l, particularly for highly excited states, and, thereby, gives rise to forbidden transitions in the emission spectrum. Results are obtained for the variation of the ionic level shifts and mixing coefficients with the distance to the nearest neighbor. Also obtained are representative computed spectra that show the density effects on the spectral line profiles, shifts, and widths, and the forbidden components in the spectrum.

  1. One- and two-photon photoluminescence excitation spectra of CdTe quantum dots in a cryogenic confocal microscopy platform.

    PubMed

    Almeida, Diogo B; de Thomaz, André A; Carvalho, Hernandes F; Cesar, Carlos L

    2015-07-27

    In this work we describe a method to obtain photoluminescente excitation spectra, through one and two photon absorption, of CdTe quantum dots, based on a confocal microscope platform. This system becomes an analytical multipurpose characterization platform with spatial, and spectral resolution with temperature control. The capabilities of such platform were demonstrated by photoluminescence and second harmonic generation spectra acquisition as a function of temperature from 10 K to room temperature. The differences for one and two photons transition selection rules between the quantum dot confined levels provide access to intra and inter band, forbidden in one photon transitions, information that could be used to validate confinement models. The results agree well with the transition selection rules calculated with a parabolic model.

  2. Effect of Fermi surface nesting on resonant spin excitations in Ba(1-x)K(x)Fe2As2.

    PubMed

    Castellan, J-P; Rosenkranz, S; Goremychkin, E A; Chung, D Y; Todorov, I S; Kanatzidis, M G; Eremin, I; Knolle, J; Chubukov, A V; Maiti, S; Norman, M R; Weber, F; Claus, H; Guidi, T; Bewley, R I; Osborn, R

    2011-10-21

    We report inelastic neutron scattering measurements of the resonant spin excitations in Ba(1-x)K(x)Fe(2)As(2) over a broad range of electron band filling. The fall in the superconducting transition temperature with hole doping coincides with the magnetic excitations splitting into two incommensurate peaks because of the growing mismatch in the hole and electron Fermi surface volumes, as confirmed by a tight-binding model with s(±)-symmetry pairing. The reduction in Fermi surface nesting is accompanied by a collapse of the resonance binding energy and its spectral weight, caused by the weakening of electron-electron correlations.

  3. Angle-resolved photoemission spectra, electronic structure and spin dependent scattering in Ni_1-xFex permalloys

    NASA Astrophysics Data System (ADS)

    Sahrakorpi, S.; Mijnarends, P. E.; Lindroos, M.; Bansil, A.

    2002-03-01

    We present the all electron charge and spin self-consistent electronic structure of Ni_1-xFex permalloys for a range of Fe concentrations, using the first principles Korringa-Kohn-Rostoker coherent potential approximation (KKR-CPA) scheme to treat disorder and the local spin density (LSD) approximation to incorporate exchange-correlation effects. Recent high resolution angle-resolved photoemission spectroscopy (ARPES) experiments on Ni_0.90Fe_0.10 and Ni_0.80Fe_0.20 permalloys are analyzed in terms of the spectral density function, A_B( k_allel, k_⊥= 0,E_F), computed from the KKR-CPA Green function for k_allel values varying along the Γ-K direction in the Brillouin zone (BZ). The widths of the majority as well as the minority spin peaks in the theoretical spectra are in excellent accord with the corresponding ARPES results in all cases, suggesting that spin-dependent disorder scattering constitutes the main scattering mechanism for the carriers in the permalloys. Majority spin states of Ni are virtually undamped by the Fe impurities, while the minority spins at the Fermi energy (E_F) are heavily damped. The nature of the Ni and Fe potentials in the permalloys is explored in detail. The effective disorder parameter in the alloy is found to be strongly dependent on the energy, momentum, spin and symmetry of the specific states involved. The evolution of the electronic states on the Ni and Fe sites as a function of Fe concentration is discussed. The magnetic moments on Ni as well as on Fe are found to remain essentially unchanged with increasing Fe content.

  4. Adsorption geometry and core excitation spectra of three phenylpropene isomers on Cu(111)

    SciTech Connect

    Kolczewski, C.; Williams, F. J.; Cropley, R. L.; Vaughan, O. P. H.; Urquhart, A. J.; Tikhov, M. S.; Lambert, R. M.; Hermann, K.

    2006-07-21

    Theoretical C 1s near edge x-ray absorption fine structure (NEXAFS) spectra for the C{sub 9}H{sub 10} isomers trans-methylstyrene, {alpha}-methylstyrene, and allylbenzene in gas phase and adsorbed at Cu(111) surfaces have been obtained from density functional theory calculations where adsorbate geometries were determined by corresponding total energy optimizations. The three species show characteristic differences in widths and peak shapes of the lowest C 1s{yields}{pi}* transitions which are explained by different coupling of the {pi}-electron system of the C{sub 6} ring with that of the side chain in the molecules as well as by the existence of nonequivalent carbon centers. The adsorbed molecules bind only weakly with the substrate which makes the use of theoretical NEXAFS spectra of the oriented free molecules meaningful for an interpretation of experimental angle-resolved NEXAFS spectra of the adsorbate systems obtained in this work. However, a detailed quantitative account of relative peak intensities requires theoretical angle-resolved NEXAFS spectra of the complete adsorbate systems which have been evaluated within the surface cluster approach. The comparison with experiment yields almost perfect agreement and confirms the reliability of the calculated equilibrium geometries of the adsorbates. This can help to explain observed differences in the catalytic epoxidation of the three molecules on Cu(111) based on purely geometric considerations.

  5. Raman spectra of normal and cancerous mouse mammary gland tissue using near infrared excitation energy

    NASA Astrophysics Data System (ADS)

    Naik, Vaman; Serhatkulu, G. K.; Dai, H.; Shukla, N.; Weber, R.; Thakur, J. S.; Freeman, D. C.; Pandya, A. K.; Auner, G. W.; Naik, R.; Miller, R. F.; Cao, A.; Klein, M. D.; Rabah, R.

    2006-03-01

    Raman spectra of normal mammary gland tissues, malignant mammary gland tumors, and lymph nodes have been recorded using fresh tissue from mice. Tumors were induced in mice by subcutaneously injecting 4T1 BALB/c mammary tumor (a highly malignant) cell line. The Raman spectra were collected using the same tissues that were examined by histopathology for determining the cancerous/normal state of the tissue. Differences in various peak intensities, peak shifts and peak ratios were analyzed to determine the Raman spectral features that differentiate mammary gland tumors from non-tumorous tissue. Tissues that were confirmed by pathology as cancerous (tumors) show several distinctive features in the Raman spectra compared to the spectra of the normal tissues. For example, the cancerous tissues show Raman peaks at 621, 642, 1004, 1032, 1175 and 1208 cm-1 that are assignable to amino acids containing aromatic side-chains such as phenylalanine, tryptophan and tyrosine. Further, the cancerous tissues show a greatly reduced level of phospholipids compared to the normal tissues. The Raman spectral regions that are sensitive to pathologic alteration in the tissue will be discussed.

  6. Persistent narrowing of nuclear-spin fluctuations in InAs quantum dots using laser excitation.

    PubMed

    Sun, Bo; Chow, Colin Ming Earn; Steel, Duncan G; Bracker, Allan S; Gammon, Daniel; Sham, L J

    2012-05-04

    We demonstrate the suppression of nuclear-spin fluctuations in an InAs quantum dot and measure the timescales of the spin narrowing effect. By initializing for tens of milliseconds with two continuous wave diode lasers, fluctuations of the nuclear spins are suppressed via the hole-assisted dynamic nuclear polarization feedback mechanism. The fluctuation narrowed state persists in the dark (absent light illumination) for well over 1 s even in the presence of a varying electron charge and spin polarization. Enhancement of the electron spin coherence time (T2*) is directly measured using coherent dark state spectroscopy. By separating the calming of the nuclear spins in time from the spin qubit operations, this method is much simpler than the spin echo coherence recovery or dynamic decoupling schemes.

  7. Floquet-Magnus expansion for general N-coupled spins systems in magic-angle spinning nuclear magnetic resonance spectra

    NASA Astrophysics Data System (ADS)

    Mananga, Eugene Stephane; Charpentier, Thibault

    2015-04-01

    In this paper we present a theoretical perturbative approach for describing the NMR spectrum of strongly dipolar-coupled spin systems under fast magic-angle spinning. Our treatment is based on two approaches: the Floquet approach and the Floquet-Magnus expansion. The Floquet approach is well known in the NMR community as a perturbative approach to get analytical approximations. Numerical procedures are based on step-by-step numerical integration of the corresponding differential equations. The Floquet-Magnus expansion is a perturbative approach of the Floquet theory. Furthermore, we address the " γ -encoding" effect using the Floquet-Magnus expansion approach. We show that the average over " γ " angle can be performed for any Hamiltonian with γ symmetry.

  8. Spin excitation spectrum in a magnetic nanodot with continuous transitions between the vortex, Bloch-type skyrmion, and Néel-type skyrmion states

    NASA Astrophysics Data System (ADS)

    Mruczkiewicz, M.; Krawczyk, M.; Guslienko, K. Y.

    2017-03-01

    We study spin-wave excitations in a circular ferromagnetic nanodot in different inhomogeneous, topologically nontrivial magnetization states, specifically, vortex and skyrmion states. Gradual change in the strength of the out-of-plane magnetic anisotropy and the Dzyaloshinskii-Moriya exchange interaction leads to continuous phase transitions between different stable magnetic configurations and allows for mapping of dynamic spin modes in and between the vortex, Bloch-type skyrmion, and Néel-type skyrmion states. Our study elucidates the connections between gyrotropic modes, azimuthal spin waves, and breathing modes in these various stable magnetization states and helps us to understand the rich spin excitation spectrum on the skyrmion background.

  9. Sensitive marker bands for the detection of spin states of heme in surface-enhanced resonance Raman scattering spectra of metmyoglobin.

    PubMed

    Kitahama, Yasutaka; Egashira, Masatoshi; Suzuki, Toshiaki; Tanabe, Ichiro; Ozaki, Yukihiro

    2014-12-21

    Surface-enhanced resonance Raman scattering (SERRS) spectra of myoglobin (Mb) with various ligands were measured. In the resonance Raman scattering (RRS) spectra, peaks at around 1610 and 1640 cm(-1) have so far been used to discriminate between the heme iron in a high or low spin state. In the SERRS spectra, however, the spin state cannot be distinguished by the corresponding peaks. Alternatively, the intensity ratio of the SERRS peak at 1560 cm(-1) to that at 1620 cm(-1) was applied to detect the spin states sensitively (1.5 × 10(5) times compared with the RRS); namely, a high ratio was obtained from met-Mb in the high spin state at pH ≤ 7 except for in a strong acid solution. The different marker bands between the SERRS and RRS spectra may be due to the enhancement order from the surface selection rule.

  10. Multiplasmon excitations in electron spectra of small systems irradiated by swift charged projectiles

    NASA Astrophysics Data System (ADS)

    Dinh, Phuong Mai; Reinhard, Paul-Gerhard; Suraud, Eric; Wopperer, Philipp

    2015-02-01

    We investigate the kinetic-energy spectrum of electrons emitted from an excited many-electron system, often called photo-electron spectrum (PES). We are particularly interested on the impact of resonant modes of the system on PES. To this end, we consider three systems with strong resonances, a Mg atom, the small alkaline cluster K9+, and the small carbon chain C3. To avoid dominant frequencies in the excitation process, we consider a collision with a fast ion which is realized by an instantaneous boost of the valence electrons, a process which excites all frequencies with equal weight. The electron dynamics is investigated from a theoretical perspective using time-dependent density-functional theory augmented by an average-density self-interaction correction. We observe patterns which are similar to PES usually obtained after irradiation by a laser pulse, in particular the appearance of clear peaks. We show that these patterns are driven by strong resonance modes of the system. Resonances are thus found to be another source of peaks in the PES, besides photons (when present) with definite frequencies.

  11. Multiplasmon excitations in electron spectra of small systems irradiated by swift charged projectiles

    NASA Astrophysics Data System (ADS)

    Dinh, Phuong Mai; Reinhard, Paul-Gerhard; Suraud, Eric; Wopperer, Philipp

    2015-02-01

    We investigate the kinetic-energy spectrum of electrons emitted from an excited many-electron system, often called photo-electron spectrum (PES). We are particularly interested on the impact of resonant modes of the system on PES. To this end, we consider three systems with strong resonances, a Mg atom, the small alkaline cluster K9 +, and the small carbon chain C3. To avoid dominant frequencies in the excitation process, we consider a collision with a fast ion which is realized by an instantaneous boost of the valence electrons, a process which excites all frequencies with equal weight. The electron dynamics is investigated from a theoretical perspective using time-dependent density-functional theory augmented by an average-density self-interaction correction. We observe patterns which are similar to PES usually obtained after irradiation by a laser pulse, in particular the appearance of clear peaks. We show that these patterns are driven by strong resonance modes of the system. Resonances are thus found to be another source of peaks in the PES, besides photons (when present) with definite frequencies.

  12. Energy spectra of 2D gravity and capillary waves with narrow frequency band excitation

    NASA Astrophysics Data System (ADS)

    Kartashova, E.

    2012-02-01

    In this letter we present a new method, called increment chain equation method (ICEM), for computing a cascade of distinct modes in a two-dimensional weakly nonlinear wave system generated by narrow frequency band excitation. The ICEM is a means for computing the quantized energy spectrum as an explicit function of frequency ω0 and stationary amplitude A0 of excitation. The physical mechanism behind the generation of the quantized cascade is modulation instability. The ICEM can be used in numerous 2D weakly nonlinear wave systems with narrow frequency band excitation appearing in hydrodynamics, nonlinear optics, electrodynamics, convection theory etc. In this letter the ICEM is demonstrated with examples of gravity and capillary waves with dispersion functions ω(k)~k1/2 and ω(k)~k3/2, respectively, and for two different levels of nonlinearity ɛ=A0k0: small (ɛ~0.1 to 0.25) and moderate (ɛ~0.25 to 0.4).

  13. Half-quantum vortex state and its excitations in a spin-orbit coupled spinor Bose-Einstein condensate

    NASA Astrophysics Data System (ADS)

    Ramachandhran, B.; Opanchuk, Bogdan; Liu, Xia-Ji; Pu, Han; Hu, Hui

    2012-02-01

    We investigate theoretically the condensate state and collective excitations of a spin-orbit coupled spinor Bose gas in two-dimensional harmonic traps. In the weakly interacting regime, when the inter-species interaction is larger than the intra-species interaction (g> g), we find that the condensate state has a half-quantum-angular-momentum vortex configuration (half-vortex state) with spatial rotational symmetry and skyrmion-type spin texture. We investigate the stability of half-vortex state in the regime when g is greater than a threshold gc, and in the regime when g< g, by solving the Bogoliubov equations for collective density oscillations. In addition, we also investigate the dynamical properties of the half-vortex state. We present the phase diagram as a function of interatomic interaction and spin-orbit coupling.

  14. From atomistic modeling to excitation transfer and two-dimensional spectra of the FMO light-harvesting complex

    PubMed Central

    Olbrich, Carsten; Jansen, Thomas L. C.; Liebers, Jörg; Aghtar, Mortaza; Strümpfer, Johan; Schulten, Klaus; Knoester, Jasper; Kleinekathöfer, Ulrich

    2011-01-01

    The experimental observation of long-lived quantum coherences in the Fenna-Matthews-Olson (FMO) light-harvesting complex at low temperatures has challenged general intuition in the field of complex molecular systems and provoked considerable theoretical effort in search for explanations. Here we report on room-temperature calculations of the excited-state dynamics in FMO using a combination of molecular dynamics simulations and electronic structure calculations. Thus we obtain trajectories for the Hamiltonian of this system which contains time-dependent vertical excitation energies of the individual bacteriochlorophyll molecules and their mutual electronic couplings. The distribution of energies and couplings are analyzed together with possible spatial correlations. It is found that in contrast to frequent assumptions the site energy distribution is non-Gaussian. In a subsequent step, averaged wave packet dynamics is used to determine the exciton dynamics in the system. Finally, with the time-dependent Hamiltonian linear and two-dimensional spectra are determined. The thus obtained linear absorption lineshape agrees well with experimental observation and is largely determined by the non-Gaussian site energy distribution. The two-dimensional spectra are in line with what one would expect by extrapolation of the experimental observations at lower temperatures and indicate almost total loss of long-lived coherences. PMID:21635010

  15. Doping dependence of the spin excitations in the Fe-based superconductors Fe1+yTe1-xSex

    NASA Astrophysics Data System (ADS)

    Christianson, A. D.; Lumsden, M. D.; Marty, K.; Wang, C. H.; Calder, S.; Abernathy, D. L.; Stone, M. B.; Mook, H. A.; McGuire, M. A.; Sefat, A. S.; Sales, B. C.; Mandrus, D.; Goremychkin, E. A.

    2013-06-01

    The Fe1+yTe1-xSex series of materials is one of the prototype families of Fe-based superconductors. To provide further insight into these materials, we present systematic inelastic neutron scattering measurements of the low-energy spin excitations for x=0.27, 0.36, 0.40, and 0.49. These measurements show an evolution of incommensurate spin excitations towards the (1/2,1/2,0) wave vector with doping. Concentrations (x=0.40 and 0.49) which exhibit the most robust superconducting properties have spin excitations closest to (1/2,1/2,0) and also exhibit a strong spin resonance in the spin excitation spectrum below Tc. The resonance signal appears to be closer to (1/2,1/2,0) than the underlying spin excitations. We discuss the possible relationship between superconductivity and spin excitations at the (1/2,1/2,0) wave vector and the role that interstitial Fe may play.

  16. Multi-angle Spectra Evolution of Langmuir Turbulence Excited by RF Ionospheric Interactions at HAARP

    NASA Astrophysics Data System (ADS)

    Sheerin, J. P.; Rayyan, N.; Watkins, B. J.; Bristow, W. A.; Spaleta, J.; Watanabe, N.; Golkowski, M.; Bernhardt, P. A.

    2013-12-01

    The high power HAARP HF transmitter is employed to generate and study strong Langmuir turbulence (SLT) in the interaction region of overdense ionospheric plasma. Diagnostics included the Modular UHF Ionospheric Radar (MUIR) sited at HAARP, the SuperDARN-Kodiak HF radar, and HF receivers to record stimulated electromagnetic emissions (SEE). Dependence of diagnostic signals on HAARP HF parameters, including pulselength, duty-cycle, aspect angle, and frequency were recorded. Short pulse, low duty cycle experiments demonstrate control of artificial field-aligned irregularities (AFAI) and isolation of ponderomotive effects. Among the effects observed and studied are: SLT spectra including cascade, collapse, and co-existence spectra and an outshifted plasma line under certain ionospheric conditions. High time resolution studies of the temporal evolution of the plasma line reveal the appearance of an overshoot effect on ponderomotive timescales. Bursty turbulence is observed in the collapse and cascade lines. For the first time, simultaneous multi-angle radar measurements of plasma line spectra are recorded demonstrating marked dependence on aspect angle with the strongest interaction region observed displaced southward of the HF zenith pointing angle. Numerous measurements of the outshifted plasma line are observed. Experimental results are compared to previous high latitude experiments and predictions from recent modeling efforts.

  17. On the truncation of the number of excited states in density functional theory sum-over-states calculations of indirect spin spin coupling constants

    NASA Astrophysics Data System (ADS)

    Zarycz, M. Natalia C.; Provasi, Patricio F.; Sauer, Stephan P. A.

    2015-12-01

    It is investigated, whether the number of excited (pseudo)states can be truncated in the sum-over-states expression for indirect spin-spin coupling constants (SSCCs), which is used in the Contributions from Localized Orbitals within the Polarization Propagator Approach and Inner Projections of the Polarization Propagator (IPPP-CLOPPA) approach to analyzing SSCCs in terms of localized orbitals. As a test set we have studied the nine simple compounds, CH4, NH3, H2O, SiH4, PH3, SH2, C2H2, C2H4, and C2H6. The excited (pseudo)states were obtained from time-dependent density functional theory (TD-DFT) calculations with the B3LYP exchange-correlation functional and the specialized core-property basis set, aug-cc-pVTZ-J. We investigated both how the calculated coupling constants depend on the number of (pseudo)states included in the summation and whether the summation can be truncated in a systematic way at a smaller number of states and extrapolated to the total number of (pseudo)states for the given one-electron basis set. We find that this is possible and that for some of the couplings it is sufficient to include only about 30% of the excited (pseudo)states.

  18. On the truncation of the number of excited states in density functional theory sum-over-states calculations of indirect spin spin coupling constants

    SciTech Connect

    Zarycz, M. Natalia C. Provasi, Patricio F.; Sauer, Stephan P. A.

    2015-12-28

    It is investigated, whether the number of excited (pseudo)states can be truncated in the sum-over-states expression for indirect spin-spin coupling constants (SSCCs), which is used in the Contributions from Localized Orbitals within the Polarization Propagator Approach and Inner Projections of the Polarization Propagator (IPPP-CLOPPA) approach to analyzing SSCCs in terms of localized orbitals. As a test set we have studied the nine simple compounds, CH{sub 4}, NH{sub 3}, H{sub 2}O, SiH{sub 4}, PH{sub 3}, SH{sub 2}, C{sub 2}H{sub 2}, C{sub 2}H{sub 4}, and C{sub 2}H{sub 6}. The excited (pseudo)states were obtained from time-dependent density functional theory (TD-DFT) calculations with the B3LYP exchange-correlation functional and the specialized core-property basis set, aug-cc-pVTZ-J. We investigated both how the calculated coupling constants depend on the number of (pseudo)states included in the summation and whether the summation can be truncated in a systematic way at a smaller number of states and extrapolated to the total number of (pseudo)states for the given one-electron basis set. We find that this is possible and that for some of the couplings it is sufficient to include only about 30% of the excited (pseudo)states.

  19. On the truncation of the number of excited states in density functional theory sum-over-states calculations of indirect spin spin coupling constants.

    PubMed

    Zarycz, M Natalia C; Provasi, Patricio F; Sauer, Stephan P A

    2015-12-28

    It is investigated, whether the number of excited (pseudo)states can be truncated in the sum-over-states expression for indirect spin-spin coupling constants (SSCCs), which is used in the Contributions from Localized Orbitals within the Polarization Propagator Approach and Inner Projections of the Polarization Propagator (IPPP-CLOPPA) approach to analyzing SSCCs in terms of localized orbitals. As a test set we have studied the nine simple compounds, CH4, NH3, H2O, SiH4, PH3, SH2, C2H2, C2H4, and C2H6. The excited (pseudo)states were obtained from time-dependent density functional theory (TD-DFT) calculations with the B3LYP exchange-correlation functional and the specialized core-property basis set, aug-cc-pVTZ-J. We investigated both how the calculated coupling constants depend on the number of (pseudo)states included in the summation and whether the summation can be truncated in a systematic way at a smaller number of states and extrapolated to the total number of (pseudo)states for the given one-electron basis set. We find that this is possible and that for some of the couplings it is sufficient to include only about 30% of the excited (pseudo)states.

  20. Photophysical properties and thermochromic shifts of electronic spectra of Nile Red in selected solvents. Excited states dipole moments

    NASA Astrophysics Data System (ADS)

    Kawski, A.; Kukliński, B.; Bojarski, P.

    2009-05-01

    Photophysical parameters, the rate constants for radiative ( kF) and nonradiative ( kIC) for Nile Red (NR) in aprotic polar solvents incapable of hydrogen bonding with NR have been determined. No regular polarity dependence on kIC were observed in contrast to other authors. The effect of temperature on absorption and fluorescence spectra of NR in two selected solvents: ethyl acetate and 1,2-dichloroethane was studied and the electric dipole moment in the excited state S 1 was determined using the Bilot and Kawski theory [L. Bilot, A. Kawski, Z. Naturforsch. 17a (1962) 621, L. Bilot, A. Kawski, Z. Naturforsch. 18a (1963) 10, 256]. For the previously obtained dipole moment in the ground state μg = 8.2 D [A. Kawski, P. Bojarski, B. Kukliński, Chem. Phys. Lett. 463 (2008) 410] the change from thermochromic measurements upon excitation of NR is equal to Δ μ = μe - μg = 1.75 ± 0.5 D and is in good agreement with the value Δ μ = 1.8 ± 1 D from solvatochromic method. A comparison of the obtained Δ μ value with those of other authors is given and discussed. It has been concluded that the difference between the excited μe and ground μg state dipole moments for NR is too small to create a TICT state.

  1. Solvent Effects on the Electronic Absorption and Fluorescence Spectra of HNP: Estimation of Ground and Excited State Dipole Moments.

    PubMed

    Desai, Vani R; Hunagund, Shirajahammad M; Basanagouda, Mahantesha; Kadadevarmath, Jagadish S; Sidarai, Ashok H

    2016-07-01

    We report the effect of solvents on absorption and fluorescence spectra of biologically active 3(2H)-pyridazinone namely 5-(2-hydroxy-naphthalen-1-yl)-2-phenyl-2H-pyridazin-3-one (HNP) in different solvents at room temperature. The ground and the excited state dipole moments of HNP molecule was estimated from Lippert's, Bakshiev's and Kawski-Chamma-Viallet's equations using the solvatochromic shift method. The ground state dipole moment (μ g ) was also estimated by Guggenheim and Higasi method using the dielectric constant and refractive index of solute at different concentrations, the μ g value obtained from these two methods are comparable to the μ g value obtained by the solvatochromic shift method. The excited state dipole moment (μ e ) is greater than the ground state dipole moment (μ g ), which indicates that the excited state is more polar than the ground state. Further, we have evaluated the change in dipole moment (Δμ) from the solvatochromic shift method and on the basis of molecular-microscopic solvent polarity parameter[Formula: see text], later on the values were compared.

  2. Jet-Cooled Excitation Spectra of Large Benzannulated Benzyl Radicals: 9-ANTHRACENYLMETHYL (C_{15}H_{11}) and 1-PYRENYLMETHYL (C_{17}H_{11})

    NASA Astrophysics Data System (ADS)

    O'Connor, Gerard D.; Bacskay, George B.; Woodhouse, Gabrielle V. G.; Troy, Tyler P.; Nauta, Klaas; Kable, Scott H.; Schmidt, Timothy W.

    2013-06-01

    The jet-cooled D_1 ← D_0 excitation spectra of two benzannulated benzyl radicals (BBRs), 9-anthracenylmethyl (9-AnMe) and 1-pyrenylmethyl (9-PyMe), have been obtained using mass-resolved resonant two-colour two-photon ionization spectroscopy (R2C2PI). Analysis of the spectra in view of symmetry and calculated vibrational frequencies indicate significant vibronic coupling. From the spectrum of 9-AnMe we elucidate significant anharmonicity in the excited state. This anharmonic behaviour is examined computationally through both TDDFT and ab initio methods. Excited state properties of 9-AnMe and 1-PyMe are examined with reference to the existing spectra of smaller BBRs. Trends in the observed spectra of BBRs allow spectroscopic properties of larger BBRs to be predicted. These predictions suggest the D_1 ← D_0 transitions of large BBRs are unlikely to be carriers of the diffuse interstellar bands.

  3. Elementary modes of excitation caused by the quadratic Zeeman term and the sensitivity of spin structures of small spin-2 condensates against the magnetic field

    SciTech Connect

    He, Y. Z.; Bao, C. G.

    2011-12-15

    The response of spin-2 small condensates to an external magnetic field B is studied. The parameters of the interaction are considered as variable. The emphasis is placed on clarifying the modes of excitation caused by the quadratic Zeeman term. The theoretical method used is beyond the mean-field theory. A set of eigenstates with the U(5) superset of SO(5) superset of SO(3) symmetry is introduced to facilitate the analysis. To obtain a quantitative evaluation on the response, the fidelity susceptibility and the B-dependent average populations of spin components have been calculated. Mostly the particle number N=30 is assumed. The effect with a larger or smaller N is also considered. It was found that the sensitivity of the response depends strongly both on the interaction and on the inherent symmetry.

  4. Skew Scattering from Correlated Systems: Impurities and Collective Excitations in the Spin Hall Effect

    NASA Astrophysics Data System (ADS)

    Ziman, Timothy; Gu, Bo; Maekawa, Sadamichi

    2017-01-01

    The spin Hall effect is affected by the Coulomb interaction as well as spin-spin correlations in metals. Here we examine the enhancement in the effect caused by resonant skew scattering induced by electron correlations. For single-impurity scattering, local Coulomb correlations may significantly change the observed spin Hall angle. There may be additional effects because of the special atomic environment close to a surface — extra degeneracies compared to the bulk, enhanced correlations that move the relative d- or f-levels, and interference effects coming from the lower local dimension. Our results may explain the very large spin Hall angle observed in CuBi alloys. We discuss the impact on the spin Hall effect from cooperative effects, firstly in an itinerant ferromagnet where there is an anomaly near the Curie temperature originating from high-order spin fluctuations. The second case considered is a metallic spin glass, where exchange via slowly fluctuating magnetic moments may lead to the precession of an injected spin current. This decreases the net spin-charge conversion from skew scattering at temperatures below a value three or four times the freezing temperature.

  5. Magnetic excitation spectra of strongly correlated quasi-one-dimensional systems: Heisenberg versus Hubbard-like behavior

    NASA Astrophysics Data System (ADS)

    Nocera, A.; Patel, N. D.; Fernandez-Baca, J.; Dagotto, E.; Alvarez, G.

    2016-11-01

    We study the effects of charge degrees of freedom on the spin excitation dynamics in quasi-one-dimensional magnetic materials. Using the density matrix renormalization group method, we calculate the dynamical spin structure factor of the Hubbard model at half electronic filling on a chain and on a ladder geometry, and compare the results with those obtained using the Heisenberg model, where charge degrees of freedom are considered frozen. For both chains and two-leg ladders, we find that the Hubbard model spectrum qualitatively resembles the Heisenberg spectrum—with low-energy peaks resembling spinonic excitations—already at intermediate on-site repulsion as small as U /t ˜2 -3 , although ratios of peak intensities at different momenta continue evolving with increasing U /t converging only slowly to the Heisenberg limit. We discuss the implications of these results for neutron scattering experiments and we propose criteria to establish the values of U /t of quasi-one-dimensional systems described by one-orbital Hubbard models from experimental information.

  6. Magnetic excitation spectra of strongly correlated quasi-one-dimensional systems: Heisenberg versus Hubbard-like behavior

    DOE PAGES

    Nocera, Alberto; Patel, Niravkumar D.; Fernandez-Baca, Jaime A.; ...

    2016-11-28

    In this paper, we study the effects of charge degrees of freedom on the spin excitation dynamics in quasi-one-dimensional magnetic materials. Using the density matrix renormalization group method, we calculate the dynamical spin structure factor of the Hubbard model at half electronic filling on a chain and on a ladder geometry, and compare the results with those obtained using the Heisenberg model, where charge degrees of freedom are considered frozen. For both chains and two-leg ladders, we find that the Hubbard model spectrum qualitatively resembles the Heisenberg spectrum—with low-energy peaks resembling spinonic excitations—already at intermediate on-site repulsion as small asmore » U/t ~ 2–3, although ratios of peak intensities at different momenta continue evolving with increasing U/t converging only slowly to the Heisenberg limit. Finally, we discuss the implications of these results for neutron scattering experiments and we propose criteria to establish the values of U/t of quasi-one-dimensional systems described by one-orbital Hubbard models from experimental information.« less

  7. Magnetic excitation spectra of strongly correlated quasi-one-dimensional systems: Heisenberg versus Hubbard-like behavior

    SciTech Connect

    Nocera, Alberto; Patel, Niravkumar D.; Fernandez-Baca, Jaime A.; Dagotto, Elbio R.; Alvarez, Gonzalo

    2016-11-28

    In this paper, we study the effects of charge degrees of freedom on the spin excitation dynamics in quasi-one-dimensional magnetic materials. Using the density matrix renormalization group method, we calculate the dynamical spin structure factor of the Hubbard model at half electronic filling on a chain and on a ladder geometry, and compare the results with those obtained using the Heisenberg model, where charge degrees of freedom are considered frozen. For both chains and two-leg ladders, we find that the Hubbard model spectrum qualitatively resembles the Heisenberg spectrum—with low-energy peaks resembling spinonic excitations—already at intermediate on-site repulsion as small as U/t ~ 2–3, although ratios of peak intensities at different momenta continue evolving with increasing U/t converging only slowly to the Heisenberg limit. Finally, we discuss the implications of these results for neutron scattering experiments and we propose criteria to establish the values of U/t of quasi-one-dimensional systems described by one-orbital Hubbard models from experimental information.

  8. Frequency spectra of magnetostrictive and Lorentz forces generated in ferromagnetic materials by a CW excited EMAT

    NASA Astrophysics Data System (ADS)

    Rouge, C.; Lhémery, A.; Aristégui, C.

    2014-04-01

    Magnetostriction arises in ferromagnetic materials subjected to magnetization, e.g., when an EMAT (Electro-Magnetic Acoustic Transducer) is used to generate ultrasonic waves. In such a case, the magnetostriction force must be taken into account as a transduction process that adds up to the Lorentz force. When the static magnetic field is high compared to the dynamic field, both forces are driven by the excitation frequency. For lower static relative values of the magnetic fields, the Lorentz force comprises both the excitation frequency and its first harmonic. In this work, a model is derived to predict the frequency content of the magnetostrictive force that comprises several harmonics. The discrete frequency spectrum strongly depends on both the static field and the relative amplitude of the dynamic field. The only material input data needed to predict it is the curve of macroscopic magnetostrictive strain that can be measured in the direction of an imposed magnetic field. Then, the various frequency-dependent distributions of Lorentz and magnetostriction body forces can be transformed into equivalent surface stresses. Examples of computation are given for different static and dynamic magnetic fields to study their influence on the frequency content of waves generated in ferromagnetic materials.

  9. Theoretical investigation of the molecular structures and excitation spectra of triphenylamine and its derivatives

    NASA Astrophysics Data System (ADS)

    Sumimoto, Michinori; Yokogawa, Daisuke; Komeda, Masahiro; Yamamoto, Hidetoshi; Hori, Kenji; Fujimoto, Hitoshi

    2011-10-01

    The molecular geometries, electronic structures, and excitation energies of NPh 3, NPh 2Me, NPhMe 2, and NMe 3, were investigated using DFT and post-Hartree Fock methods. When the structural stabilities of these compounds were compared to results obtained by using MP4(SDQ) method, it was confirmed that the optimized geometries by using MP2 method were sufficiently reliable. The excited states with large oscillator strengths consisted of transition components from the HOMO. It should be noted that the orbitals of the nitrogen atom mix with the π-orbital of the phenyl group in an anti-bonding way in the HOMO, and the orbital energy increases with this mixing. The unoccupied orbitals are generated from bonding and anti-bonding type interactions between the π-orbitals of the phenyl groups; therefore, the number of phenyl groups strongly affects the energy diagram of the compounds studied. The differences in the energy diagram cause a spectral change in these compounds in the ultraviolet region.

  10. Dressing effects in the attosecond transient absorption spectra of doubly excited states in helium

    NASA Astrophysics Data System (ADS)

    Argenti, L.; Jiménez-Galán, Á.; Marante, C.; Ott, C.; Pfeifer, T.; Martín, F.

    2015-06-01

    Strong-field manipulation of autoionizing states is a crucial aspect of electronic quantum control. Recent measurements of the attosecond transient absorption spectrum (ATAS) of helium dressed by a few-cycle visible pulse [C. Ott et al., Nature (London) 516, 374 (2014), 10.1038/nature14026] provide evidence of the inversion of Fano profiles. With the support of accurate ab initio calculations that reproduce the results of the latter experiment, here we investigate the new physics that arise from ATAS when the laser intensity is increased. In particular, we show that (i) previously unnoticed signatures of the dark 2 p21S doubly excited state are observed in the experimental spectrum, (ii) inversion of Fano profiles is predicted to be periodic in the laser intensity, and (iii) the ac Stark shift of the higher terms in the s p2,n + autoionizing series exceeds the ponderomotive energy, which is the result of a genuine two-electron contribution to the polarization of the excited atom.

  11. Solid-State Selective 13C Excitation and Spin Diffusion NMR to Resolve Spatial Dimensions in Plant Cell Walls

    SciTech Connect

    Foston, M.; Katahira, R.; Gjersing, E.; Davis, M. F.; Ragauskas, A. J.

    2012-02-15

    The average spatial dimensions between major biopolymers within the plant cell wall can be resolved using a solid-state NMR technique referred to as a {sup 13}C cross-polarization (CP) SELDOM (selectively by destruction of magnetization) with a mixing time delay for spin diffusion. Selective excitation of specific aromatic lignin carbons indicates that lignin is in close proximity to hemicellulose followed by amorphous and finally crystalline cellulose. {sup 13}C spin diffusion time constants (T{sub SD}) were extracted using a two-site spin diffusion theory developed for {sup 13}C nuclei under magic angle spinning (MAS) conditions. These time constants were then used to calculate an average lower-limit spin diffusion length between chemical groups within the plant cell wall. The results on untreated {sup 13}C enriched corn stover stem reveal that the lignin carbons are, on average, located at distances {approx}0.7-2.0 nm from the carbons in hemicellulose and cellulose, whereas the pretreated material had larger separations.

  12. Chemical shift powder spectra enhanced by multiple-contact cross-polarization under slow magic-angle spinning.

    PubMed

    Raya, Jésus; Perrone, Barbara; Hirschinger, Jérôme

    2013-02-01

    A simple multiple-contact cross-polarization (CP) scheme is applied to a powder sample of ferrocene and β-calcium formate under static and magic-angle spinning (MAS) conditions. The method is described analytically through the density matrix formalism. We show that multiple equilibrations-re-equilibrations with the proton spin bath improves the polarization transfer efficiency at short contact times and provides higher signal enhancements than state-of-the art techniques such as adiabatic passage through the Hartmann-Hahn condition CP (APHH-CP) when MAS is applied. The resulting chemical shift powder spectra then are identical to the ones obtained by using ROtor-Directed Exchange of Orientations CP (APHH-RODEO-CP) with intensity gains of a factor 1.1-1.3.

  13. Chemical shift powder spectra enhanced by multiple-contact cross-polarization under slow magic-angle spinning

    NASA Astrophysics Data System (ADS)

    Raya, Jésus; Perrone, Barbara; Hirschinger, Jérôme

    2013-02-01

    A simple multiple-contact cross-polarization (CP) scheme is applied to a powder sample of ferrocene and β-calcium formate under static and magic-angle spinning (MAS) conditions. The method is described analytically through the density matrix formalism. We show that multiple equilibrations-re-equilibrations with the proton spin bath improves the polarization transfer efficiency at short contact times and provides higher signal enhancements than state-of-the art techniques such as adiabatic passage through the Hartmann-Hahn condition CP (APHH-CP) when MAS is applied. The resulting chemical shift powder spectra then are identical to the ones obtained by using ROtor-Directed Exchange of Orientations CP (APHH-RODEO-CP) with intensity gains of a factor 1.1-1.3.

  14. Multiple spectra of electron spin resonance in chiral molecule-based magnets networked by a single chiral ligand

    NASA Astrophysics Data System (ADS)

    Mito, M.; Nagano, T.; Tsuruta, K.; Deguchi, H.; Takagi, S.; Kishine, J.; Yoshida, Y.; Inoue, K.

    2013-10-01

    A molecule-based magnet [Cr(CN)6][Mn(R/S)-pnH(H2O)](H2O) (termed R/S-GN) is a chiral crystal without an inversion center and mirror reflection, and its structural network is constructed using a chiral ligand diaminopropane (R/S)-pn. In S-GN, multiple spectra of ESR were observed below the magnetic ordering temperature by Morgunov et al. [Phys. Rev. B 77, 184419 (2008)]. They concluded that the phenomenon at the high field side occurred because the incommensurate magnetic structure resulted in a length-controllable superlattice of domain walls (the so-called chiral soliton lattice, CSL) under a dc magnetic field H applied perpendicular to the magnetic chiral axis. However, there multiple spectra were observed even for H nearly parallel to the chiral axis, a-axis, and their interpretation is unreasonable. Thus, we conducted an X-band electron spin resonance (ESR) measurement of R-GN under conditions similar to those of their experiment and performed Fourier spectrum analyses for the data of R-GN as an approach of physical characterization. By using two Lorentz spectra, the main ESR spectra for H // a were reproduced, and furthermore two prominent periodic modes were found by spectrum analyses based on Fourier transform. Two characteristic periods, p1 and p2 (spectra observed below the magnetic ordering temperature are due not to hyperfine structure but magnetic fine structure, and it certainly originates from the existence of plural nonequivalent magnetic sites. Thus, it is unreasonable to consider CSL to explain the multiple ESR spectra observed independently of the field direction, whereas the observed complex spectra appeal wealthy scientific potentiality in chiral crystals.

  15. Excitations, optical absorption spectra, and optical excitonic gaps of heterofullerenes: I. C60, C59N+ and C48N12

    SciTech Connect

    Xie, R; Bryant, G W; Sun, G; C.Nicklaus, M; Heringer, D; Frauenheim, T; Manaa, M R; Smith, Jr., V H; Araki, Y; Ito, O

    2003-10-02

    Low-energy excitations and optical absorption spectrum of C{sub 60} are computed by using time-dependent (TD) Hartree-Fock (HF), TD-density functional theory (TD-DFT), TD-DFT-based tight-binding (TD-DFT-TB) and a semiempirical ZINDO method. A detailed comparison of experiment and theory for the excitation energies, optical gap and absorption spectrum of C{sub 60} is presented. It is found that electron correlations and collective effects of exciton pairs play important roles in assigning accurately the spectral features of C{sub 60} and the TD-DFT method with non-hybrid functionals or a local spin density approximation leads to more accurate excitation energies than with hybrid functionals. The level of agreement between theory and experiment for C{sub 60} justifies similar calculations of the excitations and optical absorption spectrum of a monomeric azafullerene cation C{sub 59}N{sup +} exhibits distinguishing spectral features different from C{sub 60}: (1) the first singlet is dipole-allowed and the optical gap is redshifted by 1.44 eV; (2) several weaker absorption maxima occur in the visible region; (3) the transient triplet-triplet absorption at 1.60 eV (775 nm) is much broader and the decay of the triplet state is much faster. The calculated spectra of C{sub 59}N{sup +} characterize and explain well our measured ultraviolet-visible (UV-vis) and transient absorption spectra of the carborane anion salt [C{sub 59}N][Ag(CB{sub 11}H{sub 6}Cl{sub 6}){sub 2}]. For the most stable isomer of C{sub 48}N{sub 12}, we predict that the first singlet is dipole-allowed, the optical gap is redshifted by 1.22 eV relative to that of C{sub 60}, and optical absorption maxima occur at 585, 528, 443, 363, 340, 314 and 303 nm. We point out that the characterization of the UV-vis and transient absorption spectra of C{sub 48}N{sub 12} isomers is helpful in distinguishing the isomer structures required for applications in molecular electronics. For C{sub 59}N{sup +} and C{sub 48}N

  16. Modelling the high-mass accretion rate spectra of GX 339-4: black hole spin from reflection?

    NASA Astrophysics Data System (ADS)

    Kolehmainen, Mari; Done, Chris; Díaz Trigo, María

    2011-09-01

    We extract all the XMM-Newton European Photon Imaging Camera (EPIC) pn burst mode spectra of GX 339-4, together with simultaneous/contemporaneous RXTE data. These include three disc-dominated and two soft intermediate spectra, and the combination of broad bandpass/moderate spectral resolution gives some of the best data on these bright soft states in black hole binaries. The disc-dominated spectra span a factor of 3 in luminosity, and all show that the disc emission is broader than the simplest multicolour disc model. This is consistent with the expected relativistic smearing and changing colour temperature correction produced by atomic features in the newest disc models. However, these models do not match the data at the 5 per cent level as the predicted atomic features are not present in the data, perhaps indicating that irradiation is important even when the high-energy tail is weak. Whatever the reason, this means that the data have smaller errors than the best physical disc models, forcing use of more phenomenological models for the disc emission. We use these for the soft intermediate state data, where previous analysis using a simple disc continuum found an extremely broad residual, identified as the red wing of the iron line from reflection around a highly spinning black hole. However, the iron line energy is close to where the disc and tail have equal fluxes, so using a broader disc continuum changes the residual 'iron line' profile dramatically. With a broader disc continuum model, the inferred line is formed outside of 30Rg, so it cannot constrain black hole spin. We caution that a robust determination of black hole spin from the iron line profile is very difficult where the disc makes a significant contribution at the iron line energy, i.e. in most bright black hole states.

  17. Effects of antidot shape on the spin wave spectra of two-dimensional Ni{sub 80}Fe{sub 20} antidot lattices

    SciTech Connect

    Mandal, Ruma; Laha, Pinaki; Das, Kaustuv; Saha, Susmita; Barman, Saswati; Raychaudhuri, A. K.; Barman, Anjan

    2013-12-23

    We show that the optically induced spin wave spectra of nanoscale Ni{sub 80}Fe{sub 20} (permalloy) antidot lattices can be tuned by changing the antidot shape. The spin wave spectra also show an anisotropy with the variation of the in-plane bias field orientation. Analyses show this is due to various quantized and extended modes, whose nature changes with the antidot shape and bias field orientation as a result of the variation of the internal magnetic field profile. The observed variation and anisotropy in the spin waves with the internal and external parameters are important for their applications in magnonic devices.

  18. Exchange-only optimized effective potential calculation of excited state spectra for He and Be atoms.

    SciTech Connect

    Desjarlais, Michael Paul; Muller, Richard Partain

    2006-02-01

    The optimized effective potential (OEP) method allows orbital-dependent functionals to be used in density functional theory (DFT), which, in particular, allows exact exchange formulations of the exchange energy to be used in DFT calculations. Because the exact exchange is inherently self-interaction correcting, the resulting OEP calculations have been found to yield superior band-gaps for condensed-phase systems. Here we apply these methods to the isolated atoms He and Be, and compare to high quality experiments and calculations to demonstrate that the orbital energies accurately reproduce the excited state spectrum for these species. These results suggest that coupling the exchange-only OEP calculations with proper (orbital-dependent or other) correlation functions might allow quantitative accuracy from DFT calculations.

  19. Evanescent excitation and collection of spontaneous Raman spectra using silicon nitride nanophotonic waveguides.

    PubMed

    Dhakal, Ashim; Subramanian, Ananth Z; Wuytens, Pieter; Peyskens, Frédéric; Le Thomas, Nicolas; Baets, Roel

    2014-07-01

    We experimentally demonstrate the use of high contrast, CMOS-compatible integrated photonic waveguides for Raman spectroscopy. We also derive the dependence of collected Raman power with the waveguide parameters and experimentally verify the derived relations. Isopropyl alcohol (IPA) is evanescently excited and detected using single-mode silicon-nitride strip waveguides. We analyze the measured signal strength of pure IPA corresponding to an 819  cm⁻¹ Raman peak due to in-phase C-C-O stretch vibration for several waveguide lengths and deduce a pump power to Raman signal conversion efficiency on the waveguide to be at least 10⁻¹¹  per cm.

  20. Quantitative Analysis of Valence Photoemission Spectra and Quasiparticle Excitations at Chromophore-Semiconductor Interfaces

    NASA Astrophysics Data System (ADS)

    Patrick, Christopher E.; Giustino, Feliciano

    2012-09-01

    Investigating quasiparticle excitations of molecules on surfaces through photoemission spectroscopy forms a major part of nanotechnology research. Resolving spectral features at these interfaces requires a comprehensive theory of electron removal and addition processes in molecules and solids which captures the complex interplay of image charges, thermal effects, and configurational disorder. Here, we develop such a theory and calculate the quasiparticle energy-level alignment and the valence photoemission spectrum for the prototype biomimetic solar cell interface between anatase TiO2 and the N3 chromophore. By directly matching our calculated photoemission spectrum to experimental data, we clarify the atomistic origin of the chromophore peak at low binding energy. This case study sets a new standard in the interpretation of photoemission spectroscopy at complex chromophore-semiconductor interfaces.

  1. Excitation of XPS spectra from nanoscaled particles by local generation of x-rays

    SciTech Connect

    Mallinson, Christopher F.; Castle, James E.

    2015-09-15

    In preliminary work, the authors have shown that use of an aluminum substrate to support a distribution of copper particles enables their characteristic photoelectrons to be observed within the Auger electron spectrum generated by an incident electron beam. This observation raises the possibility of the use of chemical shifts and the corresponding Auger parameter to identify the chemical states present on the surface of individual submicrometer particles within a mixture. In this context, the technique has an advantage in that, unlike conventional Auger electron spectroscopy, the electron beam does not dwell on the particle but on the substrate adjacent to it. Given the importance, for both medical and toxicological reasons, of the surface composition of such particles, the authors have continued to explore the potential of this development. In this contribution, the authors show that proximal excitation of x-rays is equally successful with magnesium substrates. In some regions of the x-ray photoelectron spectrum, the much larger Auger peaks generated by the electron beam can cause inconvenient clustering of Auger and photoelectron peaks. As in conventional x-ray photoelectron spectroscopy, the ability to switch between Al and Mg sources is useful in such situations. In this context, the authors have extended the studies to iron particles where the authors show that use of Al or Mg substrates, as necessary, can make a contribution to clear identification of individual components in the Fe 2p peaks. For this development in electron spectroscopy to achieve its full potential, it is necessary to optimize the beam conditions used to generate the local x-ray to give good selectivity of a given particle. Measurements made in support of this will be given. Of greater concern is a possible problem of local heating associated with x-ray generation. The authors continue to explore this problem and report some progress in minimizing heating of the particle while maintaining

  2. Paradigms and challenges for bioapplication of rare earth upconversion luminescent nanoparticles: small size and tunable emission/excitation spectra.

    PubMed

    Sun, Ling-Dong; Wang, Ye-Fu; Yan, Chun-Hua

    2014-04-15

    Rare earth (RE) materials, which are excited in the ultraviolet and emit in the visible light spectrum, are widely used as phosphors for lamps and displays. In the 1960's, researchers reported an abnormal emission phenomenon where photons emitted from a RE element carried more energy than those absorbed, owing to the sequential energy transfer between two RE ions--Yb(3+)-sensitized Er(3+) or Tm(3+)--in the solid state. After further study, researchers named this abnormal emission phenomenon upconversion (UC) emission. More recent approaches take advantage of solution-based synthesis, which allows creation of homogenous RE nanoparticles (NPs) with controlled size and structure that are capable of UC emission. Such nanoparticles are useful for many applications, especially in biology. For these applications, researchers seek small NPs with high upconversion emission intensity. These UCNPs have the potential to have multicolor and tunable emissions via various activators. A vast potential for future development remains by developing molecular antennas and energy transfer within RE ions. We expect UCNPs with optimized spectra behavior to meet the increasing demand of potential applications in bioimaging, biological detection, and light conversion. This Account focuses on efforts to control the size and modulate the spectra of UCNPs. We first review efforts in size control. One method is careful control of the synthesis conditions to manipulate particle nucleation and growth, but more recently researchers have learned that the doping conditions can affect the size of UCNPs. In addition, constructing homogeneous core/shell structures can control nanoparticle size by adjusting the shell thickness. After reviewing size control, we consider how diverse applications impose different requirements on excitation and/or emission photons and review recent developments on tuning of UC spectral profiles, especially the extension of excitation/emission wavelengths and the adjustment

  3. New method for measuring time-resolved spectra of lanthanide emission using square-wave excitation

    NASA Astrophysics Data System (ADS)

    Qin, Feng; Zhao, Hua; Duan, Qianqian; Cai, Wei; Zhang, Zhiguo; Cao, Wenwu

    2013-11-01

    A method using modulated continuous wave (CW) visible laser to measure time-resolved fluorescence spectra of trivalent rare-earth ions has been developed. Electro-optic modulator was used to modulate the CW pumping laser with a rise time of 2 μs. CW Nd3+ lasers were used as examples to present the method. Upconversion dynamic process of Ho3+ was studied utilizing a 532 nm CW laser. Quantum cutting dynamic process from Tb3+ to Yb3+ was analyzed by a 473 nm CW laser. This method can be applied to any CW laser such as He-Ne laser, Ar+ laser, Kr+ laser, Ti:sapphire laser, etc.

  4. New method for measuring time-resolved spectra of lanthanide emission using square-wave excitation

    SciTech Connect

    Qin, Feng; Zhao, Hua; Cai, Wei; Duan, Qianqian; Zhang, Zhiguo; Cao, Wenwu

    2013-11-15

    A method using modulated continuous wave (CW) visible laser to measure time-resolved fluorescence spectra of trivalent rare-earth ions has been developed. Electro-optic modulator was used to modulate the CW pumping laser with a rise time of 2 μs. CW Nd{sup 3+} lasers were used as examples to present the method. Upconversion dynamic process of Ho{sup 3+} was studied utilizing a 532 nm CW laser. Quantum cutting dynamic process from Tb{sup 3+} to Yb{sup 3+} was analyzed by a 473 nm CW laser. This method can be applied to any CW laser such as He-Ne laser, Ar{sup +} laser, Kr{sup +} laser, Ti:sapphire laser, etc.

  5. Pure absorption electron spin echo envelope modulation spectra by using the filter-diagonalization method for harmonic inversion.

    PubMed

    Jeschke, G; Mandelshtam, V A; Shaka, A J

    1999-03-01

    Harmonic inversion of electron spin echo envelope (ESEEM) time-domain signals by filter diagonalization is investigated as an alternative to Fourier transformation. It is demonstrated that this method features enhanced resolution compared to Fourier-transform magnitude spectra, since it can eliminate dispersive contributions to the line shape, even if no linear phase correction is possible. Furthermore, instrumental artifacts can be easily removed from the spectra if they are narrow either in time or frequency domain. This applies to echo crossings that are only incompletely eliminated by phase cycling and to spurious spectrometer frequencies, respectively. The method is computationally efficient and numerically stable and does not require extensive parameter adjustments or advance knowledge of the number of spectral lines. Experiments on gamma-irradiated methyl-alpha-d-glucopyranoside show that more information can be obtained from typical ESEEM time-domain signals by filter-diagonalization than by Fourier transformation.

  6. Fluorescence excitation-emission matrix spectra coupled with parallel factor and regional integration analysis to characterize organic matter humification.

    PubMed

    He, Xiao-Song; Xi, Bei-Dou; Li, Xiang; Pan, Hong-Wei; An, Da; Bai, Shuo-Guo; Li, Dan; Cui, Dong-Yu

    2013-11-01

    The present several humification indexes cannot provide the whole fluorescence information on organic matter composition and the evaluation results from them are inconsistent sometimes. In this study, fluorescence excitation-emission matrix spectra coupled with parallel factor analysis and fluorescence regional integration analysis were utilized to investigate organic matter humification, and the projection pursuit cluster (PPC) model was applied to form a suitable index for overcoming the difficulties in multi-index evaluation. The result showed that the ratio between the volume of humic- and fulvic-like fluorescence region and the volume of protein-like fluorescence region not only revealed the heterogeneity of organic matter, but also provided more accurate information on organic matter humification. In addition, the results showed that the PPC model could be used to characterize integrally the humification, and the projected characteristic value calculated from the PPC model could be used as the integrated humification evaluation index.

  7. Quadrupolar magic angle spinning NMR spectra fitted using the Pearson IV function.

    PubMed

    Mironenko, Roman M; Belskaya, Olga B; Talsi, Valentin P; Likholobov, Vladimir A

    2014-01-01

    The Pearson IV function was used to fit the asymmetric solid-state (27)Al NMR spectra of alumina based catalysts. A high convergence (correlation coefficient is no less than 0.997) between experimental and simulated spectra was achieved. The decomposition of the (27)Al NMR spectra of zinc/aluminum mixed oxides with different Zn/Al molar ratio revealed an increased fraction (6-9%) of pentacoordinated aluminum atoms in these oxides as compared to γ-Al2O3. As the Zn/Al ratio is raised, the fraction of [AlO6] octahedral units decreases, while the fraction of [AlO4] tetrahedra increases.

  8. X-Ray Spectra of Young Pulsars and Their Wind Nebulae: Dependence on Spin-Down Energy Loss Rate

    NASA Technical Reports Server (NTRS)

    Gotthelf, E. V.

    2003-01-01

    An observational model is presented for the spectra of young rotation-powered pulsars and their nebulae based on a study of nine bright Crab-like pulsar systems observed with the Chandra X-ray observatory. A significant correlation is discovered between the X-ray spectra of these pulsars and that of their associated pulsar wind nebulae, both of which are observed to be a function of the spin-down energy loss rate, E. The 2-10 keV spectra of these objects are well characterized by an absorbed power-law model with photon indices, Gamma, in the range of 0.6 < Gamma (sub PSR) < 2.1 and 1.3 < Gamma(sub PWN) < 2.3, for the pulsars and their nebulae, respectively. A linear regression fit relating these two sets of indexes yields Gamma(sub PWN) = 0.91 +/- 0.18 + (0.66 +/- 0.11) Gamma (sub PSR), with a correlation coefficient of r = 0.97. The spectra of these pulsars are found to steepen as Gamma = Gamma(sub max) + alpha E (exp -1/2), with Gamma(sub max) providing an observational limit on the spectral slopes of young rotation-powered pulsars. These results reveal basic properties of young pulsar systems, allow new observational constraints on models of pulsar wind emission, and provide a means of predicting the energetics of pulsars lacking detected pulsations.

  9. Rotational Spectra of Urea in its Ground and First Excited Vibrational States

    NASA Astrophysics Data System (ADS)

    Thomas, Jessica; Medvedev, Ivan; Kisiel, Zbigniew

    2014-06-01

    Urea is an important terrestrial bio-molecule, which has been tentatively detected in the interstellar medium. To match the much improved range and sensitivities of modern sub-millimeter telescopes a broad laboratory assay of rotational transitions needs to be recorded in order to aid in the definitive identification of this molecule. This paper focuses on the spectroscopic assignment of the rotational transitions of urea in the 207-500 GHz range which belong to its ground and first excited vibrational states. Remijan, A.J., L.E. Snyder, B.A. McGuire, H.-L. Kuo, L.W. Looney, D.N. Friedel, G.Y. Golubiatnikov, F.J. Lovas, V.V. Ilyushin, E.A. Alekseev, S.F. Dyubko, B.J. McCall, and J.M. Hollis, Observational Results of a Multi-Telescope Campaign in Search of Interstellar Urea [NH22CO]. The Astrophysical Journal, 2014. 783(2): p. 77

  10. Quantitative analysis of valence photoemission spectra and quasiparticle excitations at chromophore-semiconductor interfaces

    NASA Astrophysics Data System (ADS)

    Patrick, Christopher; Giustino, Feliciano

    2013-03-01

    Understanding electron energetics at interfaces between solids and molecules is a key challenge in many areas of nanotechnology research. Here we develop a quantitative theory of quasiparticle excitations at these interfaces and apply it to the prototypical dye-sensitized solar cell interface of N3 dye molecules adsorbed on the anatase TiO2 (101) surface.[2] Our approach combines density-functional calculations on large interface models, bulk GW calculations,[3] image charge renormalization, thermal broadening and configurational disorder to obtain a quasiparticle spectrum in good agreement with experimental photoemission data. Our calculations clarify the atomistic origin of the chromophore peak at low binding energy, and illustrate the dual role played by the TiO2 substrate in screening the quasiparticle states of the N3 molecule through both long-range image-charge effects and direct charge transfer via the covalently-bonded anchor groups. Work funded by the UK EPSRC and the ERC under the EU FP7/ERC Grant No. 239578. Calculations were performed at the Oxford Supercomputing Centre.

  11. Testing Noncollinear Spin-Flip, Collinear Spin-Flip, and Conventional Time-Dependent Density Functional Theory for Predicting Electronic Excitation Energies of Closed-Shell Atoms.

    PubMed

    Xu, Xuefei; Yang, Ke R; Truhlar, Donald G

    2014-05-13

    Conventional time-dependent density functional theory (TDDFT) is based on a closed-shell Kohn-Sham (KS) singlet ground state with the adiabatic approximation, using either linear response (KS-LR) or the Tamm-Dancoff approximation (KS-TDA); these methods can only directly predict singly excited states. This deficiency can be overcome by using a triplet state as the reference in the KS-TDA approximation and "exciting" the singlet by a spin flip (SF) from the triplet; this is the method suggested by Krylov and co-workers, and we abbreviate this procedure as SF-KS-TDA. SF-KS-TDA can be applied either with the original collinear kernel of Krylov and co-workers or with a noncollinear kernel, as suggested by Wang and Ziegler. The SF-KS-TDA method does bring some new practical difficulties into play, but it can at least formally model doubly excited states and states with double-excitation character, so it might be more useful than conventional TDDFT (both KS-LR and KS-TDA) for photochemistry if these additional difficulties can be surmounted and if it is accurate with existing approximate exchange-correlation functionals. In the present work, we carried out calculations specifically designed to understand better the accuracy and limitations of the conventional TDDFT and SF-KS-TDA methods; we did this by studying closed-shell atoms and closed-shell monatomic cations because they provide a simple but challenging testing ground for what we might expect in studying the photochemistry of molecules with closed-shell ground states. To test their accuracy, we applied conventional KS-LR and KS-TDA and 18 versions of SF-KS-TDA (nine collinear and nine noncollinear) to the same set of vertical excitation energies (including both Rydberg and valence excitations) of Be, B(+), Ne, Na(+), Mg, and Al(+). We did this for 10 exchange-correlation functionals of various types, both local and nonlocal. We found that the GVWN5 and M06 functionals with nonlocal kernels in spin-flip calculations

  12. Multi-angle Spectra Evolution of Ionospheric Turbulence Excited by RF Interactions at HAARP

    NASA Astrophysics Data System (ADS)

    Sheerin, J. P.; Rayyan, N.; Watkins, B. J.; Watanabe, N.; Golkowski, M.; Bristow, W. A.; Bernhardt, P. A.; Briczinski, S. J., Jr.

    2014-12-01

    The high power HAARP HF transmitter is employed to generate and study strong Langmuir turbulence (SLT) in the interaction region of overdense ionospheric plasma. Diagnostics included the Modular UHF Ionospheric Radar (MUIR) sited at HAARP, the SuperDARN-Kodiak HF radar, and HF receivers to record stimulated electromagnetic emissions (SEE). Dependence of diagnostic signals on HAARP HF parameters, including pulselength, duty-cycle, aspect angle, and frequency were recorded. Short pulse, low duty cycle experiments demonstrate control of artificial field-aligned irregularities (AFAI) and isolation of ponderomotive effects. For the first time, simultaneous multi-angle radar measurements of plasma line spectra are recorded demonstrating marked dependence on aspect angle with the strongest interaction region observed displaced southward of the HF zenith pointing angle. For a narrow range of HF pointing between Spitze and magnetic zenith, a reduced threshold for AFAI is observed. High time resolution studies of the temporal evolution of the plasma line reveal the appearance of an overshoot effect on ponderomotive timescales. Numerous measurements of the outshifted plasma line are observed. Experimental results are compared to previous high latitude experiments and predictions from recent modeling efforts

  13. Spin-exciton interaction and related micro-photoluminescence spectra of ZnSe:Mn DMS nanoribbon.

    PubMed

    Hou, Lipeng; Zhou, Weichang; Zou, Bingsuo; Zhang, Yu; Han, Junbo; Yang, Xinxin; Gong, Zhihong; Li, Jingbo; Xie, Sishen; Shi, Li-Jie

    2017-03-10

    For their spintronic applications the magnetic and optical properties of diluted magnetic semiconductors (DMS) have been studied widely. However, the exact relationships between the magnetic interactions and optical emission behaviors in DMS are not well understood yet due to their complicated microstructural and compositional characters from different growth and preparation techniques. Manganese (Mn) doped ZnSe nanoribbons with high quality were obtained by using the chemical vapor deposition (CVD) method. Successful Mn ion doping in a single ZnSe nanoribbon was identified by elemental energy-dispersive x-ray spectroscopy mapping and micro-photoluminescence (PL) mapping of intrinsic d-d optical transition at 580 nm, i.e. the transition of (4) T 1((4) G) → (6) A 1((6) s),. Besides the d-d transition PL peak at 580 nm, two other PL peaks related to Mn ion aggregates in the ZnSe lattice were detected at 664 nm and 530 nm, which were assigned to the d-d transitions from the Mn(2+)-Mn(2+) pairs with ferromagnetic (FM) coupling and antiferromagnetic (AFM) coupling, respectively. Moreover, AFM pair formation goes along with strong coupling with acoustic phonon or structural defects. These arguments were supported by temperature-dependent PL spectra, power-dependent PL lifetimes, and first-principle calculations. Due to the ferromagnetic pair existence, an exciton magnetic polaron (EMP) is formed and emits at 460 nm. Defect existence favors the AFM pair, which also can account for its giant enhancement of spin-orbital coupling and the spin Hall effect observed in PRL 97, 126603(2006) and PRL 96, 196404(2006). These emission results of DMS reflect their relation to local sp-d hybridization, spin-spin magnetic coupling, exciton-spin or phonon interactions covering structural relaxations. This kind of material can be used to study the exciton-spin interaction and may find applications in spin-related photonic devices besides spintronics.

  14. Determination of the in vivo redox potential using roGFP and fluorescence spectra obtained from one-wavelength excitation

    NASA Astrophysics Data System (ADS)

    Wierer, S.; Elgass, K.; Bieker, S.; Zentgraf, U.; Meixner, A. J.; Schleifenbaum, F.

    2011-02-01

    The analysis of molecular processes in living (plant) cells such as signal transduction, DNA replication, carbon metabolism and senescence has been revolutionized by the use of green fluorescent protein (GFP) and its variants as specific cellular markers. Many cell biological processes are accompanied by changes in the intracellular redox potential. To monitor the redox potential, a redox-sensitive mutant of GFP (roGFP) was created, which shows changes in its optical properties in response to changes in the redox state of its surrounding medium. For a quantitative analysis in living systems, it is essential to know the optical properties of roGFP in vitro. Therefore, we applied spectrally resolved fluorescence spectroscopy on purified roGFP exposed to different redox potentials to determine shifts in both the absorption and the emission spectra of roGFP. Based on these in vitro findings, we introduce a new approach using one-wavelength excitation to use roGFP for the in vivo analysis of cell biological processes. We demonstrate the ability this technique by investigating chloroplast-located Grx1-roGFP2 expressing Arabidopsis thaliana cells as example for dynamically moving intracellular compartments. This is not possible with the two-wavelength excitation technique established so far, which hampers a quantitative analysis of highly mobile samples due to the time delay between the two measurements and the consequential displacement of the investigated area.

  15. Electronic spectra of azaindole and its excited state mixing: A symmetry-adapted cluster configuration interaction study

    NASA Astrophysics Data System (ADS)

    Arulmozhiraja, Sundaram; Coote, Michelle L.; Hasegawa, Jun-ya

    2015-11-01

    Electronic structures of azaindole were studied using symmetry-adapted cluster configuration interaction theory utilizing Dunning's cc-pVTZ basis set augmented with appropriate Rydberg spd functions on carbon and nitrogen atoms. The results obtained in the present study show good agreement with the available experimental values. Importantly, and contrary to previous theoretical studies, the excitation energy calculated for the important n-π∗ state agrees well with the experimental value. A recent study by Pratt and co-workers concluded that significant mixing of π-π∗ and n-π∗ states leads to major change in the magnitude and direction of the dipole moment of the upper state vibrational level in the 0,0 + 280 cm-1 band in the S1←S0 transition when compared to that of the zero-point level of the S1 state. The present study, however, shows that all the four lowest lying excited states, 1Lb π-π∗, 1La π-π∗, n-π∗, and π-σ∗, cross each other in one way or another, and hence, significant state mixing between them is likely. The upper state vibrational level in the 0,0 + 280 cm-1 band in the S1←S0 transition benefits from this four-state mixing and this can explain the change in magnitude and direction of the dipole moment of the S1 excited vibrational level. This multistate mixing, and especially the involvement of π-σ∗ state in mixing, could also provide a route for hydrogen atom detachment reactions. The electronic spectra of benzimidazole, a closely related system, were also investigated in the present study.

  16. Electronic spectra of azaindole and its excited state mixing: A symmetry-adapted cluster configuration interaction study

    SciTech Connect

    Arulmozhiraja, Sundaram Coote, Michelle L.; Hasegawa, Jun-ya

    2015-11-28

    Electronic structures of azaindole were studied using symmetry-adapted cluster configuration interaction theory utilizing Dunning’s cc-pVTZ basis set augmented with appropriate Rydberg spd functions on carbon and nitrogen atoms. The results obtained in the present study show good agreement with the available experimental values. Importantly, and contrary to previous theoretical studies, the excitation energy calculated for the important n–π{sup ∗} state agrees well with the experimental value. A recent study by Pratt and co-workers concluded that significant mixing of π-π{sup ∗} and n-π{sup ∗} states leads to major change in the magnitude and direction of the dipole moment of the upper state vibrational level in the 0,0 + 280 cm{sup −1} band in the S{sub 1}←S{sub 0} transition when compared to that of the zero-point level of the S{sub 1} state. The present study, however, shows that all the four lowest lying excited states, {sup 1}L{sub b} π-π{sup ∗}, {sup 1}L{sub a} π-π{sup ∗}, n-π{sup ∗}, and π-σ{sup ∗}, cross each other in one way or another, and hence, significant state mixing between them is likely. The upper state vibrational level in the 0,0 + 280 cm{sup −1} band in the S{sub 1}←S{sub 0} transition benefits from this four-state mixing and this can explain the change in magnitude and direction of the dipole moment of the S{sub 1} excited vibrational level. This multistate mixing, and especially the involvement of π-σ{sup ∗} state in mixing, could also provide a route for hydrogen atom detachment reactions. The electronic spectra of benzimidazole, a closely related system, were also investigated in the present study.

  17. Non-orthogonal spin-adaptation of coupled cluster methods: A new implementation of methods including quadruple excitations

    SciTech Connect

    Matthews, Devin A.; Stanton, John F.

    2015-02-14

    The theory of non-orthogonal spin-adaptation for closed-shell molecular systems is applied to coupled cluster methods with quadruple excitations (CCSDTQ). Calculations at this level of detail are of critical importance in describing the properties of molecular systems to an accuracy which can meet or exceed modern experimental techniques. Such calculations are of significant (and growing) importance in such fields as thermodynamics, kinetics, and atomic and molecular spectroscopies. With respect to the implementation of CCSDTQ and related methods, we show that there are significant advantages to non-orthogonal spin-adaption with respect to simplification and factorization of the working equations and to creating an efficient implementation. The resulting algorithm is implemented in the CFOUR program suite for CCSDT, CCSDTQ, and various approximate methods (CCSD(T), CC3, CCSDT-n, and CCSDT(Q))

  18. Non-orthogonal spin-adaptation of coupled cluster methods: A new implementation of methods including quadruple excitations.

    PubMed

    Matthews, Devin A; Stanton, John F

    2015-02-14

    The theory of non-orthogonal spin-adaptation for closed-shell molecular systems is applied to coupled cluster methods with quadruple excitations (CCSDTQ). Calculations at this level of detail are of critical importance in describing the properties of molecular systems to an accuracy which can meet or exceed modern experimental techniques. Such calculations are of significant (and growing) importance in such fields as thermodynamics, kinetics, and atomic and molecular spectroscopies. With respect to the implementation of CCSDTQ and related methods, we show that there are significant advantages to non-orthogonal spin-adaption with respect to simplification and factorization of the working equations and to creating an efficient implementation. The resulting algorithm is implemented in the CFOUR program suite for CCSDT, CCSDTQ, and various approximate methods (CCSD(T), CC3, CCSDT-n, and CCSDT(Q)).

  19. Non-orthogonal spin-adaptation of coupled cluster methods: A new implementation of methods including quadruple excitations

    NASA Astrophysics Data System (ADS)

    Matthews, Devin A.; Stanton, John F.

    2015-02-01

    The theory of non-orthogonal spin-adaptation for closed-shell molecular systems is applied to coupled cluster methods with quadruple excitations (CCSDTQ). Calculations at this level of detail are of critical importance in describing the properties of molecular systems to an accuracy which can meet or exceed modern experimental techniques. Such calculations are of significant (and growing) importance in such fields as thermodynamics, kinetics, and atomic and molecular spectroscopies. With respect to the implementation of CCSDTQ and related methods, we show that there are significant advantages to non-orthogonal spin-adaption with respect to simplification and factorization of the working equations and to creating an efficient implementation. The resulting algorithm is implemented in the CFOUR program suite for CCSDT, CCSDTQ, and various approximate methods (CCSD(T), CC3, CCSDT-n, and CCSDT(Q)).

  20. Nonlinear magnetic vortex dynamics in a circular nanodot excited by spin-polarized current

    PubMed Central

    2014-01-01

    We investigate analytically and numerically nonlinear vortex spin torque oscillator dynamics in a circular magnetic nanodot induced by a spin-polarized current perpendicular to the dot plane. We use a generalized nonlinear Thiele equation including spin-torque term by Slonczewski for describing the nanosize vortex core transient and steady orbit motions and analyze nonlinear contributions to all forces in this equation. Blue shift of the nano-oscillator frequency increasing the current is explained by a combination of the exchange, magnetostatic, and Zeeman energy contributions to the frequency nonlinear coefficient. Applicability and limitations of the standard nonlinear nano-oscillator model are discussed. PMID:25147490

  1. Nonlinear magnetic vortex dynamics in a circular nanodot excited by spin-polarized current.

    PubMed

    Guslienko, Konstantin Y; Sukhostavets, Oksana V; Berkov, Dmitry V

    2014-01-01

    We investigate analytically and numerically nonlinear vortex spin torque oscillator dynamics in a circular magnetic nanodot induced by a spin-polarized current perpendicular to the dot plane. We use a generalized nonlinear Thiele equation including spin-torque term by Slonczewski for describing the nanosize vortex core transient and steady orbit motions and analyze nonlinear contributions to all forces in this equation. Blue shift of the nano-oscillator frequency increasing the current is explained by a combination of the exchange, magnetostatic, and Zeeman energy contributions to the frequency nonlinear coefficient. Applicability and limitations of the standard nonlinear nano-oscillator model are discussed.

  2. Terahertz spin-orbital excitations in the paramagnetic state of multiferroic Sr2FeSi2O7

    NASA Astrophysics Data System (ADS)

    Mai, Thuc T.; Svoboda, C.; Warren, M. T.; Jang, T.-H.; Brangham, J.; Jeong, Y. H.; Cheong, S.-W.; Valdés Aguilar, R.

    2016-12-01

    We studied the novel multiferroic material Sr2FeSi2O7 and found three absorption modes above the magnetic ordering transition temperature using time-domain terahertz spectroscopy. These absorption modes can be explained as the optical transitions between the spin-orbit coupling and crystal-field split 3 d6Fe2 + ground-state term in this material. Consideration of the compressed tetrahedral environment of the Fe2 + site is crucial to understand the excitations. We point out, however, discrepancies between the single-site atomic picture and the experimental results.

  3. MRCI+Q calculations on spectroscopic properties of excited states of PbH including spin-orbit coupling

    NASA Astrophysics Data System (ADS)

    Zhao, Shutao; Li, Rui; Zhang, Hua; Li, Huiquan

    2017-03-01

    The 10 Ʌ-S states associated with the lowest four dissociation limits of PbH radical have been studied utilizing configuration interaction method. For better accuracy, the Davidson correction, core-valence correlation and spin-orbit coupling effects are included. The potential energy curves of 10 Ʌ-S states and 18 Ω states have been obtained and characterized. The computed dipole moments of 10 Ʌ-S states are used to reveal the ionic characteristics of the Ʌ-S states. Finally, the transitional dipole moments of several bound Ω states and lifetimes of vibrational states trapped in excited bound Ω states are determined.

  4. Polarization- and frequency-tunable microwave circuit for selective excitation of nitrogen-vacancy spins in diamond

    NASA Astrophysics Data System (ADS)

    Herrmann, Johannes; Appleton, Marc A.; Sasaki, Kento; Monnai, Yasuaki; Teraji, Tokuyuki; Itoh, Kohei M.; Abe, Eisuke

    2016-10-01

    We report on a planar microwave resonator providing arbitrarily polarized oscillating magnetic fields that enable selective excitation of the electronic spins of nitrogen-vacancy centers in diamond. The polarization plane is parallel to the surface of diamond, which makes the resonator fully compatible with (111)-oriented diamond. The field distribution is spatially uniform in a circular area with a diameter of 4 mm, and a near-perfect circular polarization is achieved. We also demonstrate that the original resonance frequency of 2.8 GHz can be varied in the range of 2-3.2 GHz by introducing varactor diodes that serve as variable capacitors.

  5. A simplified relativistic time-dependent density-functional theory formalism for the calculations of excitation energies including spin-orbit coupling effect.

    PubMed

    Wang, Fan; Ziegler, Tom

    2005-10-15

    In the present work we have proposed an approximate time-dependent density-functional theory (TDDFT) formalism to deal with the influence of spin-orbit coupling effect on the excitation energies for closed-shell systems. In this formalism scalar relativistic TDDFT calculations are first performed to determine the lowest single-group excited states and the spin-orbit coupling operator is applied to these single-group excited states to obtain the excitation energies with spin-orbit coupling effects included. The computational effort of the present method is much smaller than that of the two-component TDDFT formalism and this method can be applied to medium-size systems containing heavy elements. The compositions of the double-group excited states in terms of single-group singlet and triplet excited states are obtained automatically from the calculations. The calculated excitation energies based on the present formalism show that this formalism affords reasonable excitation energies for transitions not involving 5p and 6p orbitals. For transitions involving 5p orbitals, one can still obtain acceptable results for excitations with a small truncation error, while the formalism will fail for transitions involving 6p orbitals, especially 6p1/2 spinors.

  6. Effects of orbital and spin current interference in E1 and M2 nuclear excitations

    SciTech Connect

    Goncharova, N. G.

    2015-12-15

    The interference of contributions from the orbital and spin currents to the E1 and M2 resonances is investigated. The results of the current interference analysis within the shell model are compared with the experimental data.

  7. Competing effects at Pt/YIG interfaces: Spin Hall magnetoresistance, magnon excitations, and magnetic frustration

    NASA Astrophysics Data System (ADS)

    Vélez, Saül; Bedoya-Pinto, Amilcar; Yan, Wenjing; Hueso, Luis E.; Casanova, Fèlix

    2016-11-01

    We study spin Hall magnetoresistance (SMR) and magnon spin transport (MST) in Pt / Y3F e5O12(YIG ) -based devices with intentionally modified interfaces. Our measurements show that the surface treatment of the YIG film results in a slight enhancement of the spin-mixing conductance and an extraordinary increase in the efficiency of the spin-to-magnon conversion at room temperature. The surface of the YIG film develops a surface magnetic frustration at low temperatures, causing a sign change of the SMR and a dramatic suppression of the MST. Our results evidence that SMR and MST could be used to explore magnetic properties of surfaces, including those with complex magnetic textures, and stress the critical importance of the nonmagnetic/ferromagnetic interface properties in the performance of the resulting spintronic devices.

  8. Parallel parametric amplification of coherently excited propagating spin waves in a microscopic Ni{sub 81}Fe{sub 19} waveguide

    SciTech Connect

    Brächer, T.; Pirro, P.; Meyer, T.; Heussner, F.; Lägel, B.; Serga, A. A.; Hillebrands, B.

    2014-05-19

    We present parallel parametric amplification of coherently excited, propagating spin waves in a microstructured magnonic Ni{sub 81}Fe{sub 19} waveguide. Amplification is achieved by the pumping field generated by a microwave current flowing through a Cu micro-stripline underneath the waveguide. By employing microfocussed Brillouin light scattering spectroscopy, we investigate the spatial decay of the propagating spin waves and their amplification by means of parallel pumping. We analyze the dependence of the intensity of the amplified spin waves on the spin-wave excitation power, pumping power, and pumping duration, revealing the most efficient working point for a noise-free amplification. This paves the way for a frequency selective amplification of spin waves in microstructured magnonic circuits.

  9. Orbital elementary excitations as probes of entanglement and quantum phase transitions of collective spins in an entangled Bose-Einstein condensate

    NASA Astrophysics Data System (ADS)

    Wu, Rukuan; Shi, Yu

    2011-02-01

    A mixture of two species of pseudospin-(1)/(2) Bose gases exhibits interesting interplay between spin and orbital degrees of freedom. Expectation values of various quantities of the collective spins of the two species play crucial roles in the Gross-Pitaevskii-like equations governing the four orbital wave functions in which Bose-Einstein condensation occurs. Consequently, the elementary excitations of these orbital wave functions reflect properties of the collective spins. When the coupling between the two collective spins is isotropic, the energy gap of the gapped orbital excitation peaks. There is a quantum phase transition in the ground state of the effective Hamiltonian of the two collective spins, which have previously been found to be maximally entangled.

  10. Reciprocal Damon-Eshbach-type spin wave excitation in a magnonic crystal due to tunable magnetic symmetry

    NASA Astrophysics Data System (ADS)

    Huber, R.; Krawczyk, M.; Schwarze, T.; Yu, H.; Duerr, G.; Albert, S.; Grundler, D.

    2013-01-01

    We report spin-wave (SW) propagation in a one-dimensional magnonic crystal (MC) explored by all electrical spectroscopy. The MC consists of a periodic array of 255 nm wide permalloy nanowires with a small edge-to-edge separation of 45 nm. Provoking antiparallel alignment of the magnetization of neighboring nanowires, we unexpectedly find reciprocal excitation of Damon-Eshbach type SWs. The characteristics are in contrast to ferromagnetic thin films and controlled via, both, the external magnetic field and magnetic states. The observed reciprocal excitation is a metamaterial property for SWs and attributed to the peculiar magnetic symmetry of the artificially tailored magnetic material. The findings offer great perspectives for nanoscale SW interference devices.

  11. Research program in nuclear and solid state physics. [including pion absorption spectra and muon spin precession

    NASA Technical Reports Server (NTRS)

    1974-01-01

    The survey of negative pion absorption reactions on light and medium nuclei was continued. Muon spin precession was studied using an iron target. An impulse approximation model of the pion absorption process implied that the ion will absorb almost exclusively on nucleon pairs, single nucleon absorption being suppressed by energy and momentum conservation requirements. For measurements on both paramagnetic and ferromagnetic iron, the external magnetic field was supplied by a large C-type electromagnet carrying a current of about 100 amperes.

  12. [Determination of the distance between spin labels and the paramagnetic center in spin-labeled proteins according to parameters of the saturation curves of the label EPR spectra at 77 degrees K].

    PubMed

    Kulikov, A V

    1976-01-01

    A new method of estimation of the distance between spins of the spin-label and paramagnetic center is suggested. Method is based on the quantitative analys of saturation curve of spin-label EPR spectra at 77 degrees K. New approaches have been tested using haemoglobin labeled on SH-groups with various iminoxyl radicals. Values of the distances between labels and haem estimated from the saturation curve parameters and by current methods and values of distances estimated from X-ray data are in good agreement. In the case of rapid spin relaxation of he paramagnetic center, the new method allows one to determine a farther distance. Results of the present work make it possible to investigat by the spin-label technique the structure of haem-containing propeins and the structure of other proteins with known spin relaxation time of paramagnetic center.

  13. 2D correlation analysis of the magnetic excitations in Raman spectra of HoMnO3

    NASA Astrophysics Data System (ADS)

    Nguyen, Thi Huyen; Nguyen, Thi Minh Hien; Chen, Xiang-Bai; Yang, In-Sang; Park, Yeonju; Jung, Young Mee

    2014-07-01

    2D correlation analysis is performed on the temperature-dependent Raman spectra of HoMnO3 thin films. As the temperature of the HoMnO3 thin films decrease, the depletion of the spectral weight at 336, 656, and 1304 cm-1 occurs at higher temperatures than the increase of the intensity at 508, 766, and 945 cm-1 below ∼70 K, the Néel temperature. The power spectrum asserts that all the changes in the spectral weight are strongly correlated. Most of the temperature-induced spectral changes of HoMnO3 occur at lower temperature than 70 K, while there is slight depletion of the spectral weight at 336, 656, and 1304 cm-1 even at higher temperature than 70 K. PCA scores and loading vectors plots also support these 2D correlation results. Our 2D correlation analysis supports the existence of the short range spin correlations between Mn sites in HoMnO3 even above the Néel temperature.

  14. Fluorescence excitation and emission spectra of 1,8-dihydroxyanthraquinone-d0 and -d2 in n-octane at 10 K

    NASA Astrophysics Data System (ADS)

    Smulevich, Giulietta; Foggi, Paolo; Feis, Alessandro; Marzocchi, Mario P.

    1987-11-01

    The fluorescence excitation and emission spectra in n-octane of 1,8-dihydroxyanthraquinone-d0 and -d2 at 10 K have been measured. Dual excitation and emission were observed as a consequence of excited state intramolecular proton transfer. A model, based on the Lippincott-Schroeder potential function, is proposed to predict the observed energy gaps and relative intensities of the transition. The isotopic effects are also explained. The Shpolskii matrices in n-octane show only one main site allowing a detailed vibrational analysis of the ground and the excited states. This furnished further evidence for the existence of excited state tautomers. The occurrence of an extra fluorescence was explained in terms of the ν(OH) stretching mode of the high frequency transition enhanced via vibronic coupling between the two ground states.

  15. New Approach on Quantification of Porosity of Thin Films via Electron-Excited X-ray Spectra.

    PubMed

    Ortel, Erik; Hertwig, Andreas; Berger, Dirk; Esposito, Pasquale; Rossi, Andrea M; Kraehnert, Ralph; Hodoroaba, Vasile-Dan

    2016-07-19

    One of the crucial characteristics of functionalized thin films is their porosity (i.e., the ratio between the pore volume and the volume of the whole film). Due to the very low amount of material per coated area corresponding to thin films, it is a challenge for analytics to measure the film porosity. In this work, we present an approach to determine the porosity of thin films by means of electron probe microanalysis (EPMA) either by wavelength-dispersive X-ray spectrometry (WDX) or by energy-dispersive X-ray spectrometry (EDX) with a scanning electron microscope (SEM). The procedure is based on the calculation of the film mass deposition from electron-excited X-ray spectra. The mass deposition is converted into film density by division of measured film thickness. Finally, the film porosity is calculated from the measured film density and the density of bulk, nonporous film material. The general applicability of the procedure to determine the porosity is demonstrated on thin templated mesoporous TiO2 films, dip-coated on silicon wafer, with controlled porosity in the range of 15 to 50%. The high accuracy of the mass deposition as determined from X-ray spectra was validated with independent methods (ICP-OES and weighing). Furthermore, for the validation of the porosity results, ellipsometry, interference fringes method (IFM), and focused ion beam (FIB) cross sectioning were employed as independent techniques. Hence, the approach proposed in the present study is proven to be suited as a new analytical tool for accurate and relatively fast determination of the porosity of thin films.

  16. Nuclear magnetic resonance spectra for l > 1 spins in dynamically heterogeneous systems with chemical exchange among environments.

    PubMed

    Zhang, H; Bryant, R G

    1995-06-01

    Nuclear magnetic resonance spectra for nuclei with spin l > 1 are considered in cases in which the observed nucleus may sample a rotationally immobilized and an isotropic environment that are coupled by a chemical exchange process. Spectra are simulated for the central (1/2, -1/2) transition for a 3/2 nucleus as a function of the concentrations of the two environments and as a function of the exchange rate between them. It is shown that a crucial feature determining the shape of the observable spectra is the spatial extent or the local order in the immobilized phase. In the case for which all rotationally immobilized sites sampled by the exchanging nucleus are identically oriented but where there is a distribution of these microdomain orientations with respect to the magnetic field direction, a powder pattern for the central transition is observed that carries whatever dynamic information may be derived from it. In the fast exchange limit, the width of the powder pattern scales inversely with the concentration of the isotropic environment as usual. In the intermediate exchange regimes, a complex line shape results that may mask the anisotropic character of the spectrum. In the slow exchange limit, superposition of the spectral contributions results; however, if the isotropic environment concentration is significantly larger than the anisotropic environment concentration, the anisotropic contribution is very difficult to detect because of the dynamic range problem and the possibly large difference in the effective line widths. In the case for which the exchanging nucleus samples a considerable distribution of rotationally immobilized site orientations, the anisotropic character of the spectrum is lost and a super-Lorentzian line shape results. These effects are demonstrated experimentally by 35Cl nuclear magnetic resonance spectra obtained on a lamellar liquid crystal that is modified with the addition of a thiolmercurate to provide a site of large quadrupole

  17. Spin crossover in iron(II) tris(2-(2 '-pyridyl)benzimidazole) complex monitored by variable temperature methods: synchrotron powder diffraction, DSC, IR spectra, Mössbauer spectra, and magnetic susceptibility

    NASA Astrophysics Data System (ADS)

    Boča, R.; Boča, M.; Ehrenberg, H.; Fuess, H.; Linert, W.; Renz, F.; Svoboda, I.

    2003-09-01

    The thermal expansion of the spin crossover system [Fe(pybzim) 3](ClO 4) 2 · H 2O (pybzim=2-(2 '-pyridyl)benzimidazole) has been determined from powder X-ray data between 50 and 250 K; the wavelength of the synchrotron source was 1.21888(1) Å. The unit cell parameters of the triclinic crystal system were a=12.091 Å, b=12.225 Å, c=14.083 Å, α=77.70°, β=80.35°, γ=74.35°, and V=1944.9 Å 3 at 250 K. In addition to the linear thermal expansion of the unit cell volume, an extra expansion due to the low-spin (LS) to high-spin (HS) transition is observed. The V( T) function shows a sudden increase comparable with the step in the effective magnetic moment at the transition region (140 K). A similar behavior is obtained on the basis of the infrared spectra. The absorption bands corresponding to the metal-ligand stretching modes change their intensities upon heating: the bands corresponding to the low-spin molecules (at ca. 409, 430, 443, and 460 cm -1) disappear in the gain of the high-spin bands (at 259 and 285 cm -1). The variable-temperature data obtained by different techniques (powder diffraction, EXAFS, IR spectra, Mössbauer spectra, magnetic susceptibility, DSC) have been transformed to a common basis - the temperature dependence of the high-spin mole fraction xHS( T). The application of the Ising-like (two-level) model of the spin crossover led to the thermodynamic data Δ H=2.6 kJ mol -1 and Δ S=19 J K -1 mol -1 as well as to the cooperativeness J/ k≈110 K (subtracted from the susceptibility data) that characterizes the abruptness of the spin crossover in the solid state.

  18. Long-range quantum Ising spin glasses at t=0: gapless collective excitations and universality.

    PubMed

    Andreanov, A; Müller, M

    2012-10-26

    We solve the Sherrington-Kirkpatrick model in a transverse field Γ deep in its quantum glass phase at zero temperature. We show that the glass phase is critical everywhere, exhibiting collective excitations with a gapless Ohmic spectral function. Using an effective potential approach, we interpret the latter as arising from disordered collective excitations behaving like weakly coupled, underdamped oscillators. For a small transverse field Γ, the low-frequency spectrum takes a form independent of the fluctuation strength Γ.

  19. Long-Range Quantum Ising Spin Glasses at T=0: Gapless Collective Excitations and Universality

    NASA Astrophysics Data System (ADS)

    Andreanov, A.; Müller, M.

    2012-10-01

    We solve the Sherrington-Kirkpatrick model in a transverse field Γ deep in its quantum glass phase at zero temperature. We show that the glass phase is critical everywhere, exhibiting collective excitations with a gapless Ohmic spectral function. Using an effective potential approach, we interpret the latter as arising from disordered collective excitations behaving like weakly coupled, underdamped oscillators. For a small transverse field Γ, the low-frequency spectrum takes a form independent of the fluctuation strength Γ.

  20. Inelastic Neutron Scattering Studies of High-Energy Spin Excitations in Superconducting BaFe1.9Ni0.1As2

    NASA Astrophysics Data System (ADS)

    Liu, Mengshu; Abernathy, Douglas; Zhao, Jun; Wang, Meng; Zhang, Chenglin; Wang, Miaoyin; Dai, Pengcheng

    2010-03-01

    Understanding how the spin fluctuations evolve with doping in iron pnictide superconductors is important because spin fluctuations may mediate electron pairing for superconductivity in these materials. Upon doping, the spin fluctuation persists long after the long-range antiferromagnetism is destroyed. More importantly, spin excitations are coupled to superconductivity in the appearance of a neutron magnetic resonance and a superconductivity-induced spin gap. However, all current neutron scattering results in iron based superconductors are confined to low energy excitations except for the ``11'' FeTe1-xSex system, which shows incommensurate excitations that are not found in other iron pnictide systems. Therefore, how the spin waves in parent compounds of the ``122'' (AFe2As2, A = Ca, Sr, Ba) system will evolve when the system becomes an optimal superconductor is still an open question. We use time-of-flight spectroscopy to determine S (Q,φ) at energy regions not accessed before. We compare spin fluctuations of iron arsenide superconductors with those of high-Tc copper oxides and discuss their role in the superconductivity of these materials.

  1. Characterization of Self-Excited, Nearly Axisymmetric, Spinning Rigid-Body Motion as an Oblate Epicycloid

    NASA Astrophysics Data System (ADS)

    McNair, S. Lauren; Tragesser, Steven

    2017-03-01

    A unique formulation of the solution to a spinning, nearly axisymmetric rigid-body is presented. Direct integration of the linearized equations of motion gives accurate results for nearly axisymmetric inertia ellipsoids while avoiding the complexity of more general formulations. The simplicity of the formulation lends itself to a better understanding of the system behavior. Specifically, the motion of the spin axis for this nearly axisymmetric case is described by an oblate epicycloid, providing an extension of the classic epicycloid solution for axisymmetric objects.

  2. The Excitation of High Spin States with Quasielastic and Deep Inelastic Reactions.

    NASA Astrophysics Data System (ADS)

    Knott, Clinton Neal

    1988-12-01

    The feasibility of populating high spin states using reactions induced by a 220 MeV ^{22 }Ne beam on a ^{170} Er target was studied. The experiment was carried out using a multidetector array for high resolution gamma-ray spectroscopy, a 14 element sum multiplicity spectrometer and six DeltaE-E particle telescopes. Detailed information was obtained concerning the reaction mechanisms associated with various reaction channels. Deep inelastic collisions are shown to be a promising tool for high spin spectroscopy in regions of the chart of nuclides which are not accessible by other reactions.

  3. The excitation of high spin states with quasi-elastic and deep inelastic reactions

    SciTech Connect

    Knott, C.N.

    1988-01-01

    The feasibility of populating high spin states using reactions induced by a 220 MeV {sup 22}Ne beam on a {sup 170}Er target was studied. The experiment was carried out using a multidetector array for high resolution {gamma}-ray spectroscopy, a 14 element sum multiplicity spectrometer and six {Delta}E-E particle telescopes. Detailed information was obtained concerning the reaction mechanisms associated with various reaction channels. Deep inelastic collisions are shown to be a promising tool for high spin spectroscopy in regions of the chart of nuclides which are not accessible by other reactions.

  4. Singlet-Triplet Excitations and Long-Range Entanglement in the Spin-Orbital Liquid Candidate FeSc2S4.

    PubMed

    Laurita, N J; Deisenhofer, J; Pan, LiDong; Morris, C M; Schmidt, M; Johnsson, M; Tsurkan, V; Loidl, A; Armitage, N P

    2015-05-22

    Theoretical models of the spin-orbital liquid (SOL) FeSc2S4 have predicted it to be in close proximity to a quantum critical point separating a spin-orbital liquid phase from a long-range ordered magnetic phase. Here, we examine the magnetic excitations of FeSc2S4 through time-domain terahertz spectroscopy under an applied magnetic field. At low temperatures an excitation emerges that we attribute to a singlet-triplet excitation from the SOL ground state. A threefold splitting of this excitation is observed as a function of applied magnetic field. As singlet-triplet excitations are typically not allowed in pure spin systems, our results demonstrate the entangled spin and orbital character of singlet ground and triplet excited states. Using experimentally obtained parameters we compare to existing theoretical models to determine FeSc2S4's proximity to the quantum critical point. In the context of these models, we estimate the characteristic length of the singlet correlations to be ξ/(a/2)≈8.2 (where a/2 is the nearest neighbor lattice constant), which establishes FeSc2S4 as a SOL with long-range entanglement.

  5. Excited S 1 state dipole moments of nitrobenzene and p-nitroaniline from thermochromic effect on electronic absorption spectra

    NASA Astrophysics Data System (ADS)

    Kawski, A.; Kukliński, B.; Bojarski, P.

    2006-11-01

    The effect of temperature on the absorption spectra of nitrobenzene (NB) and p-nitroaniline (NA) in 1,2-dichloroethane was studied for temperature ranging from 295 K to 378 K and from 296 K to 408 K, respectively. With temperature increase the absorption bands of both compounds are blue shifted, which is caused by the decrease of permittivity ɛ and refractive index n. From the band shifts and by using the Bilot and Kawski theory [ L. Bilot, A. Kawski, Z. Naturforsch. 17a (1962) 621] the dipole moments in the excited singlet state μe = 6.59 D of NB and μe = 13.35 D of NA were determined. The influence of polarizability α, the Onsager cavity radius a and dipole moment in the ground state μg on the determined values of μe are discussed. A comparison of the obtained μe values with those of other authors is given. In the case of p-NA a strong intramolecular charge transfer (ICT) was confirmed.

  6. Excited state dipole moments of N, N-dimethylaniline from thermochromic effect on electronic absorption and fluorescence spectra

    NASA Astrophysics Data System (ADS)

    Kawski, A.; Kukliński, B.; Bojarski, P.

    2006-01-01

    The effect of temperature on absorption and fluorescence spectra of N, N-dimethylaniline (DMA) in ethyl acetate has been studied for temperature ranging from 293 to 388 K. The permittivity ɛ and refractive index n of the solvent decrease with temperature increase and the absorption and fluorescence bands are blue shifted (so-called "thermochromic shift"). Based on this phenomenon, the dipole moment μe in the excited singlet state and the Onsager interaction radius a for DMA were determined using the Bilot and Kawski theory [L. Bilot, A. Kawski, Z. Naturforsch. 17a (1962) 621; 18a (1963) 10, 256]. For the known dipole moment in the ground state μg = 1.61 D and for α/ a3 = 0.54 ( α is the polarizability of the solute) the average value of μe = 3.55 D and a = 3.1 Å were determined. The obtained values for DMA are compared with the experimental values determined by other authors.

  7. Theoretical and experimental analysis of the photoluminescence and photoluminescence excitation spectroscopy spectra of m-plane InGaN/GaN quantum wells

    NASA Astrophysics Data System (ADS)

    Schulz, S.; Tanner, D. S. P.; O'Reilly, E. P.; Caro, M. A.; Tang, F.; Griffiths, J. T.; Oehler, F.; Kappers, M. J.; Oliver, R. A.; Humphreys, C. J.; Sutherland, D.; Davies, M. J.; Dawson, P.

    2016-11-01

    We present a combined theoretical and experimental analysis of the optical properties of m-plane InGaN/GaN quantum wells. The sample was studied by photoluminescence and photoluminescence excitation spectroscopy at low temperature. The spectra show a large Stokes shift between the lowest exciton peak in the excitation spectra and the peak of the photoluminescence spectrum. This behavior is indicative of strong carrier localization effects. These experimental results are complemented by tight-binding calculations, accounting for random alloy fluctuations and Coulomb effects. The theoretical data explain the main features of the experimental spectra. Moreover, by comparison with calculations based on a virtual crystal approximation, the importance of carrier localization effects due to random alloy fluctuations is explicitly shown.

  8. Description of excited states in [Re(Imidazole)(CO)3 (Phen)](+) including solvent and spin-orbit coupling effects: Density functional theory versus multiconfigurational wavefunction approach.

    PubMed

    Fumanal, Maria; Daniel, Chantal

    2016-10-15

    The low-lying electronic excited states of [Re(imidazole)(CO)3 (phen)](+) (phen = 1,10-phenanthroline) ranging between 420 nm and 330 nm have been calculated by means of relativistic spin-orbit time-dependent density functional theory (TD-DFT) and wavefunction approaches (state-average-CASSCF/CASPT2). A direct comparison between the theoretical absorption spectra obtained with different methods including SOC and solvent corrections for water points to the difficulties at describing on the same footing the bands generated by metal-to-ligand charge transfer (MLCT), intraligand (IL) transition, and ligand-to-Ligand- charge transfer (LLCT). While TD-DFT and three-roots-state-average CASSCF (10,10) reproduce rather well the lowest broad MLCT band observed in the experimental spectrum between 420 nm and 330 nm, more flexible wavefunctions enlarged either by the number of roots or by the number of active orbitals and electrons destabilize the MLCT states by introducing IL and LLCT character in the lowest part of the absorption spectrum. © 2016 Wiley Periodicals, Inc.

  9. Low energy nuclear spin excitations in Ho metal investigated by high resolution neutron spectroscopy.

    PubMed

    Chatterji, Tapan; Jalarvo, Niina

    2013-04-17

    We have investigated the low energy excitations in metallic Ho by high resolution neutron spectroscopy. We found at T = 3 K clear inelastic peaks in the energy loss and energy gain sides, along with the central elastic peak. The energy of this low energy excitation, which is 26.59 ± 0.02 μeV at T = 3 K, decreased continuously and became zero at TN ≈ 130 K. By fitting the data in the temperature range 100-127.5 K with a power law we obtained the power-law exponent β = 0.37 ± 0.02, which agrees with the expected value β = 0.367 for a three-dimensional Heisenberg model. Thus the energy of the low energy excitations can be associated with the order parameter.

  10. The structure of the high-energy spin excitations in YBa2Cu3O6+x

    NASA Astrophysics Data System (ADS)

    Hayden, Stephen

    2005-03-01

    The most obvious feature in the magnetic excitations of high-Tc superconductors is the so-called `resonance-mode'. This mode is strongly coupled to the superconductivity, however, it has not been found in the La2-x(Ba,Sr)xCuO4 family and is not universally present in Bi2Sr2CaCu2O8+δ. Here we use inelastic neutron scattering to characterize other excitations at higher energies which may be relevant to the superconductive pairing in YBa2Cu3O6.6. We observe a square-shaped continuum of excitations in reciprocal space [1]. These excitations have energies greater than the superconducting pairing energy, are present at Tc, and have spectral weight far exceeding that of the `resonance'. The discovery of similar excitations in La2-xBaxCuO4 [2] suggests that they are a general property of the copper oxides, and a candidate for mediating the electron pairing. Our data show that the high-energy magnetic excitations in the high-temperature superconductor YBa2Cu3O6.6 consists of a continuum of scattering bounded by a square and peaked at wavevector positions Qɛ =(1/2±ɛ,1/2±ɛ) and (1/2±ɛ,1/2ɛ). A similar structure is observed in the high-energy magnetic excitations of the magnetically ordered but weakly superconducting compound La1.85Ba0.125CuO4 [2]. This suggests there is universality, both in the low-energy and the high-energy spin dynamics between two very different classes of high-Tc superconductor. [1] S.M. Hayden, H.A. Mook, P.C. Dai, T.G. Perring, and F. Dogan, Nature 429, 531-534 (2004) [2] J.M. Tranquada, H. Woo, T.G. Perring, H. Goka, G.D. Gu , G. Xu, M. Fujita, K.Yamada K, Nature 429, 534-538 (2004).

  11. Resonant magnetization switching conditions of an exchange-coupled bilayer under spin wave excitation

    NASA Astrophysics Data System (ADS)

    Zhou, W.; Yamaji, T.; Seki, T.; Imamura, H.; Takanashi, K.

    2017-02-01

    We systematically investigated spin wave-assisted magnetization switching (SWAS) of a L10-FePt/Ni81Fe19 (permalloy; Py) exchange-coupled bilayer by using a pulse-like rf field (hrf) and mapped the switching events in the magnetic field (H)-hrf frequency (f) plane in order to reveal the switching conditions. Switching occurred only in a limited region followed by the dispersion relationship of the perpendicular standing spin wave modes in the Py. The results indicate that SWAS is a resonant magnetization switching process, which is different from the conventional microwave assisted switching and has the potential to be used for selective switching in multilevel recording media.

  12. Magnetic studies of spin wave excitations in Fe/Mn multilayers

    NASA Astrophysics Data System (ADS)

    Salhi, H.; Moubah, R.; El Bahoui, A.; Lassri, H.

    2017-04-01

    The structural and magnetic properties of Fe/Mn multilayers grown by thermal evaporation technique were investigated by transmission electron microscopy, vibrating sample magnetometer and spin wave theory. Transmission electron microscopy shows that the Fe and Mn layers are continuous with a significant interfacial roughness. The magnetic properties of Fe/Mn multilayers were studied for various Fe thicknesses (tFe). The change of magnetization as a function of temperature is well depicted by a T3/2 law. The Fe spin-wave constant was extracted and found to be larger than that reported for bulk Fe, which we attribute to the fluctuation of magnetic moments at the interface, due to the interfacial roughness. The experimental M (T) data were satisfactory fitted for multilayers with different Fe thicknesses; and several exchange interactions were extracted.

  13. The excited spin-triplet state of a charged exciton in quantum dots

    NASA Astrophysics Data System (ADS)

    Molas, M. R.; Nicolet, A. A. L.; Piętka, B.; Babiński, A.; Potemski, M.

    2016-09-01

    We report on spectroscopic studies of resonances related to ladder of states of a charged exciton in single GaAlAs/AlAs quantum dot structures. Polarization-resolved photoluminescence, photoluminescence excitation and photon-correlation measurements were performed at low (T  =  4.2 K) temperature also in magnetic field applied in Faraday configuration. The investigated resonances are assigned to three different configurations of a positively charged exciton. Together with a singlet ground state and a conventional triplet state (involving an electron from the ground state electronic s-shell), an excited triplet state, which involved an electron from the excited electronic p-shell was identified in single dots. The appearance of an emission line related to the latter complex is due to a partially suppressed electron relaxation in the investigated dots. An analysis of this emission line allows us to scrupulously determine properties of the excited triplet state and compare them with those of the conventional triplet state. Both triplets exhibit similar patterns of anisotropic fine structure and Zeeman splitting, however their amplitudes significantly differ for those two states. Presented results emphasize the role of the symmetry of the electronic state on the properties of the triplet states of two holes  +  electron excitonic complex.

  14. Magnetic excitations in the spin-1/2 triangular-lattice antiferromagnet Cs2CuBr4

    SciTech Connect

    Zvyagin, S. A.; Ozerov, M.; Kamenskyi, D.; Wosnitza, J.; Krzystek, J.; Yoshizawa, D.; Hagiwara, M.; Hu, Rongwei; Ryu, Hyejin; Petrovic, C.; Zhitomirsky, M. E.

    2015-11-27

    We present on high- field electron spin resonance (ESR) studies of magnetic excitations in the spin- 1/2 triangular-lattice antiferromagnet Cs2CuBr4. Frequency- field diagrams of ESR excitations are measured for different orientations of magnetic fields up to 25 T. We show that the substantial zero- field energy gap, Δ ≈ 9.5 K, observed in the low-temperature excitation spectrum of Cs2CuBr4 [Zvyagin et al:, Phys. Rev. Lett. 112, 077206 (2014)], is present well above TN. Noticeably, the transition into the long-range magnetically ordered phase does not significantly affect the size of the gap, suggesting that even below TN the high-energy spin dynamics in Cs2CuBr4 is determined by short-range-order spin correlations. The experimental data are compared with results of model spin-wave-theory calculations for spin-1/2 triangle-lattice antiferromagnet.

  15. Triggering of spin-flipping-modulated exchange bias in FeCo nanoparticles by electronic excitation

    PubMed Central

    Sarker, Debalaya; Bhattacharya, Saswata; Srivastava, Pankaj; Ghosh, Santanu

    2016-01-01

    The exchange coupling between ferromagnetic (FM)-antiferromagnetic (AF) interfaces is a key element of modern spintronic devices. We here introduce a new way of triggering exchange bias (EB) in swift heavy ion (SHI) irradiated FeCo-SiO2 films, which is a manifestation of spin-flipping at high irradiation fluence. The elongation of FeCo nanoparticles (NPs) in SiO2 matrix gives rise to perpendicular magnetic anisotropy at intermediate fluence. However, a clear shift in hysteresis loop is evident at the highest fluence. This reveals the existence of an AF exchange pinning domain in the NPs, which is identified not to be oxide shell from XANES analysis. Thermal spike calculations along with first-principles based simulations under the framework of density functional theory (DFT) demonstrate that spin flipping of 3d valence electrons is responsible for formation of these AF domains inside the FM NPs. EXAFS experiments at Fe and Co K-edges further unravel that spin-flipping in highest fluence irradiated film results in reduced bond lengths. The results highlight the possibility of miniaturization of magnetic storage devices by using irradiated NPs instead of conventionally used FM-AF multilayers. PMID:27991552

  16. Triggering of spin-flipping-modulated exchange bias in FeCo nanoparticles by electronic excitation

    NASA Astrophysics Data System (ADS)

    Sarker, Debalaya; Bhattacharya, Saswata; Srivastava, Pankaj; Ghosh, Santanu

    2016-12-01

    The exchange coupling between ferromagnetic (FM)-antiferromagnetic (AF) interfaces is a key element of modern spintronic devices. We here introduce a new way of triggering exchange bias (EB) in swift heavy ion (SHI) irradiated FeCo-SiO2 films, which is a manifestation of spin-flipping at high irradiation fluence. The elongation of FeCo nanoparticles (NPs) in SiO2 matrix gives rise to perpendicular magnetic anisotropy at intermediate fluence. However, a clear shift in hysteresis loop is evident at the highest fluence. This reveals the existence of an AF exchange pinning domain in the NPs, which is identified not to be oxide shell from XANES analysis. Thermal spike calculations along with first-principles based simulations under the framework of density functional theory (DFT) demonstrate that spin flipping of 3d valence electrons is responsible for formation of these AF domains inside the FM NPs. EXAFS experiments at Fe and Co K-edges further unravel that spin-flipping in highest fluence irradiated film results in reduced bond lengths. The results highlight the possibility of miniaturization of magnetic storage devices by using irradiated NPs instead of conventionally used FM-AF multilayers.

  17. Triggering of spin-flipping-modulated exchange bias in FeCo nanoparticles by electronic excitation.

    PubMed

    Sarker, Debalaya; Bhattacharya, Saswata; Srivastava, Pankaj; Ghosh, Santanu

    2016-12-19

    The exchange coupling between ferromagnetic (FM)-antiferromagnetic (AF) interfaces is a key element of modern spintronic devices. We here introduce a new way of triggering exchange bias (EB) in swift heavy ion (SHI) irradiated FeCo-SiO2 films, which is a manifestation of spin-flipping at high irradiation fluence. The elongation of FeCo nanoparticles (NPs) in SiO2 matrix gives rise to perpendicular magnetic anisotropy at intermediate fluence. However, a clear shift in hysteresis loop is evident at the highest fluence. This reveals the existence of an AF exchange pinning domain in the NPs, which is identified not to be oxide shell from XANES analysis. Thermal spike calculations along with first-principles based simulations under the framework of density functional theory (DFT) demonstrate that spin flipping of 3d valence electrons is responsible for formation of these AF domains inside the FM NPs. EXAFS experiments at Fe and Co K-edges further unravel that spin-flipping in highest fluence irradiated film results in reduced bond lengths. The results highlight the possibility of miniaturization of magnetic storage devices by using irradiated NPs instead of conventionally used FM-AF multilayers.

  18. Spin excitations in stripe-ordered La 2- xSr xNiO 4 ( x=0.275 and {1}/{3})

    NASA Astrophysics Data System (ADS)

    Boothroyd, A. T.; Freeman, P. G.; Prabhakaran, D.; Woo, H.; Nakajima, K.; Tranquada, J. M.; Yamada, K.; Frost, C. D.

    2004-05-01

    We report neutron scattering measurements of the spectrum of magnetic excitations in the stripe-ordered phase of La 2- xSr xNiO 4 ( x=0.275 and {1}/{3}). The propagating spin excitations follow a similar dispersion relation for the two compositions, but the line widths are broader for x=0.275 than for {1}/{3}.

  19. Anharmonic Franck-Condon simulation of the absorption and fluorescence spectra for the low-lying S1 and S2 excited states of pyridine.

    PubMed

    Wang, Huan; Zhu, Chaoyuan; Yu, Jian-Guo; Lin, Sheng Hsien

    2009-12-31

    Anharmonic effects of the absorption and fluorescence spectra of pyridine molecule are studied and analyzed for the two-low lying singlet excited states S(1)((1)B(1)) and S(2)((1)B(2)). The complete active space self-consistent field (CASSCF) method is utilized to compute equilibrium geometries and all 27 vibrational normal-mode frequencies for the ground state and the two excited states. The present calculations show that the frequency differences between the ground and two excited states are small for the ten totally symmetric vibrational modes so that the displaced oscillator approximation can be used for spectrum simulations. The Franck-Condon factors within harmonic approximation basically grasp the main features of molecular spectra, but simulated 0-0 transition energy position and spectrum band shapes are not satisfactorily good for S(1)((1)B(1)) absorption and fluorescence spectra in comparison with experiment observation. As the first-order anharmonic correction added to Franck-Condon factors, both spectrum positions and band shapes can be simultaneously improved for both absorption and fluorescence spectra. It is concluded that the present anharmonic correction produces a significant dynamic shifts for spectrum positions and improves spectrum band shapes as well. The detailed structures of absorption spectrum of S(2)((1)B(2)) state observed from experiment can be also reproduced with anharmonic Franck-Condon simulation, and these were not shown in the harmonic Franck-Condon simulation with either distorted or Duschinsky effects in the literature.

  20. Magnetic moments, E3 transitions and the structure of high-spin core excited states in 211Rn

    NASA Astrophysics Data System (ADS)

    Poletti, A. R.; Dracoulis, G. D.; Byrne, A. P.; Stuchbery, A. E.; Poletti, S. J.; Gerl, J.; Lewis, P. M.

    1985-05-01

    The results of g-factor measurements of high-spin states in 211Rn are: Ex = 8856 + Δ' keV (Jπ = 63/2-), g = 0.626(7); 6101 + Δ' KeV (49/2+), 0.766(8); 5347 + Δ' KeV (43/2-), 0.74(2); 3927 + Δ KeV (35/2+), 1.017(12); 1578 + Δ KeV (17/2-), 0.912(9). These results together with measured E3 transition strengths and shell model calculations are used to assign configurations to the core excited states in 211Rn. Mixed configurations are required to explain the g-factors and enhanced E3 strengths simultaneously.

  1. High-spin structure of {sup 37}Cl, intruder excitations, and the sd-fp shell gap

    SciTech Connect

    Ionescu-Bujor, M.; Iordachescu, A.; Marginean, N.; Bucurescu, D.; Lenzi, S. M.; Bazzacco, D.; Della Vedova, F.; Farnea, E.; Menegazzo, R.; Lunardi, S.; Zilio, S.; Napoli, D. R.; De Angelis, G.; Gadea, A.; Medina, N. H.; Ur, C. A.; Otsuka, T.; Utsuno, Y.

    2009-09-15

    The structure of the N=20 nucleus {sup 37}Cl has been investigated in the {sup 24}Mg({sup 16}O,3p) reaction with a 70 MeV {sup 16}O beam. A complex level scheme extended up to an excitation energy of 17 MeV and spins (29/2{sup +}) and (27/2{sup -}) on positive and negative parity, respectively, has been established. Lifetimes for the new states have been investigated by the Doppler shift attenuation method. Large-scale shell-model calculations have been performed in a valence space involving orbitals in the sd and fp shells using the sdfp and SDPF-M effective interactions. The comparison with the experimental data indicates the need for slight changes of the sd-fp energy gaps produced by these interactions.

  2. Spin-orbit interaction driven collective electron-hole excitations in a noncentrosymmetric nodal loop Weyl semimetal

    NASA Astrophysics Data System (ADS)

    Ahn, Kyo-Hoon; Lee, Kwan-Woo; Pickett, Warren E.

    2015-09-01

    NbP is one member of a new class of nodal loop semimetals characterized by the cooperative effects of spin-orbit coupling (SOC) and a lack of inversion center. Here transport and spectroscopic properties of NbP are evaluated using density functional theory methods. SOC together with the lack of inversion symmetry splits degeneracies, giving rise to "Russian doll nested" Fermi surfaces containing 4 ×10-4 electron (hole) carriers/f.u. Due to the modest SOC strength in Nb, the Fermi surfaces map out the Weyl nodal loops. Calculated structure around T*≈100 K in transport properties reproduces well the observed transport behavior only when SOC is included, attesting to the precision of the (delicate) calculations and the stoichiometry of the samples. Low-energy collective electron-hole excitations (plasmons) in the 20-60 meV range result from the nodal loop splitting.

  3. Extensive spin-orbit multi-reference computations on the excited states of the phosphorus monochloride molecule

    NASA Astrophysics Data System (ADS)

    Zhang, Xiaomei; Yan, Peiyuan; Li, Rui; Gai, Zhiqiang; Liang, Guiying; Xu, Haifeng; Yan, Bing

    2016-09-01

    Total 34 Λ-S states of the PCl molecule have been studied by using the multi-reference configuration interaction plus the Davidson correction (MRCI+Q) method with the correlation consistent quadruple-zeta quality basis set. These states are correlated to three dissociation limits P(4Su)+Cl(2Pu), P(2Du)+Cl(2Pu), and P(2Pu)+Cl(2Pu), respectively. The potential energy curves (PECs) of the Λ-S states have been calculated, from which the spectroscopic constants of the bound states are determined. The calculated spectroscopic results well reproduce the available measurements. The spin-orbit matrix elements between the Λ-S states have been calculated, which indicate that the perturbations exist in the interacting system 11Π-23Π and 11Π-23Σ-. And the excited a1Δ, b1Σ+, 21Σ+ states could be predissociated induced by the spin-orbit coupling (SOC) effect. The SOC calculation on the PCl molecule has been performed with the state interaction method. This is the first time that the SOC effect of the PCl has been studied theoretically. The SOC effect leads to the 34 Λ-S states split into the 74 Ω states. The ground state X3Σ- splits into the X3 Σ0-+ (X10+) and X3Σ1- (X21) states. For the zero-field splitting of the X3Σ- state, the spin-orbit contribution of 6 cm-1 is much larger than spin-spin contribution of 0.32 cm-1. Under the influence of the SOC effect, the spectroscopic results of the a1Δ and b1Σ+ states have very small changes, but the dissociation energies strongly decrease. The transition properties of PCl are also predicted, including the E1, M1, and E2 transition moments, the Franck-Condon factors, the transition probabilities, and the radiative lifetimes. For the transitions from a1Δ-X3Σ- and b1Σ+-X3Σ-, the transition probabilities are in order of AE1 > AM1 ≫ AE2. The lifetimes for the b1Σ+(v'=0) state are 4.87ms (E1) and 4.57 ms (E1+M1), in good agreement with the available experimental result of 4.9±0.8 ms.

  4. Spin wave quantization in continuous film with stripe domains

    NASA Astrophysics Data System (ADS)

    Ha, Seung-Seok; Yoon, Jungbum; Lee, Sukmock; You, Chun-Yeol; Jung, Myung-Hwa; Kim, Young Keun

    2009-04-01

    We investigated the spin wave dynamics of CoFeSiB film, which has a stripe domain structure at a low magnetic field region (<1 kOe). We measured the spin wave excitation spectra by employing Brillouin light scattering. Abnormal field dependence and dispersion relations were observed, and they are similar to spin wave quantization in laterally confined magnetic structures such as arrays of magnetic nanowires. The observed spin wave excitation spectra must be interpreted with spin wave quantization such as Damon-Eshbach mode separation. It was found that the spin wave quantization is related to the stripe magnetic domain structure in continuous film. The physical origin of the quantization is the partial reflection of the propagating spin wave at the periodic stripe domain boundaries.

  5. High spin spectroscopy near the N=Z line: Channel selection and excitation energy systematics

    SciTech Connect

    Svensson, C.E.; Cameron, J.A.; Flibotte, S.

    1996-12-31

    The total {gamma}-ray and charged-particle energies emitted in fusion-evaporation reactions leading to N=Z compound systems in the A = 50-70 mass region have been measured with the 8{pi} {gamma}-ray spectrometer and the miniball charged-particle detector array. A new method of channel selection has been developed which combines particle identification with these total energy measurements and greatly improves upon the selectivity possible with particle detection alone. In addition, the event by event measurement of total {gamma}-ray energies using the BGO ball of the 8{pi} spectrometer has allowed a determination of excitation energies following particle evaporation for a large number of channels in several different reactions. The new channel selection procedure and excitation energy systematics are illustrated with data from the reaction of {sup 24}Mg on {sup 40}Ca at E{sub lab} = 80MeV.

  6. Non-local dynamics of weakly nonlinear spin excitations in thin ferromagnetic films

    NASA Astrophysics Data System (ADS)

    Kiseliev, V. V.; Tankeyev, A. P.

    1996-12-01

    Effective integro-differential equations of weakly nonlinear dynamics describing the interaction of quasi-one-dimensional exchange-dipole spin-waves are derived for a thin ferromagnetic slab (film). The non-local part of the magnetostatic dispersion of these waves has been taken into account. Algebraic soliton-like states have been predicted. The conditions of their existence and their dynamic properties are investigated depending on the film thickness and on the magnitude and orientation of the external magnetic field. The role of crystallographic magnetic anisotropy in the formation of these states is analysed.

  7. DFT spin-orbit coupling between singlet and triplet excited states: A case of psoralen compounds

    NASA Astrophysics Data System (ADS)

    Chiodo, Sandro G.; Russo, Nino

    2010-04-01

    We present a computational protocol in which our method is used to compute spin-orbit (SO) matrix elements on time-dependent-density functional theory (TD-DFT). These SO contributions, computed employing our SO program package, MolSOC, have been expressed, in turn, in terms of weighted coefficients and SO matrix elements between singlet and triplet wave functions arising from a given one-electron transition. The protocol has been applied to study psoralen compound and its derivatives obtained from the replacement of one oxygen with sulfur or selenium. The obtained results have been compared with those reported in literature.

  8. Spin-orbit-driven magnetic structure and excitation in the 5d pyrochlore Cd2Os2O7

    DOE PAGES

    Calder, Stuart A; Vale, James G.; Bogdanov, Nikolay; ...

    2016-06-07

    Here, much consideration has been given to the role of spin-orbit coupling (SOC) in 5d oxides, particularly on the formation of novel electronic states and manifested metal-insulator transitions (MITs). SOC plays a dominant role in 5d5 iridates (Ir4+), undergoing MITs both concurrent (pyrochlores) and separated (perovskites) from the onset of magnetic order. However, the role of SOC for other 5d configurations is less clear. For example, 5d3 (Os5+) systems are expected to have an orbital singlet with reduced effective SOC. The pyrochlore Cd2Os2O7 nonetheless exhibits a MIT entwined with magnetic order phenomenologically similar to pyrochlore iridates. Here, we resolve themore » magnetic structure in Cd2Os2O7 with neutron diffraction and then via resonant inelastic X-ray scattering determine the salient electronic and magnetic energy scales controlling the MIT. In particular, SOC plays a subtle role in creating the electronic ground state but drives the magnetic order and emergence of a multiple spin-flip magnetic excitation.« less

  9. Spin-orbit-driven magnetic structure and excitation in the 5d pyrochlore Cd2Os2O7

    PubMed Central

    Calder, S.; Vale, J. G.; Bogdanov, N. A.; Liu, X.; Donnerer, C.; Upton, M. H.; Casa, D.; Said, A. H.; Lumsden, M. D.; Zhao, Z.; Yan, J. -Q.; Mandrus, D.; Nishimoto, S.; van den Brink, J.; Hill, J. P.; McMorrow, D. F.; Christianson, A. D.

    2016-01-01

    Much consideration has been given to the role of spin-orbit coupling (SOC) in 5d oxides, particularly on the formation of novel electronic states and manifested metal-insulator transitions (MITs). SOC plays a dominant role in 5d5 iridates (Ir4+), undergoing MITs both concurrent (pyrochlores) and separated (perovskites) from the onset of magnetic order. However, the role of SOC for other 5d configurations is less clear. For example, 5d3 (Os5+) systems are expected to have an orbital singlet with reduced effective SOC. The pyrochlore Cd2Os2O7 nonetheless exhibits a MIT entwined with magnetic order phenomenologically similar to pyrochlore iridates. Here, we resolve the magnetic structure in Cd2Os2O7 with neutron diffraction and then via resonant inelastic X-ray scattering determine the salient electronic and magnetic energy scales controlling the MIT. In particular, SOC plays a subtle role in creating the electronic ground state but drives the magnetic order and emergence of a multiple spin-flip magnetic excitation. PMID:27273216

  10. Excited-state intramolecular proton transfer in 3-hyroxyflavone isolated in solid argon: fluorescence and fluorescence-excitation spectra and tautomer fluorescence rise time

    SciTech Connect

    Dick, B.; Ernsting, N.P.

    1987-07-30

    The fluorescence properties of 3-hydroxyflavone isolated in solid argon at 15 K have been investigated. Upon electronic excitation the molecules undergo rapid intramolecular proton transfer. No fluorescence from the excited state of the normal form of the molecule could be detected. Perturbations due to hydrogen-bonding impurities which produce serious experimental problems in hydrocarbon glasses are largely suppressed in argon matrices. The rise of the green fluorescence of the tautomer was studied with excitation pulses of 230-fs duration and streak camera detection. An apparent tautomer fluorescence rise time of 2.7 ps was obtained by deconvolution. A comparative measurement of the dye coumarine 6 yielded an apparent fluorescence rise time of 2.5 ps, which can be entirely attributed to the group velocity dispersion of the streak camera optics. This indicates a rate constant for excited-state intramolecular proton transfer in 3-hydroxyflavone of greater than 10/sup 12/ s/sup -1/.

  11. Proton versus neutron excitations in the high-spin spectrum of 102Cd

    NASA Astrophysics Data System (ADS)

    Lieb, K. P.; Kast, D.; Jungclaus, A.; Johnstone, I. P.; de Angelis, G.; Bizzeti, P. G.; Dewald, A.; Fahlander, C.; Górska, M.; Grawe, H.; Peusquens, R.; de Poli, M.; Tiesler, H.

    The structures of the light Cd (Z = 48) isotopes are dominated by two g9/2 proton holes and several neutrons in the d5/2, g7/2, s1/2, d3/2 and/or h11/2 orbits1-5 Up to spin 8+, the even-A isotopes 100,102Cd exhibit two well separated "families" of either proton-hole or neutron-particle character, which communicate by extremely retarded E2 transitions, as small as 10-2 Wu. This implies that the configurations have rather good proton and neutron seniorities. Indeed, the magnetic dipole and electric quadrupole moments of the isomeric {8^+_1} state in 102Cd prove its π-2(99/2)proton-hole structure1 At higher spins, both proton-hole and neutron-particle pairs are broken, giving rise to magnetic dipole bands. It was the aim of the present lifetime measurements to determine absolute Ml and E2 transition strengths in this nucleus in order to test the predictions of two shell model calculations…

  12. Intrinsic spin dynamics in optically excited nanoscale magnetic tunnel junction arrays restored by dielectric coating

    NASA Astrophysics Data System (ADS)

    Jaris, M.; Yahagi, Y.; Mahato, B. K.; Dhuey, S.; Cabrini, S.; Nikitin, V.; Stout, J.; Hawkins, A. R.; Schmidt, H.

    2016-11-01

    We report the all-optical observation of intrinsic spin dynamics and extraction of magnetic material parameters from arrays of sub-100 nm spin-transfer torque magnetic random access memory (STT-MRAM) devices with a CoFeB/MgO interface. To this end, the interference of surface acoustic waves with time-resolved magneto-optic signals via magneto-elastic coupling was suppressed using a dielectric coating. The efficacy of this method is demonstrated experimentally and via modeling on a nickel nanomagnet array. The magnetization dynamics for both coated nickel and STT-MRAM arrays shows a restored field-dependent Kittel mode from which the effective damping can be extracted. We observe an increased low-field damping due to extrinsic contributions from magnetic inhomogeneities and variations in the nanomagnet shape, while the intrinsic Gilbert damping remains unaffected by patterning. The data are in excellent agreement with a local resonance model and have direct implications for the design of STT-MRAM devices as well as other nanoscale spintronic technologies.

  13. Evidence for phonon-like charge and spin fluctuations from an analysis of angle-resolved photoemission spectra of La2-xSrxCuO4 superconductors

    NASA Astrophysics Data System (ADS)

    Mazza, G.; Grilli, M.; Di Castro, C.; Caprara, S.

    2013-01-01

    In high temperature superconductors we provide evidence of spin and mixed phonon-charge collective modes as mediators of the effective electron-electron interaction and suggestive of a charge and spin density wave instability competing with superconductivity. Indeed, we show that the so-called kinks and waterfalls observed in angle-resolved photoemission spectra of La2-xSrxCuO4, a prototypical high-Tc superconducting cuprate, are due to the coupling of quasiparticles with two distinct nearly critical collective modes with finite characteristic wave vectors, typical of charge and spin fluctuations. The simultaneous presence of these two modes reconciles the long standing dichotomy whether kinks are due to phonons or spin waves.

  14. Electron spin polarization transfer to the charge-separated state from locally excited triplet configuration: theory and its application to characterization of geometry and electronic coupling in the electron donor-acceptor system.

    PubMed

    Kobori, Yasuhiro; Fuki, Masaaki; Murai, Hisao

    2010-11-18

    We present a theoretical model of analysis of the time-resolved electron paramagnetic resonance (TREPR) spectrum of the charge-separated (CS) state generated by the photoinduced electron transfer (ET) reaction via the locally excited triplet state in an electron donor-acceptor (D-A) system with a fixed molecular orientation. We show, by the stochastic-Liouville equation, that chemically induced dynamic electron polarization (CIDEP) of the triplet mechanism is explained by lack of transfer of quantum coherence terms in the primary triplet spin state, resulting in net emissive or absorptive electron spin polarization (ESP) which is dependent on anisotropy of the singlet-triplet intersystem crossing in the precursor excited state. This disappearance of the coherence is clearly shown to occur when the photoinduced ET rate is smaller than the angular frequency of the Zeeman splitting: the transferred coherence terms are averaged to be zero due to effective quantum oscillations during the time that the chemical reaction proceeds. The above theory has been applied to elucidate the molecular geometries and spin-spin exchange interactions (2J) of the CS states for both folded and extended conformers by computer simulations of TREPR spectra of the zinc porphyrin-fullerene dyad (ZnP-C(60)) bridged by diphenyldisilane. On the extended conformation, the electronic coupling is estimated from the 2J value. It has been revealed that the coupling term is smaller than the reported electronic interactions of the porphyrin-C(60) systems bridged by diphenylamide spacers. The difference in the electronic couplings has been explained by the difference in the LUMO levels of the bridge moieties that mediate the superexchange coupling for the long-range ET reaction.

  15. Direct observation of low energy nuclear spin excitations in HoCrO3 by high resolution neutron spectroscopy.

    PubMed

    Chatterji, T; Jalarvo, N; Kumar, C M N; Xiao, Y; Brückel, Th

    2013-07-17

    We have investigated low energy nuclear spin excitations in the strongly correlated electron compound HoCrO3. We observe clear inelastic peaks at E = 22.18 ± 0.04 μeV in both energy loss and gain sides. The energy of the inelastic peaks remains constant in the temperature range 1.5-40 K at which they are observed. The intensity of the inelastic peak increases at first with increasing temperature and then decreases at higher temperatures. The temperature dependence of the energy and intensity of the inelastic peaks is very unusual compared to that observed in other Nd, Co, V and also simple Ho compounds. Huge quasielastic scattering appears at higher temperatures presumably due to the fluctuating electronic moments of the Ho ions that get increasingly disordered at higher temperatures. The strong quasielastic scattering may also originate in the first Ho crystal-field excitations at about 1.5 meV.

  16. Dynamic Spin Rig Upgraded With a Five- Axis-Controlled Three-Magnetic-Bearing Support System With Forward Excitation

    NASA Technical Reports Server (NTRS)

    Morrison, Carlos R.; Mehmed, Oral

    2003-01-01

    The NASA Glenn Research Center Dynamic Spin Rig is used for experimental evaluation of vibration analysis methods and dynamic characteristics for rotating systems. Measurements are made while rotors are spun and vibrated in a vacuum chamber. The rig has been upgraded with a new active magnetic bearing rotor support and excitation system. This design is expected to provide operational improvements over the existing rig. The rig will be able to be operated in either the old or new configuration. In the old configuration, two ball bearings support the vertical shaft of the rig, with the test article located between the bearings. Because the bearings operate in a vacuum, lubrication is limited to grease. This limits bearing life and speed. In addition, the old configuration employs two voice-coil electromagnetic shakers to apply oscillatory axial forces or transverse moments to the rotor shaft through a thrust bearing. The excitation amplitudes that can be imparted to the test article with this system are not adequate for components that are highly damped. It is expected that the new design will overcome these limitations.

  17. New insight into the spin-conserving excitation of the negatively charged nitrogen-vacancy center in diamond

    PubMed Central

    Deng, Bei; Zhang, R. Q.; Shi, X. Q.

    2014-01-01

    The negatively charged nitrogen-vacancy (N-V−) color center in diamond is an important solid-state single photon source for applications to quantum communication and distributed quantum computation. Its full usefulness relies on sufficient radiative emission of the optical photons which requires realizable control to enhance emission into the zero-phonon line (ZPL) but until now is still a challenge. Detailed understanding of the associated excitation process would be of essential importance for such objective. Here we report a theoretical work that probes the spin-conserving optical excitation of the N-V− center. Using density-functional-theory (DFT) calculations, we find that the ZPL and the phonon-side band (PSB) depend sensitively on the axial strain of the system. Besides, we find a relatively small PSB appearing at about 100 GPa in the emission spectrum at low temperatures, which provides a means to enhance the coherent emission of the N-V− center in quantum optical networks. PMID:24888367

  18. Excitation of spin-isospin modes in the quasifree scattering region

    SciTech Connect

    Ichimura, M.; Kawahigashi, K.; Joergensen, T.S.; Gaarde, C.

    1989-04-01

    Nuclear spin longitudinal and transverse response functions in the isovector channel are calculated by the continuum random-phase approximation with the orthogonality condition. This method treats the nucleus as of finite size and with a continuum single-particle spectrum. It can include an imaginary potential for the particle states. The corresponding longitudinal and transverse cross sections for /sup 40/Ca(p,p') at E/sub p/ = 500 MeV are calculated by distorted-wave impulse approximation fully quantum mechanically which is beyond the previous analyses by the Glauber approximation. The results are compared with the longitudinal-transverse response ratio extracted from the polarization transfer observables of the Los Alamos experiment. Large effects of the finiteness of the nucleus are seen especially in the longitudinal response. Effects of the distortion diminish the softening and hardening due to nuclear correlation, but the enhancement and quenching still remain. These effects cooperatively reduce the ratio.

  19. Simultaneous laser excitation of backward volume and perpendicular standing spin waves in full-Heusler Co2FeAl0.5Si0.5 films

    PubMed Central

    Chen, Zhifeng; Yan, Yong; Li, Shufa; Xu, Xiaoguang; Jiang, Yong; Lai, Tianshu

    2017-01-01

    Spin-wave dynamics in full-Heusler Co2FeAl0.5Si0.5 films are studied using all-optical pump-probe magneto-optical polar Kerr spectroscopy. Backward volume magnetostatic spin-wave (BVMSW) mode is observed in films with thickness ranging from 20 to 100 nm besides perpendicular standing spin-wave (PSSW) mode, and found to be excited more efficiently than the PSSW mode. The field dependence of the effective Gilbert damping parameter appears especial extrinsic origin. The relationship between the lifetime and the group velocity of BVMSW mode is revealed. The frequency of BVMSW mode does not obviously depend on the film thickness, but the lifetime and the effective damping appear to do so. The simultaneous excitation of BVMSW and PSSW in Heusler alloy films as well as the characterization of their dynamic behaviors may be of interest for magnonic and spintronic applications. PMID:28195160

  20. Simultaneous laser excitation of backward volume and perpendicular standing spin waves in full-Heusler Co2FeAl0.5Si0.5 films

    NASA Astrophysics Data System (ADS)

    Chen, Zhifeng; Yan, Yong; Li, Shufa; Xu, Xiaoguang; Jiang, Yong; Lai, Tianshu

    2017-02-01

    Spin-wave dynamics in full-Heusler Co2FeAl0.5Si0.5 films are studied using all-optical pump-probe magneto-optical polar Kerr spectroscopy. Backward volume magnetostatic spin-wave (BVMSW) mode is observed in films with thickness ranging from 20 to 100 nm besides perpendicular standing spin-wave (PSSW) mode, and found to be excited more efficiently than the PSSW mode. The field dependence of the effective Gilbert damping parameter appears especial extrinsic origin. The relationship between the lifetime and the group velocity of BVMSW mode is revealed. The frequency of BVMSW mode does not obviously depend on the film thickness, but the lifetime and the effective damping appear to do so. The simultaneous excitation of BVMSW and PSSW in Heusler alloy films as well as the characterization of their dynamic behaviors may be of interest for magnonic and spintronic applications.

  1. Synchrotron-radiation study of weak fluorescence from neat liquids of simple alkenes: Anomalous excitation spectra as evidence for wavelength-dependent photochemistry

    SciTech Connect

    Inoue, Yoshihisa; Daino, Yoshihiko; Tai, Akira; Hakushi, Tadao ); Okada, Tadashi )

    1989-07-19

    Fluorescence excitation spectra of trans-2-octene, trans-cyclooctene, 2-methyl-2-butene, and 2,3-dimethyl-2-butene were measured by using synchrotron radiation as a tunable light source in the vacuum UV and UV region. The wavelength dependence of the fluorescence yields provides direct evidence for the long-proposed assignment that the emissive state is the {pi},R(3s) Rydberg state, which in turn gives the carbene-derived photoproducts.

  2. A new Lanczos-based algorithm for simulating high-frequency two-dimensional electron spin resonance spectra

    PubMed Central

    Chiang, Yun-Wei; Freed, Jack H.

    2011-01-01

    The Lanczos algorithm (LA) is a useful iterative method for the reduction of a large matrix to tridiagonal form. It is a storage efficient procedure requiring only the preceding two Lanczos vectors to compute the next. The quasi-minimal residual (QMR) method is a powerful method for the solution of linear equation systems, Ax = b. In this report we provide another application of the QMR method: we incorporate QMR into the LA to monitor the convergence of the Lanczos projections in the reduction of large sparse matrices. We demonstrate that the combined approach of the LA and QMR can be utilized efficiently for the orthogonal transformation of large, but sparse, complex, symmetric matrices, such as are encountered in the simulation of slow-motional 1D- and 2D-electron spin resonance (ESR) spectra. Especially in the 2D-ESR simulations, it is essential that we store all of the Lanczos vectors obtained in the course of the LA recursions and maintain their orthogonality. In the LA-QMR application, the QMR weight matrix mitigates the problem that the Lanczos vectors lose orthogonality after many LA projections. This enables substantially more Lanczos projections, as required to achieve convergence for the more challenging ESR simulations. It, therefore, provides better accuracy for the eigenvectors and the eigenvalues of the large sparse matrices originating in 2D-ESR simulations than does the previously employed method, which is a combined approach of the LA and the conjugate-gradient (CG) methods, as evidenced by the quality and convergence of the 2D-ESR simulations. Our results show that very slow-motional 2D-ESR spectra at W-band (95 GHz) can be reliably simulated using the LA-QMR method, whereas the LA-CG consistently fails. The improvements due to the LA-QMR are of critical importance in enabling the simulation of high-frequency 2D-ESR spectra, which are characterized by their very high resolution to molecular orientation. PMID:21261335

  3. A new Lanczos-based algorithm for simulating high-frequency two-dimensional electron spin resonance spectra.

    PubMed

    Chiang, Yun-Wei; Freed, Jack H

    2011-01-21

    The Lanczos algorithm (LA) is a useful iterative method for the reduction of a large matrix to tridiagonal form. It is a storage efficient procedure requiring only the preceding two Lanczos vectors to compute the next. The quasi-minimal residual (QMR) method is a powerful method for the solution of linear equation systems, Ax = b. In this report we provide another application of the QMR method: we incorporate QMR into the LA to monitor the convergence of the Lanczos projections in the reduction of large sparse matrices. We demonstrate that the combined approach of the LA and QMR can be utilized efficiently for the orthogonal transformation of large, but sparse, complex, symmetric matrices, such as are encountered in the simulation of slow-motional 1D- and 2D-electron spin resonance (ESR) spectra. Especially in the 2D-ESR simulations, it is essential that we store all of the Lanczos vectors obtained in the course of the LA recursions and maintain their orthogonality. In the LA-QMR application, the QMR weight matrix mitigates the problem that the Lanczos vectors lose orthogonality after many LA projections. This enables substantially more Lanczos projections, as required to achieve convergence for the more challenging ESR simulations. It, therefore, provides better accuracy for the eigenvectors and the eigenvalues of the large sparse matrices originating in 2D-ESR simulations than does the previously employed method, which is a combined approach of the LA and the conjugate-gradient (CG) methods, as evidenced by the quality and convergence of the 2D-ESR simulations. Our results show that very slow-motional 2D-ESR spectra at W-band (95 GHz) can be reliably simulated using the LA-QMR method, whereas the LA-CG consistently fails. The improvements due to the LA-QMR are of critical importance in enabling the simulation of high-frequency 2D-ESR spectra, which are characterized by their very high resolution to molecular orientation.

  4. A new Lanczos-based algorithm for simulating high-frequency two-dimensional electron spin resonance spectra

    NASA Astrophysics Data System (ADS)

    Chiang, Yun-Wei; Freed, Jack H.

    2011-01-01

    The Lanczos algorithm (LA) is a useful iterative method for the reduction of a large matrix to tridiagonal form. It is a storage efficient procedure requiring only the preceding two Lanczos vectors to compute the next. The quasi-minimal residual (QMR) method is a powerful method for the solution of linear equation systems, Ax = b. In this report we provide another application of the QMR method: we incorporate QMR into the LA to monitor the convergence of the Lanczos projections in the reduction of large sparse matrices. We demonstrate that the combined approach of the LA and QMR can be utilized efficiently for the orthogonal transformation of large, but sparse, complex, symmetric matrices, such as are encountered in the simulation of slow-motional 1D- and 2D-electron spin resonance (ESR) spectra. Especially in the 2D-ESR simulations, it is essential that we store all of the Lanczos vectors obtained in the course of the LA recursions and maintain their orthogonality. In the LA-QMR application, the QMR weight matrix mitigates the problem that the Lanczos vectors lose orthogonality after many LA projections. This enables substantially more Lanczos projections, as required to achieve convergence for the more challenging ESR simulations. It, therefore, provides better accuracy for the eigenvectors and the eigenvalues of the large sparse matrices originating in 2D-ESR simulations than does the previously employed method, which is a combined approach of the LA and the conjugate-gradient (CG) methods, as evidenced by the quality and convergence of the 2D-ESR simulations. Our results show that very slow-motional 2D-ESR spectra at W-band (95 GHz) can be reliably simulated using the LA-QMR method, whereas the LA-CG consistently fails. The improvements due to the LA-QMR are of critical importance in enabling the simulation of high-frequency 2D-ESR spectra, which are characterized by their very high resolution to molecular orientation.

  5. Comparative assessment of density functional methods for evaluating essential parameters to simulate SERS spectra within the excited state energy gradient approximation

    NASA Astrophysics Data System (ADS)

    Mohammadpour, Mozhdeh; Jamshidi, Zahra

    2016-05-01

    The prospect of challenges in reproducing and interpretation of resonance Raman properties of molecules interacting with metal clusters has prompted the present research initiative. Resonance Raman spectra based on the time-dependent gradient approximation are examined in the framework of density functional theory using different methods for representing the exchange-correlation functional. In this work the performance of different XC functionals in the prediction of ground state properties, excitation state energies, and gradients are compared and discussed. Resonance Raman properties based on time-dependent gradient approximation for the strongly low-lying charge transfer states are calculated and compared for different methods. We draw the following conclusions: (1) for calculating the binding energy and ground state geometry, dispersion-corrected functionals give the best performance in comparison to ab initio calculations, (2) GGA and meta GGA functionals give good accuracy in calculating vibrational frequencies, (3) excited state energies determined by hybrid and range-separated hybrid functionals are in good agreement with EOM-CCSD calculations, and (4) in calculating resonance Raman properties GGA functionals give good and reasonable performance in comparison to the experiment; however, calculating the excited state gradient by using the hybrid functional on the hessian of GGA improves the results of the hybrid functional significantly. Finally, we conclude that the agreement of charge-transfer surface enhanced resonance Raman spectra with experiment is improved significantly by using the excited state gradient approximation.

  6. Spin polarization of the split Kondo state.

    PubMed

    von Bergmann, Kirsten; Ternes, Markus; Loth, Sebastian; Lutz, Christopher P; Heinrich, Andreas J

    2015-02-20

    Spin-resolved scanning tunneling microscopy is employed to quantitatively determine the spin polarization of the magnetic field-split Kondo state. Tunneling conductance spectra of a Kondo-screened magnetic atom are evaluated within a simple model taking into account inelastic tunneling due to spin excitations and two Kondo peaks positioned symmetrically around the Fermi energy. We fit the spin state of the Kondo-screened atom with a spin Hamiltonian independent of the Kondo effect and account for Zeeman splitting of the Kondo peak in the magnetic field. We find that the width and the height of the Kondo peaks scales with the Zeeman energy. Our observations are consistent with full spin polarization of the Kondo peaks, i.e., a majority spin peak below the Fermi energy and a minority spin peak above.

  7. Electronic excitation spectra of molecules in solution calculated using the symmetry-adapted cluster-configuration interaction method in the polarizable continuum model with perturbative approach

    SciTech Connect

    Fukuda, Ryoichi Ehara, Masahiro; Cammi, Roberto

    2014-02-14

    A perturbative approximation of the state specific polarizable continuum model (PCM) symmetry-adapted cluster-configuration interaction (SAC-CI) method is proposed for efficient calculations of the electronic excitations and absorption spectra of molecules in solutions. This first-order PCM SAC-CI method considers the solvent effects on the energies of excited states up to the first-order with using the zeroth-order wavefunctions. This method can avoid the costly iterative procedure of the self-consistent reaction field calculations. The first-order PCM SAC-CI calculations well reproduce the results obtained by the iterative method for various types of excitations of molecules in polar and nonpolar solvents. The first-order contribution is significant for the excitation energies. The results obtained by the zeroth-order PCM SAC-CI, which considers the fixed ground-state reaction field for the excited-state calculations, are deviated from the results by the iterative method about 0.1 eV, and the zeroth-order PCM SAC-CI cannot predict even the direction of solvent shifts in n-hexane for many cases. The first-order PCM SAC-CI is applied to studying the solvatochromisms of (2,2{sup ′}-bipyridine)tetracarbonyltungsten [W(CO){sub 4}(bpy), bpy = 2,2{sup ′}-bipyridine] and bis(pentacarbonyltungsten)pyrazine [(OC){sub 5}W(pyz)W(CO){sub 5}, pyz = pyrazine]. The SAC-CI calculations reveal the detailed character of the excited states and the mechanisms of solvent shifts. The energies of metal to ligand charge transfer states are significantly sensitive to solvents. The first-order PCM SAC-CI well reproduces the observed absorption spectra of the tungsten carbonyl complexes in several solvents.

  8. Spin-transfer torque induced spin waves in antiferromagnetic insulators

    SciTech Connect

    Daniels, Matthew W.; Guo, Wei; Stocks, George Malcolm; Xiao, Di; Xiao, Jiang

    2015-01-01

    We explore the possibility of exciting spin waves in insulating antiferromagnetic films by injecting spin current at the surface. We analyze both magnetically compensated and uncompensated interfaces. We find that the spin current induced spin-transfer torque can excite spin waves in insulating antiferromagnetic materials and that the chirality of the excited spin wave is determined by the polarization of the injected spin current. Furthermore, the presence of magnetic surface anisotropy can greatly increase the accessibility of these excitations.

  9. Describing synchronization and topological excitations in arrays of magnetic spin torque oscillators through the Kuramoto model

    PubMed Central

    Flovik, Vegard; Macià, Ferran; Wahlström, Erik

    2016-01-01

    The collective dynamics in populations of magnetic spin torque oscillators (STO) is an intensely studied topic in modern magnetism. Here, we show that arrays of STO coupled via dipolar fields can be modeled using a variant of the Kuramoto model, a well-known mathematical model in non-linear dynamics. By investigating the collective dynamics in arrays of STO we find that the synchronization in such systems is a finite size effect and show that the critical coupling—for a complete synchronized state—scales with the number of oscillators. Using realistic values of the dipolar coupling strength between STO we show that this imposes an upper limit for the maximum number of oscillators that can be synchronized. Further, we show that the lack of long range order is associated with the formation of topological defects in the phase field similar to the two-dimensional XY model of ferromagnetism. Our results shed new light on the synchronization of STO, where controlling the mutual synchronization of several oscillators is considered crucial for applications. PMID:27580938

  10. Describing synchronization and topological excitations in arrays of magnetic spin torque oscillators through the Kuramoto model.

    PubMed

    Flovik, Vegard; Macià, Ferran; Wahlström, Erik

    2016-09-01

    The collective dynamics in populations of magnetic spin torque oscillators (STO) is an intensely studied topic in modern magnetism. Here, we show that arrays of STO coupled via dipolar fields can be modeled using a variant of the Kuramoto model, a well-known mathematical model in non-linear dynamics. By investigating the collective dynamics in arrays of STO we find that the synchronization in such systems is a finite size effect and show that the critical coupling-for a complete synchronized state-scales with the number of oscillators. Using realistic values of the dipolar coupling strength between STO we show that this imposes an upper limit for the maximum number of oscillators that can be synchronized. Further, we show that the lack of long range order is associated with the formation of topological defects in the phase field similar to the two-dimensional XY model of ferromagnetism. Our results shed new light on the synchronization of STO, where controlling the mutual synchronization of several oscillators is considered crucial for applications.

  11. Describing synchronization and topological excitations in arrays of magnetic spin torque oscillators through the Kuramoto model

    NASA Astrophysics Data System (ADS)

    Flovik, Vegard; Macià, Ferran; Wahlström, Erik

    2016-09-01

    The collective dynamics in populations of magnetic spin torque oscillators (STO) is an intensely studied topic in modern magnetism. Here, we show that arrays of STO coupled via dipolar fields can be modeled using a variant of the Kuramoto model, a well-known mathematical model in non-linear dynamics. By investigating the collective dynamics in arrays of STO we find that the synchronization in such systems is a finite size effect and show that the critical coupling—for a complete synchronized state—scales with the number of oscillators. Using realistic values of the dipolar coupling strength between STO we show that this imposes an upper limit for the maximum number of oscillators that can be synchronized. Further, we show that the lack of long range order is associated with the formation of topological defects in the phase field similar to the two-dimensional XY model of ferromagnetism. Our results shed new light on the synchronization of STO, where controlling the mutual synchronization of several oscillators is considered crucial for applications.

  12. Etats excites en couche interne de haut spin de neon hautement ionise

    NASA Astrophysics Data System (ADS)

    Lapierre, Alain

    En plus d'être observés lors de plusieurs phénomènes d'interactions multi- électroniques et multi-atomiques, la description des états excités en couche interne est un test sensible à celle de la corrélation électronique. Suivant une spectroscopie faisceau- lame effectuée antérieurement des régions spectrales de l'ultraviolet et du visible (1800-5300 Å) de néon à 10 MeV, des raies spectrales (d'émission) satellites de celles des transitions hydrogéniques (l = n - 1) et l < n - 1, n = 6 - n' = 7, n = 7 - n' = 8 et n = 8 - n' = 9 du néon lithiumoïde (Ne VIII) sont assignées à l'aide de calculs Hartree-Fock, à des transitions de mêmes nombres quantiques principaux entre des états quadruplet dont le cœur est excité en 1s2s 3S. Quelques raies sont assignées à des transitions entre des niveaux n = 3 pour le Ne VI, VII et IX. Par la suite, les transitions quadruplet, quintuplet et sextuplet n = 2 - n' = 3 et n = 2 - n' = 4 du néon lithiumoïde, bérylliumoïde (Ne VII) et boroïde (Ne VI), respectivement, ont été investiguées par spectroscopie faisceau-lame dans la région spectrale des XUV (60-125 Å). Ces investigations sont supportées par des calculs Hartree-Fock et des régressions linéaires sur les séquences isoélectroniques, effectués en parallèle. Des mesures de la durée de vie moyenne de termes n = 3 ont été réalisées et plusieurs raies sont nouvellement identifiées à des transitions de Ne VI à IX.

  13. Selective excitation enables assignment of proton resonances and (1)H-(1)H distance measurement in ultrafast magic angle spinning solid state NMR spectroscopy.

    PubMed

    Zhang, Rongchun; Ramamoorthy, Ayyalusamy

    2015-07-21

    Remarkable developments in ultrafast magic angle spinning (MAS) solid-state NMR spectroscopy enabled proton-based high-resolution multidimensional experiments on solids. To fully utilize the benefits rendered by proton-based ultrafast MAS experiments, assignment of (1)H resonances becomes absolutely necessary. Herein, we propose an approach to identify different proton peaks by using dipolar-coupled heteronuclei such as (13)C or (15)N. In this method, after the initial preparation of proton magnetization and cross-polarization to (13)C nuclei, transverse magnetization of desired (13)C nuclei is selectively prepared by using DANTE (Delays Alternating with Nutations for Tailored Excitation) sequence and then, it is transferred to bonded protons with a short-contact-time cross polarization. Our experimental results demonstrate that protons bonded to specific (13)C atoms can be identified and overlapping proton peaks can also be assigned. In contrast to the regular 2D HETCOR experiment, only a few 1D experiments are required for the complete assignment of peaks in the proton spectrum. Furthermore, the finite-pulse radio frequency driven recoupling sequence could be incorporated right after the selection of specific proton signals to monitor the intensity buildup for other proton signals. This enables the extraction of (1)H-(1)H distances between different pairs of protons. Therefore, we believe that the proposed method will greatly aid in fast assignment of peaks in proton spectra and will be useful in the development of proton-based multi-dimensional solid-state NMR experiments to study atomic-level resolution structure and dynamics of solids.

  14. Selective excitation enables assignment of proton resonances and 1H-1H distance measurement in ultrafast magic angle spinning solid state NMR spectroscopy

    NASA Astrophysics Data System (ADS)

    Zhang, Rongchun; Ramamoorthy, Ayyalusamy

    2015-07-01

    Remarkable developments in ultrafast magic angle spinning (MAS) solid-state NMR spectroscopy enabled proton-based high-resolution multidimensional experiments on solids. To fully utilize the benefits rendered by proton-based ultrafast MAS experiments, assignment of 1H resonances becomes absolutely necessary. Herein, we propose an approach to identify different proton peaks by using dipolar-coupled heteronuclei such as 13C or 15N. In this method, after the initial preparation of proton magnetization and cross-polarization to 13C nuclei, transverse magnetization of desired 13C nuclei is selectively prepared by using DANTE (Delays Alternating with Nutations for Tailored Excitation) sequence and then, it is transferred to bonded protons with a short-contact-time cross polarization. Our experimental results demonstrate that protons bonded to specific 13C atoms can be identified and overlapping proton peaks can also be assigned. In contrast to the regular 2D HETCOR experiment, only a few 1D experiments are required for the complete assignment of peaks in the proton spectrum. Furthermore, the finite-pulse radio frequency driven recoupling sequence could be incorporated right after the selection of specific proton signals to monitor the intensity buildup for other proton signals. This enables the extraction of 1H-1H distances between different pairs of protons. Therefore, we believe that the proposed method will greatly aid in fast assignment of peaks in proton spectra and will be useful in the development of proton-based multi-dimensional solid-state NMR experiments to study atomic-level resolution structure and dynamics of solids.

  15. Selective excitation enables assignment of proton resonances and {sup 1}H-{sup 1}H distance measurement in ultrafast magic angle spinning solid state NMR spectroscopy

    SciTech Connect

    Zhang, Rongchun; Ramamoorthy, Ayyalusamy

    2015-07-21

    Remarkable developments in ultrafast magic angle spinning (MAS) solid-state NMR spectroscopy enabled proton-based high-resolution multidimensional experiments on solids. To fully utilize the benefits rendered by proton-based ultrafast MAS experiments, assignment of {sup 1}H resonances becomes absolutely necessary. Herein, we propose an approach to identify different proton peaks by using dipolar-coupled heteronuclei such as {sup 13}C or {sup 15}N. In this method, after the initial preparation of proton magnetization and cross-polarization to {sup 13}C nuclei, transverse magnetization of desired {sup 13}C nuclei is selectively prepared by using DANTE (Delays Alternating with Nutations for Tailored Excitation) sequence and then, it is transferred to bonded protons with a short-contact-time cross polarization. Our experimental results demonstrate that protons bonded to specific {sup 13}C atoms can be identified and overlapping proton peaks can also be assigned. In contrast to the regular 2D HETCOR experiment, only a few 1D experiments are required for the complete assignment of peaks in the proton spectrum. Furthermore, the finite-pulse radio frequency driven recoupling sequence could be incorporated right after the selection of specific proton signals to monitor the intensity buildup for other proton signals. This enables the extraction of {sup 1}H-{sup 1}H distances between different pairs of protons. Therefore, we believe that the proposed method will greatly aid in fast assignment of peaks in proton spectra and will be useful in the development of proton-based multi-dimensional solid-state NMR experiments to study atomic-level resolution structure and dynamics of solids.

  16. Glass-like recovery of antiferromagnetic spin ordering in a photo-excited manganite Pr0.7Ca0.3MnO3

    NASA Astrophysics Data System (ADS)

    Zhou, S. Y.; Langner, M. C.; Zhu, Y.; Chuang, Y.-D.; Rini, M.; Glover, T. E.; Hertlein, M. P.; Gonzalez, A. G. Cruz; Tahir, N.; Tomioka, Y.; Tokura, Y.; Hussain, Z.; Schoenlein, R. W.

    2014-02-01

    Electronic orderings of charges, orbitals and spins are observed in many strongly correlated electron materials, and revealing their dynamics is a critical step toward undertsanding the underlying physics of important emergent phenomena. Here we use time-resolved resonant soft x-ray scattering spectroscopy to probe the dynamics of antiferromagnetic spin ordering in the manganite Pr0.7Ca0.3MnO3 following ultrafast photo-exitation. Our studies reveal a glass-like recovery of the spin ordering and a crossover in the dimensionality of the restoring interaction from quasi-1D at low pump fluence to 3D at high pump fluence. This behavior arises from the metastable state created by photo-excitation, a state characterized by spin disordered metallic droplets within the larger charge- and spin-ordered insulating domains. Comparison with time-resolved resistivity measurements suggests that the collapse of spin ordering is correlated with the insulator-to-metal transition, but the recovery of the insulating phase does not depend on the re-establishment of the spin ordering.

  17. Glass-like recovery of antiferromagnetic spin ordering in a photo-excited manganite Pr₀.₇Ca₀.₃MnO₃.

    PubMed

    Zhou, S Y; Langner, M C; Zhu, Y; Chuang, Y-D; Rini, M; Glover, T E; Hertlein, M P; Gonzalez, A G Cruz; Tahir, N; Tomioka, Y; Tokura, Y; Hussain, Z; Schoenlein, R W

    2014-02-13

    Electronic orderings of charges, orbitals and spins are observed in many strongly correlated electron materials, and revealing their dynamics is a critical step toward undertsanding the underlying physics of important emergent phenomena. Here we use time-resolved resonant soft x-ray scattering spectroscopy to probe the dynamics of antiferromagnetic spin ordering in the manganite Pr₀.₇Ca₀.₃MnO₃ following ultrafast photo-exitation. Our studies reveal a glass-like recovery of the spin ordering and a crossover in the dimensionality of the restoring interaction from quasi-1D at low pump fluence to 3D at high pump fluence. This behavior arises from the metastable state created by photo-excitation, a state characterized by spin disordered metallic droplets within the larger charge- and spin-ordered insulating domains. Comparison with time-resolved resistivity measurements suggests that the collapse of spin ordering is correlated with the insulator-to-metal transition, but the recovery of the insulating phase does not depend on the re-establishment of the spin ordering.

  18. Glass-like recovery of antiferromagnetic spin ordering in a photo-excited manganite Pr0.7Ca0.3MnO3

    SciTech Connect

    Zhou, S. Y.; Langner, M. C.; Zhu, Y.; Chuang, Y. -D.; Rini, M.; Glover, T. E.; Hertlein, M. P.; Gonzalez, A.G. Cruz; Tahir, N.; Tomioka, Y.; Tokura, Y.; Hussain, Z.; Schoenlein, R. W.

    2014-01-16

    Electronic orderings of charges, orbitals and spins are observed in many strongly correlated electron materials, and revealing their dynamics is a critical step toward understanding the underlying physics of important emergent phenomena. Here we use time-resolved resonant soft x-ray scattering spectroscopy to probe the dynamics of antiferromagnetic spin ordering in the manganite Pr0:7Ca0:3MnO3 following ultrafast photo-exitation. Our studies reveal a glass-like recovery of the spin ordering and a crossover in the dimensionality of the restoring interaction from quasi-1D at low pump fluence to 3D at high pump fluence. This behavior arises from the metastable state created by photo-excitation, a state characterized by spin disordered metallic droplets within the larger charge- and spin-ordered insulating domains. Comparison with time-resolved resistivity measurements suggests that the collapse of spin ordering is correlated with the insulator-to-metal transition, but the recovery of the insulating phase does not depend on the re-establishment of the spin ordering.

  19. Glass-like recovery of antiferromagnetic spin ordering in a photo-excited manganite Pr0.7Ca0.3MnO3

    PubMed Central

    Zhou, S. Y.; Langner, M. C.; Zhu, Y.; Chuang, Y.-D.; Rini, M.; Glover, T. E.; Hertlein, M. P.; Gonzalez, A. G. Cruz; Tahir, N.; Tomioka, Y.; Tokura, Y.; Hussain, Z.; Schoenlein, R. W.

    2014-01-01

    Electronic orderings of charges, orbitals and spins are observed in many strongly correlated electron materials, and revealing their dynamics is a critical step toward undertsanding the underlying physics of important emergent phenomena. Here we use time-resolved resonant soft x-ray scattering spectroscopy to probe the dynamics of antiferromagnetic spin ordering in the manganite Pr0.7Ca0.3MnO3 following ultrafast photo-exitation. Our studies reveal a glass-like recovery of the spin ordering and a crossover in the dimensionality of the restoring interaction from quasi-1D at low pump fluence to 3D at high pump fluence. This behavior arises from the metastable state created by photo-excitation, a state characterized by spin disordered metallic droplets within the larger charge- and spin-ordered insulating domains. Comparison with time-resolved resistivity measurements suggests that the collapse of spin ordering is correlated with the insulator-to-metal transition, but the recovery of the insulating phase does not depend on the re-establishment of the spin ordering. PMID:24522173

  20. Near-yrast, medium-spin, excited states of {sup 91}Rb, {sup 93}Rb, and {sup 95}Rb

    SciTech Connect

    Simpson, G. S.; Sieja, K.; Dare, J. A.; Orlandi, R.; Smith, A. G.; Tsekhanovich, I.; Varley, B. J.; Durell, J. L.; Smith, J. F.; Jolie, J.; Linneman, A.; Scherillo, A.; Soldner, T.; Faust, H.; Zlomaniec, A.; Rzaca-Urban, T.; Ahmad, I.; Greene, J. P.

    2010-08-15

    The medium-spin structure of the nuclei {sup 93}Rb and {sup 95}Rb is studied following the neutron-induced fission of {sup 235}U at the PF1B neutron guide, using the FIFI spectrometer, and at the Lohengrin mass spectrometer of the Institut Laue-Langevin Grenoble. These nuclei, plus {sup 91}Rb, are also studied following the spontaneous fission of {sup 248}Cm and {sup 252}Cf sources, using the EUROGAM-II and Gammasphere detector arrays, respectively. A high-spin isomeric state, with a half-life of 111(11) ns, is found in {sup 93}Rb at an excitation energy of 4422.4 keV, which most likely corresponds to the fully aligned [{pi}(g{sub 9/2}) x {nu}(g{sub 7/2}h{sub 11/2})]{sub 27/2}{sup -} configuration. An analogous configuration is proposed for the 5297.9-keV level observed in {sup 91}Rb. A new E3 decay branch of the 1133.9-keV isomer in {sup 91}Rb is found, for which the rather low transition rate of B(E3)=3.8(10) W.u. is determined. The energy of the isomeric state of {sup 95}Rb is now proposed to be at 810.6 keV, with a spin of (9/2{sup +}), and its half-life determined to be T{sub 1/2}=94(7) ns. A cascade of prompt transitions is observed on top of the 810.6-keV isomer in {sup 95}Rb. The near-yrast structures of {sup 91}Rb, {sup 93}Rb, and {sup 95}Rb are compared to the results of shell-model calculations, which support the proposed 27/2{sup -} interpretation of states in {sup 91}Rb and {sup 93}Rb. An analogous 27/2{sup -} state is expected to occur in {sup 95}Rb, as a long-lived isomer at 3.24 MeV. No such isomeric decay could be observed in a measurement using the Lohengrin spectrometer, which shows that, if it exists, its population, following the fission of {sup 235}U, is at least four times lower than that of the analogous 27/2{sup -} isomer in {sup 97}Y.

  1. Infrared, Raman, and ultraviolet absorption spectra and theoretical calculations and structure of 2,6-difluoropyridine in its ground and excited electronic states.

    PubMed

    Sheu, Hong-Li; Kim, Sunghwan; Laane, Jaan

    2013-12-19

    The infrared and Raman spectra of 2,6-difluoropyridine (26DFPy) along with ab initio and DFT computations have been used to assign the vibrations of the molecule in its S0 electronic ground state and to calculate its structure. The ultraviolet absorption spectrum showed the electronic transition to the S1(π,π*) state to be at 37,820.2 cm(-1). With the aid of ab initio computations the vibrational frequencies for this excited state were also determined. TD-B3LYP and CASSCF computations for the excited states were carried out to calculate the structures for the S1(π,π*) and S2(n,π*) excited states. The CASSCF results predict that the S1(π,π*) state is planar and that the S2(n,π*) state has a barrier to planarity of 256 cm(-1). The TD-B3LYP computations predict a barrier of 124 cm(-1) for the S1(π,π*) state, but the experimental results support the planar structure. Hypothetical models for the ring-puckering potential energy function were calculated for both electronic excited states to show the predicted quantum states. The changes in the vibrational frequencies in the two excited states reflect the weaker π bonding within the pyridine ring.

  2. Development of spin-wave-like dispersive excitations below the pseudogap temperature in the high-temperature superconductor La2 -xSrxCuO4

    NASA Astrophysics Data System (ADS)

    Matsuura, M.; Kawamura, S.; Fujita, M.; Kajimoto, R.; Yamada, K.

    2017-01-01

    Inelastic neutron scattering measurements of magnetic excitations in hole-doped high-Tc cuprates La2 -xSrxCuO4 (x =0 and 0.075) have been performed over a wide temperature range of 5-500 K extending beyond the pseudogap temperature of ˜360 K for x =0.075 . For x =0 , the two-dimensional spin-wave excitations at low temperatures are thermally robust and the dispersion is slightly softened on heating up to T =400 K. For x =0.075 , the spin-wave-like excitations in the upper part of the hourglass-shaped dispersion remain at T =300 K. However, further heating above T =400 K induces a broad ridge centered at (1 /2 ,1 /2 ) ; thereby the hourglass-shaped dispersion becomes blurred above the pseudogap temperature. The localized spin nature of magnetic excitations below T* suggests that the pseudogap is related to the proximity to a Mott insulator rather than being a precursor of Cooper pairs.

  3. Equation-of-Motion Coupled-Cluster Theory for Excitation Energies of Closed-Shell Systems with Spin-Orbit Coupling.

    PubMed

    Wang, Zhifan; Tu, Zheyan; Wang, Fan

    2014-12-09

    Excitation energies of closed-shell systems based on the equation-of-motion (EOM) coupled-cluster theory at the singles and doubles (CCSD) level with spin-orbit coupling (SOC) included in the post-Hartree-Fock treatment are implemented in the present work. SOC can be included in both the CC and EOM steps (EOM-SOC-CCSD) or only in the EOM part (SOC-EOM-CCSD). The latter approach is an economical way to account for SOC effects, but excitation energies with this approach are not size-intensive. When the unlinked term in the latter approach is neglected (cSOC-EOM-CCSD), size-intensive excitation energies can be obtained. Time-reversal symmetry and spatial symmetry are exploited to reduce the computational effort. Imposing time-reversal symmetry results in a real matrix representation for the similarity-transformed Hamiltonian, which facilitates the requirement of time-reversal symmetry for new trial vectors in Davidson's algorithm. Results on some closed-shell atoms and molecules containing heavy elements show that EOM-SOC-CCSD can provide excitation energies and spin-orbit splittings with reasonable accuracy. On the other hand, the SOC-EOM-CCSD approach is able to afford accurate estimates of SOC effects for valence electrons of systems containing elements up to the fifth row, while cSOC-EOM-CCSD is less accurate for spin-orbit splittings of transitions involving p1/2 spinors, even for Kr.

  4. Energy dependence of the spin excitation anisotropy in uniaxial-strained BaFe1.9Ni0.1As2

    DOE PAGES

    Song, Yu; Lu, Xingye; Abernathy, Douglas L.; ...

    2015-11-06

    In this study, we use inelastic neutron scattering to study the temperature and energy dependence of the spin excitation anisotropy in uniaxial-strained electron-doped iron pnictide BaFe1.9Ni0.1As2 near optimal superconductivity (Tc = 20K). Our work has been motivated by the observation of in-plane resistivity anisotropy in the paramagnetic tetragonal phase of electron-underdoped iron pnictides under uniaxial pressure, which has been attributed to a spin-driven Ising-nematic state or orbital ordering. Here we show that the spin excitation anisotropy, a signature of the spin-driven Ising-nematic phase, exists for energies below 60 meV in uniaxial-strained BaFe1.9Ni0.1As2. Since this energy scale is considerably larger thanmore » the energy splitting of the dxz and dyz bands of uniaxial-strained Ba(Fe1–xCox)2As2 near optimal superconductivity, spin Ising-nematic correlations are likely the driving force for the resistivity anisotropy and associated electronic nematic correlations.« less

  5. Quantum dynamics of excitations and decoherence in many-spin systems detected with Loschmidt echoes: its relation to their spreading through the Hilbert space.

    PubMed

    Sánchez, C M; Levstein, P R; Buljubasich, L; Pastawski, H M; Chattah, A K

    2016-06-13

    In this work, we overview time-reversal nuclear magnetic resonance (NMR) experiments in many-spin systems evolving under the dipolar Hamiltonian. The Loschmidt echo (LE) in NMR is the signal of excitations which, after evolving with a forward Hamiltonian, is recovered by means of a backward evolution. The presence of non-diagonal terms in the non-equilibrium density matrix of the many-body state is directly monitored experimentally by encoding the multiple quantum coherences. This enables a spin counting procedure, giving information on the spreading of an excitation through the Hilbert space and the formation of clusters of correlated spins. Two samples representing different spin systems with coupled networks were used in the experiments. Protons in polycrystalline ferrocene correspond to an 'infinite' network. By contrast, the liquid crystal N-(4-methoxybenzylidene)-4-butylaniline in the nematic mesophase represents a finite proton system with a hierarchical set of couplings. A close connection was established between the LE decay and the spin counting measurements, confirming the hypothesis that the complexity of the system is driven by the coherent dynamics.

  6. Excitation energies and spins of a superdeformed band in {sup 194}{ital H}{ital g} from one-step discrete decays to the yrast line

    SciTech Connect

    Khoo, T.L.; Carpenter, M.P.; Lauritsen, T.; Ackermann, D.; Ahmad, I.; Blumenthal, D.J.; Fischer, S.M.; Janssens, R.V.; Nisius, D.; Moore, E.F.; Lopez-Martens, A.; Do Kruecken, R.; Asztalos, S.J.; Becker, J.A.; Bernstein, L.; Clark, R.M.; Deleplanque, M.A.; Diamond, R.M.; Fallon, P.; Farris, L.P.; Hannachi, F.; Henry, E.A.; Korichi, A.; Lee, I.Y.; Macchiavelli, A.O.; Stephens, F.S. ||||||

    1996-03-01

    Discrete {gamma} rays directly connecting states of a superdeformed (SD) band in {sup 194}Hg to the yrast states have been discovered. Thus, the excitation energies and spins of all members of the lowest SD band are established for the first time, together with their likely parity. The SD band decays from its 10{sup +} and 12{sup +} states, which lie 4204.8 and 4407.4 keV above the normal-deformed yrast states of the same spins. {copyright} {ital 1996 The American Physical Society.}

  7. Simulated infrared emission spectra of highly excited polyatomic molecules: a detailed model of the PAH-UIR hypothesis.

    PubMed

    Cook, D J; Saykally, R J

    1998-02-01

    A detailed description of the polycyclic aromatic hydrocarbon (PAH)/unidentified infrared band (UIR) mechanism is presented in which experimental spectral bandshape functions are used to simulate IR emission spectra for individual molecules. These spectra are additively superimposed to produce a conglomerate spectrum representative of a family of PAH molecules. Ab initio vibrational frequencies and intensities for nine PAHs (neutral and cationic) as large as ovalene are used in conjunction with measured bandshape and temperature-dependent redshift data to simulate the UIR bands. The calculated spectra of cations provide a closer match to the UIRs than do those of the neutrals. However, the PAH cations used in the simulations fail to reproduce the details of the UIR emission spectra. The discrepancies are potentially alleviated if both larger PAHs and a greater number of PAHs were included in the simulation.

  8. Simulated infrared emission spectra of highly excited polyatomic molecules: a detailed model of the PAH-UIR hypothesis

    NASA Technical Reports Server (NTRS)

    Cook, D. J.; Saykally, R. J.

    1998-01-01

    A detailed description of the polycyclic aromatic hydrocarbon (PAH)/unidentified infrared band (UIR) mechanism is presented in which experimental spectral bandshape functions are used to simulate IR emission spectra for individual molecules. These spectra are additively superimposed to produce a conglomerate spectrum representative of a family of PAH molecules. Ab initio vibrational frequencies and intensities for nine PAHs (neutral and cationic) as large as ovalene are used in conjunction with measured bandshape and temperature-dependent redshift data to simulate the UIR bands. The calculated spectra of cations provide a closer match to the UIRs than do those of the neutrals. However, the PAH cations used in the simulations fail to reproduce the details of the UIR emission spectra. The discrepancies are potentially alleviated if both larger PAHs and a greater number of PAHs were included in the simulation.

  9. An efficient computational scheme for electronic excitation spectra of molecules in solution using the symmetry-adapted cluster–configuration interaction method: The accuracy of excitation energies and intuitive charge-transfer indices

    SciTech Connect

    Fukuda, Ryoichi Ehara, Masahiro

    2014-10-21

    Solvent effects on electronic excitation spectra are considerable in many situations; therefore, we propose an efficient and reliable computational scheme that is based on the symmetry-adapted cluster-configuration interaction (SAC-CI) method and the polarizable continuum model (PCM) for describing electronic excitations in solution. The new scheme combines the recently proposed first-order PCM SAC-CI method with the PTE (perturbation theory at the energy level) PCM SAC scheme. This is essentially equivalent to the usual SAC and SAC-CI computations with using the PCM Hartree-Fock orbital and integrals, except for the additional correction terms that represent solute-solvent interactions. The test calculations demonstrate that the present method is a very good approximation of the more costly iterative PCM SAC-CI method for excitation energies of closed-shell molecules in their equilibrium geometry. This method provides very accurate values of electric dipole moments but is insufficient for describing the charge-transfer (CT) indices in polar solvent. The present method accurately reproduces the absorption spectra and their solvatochromism of push-pull type 2,2{sup ′}-bithiophene molecules. Significant solvent and substituent effects on these molecules are intuitively visualized using the CT indices. The present method is the simplest and theoretically consistent extension of SAC-CI method for including PCM environment, and therefore, it is useful for theoretical and computational spectroscopy.

  10. The role of core excitations in the structure and decay of the 16+ spin-gap isomer in 96Cd

    NASA Astrophysics Data System (ADS)

    Davies, P. J.; Grawe, H.; Moschner, K.; Blazhev, A.; Wadsworth, R.; Boutachkov, P.; Ameil, F.; Yagi, A.; Baba, H.; Bäck, T.; Dewald, M.; Doornenbal, P.; Faestermann, T.; Gengelbach, A.; Gerl, J.; Gernhäeuser, R.; Go, S.; Górska, M.; Gregor, E.; Isobe, T.; Jenkins, D. G.; Hotaka, H.; Jolie, J.; Kojouharov, I.; Kurz, N.; Lewitowicz, M.; Lorusso, G.; Maier, L.; Merchan, E.; Naqvi, F.; Nishibata, H.; Nishimura, D.; Nishimura, S.; Nowacki, F.; Pietralla, N.; Schaffner, H.; Söderström, P.-A.; Jung, H. S.; Steiger, K.; Sumikama, T.; Taprogge, J.; Thöle, P.; Warr, N.; Watanabe, H.; Werner, V.; Xu, Z. Y.; Yoshinaga, K.; Zhu, Y.

    2017-04-01

    The first evidence for β-delayed proton emission from the 16+ spin gap isomer in 96Cd is presented. The data were obtained from the Rare Isotope Beam Factory, at the RIKEN Nishina Center, using the BigRIPS spectrometer and the EURICA decay station. βp branching ratios for the ground state and 16+ isomer have been extracted along with more precise lifetimes for these states and the lifetime for the ground state decay of 95Cd. Large scale shell model (LSSM) calculations have been performed and WKB estimates made for ℓ = 0 , 2 , 4 proton emission from three resonance-like states in 96Ag, that are populated by the β decay of the isomer, and the results compared to the new data. The calculations suggest that ℓ = 2 proton emission from the resonance states, which reside ∼ 5 MeV above the proton separation energy, dominates the proton decay. The results highlight the importance of core-excited wavefunction components for the 16+ state.

  11. Estimation of ground and excited state dipole moment of laser dyes C504T and C521T using solvatochromic shifts of absorption and fluorescence spectra

    NASA Astrophysics Data System (ADS)

    Basavaraja, Jana; Suresh Kumar, H. M.; Inamdar, S. R.; Wari, M. N.

    2016-02-01

    The absorption and fluorescence spectra of laser dyes: coumarin 504T (C504T) and coumarin 521T (C521T) have been recorded at room temperature in a series of non-polar and polar solvents. The spectra of these dyes showed bathochromic shift with increasing in solvent polarity indicating the involvement of π → π* transition. Kamlet-Taft and Catalan solvent parameters were used to analyze the effect of solvents on C504T and C521T molecules. The study reveals that both general solute-solvent interactions and specific interactions are operative in these two systems. The ground state dipole moment was estimated using Guggenheim's method and also by quantum mechanical calculations. The solvatochromic data were used to determine the excited state dipole moment (μe). It is observed that dipole moment value of excited state (μe) is higher than that of the ground state in both the laser dyes indicating that these dyes are more polar in nature in the excited state than in the ground state.

  12. Estimation of ground and excited state dipole moment of laser dyes C504T and C521T using solvatochromic shifts of absorption and fluorescence spectra.

    PubMed

    Basavaraja, Jana; Kumar, H M Suresh; Inamdar, S R; Wari, M N

    2016-02-05

    The absorption and fluorescence spectra of laser dyes: coumarin 504T (C504T) and coumarin 521T (C521T) have been recorded at room temperature in a series of non-polar and polar solvents. The spectra of these dyes showed bathochromic shift with increasing in solvent polarity indicating the involvement of π→π⁎ transition. Kamlet-Taft and Catalan solvent parameters were used to analyze the effect of solvents on C504T and C521T molecules. The study reveals that both general solute-solvent interactions and specific interactions are operative in these two systems. The ground state dipole moment was estimated using Guggenheim's method and also by quantum mechanical calculations. The solvatochromic data were used to determine the excited state dipole moment (μ(e)). It is observed that dipole moment value of excited state (μ(e)) is higher than that of the ground state in both the laser dyes indicating that these dyes are more polar in nature in the excited state than in the ground state.

  13. S1←S0 vibronic spectra and structure of cyclopropanecarboxaldehyde molecule in the S1 lowest excited singlet electronic state

    NASA Astrophysics Data System (ADS)

    Godunov, I. A.; Yakovlev, N. N.; Terentiev, R. V.; Maslov, D. V.; Bataev, V. A.; Abramenkov, A. V.

    2016-11-01

    The S1←S0 vibronic spectra of gas-phase absorption at room temperature and fluorescence excitation of jet-cooled cyclopropanecarboxaldehyde (CPCA, c-C3H5CHO)were obtained and analyzed. In addition, the quantum chemical calculation (CASPT2/cc-pVTZ)was carried out for CPCA in the ground (S0) and lowest excited singlet (S1) electronic states. As a result, it was proved that the S1←S0 electronic excitation of the CPCA conformers (syn and anti) causes (after geometrical relaxation) significant structural changes, namely, the carbonyl fragments become non-planar and the cyclopropyl groups rotate around the central C-C bond. As a consequence, the potential energy surface of CPCA in the S1 state has six minima, 1ab, 2ab, and 3ab, corresponding to three pairs of mirror symmetry conformers: a and b. It was shown that vibronic bands of experimental spectra can be assigned to the 2(S1)←syn(S0) electronic transition with the origin at 30,481 cm-1. A number of fundamental vibrational frequencies for the 2 conformer of CPCA were assigned. In addition, several inversional energy levels for the 2 conformer were found and the 2a↔2b potential function of inversion was determined. The experimental barrier to inversion and the equilibrium angle between the CH bond and the CCO plane were calculated as 570 cm-1 and 28°, respectively.

  14. Zero-field splitting of the ground and excited triplet states of 2-naphthylphenylcarbene studied by hole-burning on triplet-triplet fluorescence excitation spectra

    NASA Astrophysics Data System (ADS)

    Kozankiewicz, B.; Bernard, J.; Migirdicyan, E.; Orrit, M.; Platz, M. S.

    1995-11-01

    Spectral holes were burned in the two main lines of the triplet-triplet 0-0 fluorescence excitation spectrum of 2-napththylphenylcarbene in n-hexane at 1.8 K. For the line assigned to pseudo-E/trans conformer, the central hole at the frequency of burning light has several narrow components separated by 0.3 ± 0.05 and 1.0 ± 0.1 GHz and a satellite doublet line on the low energy side, 14.5 ± 0.5 and 15.5 ± 0.5 GHz away. For the line assigned to the psuedo-Z/cis conformer, the central hole is accompanied by holes burned on the low energy side, 0.8 ± 0.1, 5.2 ± 0.1, 11.9 ± 0.1 and 16.2 ± 0.1 GHz away. The hole-burning pattern is explained by a model taking into account the zero-field splitting (ZFS) of the ground T 0 and excited T 1 triplet states as well as the selectivity of excitation relaxation by the intersystem crossing channel. Analysis provides information about the ZFS parameters of the T 1 state. For the pseudo-E/trans 2-NPC they are: D0 = 0.47 ± 0.02 cm -1, E0 = 0.017 ± 0.003 cm -1, D1 = 0.038 ± 0.003 cm -1 and E1 = 0.005 ± 0.001 cm -1.

  15. Ultrafast deactivation mechanism of the excited singlet in the light-induced spin crossover of [Fe(2,2'-bipyridine)3]2+.

    PubMed

    Sousa, Carmen; de Graaf, Coen; Rudavskyi, Andrii; Broer, Ria; Tatchen, Jörg; Etinski, Mihajlo; Marian, Christel M

    2013-12-16

    The mechanism of the light-induced spin crossover of the [Fe(bpy)3](2+) complex (bpy=2,2'-bipyridine) has been studied by combining accurate electronic-structure calculations and time-dependent approaches to calculate intersystem-crossing rates. We investigate how the initially excited metal-to-ligand charge transfer (MLCT) singlet state deactivates to the final metastable high-spin state. Although ultrafast X-ray free-electron spectroscopy has established that the total timescale of this process is on the order of a few tenths of a picosecond, the details of the mechanisms still remain unclear. We determine all the intermediate electronic states along the pathway from low spin to high spin and give estimates for the deactivation times of the different stages. The calculations result in a total deactivation time on the same order of magnitude as the experimentally determined rate and indicate that the complex can reach the final high-spin state by means of different deactivation channels. The optically populated excited singlet state rapidly decays to a triplet state with an Fe d(6)(t(2g)(5)e(g)(1)) configuration either directly or by means of a triplet MLCT state. This triplet ligand-field state could in principle decay directly to the final quintet state, but a much faster channel is provided by internal conversion to a lower-lying triplet state and subsequent intersystem crossing to the high-spin state. The deactivation rate to the low-spin ground state is much smaller, which is in line with the large quantum yield reported for the process.

  16. Recent research directions in Fribourg: nuclear dynamics in resonances revealed by 2-dimensional EEL spectra, electron collisions with ionic liquids and electronic excitation of pyrimidine

    NASA Astrophysics Data System (ADS)

    Allan, Michael; Regeta, Khrystyna; Gorfinkiel, Jimena D.; Mašín, Zdeněk; Grimme, Stefan; Bannwarth, Christoph

    2016-05-01

    The article briefly reviews three subjects recently investigated in Fribourg: (i) electron collisions with surfaces of ionic liquids, (ii) two-dimensional (2D) electron energy loss spectra and (iii) resonances in absolute cross sections for electronic excitation of unsaturated compounds. Electron energy loss spectra of four ionic liquids revealed a number of excited states, including triplet states. A solution of a dye in an ionic liquid showed an energy-loss band of the solute, but not in all ionic liquids. 2D spectra reveal state-to-state information (given resonance to given final state) and are shown to be an interesting means to gain insight into dynamics of nuclear motion in resonances. Absolute cross sections for pyrimidine are reported as a function of scattering angle and as a function of electron energy. They reveal resonant structure which was reproduced very nicely by R-matrix calculations. The calculation provided an assignment of the resonances which reveals common patterns in compounds containing double bonds.

  17. Optically Induced Nuclear Spin Polarization in the Quantum Hall Regime: The Effect of Electron Spin Polarization through Exciton and Trion Excitations.

    PubMed

    Akiba, K; Kanasugi, S; Yuge, T; Nagase, K; Hirayama, Y

    2015-07-10

    We study nuclear spin polarization in the quantum Hall regime through the optically pumped electron spin polarization in the lowest Landau level. The nuclear spin polarization is measured as a nuclear magnetic field B(N) by means of the sensitive resistive detection. We find the dependence of B(N) on the filling factor nonmonotonic. The comprehensive measurements of B(N) with the help of the circularly polarized photoluminescence measurements indicate the participation of the photoexcited complexes, i.e., the exciton and trion (charged exciton), in nuclear spin polarization. On the basis of a novel estimation method of the equilibrium electron spin polarization, we analyze the experimental data and conclude that the filling factor dependence of B(N) is understood by the effect of electron spin polarization through excitons and trions.

  18. FractionalSzExcitation and Its Boundstate for theS=1/2 Antiferromagnetic Zigzag Spin Chain in a Magnetic Field

    NASA Astrophysics Data System (ADS)

    Okunishi, Kouichi; Tonegawa, Takashi

    2005-01-01

    We demonstrate that domain-wall type excitations carrying the fractional magnetization $S^z=\\pm1/3$ and their bound state describe the low-energy physics around the 1/3 plateau of the antiferromagnetic zigzag spin chain in the strongly frustrated region. In particular we discuss the relevance of such domain-wall excitations to the characteristic properties of the magnetization curves: the 1/3 plateau accompanying the spontaneous symmetry breaking of the translation, the cusp singularities above and/or below the plateau, and the even-odd effect in the magnetization curve.

  19. Effect of the chirality of residues and γ-turns on the electronic excitation spectra, excited-state reaction paths and conical intersections of capped phenylalanine-alanine dipeptides.

    PubMed

    Shemesh, Dorit; Domcke, Wolfgang

    2011-07-11

    The capped dipeptides Ac-L-Phe-Xxx-NH(2) , Xxx=L-Ala, D-Ala, Aib, where Aib (aminoisobutyric acid) is a non-chiral amino acid, have been investigated by means of UV/IR double-resonance spectroscopy in supersonic jets and density functional theory calculations by Gloaguen et al. [Phys. Chem. Chem. Phys. 2007, 9, 4491]. The UV and IR spectra of five different species were observed and their structures assigned by comparison with calculated vibrational frequencies in the NH-stretching region. The peptides with two chiral residues can form homochiral or heterochiral species. In addition, γ-turns exist as two helical forms (γ(D), γ(L)) of opposite handedness. Herein, we explore the excited-state potential-energy surfaces of these dipeptides with ab initio calculations. Vertical and adiabatic excitation energies, excited-state reaction paths and conical intersections are characterized with the ADC(2) propagator method. It is shown that electron/proton transfer along the hydrogen bond of the γ-turn gives rise to efficient radiationless deactivation of the (1)ππ* state of the chromophore via several conical intersections. While the homo/hetero chirality of the residues appears to have a negligible effect on the photophysical dynamics, we found evidence that the γ(L) conformers may have shorter excited-state lifetimes (and thus higher photostability) than the γ(D) conformers.

  20. Quantitative treatment of the solvent effects on the electronic absorption and fluorescence spectra of acridines and phenazines. The ground and first excited singlet-state dipole moments

    NASA Astrophysics Data System (ADS)

    Aaron, Jean Jacques; Maafi, Mounir; Párkányi, Cyril; Boniface, Christian

    1995-04-01

    Electronic absorption and fluorescence excitation and emission spectra of four acridines (acridine, Acridine Yellow, 9-aminoacridine and proflavine) and three phenazines (phenazine, neutral Red and safranine) are determined at room temperature (298 K) in several solvents of various polarities (dioxane, chloroform, ethyl ether, ethyl acetate, 1-butanol, 2-propanol, ethanol, methanol, dimethylformamide, acetonitrile and dimethyl sulfoxide). The effect of the solvent upon the spectral characteristics of the above compounds, is studied. In combination with the ground-state dipole moments of these compounds, the spectral data are used to evaluate their first excited singlet-state dipole moments by means of the solvatochromic shift method (Bakhshiev's and Kawski-Chamma-Viallet's correlations). The theoretical ground and excited singlet-state dipole moments for acridines and phenazines are also calculated as a vector sum of the π-component (obtained by the PPP method) and the σ-component (obtained from σ-bond moments). For most acridines and phenazines under study, the experimental excited singlet-state dipole moments are found to be higher than their ground state counterpart. The application of the Kamlet-Abboud-Taft solvatochromic parameters to the solvent effect on spectral properties of acridine and phenazine derivatives is discussed.

  1. Solvent effect on the absorption and fluorescence spectra of 7-acetoxy-6-(2,3-dibromopropyl)-4,8-dimethylcoumarin: determination of ground and excited state dipole moments.

    PubMed

    Gülseven Sıdır, Yadigar; Sıdır, Isa

    2013-02-01

    The ground state (μ(g)) and excited state (μ(e)) dipole moments of 7-acetoxy-6-(2,3-dibromopropyl)-4,8-dimethylcoumarin (abbreviated as 7ADDC) are estimated from solvatochromic shifts of absorption and fluorescence spectra as a function of the dielectric constant (ε) and refractive index (n). While the ground state dipole moment is determined by using Bilot-Kawski method, the excited state dipole moment is calculated by using Bilot-Kawski, Lippert-Mataga, Bakhshiev, Kawski-Chamma-Viallet and Reichardt correlation methods. Excited state dipole moment is observed as larger than the ground state dipole moment due to substantial π-electron density redistribution. The ground state and excited state dipole moments are observed as parallel to each other with angle of 0°. Solute-solvent interactions are analyzed by means of linear solvation free energy relationships (LSER) using dielectric constant function (f(ε)), refractive index function (f(n)) and Kamlet-Taft parameters (α and β). Atomic charges, electron densities and molecular orbitals are calculated in vacuum and with solvent effect by using both DFT and TDDFT methods. Solvent accessible surface, molecular electrostatic potential (MEP) and electrostatic potential (ESP) are visualized as a result of DFT calculations.

  2. Quantitative treatment of the effect of solvent on the electronic absorption and fluorescence spectra of substituted coumarins: Evaluation of the first excited singlet-state dipole moments.

    PubMed

    Aaron, J J; Buna, M; Parkanyi, C; Antonious, M S; Tine, A; Cisse, L

    1995-12-01

    The electronic absorption and fluorescence spectra of coumarin and 11 substituted coumarins were measured in several solvents (dioxane, ethyl ether, ethyl acetate, ethanol, dimethylformamide, acetonitrile, and dimethyl sulfoxide). Ground-state dipole moments were determined in dioxane at 298 K. The results were used to obtain the first excited singlet-state dipole moments of the coumarins under study by the solvatochromic shift method (Bakhshiev, Kawski-Chamma-Viallet, McRae, and Suppan correlations). Also, the ground- and the first excited singlet-state dipole moments were calculated using a combination of the PPP method (π-contribution) and the vector sum of the σ-bond and group moments (σ-contribution). In general, the first excited singlet-state dipole moments of the coumarins are noticeably higher than the corresponding ground-state values, indicating a substantial redistribution of theπ-electron densities resulting in a more polar excited state. There is a reasonably good agreement between the calculated and the experimental dipole moments.

  3. Solvent effect on the absorption and fluorescence spectra of 7-acetoxy-6-(2,3-dibromopropyl)-4,8-dimethylcoumarin: Determination of ground and excited state dipole moments

    NASA Astrophysics Data System (ADS)

    Gülseven Sıdır, Yadigar; Sıdır, İsa

    2013-02-01

    The ground state (μg) and excited state (μe) dipole moments of 7-acetoxy-6-(2,3-dibromopropyl)-4,8-dimethylcoumarin (abbreviated as 7ADDC) are estimated from solvatochromic shifts of absorption and fluorescence spectra as a function of the dielectric constant (ɛ) and refractive index (n). While the ground state dipole moment is determined by using Bilot-Kawski method, the excited state dipole moment is calculated by using Bilot-Kawski, Lippert-Mataga, Bakhshiev, Kawski-Chamma-Viallet and Reichardt correlation methods. Excited state dipole moment is observed as larger than the ground state dipole moment due to substantial π-electron density redistribution. The ground state and excited state dipole moments are observed as parallel to each other with angle of 0°. Solute-solvent interactions are analyzed by means of linear solvation free energy relationships (LSER) using dielectric constant function (f(ɛ)), refractive index function (f(n)) and Kamlet-Taft parameters (α and β). Atomic charges, electron densities and molecular orbitals are calculated in vacuum and with solvent effect by using both DFT and TDDFT methods. Solvent accessible surface, molecular electrostatic potential (MEP) and electrostatic potential (ESP) are visualized as a result of DFT calculations.

  4. Impact of magnetic fluctuations on lattice excitations in fcc nickel.

    PubMed

    Körmann, Fritz; Ma, Pui-Wai; Dudarev, Sergei L; Neugebauer, Jörg

    2016-02-24

    The spin-space averaging formalism is applied to compute atomic forces and phonon spectra for magnetically excited states of fcc nickel. Transverse and longitudinal magnetic fluctuations are taken into account by a combination of magnetic special quasi random structures and constrained spin-density-functional theory. It turns out that for fcc Ni interatomic force constants and phonon spectra are almost unaffected by both kinds of spin fluctuations. Given the computational expense to simulate coupled magnetic and atomic fluctuations, this insight facilitates computational modeling of magnetic alloys such as Ni-based superalloys.

  5. Calculating vibrational spectra without determining excited eigenstates: Solving the complex linear equations of damped response theory for vibrational configuration interaction and vibrational coupled cluster states.

    PubMed

    Godtliebsen, Ian H; Christiansen, Ove

    2015-10-07

    It is demonstrated how vibrational IR and Raman spectra can be calculated from damped response functions using anharmonic vibrational wave function calculations, without determining the potentially very many eigenstates of the system. We present an implementation for vibrational configuration interaction and vibrational coupled cluster, and describe how the complex equations can be solved using iterative techniques employing only real trial vectors and real matrix-vector transformations. Using this algorithm, arbitrary frequency intervals can be scanned independent of the number of excited states. Sample calculations are presented for the IR-spectrum of water, Raman spectra of pyridine and a pyridine-silver complex, as well as for the infra-red spectrum of oxazole, and vibrational corrections to the polarizability of formaldehyde.

  6. Calculating vibrational spectra without determining excited eigenstates: Solving the complex linear equations of damped response theory for vibrational configuration interaction and vibrational coupled cluster states

    NASA Astrophysics Data System (ADS)

    Godtliebsen, Ian H.; Christiansen, Ove

    2015-10-01

    It is demonstrated how vibrational IR and Raman spectra can be calculated from damped response functions using anharmonic vibrational wave function calculations, without determining the potentially very many eigenstates of the system. We present an implementation for vibrational configuration interaction and vibrational coupled cluster, and describe how the complex equations can be solved using iterative techniques employing only real trial vectors and real matrix-vector transformations. Using this algorithm, arbitrary frequency intervals can be scanned independent of the number of excited states. Sample calculations are presented for the IR-spectrum of water, Raman spectra of pyridine and a pyridine-silver complex, as well as for the infra-red spectrum of oxazole, and vibrational corrections to the polarizability of formaldehyde.

  7. Estimation of ground- and excited-state dipole moments of Nile Red dye from solvatochromic effect on absorption and fluorescence spectra

    NASA Astrophysics Data System (ADS)

    Kawski, A.; Bojarski, P.; Kukliński, B.

    2008-10-01

    The effect of various nonpolar and polar solvents on the location of absorption and fluorescence of Nile Red at room temperature was investigated. Based on the batochromic shift of electronic spectra of Nile Red and Bilot-Kawski theory the following values of ground- and excited-state dipole moments μg = 8.2 ± 1.0 D and μe = 10.0 ± 1.0 D were found. The reasons of high discrepancy between the literature results were discussed.

  8. Excited state solvatochromic and prototropic behaviour of 4-aminodiphenylamine and 4,4'-diaminodiphenylamine—A comparative study by electronic spectra

    NASA Astrophysics Data System (ADS)

    Nayaki, S. Kothai; Swaminathan, M.

    2006-06-01

    Solvatochromic and prototropic behaviour of 4-aminodiphenylamine (4ADA) and 4,4'-diaminodiphenylamine (DADA) have been investigated in the solvents of different polarity and at various acid-base concentrations in the ground and excited states using absorption and fluorescence spectra. Solvatochromic shifts have been analysed and observed shifts are explained by the hydrogen bonding interactions. The prototropic study reveals that (i) absorption maximum of monocation of DADA is red shifted to its neutral form, and (ii) the fluorescence of 4ADA is red shifted on protonation. The abnormal fluorescence of 4ADA + is found to be due to large solvent relaxation in polar medium.

  9. Electronic Raman scattering with excitation between localized states observed in the zinc M{sub 2,3} soft x-ray spectra of ZnS

    SciTech Connect

    Zhou, L.; Callcott, T.A.; Jia, J.J.

    1997-04-01

    Zn M{sub 2,3} soft x-ray fluorescence (SXF) spectra of ZnS and ZnS{sub .5}Se{sub .5} excited near threshold show strong inelastic scattering effects that can be explained using a simple model and an inelastic scattering theory based on second order perturbation theory. This scattering is often called electronic resonance Raman scattering. Tulkki and Aberg have developed this theory in detail for atomic systems, but their treatment can be applied to solid systems by utilizing electronic states characteristic of solids rather than of atomic systems.

  10. Intramolecular hydrogen bonding and excited state proton transfer in hydroxyanthraquinones as studied by electronic spectra, resonance Raman scattering, and transform analysis

    NASA Astrophysics Data System (ADS)

    Marzocchi, Mario P.; Mantini, Anna R.; Casu, Maurizio; Smulevich, Giulietta

    1998-01-01

    The scheme of energy levels previously proposed to describe dual excitation and emission associated to excited state intramolecular proton transfer (ESIPT) of some hydroxyanthraquinones (HAQ's) has been made more quantitative in the present paper. The zero-point energy and the frequency of the νOH mode for the HAQ's have been calculated on the basis of the Lippincott-Schroeder double-minimum potential for the O-H⋯O hydrogen bond. The second derivative absorption (D2) spectra show that the vibrational structures of the electronic excited state of HAQ's giving rise to ESIPT are characterized by the progression of the νOH stretching mode. The νOH mode in the ground state is observed as a very strong band in the vibrational structure of the short wavelength emission for HAQ's showing ESIPT. The combined resonance Raman band assignment of four hydroxyanthraquinones and transform analysis show that the visible transition involves the hydrogen bonded cycle and induces proton transfer in the excited state in most cases. On the basis of the isotopic effects, some vibrations of the hydrogen bonded cycle, namely the νC=O, δC=O, νCOH, and δOH modes, have been identified. The transform method, including the combined analysis of the absorption and D2 spectra in terms of sum-over-states, was checked by directly deriving the displacement parameters (Franck-Condon factors) of 1,4-DHAQ from the high resolution free-jet spectrum. The values of the displacement parameters of the νOH mode are quite large for the HAQ's showing ESIPT, while are negligible for 1,4-DHAQ. High values of the displacement parameters for the other vibrations of the hydrogen bonded cycle were found for all HAQ's.

  11. Femtosecond laser excitation of multiple spin waves and composition dependence of Gilbert damping in full-Heusler Co2Fe1-xMnxAl films

    NASA Astrophysics Data System (ADS)

    Cheng, Chuyuan; Meng, Kangkang; Li, Shufa; Zhao, Jianhua; Lai, Tianshu

    2013-12-01

    Spin-wave dynamics in 30 nm thick Co2Fe1-xMnxAl full-Heusler films is investigated using time-resolved magneto-optical polar Kerr spectroscopy under an external field perpendicular to films. Damon-Eshbach (DE) and the first-order perpendicular standing spin-wave (PSSW) modes are observed simultaneously in four samples with x = 0, 0.3, 0.7, and 1. The frequency of DE and PSSW modes does not apparently depend on composition x, but damping of DE mode significantly on x and reaches the minimum as x = 0.7. The efficient coherent excitation of DE spin wave exhibits the promising application of Co2Fe0.3Mn0.7Al films in magnonic devices.

  12. Quasi-two-dimensional spin and phonon excitations in La1.965Ba0.035CuO4

    DOE PAGES

    Wagman, J. J.; Parshall, D.; Stone, Matthew B.; ...

    2015-06-03

    Here, we present time-of-fight inelastic neutron scattering measurements of La1.965Ba0.035CuO4 (LBCO), a lightly doped member of the high temperature superconducting La-based cuprate family. By using time-of-flight neutron instrumentation coupled with single crystal sample rotation we obtain a four-dimensional data set (three Q and one energy) that is both comprehensive and spans a large region of reciprocal space. Our measurements identify rich structure in the energy dependence of the highly dispersive spin excitations, which are centered at equivalent (1/2, 1/2, L) wave-vectors. These structures correlate strongly with several crossings of the spin excitations with the lightly dispersive phonons found in thismore » system. These eects are signicant and account for on the order of 25% of the total inelastic scattering for energies between ≈5 and 40meV at low |Q|. Interestingly, this scattering also presents little or no L-dependence. As the phonons and dispersive spin excitations centred at equivalent (1/2, 1/2, L) wave-vectors are common to all members of La-based 214 copper oxides, we conclude such strong quasi-two dimensional scattering enhancements are likely to occur in all such 214 families of materials, including those concentrations corresponding to superconducting ground states. Such a phenomenon appears to be a fundamental characteristic of these materials and is potentially related to superconducting pairing.« less

  13. The rotational spectra of the ground and first excited bending states of deuterium isocyanide, DNC, up to 2 THz

    NASA Astrophysics Data System (ADS)

    Brünken, S.; Müller, H. S. P.; Thorwirth, S.; Lewen, F.; Winnewisser, G.

    2006-01-01

    The pure rotational spectrum of deuterium isocyanide (DNC) was recorded in the frequency range from approximately 680 to 1985 GHz. Twenty-one new transitions in the vibrational ground and first excited bending states (01e,f 0) have been assigned, namely R-branch transitions from J=9-8 to 25-24. In a least squares analysis of these new transition frequencies together with previously reported millimeter-wave data, spectroscopic parameters up to sextic order could be derived with high precision for both states. Furthermore, the l-type doubling constant q and its centrifugal distortion terms qJ and qJJ were obtained for the first excited bending state.

  14. Fluorescence Excitation Spectra of Photo-Fragmented Nitrobenzene Using a Picosecond Laser: Potential Evidence for no Produced by Two Distinct Channels.

    NASA Astrophysics Data System (ADS)

    Lue, Christopher J.; Tanjaroon, Chakree; Johnson, J. Bruce; Reeve, Scott W.; Allen, Susan D.

    2013-06-01

    Upon absorption of a UV photon, nitrobenzene can dissociate into C_6H_5O and NO through two different mechanisms. Evidence for these mechanisms was obtained from velocity map imaging (VMI) studies and theoretical calculations. VMI experiments showed NO produced with two distinct rotational distributions, which the calculations explained as a fast and a slow channel for NO production. We have recorded high resolution fluorescence excitation spectra of the NO resulting from photo-fragmented nitrobenzene using a pulsed picosecond tunable laser (pulse width ≈ 15 ps) by means of a two-color process. In the two-color process, photons of a particular energy dissociated the nitrobenzene while photons of a different energy probed the A^2Σ^+← X^2Π_{(1/2,3/2)} NO band system between 225-260 nm. This laser system allowed us to vary the delay between the photolysis and excitation pulses. At longer delays (>1 ns), we observed an increase in the population of NO, which may be evidence that at least two photolysis channels produce NO. We present the spectra we recorded at various photolysis/probe delays ranging from 0.025 to 1.5 ns. The spectral subtraction method we used to observe the production increase is introduced. Hause, M. L.; Herath, N.; Zhu, R.; Lin, M. C. and Suits, A. G. Nat Chem, Nature Publishing Group, 2011, 3, 932-937

  15. Spin-flip, tensor equation-of-motion configuration interaction with a density-functional correction: A spin-complete method for exploring excited-state potential energy surfaces

    SciTech Connect

    Zhang, Xing; Herbert, John M.

    2015-12-21

    We revisit the formalism of the spin-adapted, spin-flip (SA-SF) configuration-interaction singles (CIS) method based on a tensor equation-of-motion formalism that affords proper spin eigenstates without sacrificing single-reference simplicity. Matrix elements for SA-SF-CIS are then modified in a manner similar to collinear spin-flip time-dependent density functional theory (SF-TDDFT), to include a DFT exchange-correlation correction. The performance of this method, which we call SA-SF-DFT, is evaluated numerically and we find that it systematically improves the energies of electronic states that exhibit significant spin contamination within the conventional SF-TDDFT approach. The new method cures the state assignment problem that plagues geometry optimizations and ab initio molecular dynamics simulations using traditional SF-TDDFT, without sacrificing computational efficiency, and furthermore provides correct topology at conical intersections, including those that involve the ground state, unlike conventional TDDFT. As such, SA-SF-DFT appears to be a promising method for generating excited-state potential energy surfaces at DFT cost.

  16. Near infrared excited micro-Raman spectra of 4:1 methanol-ethanol mixture and ruby fluorescence at high pressure

    NASA Astrophysics Data System (ADS)

    Wang, X. B.; Shen, Z. X.; Tang, S. H.; Kuok, M. H.

    1999-06-01

    Near infrared (NIR) lasers, as a new excitation source for Raman spectroscopy, has shown its unique advantages and is being increasingly used for some special samples, such as those emitting strong fluorescence in the visible region. This article focuses on some issues related to high-pressure micro-Raman spectroscopy using NIR excitation source. The Raman spectra of 4:1 methanol-ethanol mixture (4:1 M-E) show a linear variation in both Raman shifts and linewidths under pressure up to 18 GPa. This result is useful in distinguishing Raman scattering of samples from that of the alcohol mixture, an extensively used pressure-transmitting medium. The R1 fluorescence in the red region induced by two-photon absorption of the NIR laser is strong enough to be used as pressure scale. The frequency and line width of the R1 lines are very sensitive to pressure change and the glass transition of the pressure medium. Our results manifest that it is reliable and convenient to use NIR induced two-photon excited fluorescence of ruby for both pressure calibration and distribution of pressure in the 4:1 M-E pressure transmitting medium.

  17. Lowest excited states and optical absorption spectra of donor-acceptor copolymers for organic photovoltaics: a new picture emerging from tuned long-range corrected density functionals.

    PubMed

    Pandey, Laxman; Doiron, Curtis; Sears, John S; Brédas, Jean-Luc

    2012-11-07

    Polymers with low optical gaps are of importance to the organic photovoltaics community due to their potential for harnessing a large portion of the solar energy spectrum. The combination along their backbones of electron-rich and electron-deficient fragments contributes to the presence of low-lying excited states that are expected to display significant charge-transfer character. While conventional hybrid functionals are known to provide unsatisfactory results for charge-transfer excitations at the time-dependent DFT level, long-range corrected (LRC) functionals have been reported to give improved descriptions in a number of systems. Here, we use such LRC functionals, considering both tuned and default range-separation parameters, to characterize the absorption spectra of low-optical-gap systems of interest. Our results indicate that tuned LRC functionals lead to simulated optical-absorption properties in good agreement with experimental data. Importantly, the lowest-lying excited states (excitons) are shown to present a much more localized nature than initially anticipated.

  18. Excitation and propagation of X-ray fluorescence through thin devices with hollowed ordered structures: comparison of experimental and theoretical spectra.

    PubMed

    Mazuritskiy, M I; Dabagov, S B; Marcelli, A; Lerer, A M; Dziedzic-Kocurek, K

    2016-01-01

    The lack of models describing the propagation of X-rays in waveguides and the interference mechanism between incident and reflected radiation waves hamper the understanding and the control of wave propagation phenomena occurring in many real systems. Here, experimental spectra collected at the exit of microchannel plates (MCPs) under the total X-ray reflection condition are presented. The results are discussed in the framework of a theoretical model in which the wave propagation is enhanced by the presence of a transition layer at the surface. The angular distributions of the propagating radiation at the exit of these MCPs with microchannels of ∼3 µm diameter will also be presented and discussed. These spectra show contributions associated with the reflection of the primary monochromatic beam and with the fluorescence radiation originating from the excitation of atoms composing the surface of the microchannel. The soft X-ray fluorescence spectra collected at the exit of microcapillaries were analyzed in the framework of a wave approximation while diffraction contributions observed at the exit of these hollow X-ray waveguides have been calculated using the Fraunhofer diffraction model for waves in the far-field domain. Data collected at the Si L-edge show that in glassy MCPs the fluorescence radiation can be detected only when the energy of the primary monochromatic radiation is above the absorption edge for grazing angles higher than half of the critical angle of the total reflection phenomenon. Experimental data and simulations of the propagating radiation represent a clear experimental confirmation of the channeling phenomenon of the excited fluorescence radiation inside a medium and point out that a high transmission can be obtained in waveguide optics for parameters relevant to X-ray imaging.

  19. Simulating the absorption spectra of helium clusters (N = 70, 150, 231, 300) using a charge transfer correction to superposition of fragment single excitations.

    PubMed

    Ge, Qinghui; Mao, Yuezhi; White, Alec F; Epifanovsky, Evgeny; Closser, Kristina D; Head-Gordon, Martin

    2017-01-28

    Simulations of the n = 2 absorption spectra of HeN (N = 70, 150, 231, 300) clusters are reported, with nuclear configurations sampled by path integral molecular dynamics. The electronic structure is treated by a new approach, ALMO-CIS+CT, which is a formulation of configuration interaction singles (CIS) based on absolutely localized molecular orbitals (ALMOs). The method generalizes the previously reported ALMO-CIS model [K. D. Closser et al. J. Chem. Theory Comput. 11, 5791 (2015)] to include spatially localized charge transfer (CT) effects. It is designed to recover large numbers of excited states in atomic and molecular clusters, such as the entire n = 2 Rydberg band in helium clusters. ALMO-CIS+CT is shown to recover most of the error caused by neglecting charge transfer in ALMO-CIS and has comparable accuracy to standard CIS for helium clusters. For the n = 2 band, CT stabilizes states towards the blue edge by up to 0.5 eV. ALMO-CIS+CT retains the formal cubic scaling of ALMO-CIS with respect to system size. With improvements to the implementation over that originally reported for ALMO-CIS, ALMO-CIS+CT is able to treat helium clusters with hundreds of atoms using modest computing resources. A detailed simulation of the absorption spectra associated with the 2s and 2p bands of helium clusters up to 300 atoms is reported, using path integral molecular dynamics with a spherical boundary condition to generate atomic configurations at 3 K. The main features of experimentally reported fluorescence excitation spectra for helium clusters are reproduced.

  20. Simulating the absorption spectra of helium clusters (N = 70, 150, 231, 300) using a charge transfer correction to superposition of fragment single excitations

    NASA Astrophysics Data System (ADS)

    Ge, Qinghui; Mao, Yuezhi; White, Alec F.; Epifanovsky, Evgeny; Closser, Kristina D.; Head-Gordon, Martin

    2017-01-01

    Simulations of the n = 2 absorption spectra of HeN (N = 70, 150, 231, 300) clusters are reported, with nuclear configurations sampled by path integral molecular dynamics. The electronic structure is treated by a new approach, ALMO-CIS+CT, which is a formulation of configuration interaction singles (CIS) based on absolutely localized molecular orbitals (ALMOs). The method generalizes the previously reported ALMO-CIS model [K. D. Closser et al. J. Chem. Theory Comput. 11, 5791 (2015)] to include spatially localized charge transfer (CT) effects. It is designed to recover large numbers of excited states in atomic and molecular clusters, such as the entire n = 2 Rydberg band in helium clusters. ALMO-CIS+CT is shown to recover most of the error caused by neglecting charge transfer in ALMO-CIS and has comparable accuracy to standard CIS for helium clusters. For the n = 2 band, CT stabilizes states towards the blue edge by up to 0.5 eV. ALMO-CIS+CT retains the formal cubic scaling of ALMO-CIS with respect to system size. With improvements to the implementation over that originally reported for ALMO-CIS, ALMO-CIS+CT is able to treat helium clusters with hundreds of atoms using modest computing resources. A detailed simulation of the absorption spectra associated with the 2s and 2p bands of helium clusters up to 300 atoms is reported, using path integral molecular dynamics with a spherical boundary condition to generate atomic configurations at 3 K. The main features of experimentally reported fluorescence excitation spectra for helium clusters are reproduced.

  1. Electronic spectra and excited state dynamics of pentafluorophenol: Effects of low-lying πσ∗ states

    NASA Astrophysics Data System (ADS)

    Karmakar, Shreetama; Mukhopadhyay, Deb Pratim; Chakraborty, Tapas

    2015-05-01

    Multiple fluorine atom substitution effect on photophysics of an aromatic chromophore has been investigated using phenol as the reference system. It has been noticed that the discrete vibronic structure of the S1←S0 absorption system of phenol vapor is completely washed out for pentafluorophenol (PFP), and the latter also shows very large Stokes shift in the fluorescence spectrum. For excitations beyond S1 origin, the emission yield of PFP is reduced sharply with increase in excess vibronic energy. However, in a collisional environment like liquid hydrocarbon, the underlying dynamical process that drives the non-radiative decay is hindered drastically. Electronic structure theory predicts a number of low-lying dark electronic states of πσ∗ character in the vicinity of the lowest valence ππ∗ state of this molecule. Tentatively, we have attributed the excitation energy dependent non-radiative decay of the molecule observed only in the gas phase to an interplay between the lowest ππ∗ and a nearby dissociative πσ∗ state. Measurements in different liquids reveal that some of the dark excited states light up with appreciable intensity only in protic liquids like methanol and water due to hydrogen bonding between solute and solvents. Electronic structure theory methods indeed predict that for PFP-(H2O)n clusters (n = 1-11), intensities of a number of πσ∗ states are enhanced with increase in cluster size. In contrast with emitting behavior of the molecule in the gas phase and solutions of nonpolar and polar aprotic liquids, the fluorescence is completely switched off in polar protic liquids. This behavior is a chemically significant manifestation of perfluoro effect, because a very opposite effect occurs in the case of unsubstituted phenol for which fluorescence yield undergoes a very large enhancement in protic liquids. Several dynamical mechanisms have been suggested to interpret the observed photophysical behavior.

  2. Spin-phonon interactions of multiferroic Bi4Ti3O12-BiFeO3 ceramics: Low-temperature Raman scattering and infrared reflectance spectra investigations

    NASA Astrophysics Data System (ADS)

    Jiang, P. P.; Zhang, X. L.; Chang, P.; Hu, Z. G.; Bai, W.; Li, Y. W.; Chu, J. H.

    2014-04-01

    Optical phonons of multiferroic Bi4Ti3O12-BiFeO3 ceramic have been investigated by low temperature Raman scattering and infrared reflectance spectra. Anomalies at about 85 K can be observed from the temperature dependence of the Raman and infrared modes, which arise from spin-phonon interaction during antiferromagnetic to paramagnetic phase transition. It was found that the change of exchange interaction in magnetic phase transition can be induced by Fe-O-Fe octahedral tilting driven from the A-site atoms. Moreover, ferroelectricity-related displacement of Bismuth atoms suggests the coupling of magnetic and ferroelectric orders.

  3. Vibrational spectra of the ground and the singlet excited ππ* state of 6,7-dimethyl-8-ribityllumazine.

    PubMed

    Schreier, Wolfgang J; Pugliesi, Igor; Koller, Florian O; Schrader, Tobias E; Zinth, Wolfgang; Braun, Markus; Kacprzak, Sylwia; Weber, Stefan; Römisch-Margl, Werner; Bacher, Adelbert; Illarionov, Boris; Fischer, Markus

    2011-04-07

    6,7-Dimethyl-8-ribityllumazine serves as fluorophore in lumazine proteins (LumP) of luminescent bacteria. The molecule exhibits several characteristic vibrational absorption bands between 1300 and 1750 cm(-1) in its electronic ground state. The IR-absorption pattern of the singlet excited ππ* state was monitored via ultrafast infrared spectroscopy after photoexcitation at 404 nm. The comparison of experimentally observed band shifts for a number of isotopologues allows for a clear assignment of several absorption bands--most importantly the two carbonyl bands. This assignment is confirmed by normal-mode calculations by means of either density functional theory (DFT) calculations for the ground state or the configuration interaction singles (CIS) method for the excited singlet state. A good agreement between experiment and calculation is obtained for models including explicitly a first solvation shell. The results provide a basis for further investigations of lumazine protein and demonstrate the necessity of proper accounting for explicit hydrogen bonding in case of strongly polar molecular systems.

  4. Excited light meson spectroscopy from lattice QCD

    SciTech Connect

    Christopher Thomas, Hadron Spectrum Collaboration

    2012-04-01

    I report on recent progress in calculating excited meson spectra using lattice QCD, emphasizing results and phenomenology. With novel techniques we can now extract extensive spectra of excited mesons with high statistical precision, including spin-four states and those with exotic quantum numbers. As well as isovector meson spectra, I will present new calculations of the spectrum of excited light isoscalar mesons, something that has up to now been a challenge for lattice QCD. I show determinations of the flavor content of these mesons, including the eta-eta' mixing angle, providing a window on annihilation dynamics in QCD. I will also discuss recent work on using lattice QCD to map out the energy-dependent phase shift in pi-pi scattering and future applications of the methodology to the study of resonances and decays.

  5. Experimental confirmation of photon-induced spin-flip transitions in helium via triplet metastable yield spectra

    SciTech Connect

    Rubensson, Jan-Erik; Moise, Angelica; Richter, Robert; Mihelic, Andrej; Bucar, Klemen; Zitnik, Matjaz

    2010-06-15

    Doubly excited states below the N=2 ionization threshold are populated by exciting helium atoms in a supersonic beam with monochromatized synchrotron radiation. The fluorescence decay of these states triggers a radiative cascade back to the ground state with large probability to populate long lived singlet and triplet helium metastable states. The yield of metastables is measured using a multichannel plate detector after the beam has passed a singlet-quenching discharge lamp. The variation of the yield observed with the lamp switched on or off is related to the triplet-singlet mixing of the doubly excited states.

  6. Highly excited and exotic meson spectroscopy from lattice QCD

    SciTech Connect

    Christopher Thomas

    2011-05-01

    I will discuss recent progress in extracting highly excited and exotic meson spectra using lattice QCD. New results in the light meson sector will be presented, where a combination of techniques have enabled us to confidently identify the spin of extracted states. Highlights include many states with exotic quantum numbers and, for the first time in a lattice QCD calculation, spin-four states. I will conclude with comments on future prospects.

  7. Breakdown of linear response theory under low-power excitation in NMR. I. The case of long-lived signals in inhomogeneously broadened spin systems

    NASA Astrophysics Data System (ADS)

    Gong, Zhaoyuan; Walls, Jamie D.

    2016-10-01

    In this work, we examine the application of linear response theory to the problem of low-power excitation in inhomogeneously broadened spin systems when the strength of the radiofrequency (RF) pulse, νRF, is smaller than the inhomogeneous linewidth. Even for small overall excitations [Θ = 2πνRFTp ≪ 1 where Tp is the RF pulse length], linear response theory is shown to break down for spins with resonance frequencies that are on the order of νRF, which is due to the fact that the RF interaction cannot be treated as a small perturbation in this case. This breakdown in linear response theory can be partially corrected for by enforcing unitarity in the linear response. Furthermore, the nature of the spin echo generated by a πX-pulse applied immediately after a low-power pulse is investigated. Numerical calculations and experiments performed in an inhomogeneously broadened H2O/D2O solution confirm the theoretical predictions presented in this work.

  8. Breakdown of linear response theory under low-power excitation in NMR. I. The case of long-lived signals in inhomogeneously broadened spin systems.

    PubMed

    Gong, Zhaoyuan; Walls, Jamie D

    2016-10-28

    In this work, we examine the application of linear response theory to the problem of low-power excitation in inhomogeneously broadened spin systems when the strength of the radiofrequency (RF) pulse, νRF, is smaller than the inhomogeneous linewidth. Even for small overall excitations [Θ = 2πνRFTp ≪ 1 where Tp is the RF pulse length], linear response theory is shown to break down for spins with resonance frequencies that are on the order of νRF, which is due to the fact that the RF interaction cannot be treated as a small perturbation in this case. This breakdown in linear response theory can be partially corrected for by enforcing unitarity in the linear response. Furthermore, the nature of the spin echo generated by a πX-pulse applied immediately after a low-power pulse is investigated. Numerical calculations and experiments performed in an inhomogeneously broadened H2O/D2O solution confirm the theoretical predictions presented in this work.

  9. Electronic spectra and excited state dynamics of pentafluorophenol: Effects of low-lying πσ{sup ∗} states

    SciTech Connect

    Karmakar, Shreetama; Mukhopadhyay, Deb Pratim; Chakraborty, Tapas

    2015-05-14

    Multiple fluorine atom substitution effect on photophysics of an aromatic chromophore has been investigated using phenol as the reference system. It has been noticed that the discrete vibronic structure of the S{sub 1}←S{sub 0} absorption system of phenol vapor is completely washed out for pentafluorophenol (PFP), and the latter also shows very large Stokes shift in the fluorescence spectrum. For excitations beyond S{sub 1} origin, the emission yield of PFP is reduced sharply with increase in excess vibronic energy. However, in a collisional environment like liquid hydrocarbon, the underlying dynamical process that drives the non-radiative decay is hindered drastically. Electronic structure theory predicts a number of low-lying dark electronic states of πσ{sup ∗} character in the vicinity of the lowest valence ππ{sup ∗} state of this molecule. Tentatively, we have attributed the excitation energy dependent non-radiative decay of the molecule observed only in the gas phase to an interplay between the lowest ππ{sup ∗} and a nearby dissociative πσ{sup ∗} state. Measurements in different liquids reveal that some of the dark excited states light up with appreciable intensity only in protic liquids like methanol and water due to hydrogen bonding between solute and solvents. Electronic structure theory methods indeed predict that for PFP-(H{sub 2}O){sub n} clusters (n = 1-11), intensities of a number of πσ{sup ∗} states are enhanced with increase in cluster size. In contrast with emitting behavior of the molecule in the gas phase and solutions of nonpolar and polar aprotic liquids, the fluorescence is completely switched off in polar protic liquids. This behavior is a chemically significant manifestation of perfluoro effect, because a very opposite effect occurs in the case of unsubstituted phenol for which fluorescence yield undergoes a very large enhancement in protic liquids. Several dynamical mechanisms have been suggested to interpret the

  10. The spin chemistry and magnetic resonance of H2@C60. From the Pauli principle to trapping a long lived nuclear excited spin state inside a buckyball.

    PubMed

    Turro, Nicholas J; Chen, Judy Y-C; Sartori, Elena; Ruzzi, Marco; Marti, Angel; Lawler, Ronald; Jockusch, Steffen; López-Gejo, Juan; Komatsu, Koichi; Murata, Yasujiro

    2010-02-16

    One of the early triumphs of quantum mechanics was Heisenberg's prediction, based on the Pauli principle and wave function symmetry arguments, that the simplest molecule, H(2), should exist as two distinct species-allotropes of elemental hydrogen. One allotrope, termed para-H(2) (pH(2)), was predicted to be a lower energy species that could be visualized as rotating like a sphere and possessing antiparallel ( upward arrow downward arrow) nuclear spins; the other allotrope, termed ortho-H(2) (oH(2)), was predicted to be a higher energy state that could be visualized as rotating like a cartwheel and possessing parallel ( upward arrow upward arrow) nuclear spins. This remarkable prediction was confirmed by the early 1930s, and pH(2) and oH(2) were not only separated and characterized but were also found to be stable almost indefinitely in the absence of paramagnetic "spin catalysts", such as molecular oxygen, or traces of paramagnetic impurities, such as metal ions. The two allotropes of elemental hydrogen, pH(2) and oH(2), may be quantitatively incarcerated in C(60) to form endofullerene guest@host complexes, symbolized as pH(2)@C(60) and oH(2)@C(60), respectively. How does the subtle difference in nuclear spin manifest itself when hydrogen allotropes are incarcerated in a buckyball? Can the incarcerated "guests" communicate with the outside world and vice versa? Can a paramagnetic spin catalyst in the outside world cause the interconversion of the allotropes and thereby effect a chemical transformation inside a buckyball? How close are the measurable properties of H(2)@C(60) to those computed for the "quantum particle in a spherical box"? Are there any potential practical applications of this fascinating marriage of the simplest molecule, H(2), with one of the most beautiful of all molecules, C(60)? How can one address such questions theoretically and experimentally? A goal of our studies is to produce an understanding of how the H(2) guest molecules incarcerated in

  11. Microscopic study of edge excitations of spin-polarized and spin-unpolarized ν=2/3 fractional quantum Hall effect

    NASA Astrophysics Data System (ADS)

    Wu, Ying-Hai; Sreejith, G. J.; Jain, Jainendra K.

    2012-09-01

    The edge of spin-unpolarized or spin-polarized ν=2/3 fractional quantum Hall states is predicted by the effective theory to support a backward-moving neutral mode in addition to a forward-moving charge mode. We study this issue from a microscopic perspective where these states are identified with an effective filling factor of 2 of composite fermions, but with an effective magnetic field that is antiparallel to the external field. A simple counting from the composite fermion description suggests that there might be two backward-moving edge modes, but explicit calculations show that one of these is projected out of the low-energy sector, while the remaining mode provides a good microscopic account of the actual counterpropagating edge mode. The forward-moving modes are identified as “Schur modes,” obtained by multiplying the ground-state wave function by the symmetric Schur polynomials. The edge of the 2/3 spin unpolarized state provides a particularly striking realization of “spin-charge separation” in one-dimensional Tomonaga-Luttinger liquids, with the spin and charge modes moving in opposite directions.

  12. Charge-exchange x-ray spectra: Evidence for significant contributions from radiative decays of doubly excited states

    NASA Astrophysics Data System (ADS)

    Ali, R.; Beiersdorfer, P.; Harris, C. L.; Neill, P. A.

    2016-01-01

    Charge-exchange collisions of slow Ne+10 ions with He, Ne, and Ar targets were studied with simultaneous x-ray and cold-target recoil-ion-momentum spectroscopy proving the contribution of several mechanisms to the radiative stabilization of apparent (4,4) doubly excited states for He and Ne targets and of (5,6) states for Ar. In particular, the stabilization efficiency of the mechanism of dynamic auto-transfer to Rydberg states is confirmed. Moreover, we present evidence for direct radiative decays of (4,4) states populated in collisions with He, which is an experimental indication of the population of so-called unnatural-parity states in such collisions. These mechanisms lead to the emission of x-rays that have considerably higher energies than those predicted by current spectral models and may explain recent observations of anomalously large x-ray emission from Rydberg levels.

  13. Submillimeter-wave rotational spectra of DNC in highly excited vibrational states observed in an extended negative glow discharge

    NASA Astrophysics Data System (ADS)

    Amano, T.

    2011-05-01

    Rotational transitions of DNC have been observed in the submillimeter-wave region in an extended negative glow discharge in a gas mixture of CD 4 and N 2. The dissociative recombination reaction of DCND + with electrons is thought to be a dominant channel to produce DNC in highly excited vibrational states. The vibrational temperature for the ν3 vibrational mode is found to be about 4000 K, and the rotational lines in levels up to (0 0 8) are observed. The rotational and centrifugal distortion constants are determined for these states along with those for the (1 0 0) state. The measurement accuracy is high enough to determine some higher order vibration-rotation interaction constants.

  14. Exciton Lines in Luminescence Spectra of NixZn1-xO under Inner Shell Excitation

    NASA Astrophysics Data System (ADS)

    Churmanov, V. N.; Sokolov, V. I.; Gruzdev, N. B.; Ivanov, V. Yu.; Pustovarov, V. A.

    The paper presents the results of the study of two narrow luminescence lines I1 and I2 at the energies of 3.339 and 3.393 eV respectively in NiO and solid state solution Ni0.6Zn0.4O. The luminescence spectroscopy with a sub-nanosecond time resolution upon selective photoexcitation in the energy range of absorption of the inner shells Zn M- and Ni L2,3- edges of Zn- and Ni- ions was used to promote proposed earlier mechanism of origin of luminescence lines I1 and I2. Photoluminescence decay kinetics of NiO and solid state solution Ni0.6Zn0.4O under soft x-ray excitation are discussed. The doublet of I1 and I2 lines is believed to arise due to the radiative annihilation of p-d excitons.

  15. Oxygen-assisted excitation of methyl iodide as a test of double spin-flip transition in van der Waals complex CH3I-O2

    NASA Astrophysics Data System (ADS)

    Bogomolov, Alexandr S.; Kochubei, Sergei A.; Baklanov, Alexey V.

    2016-09-01

    Photoexcitation of van der Waals (vdW) complex CH3I-O2 has been studied with velocity map imaging of I atoms arising in photodissociation. A new scheme of resonance-enhanced multiphoton ionization of iodine atoms has been applied with simultaneous use of UV and VIS radiation. The measured kinetic energy of I(2P3/2) atoms indicates photogeneration of precursor CH3I molecules via complex-specific channel with excitation energy expected for double spin-flip transition in complex CH3I-O2. The angular distribution for recoil directions of I(2P3/2) atoms coming from vdW complexes also corresponds to that expected for double spin-flip transition.

  16. The influence of visible light and inorganic pigments on fluorescence excitation emission spectra of egg-, casein- and collagen-based painting media

    NASA Astrophysics Data System (ADS)

    Nevin, A.; Anglos, D.; Cather, S.; Burnstock, A.

    2008-07-01

    Spectrofluorimetric analysis of proteinaceous binding media is particularly promising because proteins employed in paintings are often fluorescent and media from different sources have significantly different fluorescence spectral profiles. Protein-based binding media derived from eggs, milk and animal tissue have been used for painting and for conservation, but their analysis using non-destructive techniques is complicated by interferences with pigments, their degradation and their low concentration. Changes in the fluorescence excitation emission spectra of films of binding media following artificial ageing to an equivalent of 50 and 100 years of museum lighting include the reduction of bands ascribed to tyrosine, tryptophan and Maillard reaction products and an increase in fluorescent photodegradation. Fluorescence of naturally aged paint is dependent on the nature of the pigment present and, with egg-based media, in comparison with un-pigmented films, emissions ascribed to amino acids are more pronounced.

  17. Increasing spin-flips and decreasing cost: Perturbative corrections for external singles to the complete active space spin flip model for low-lying excited states and strong correlation

    SciTech Connect

    Mayhall, Nicholas J.; Head-Gordon, Martin

    2014-07-28

    An approximation to the spin-flip extended configuration interaction singles method is developed using a second-order perturbation theory approach. In addition to providing significant efficiency advantages, the new framework is general for an arbitrary number of spin-flips, with the current implementation being applicable for up to around 4 spin-flips. Two new methods are introduced: one which is developed using non-degenerate perturbation theory, spin-flip complete active-space (SF-CAS(S)), and a second quasidegenerate perturbation theory method, SF-CAS(S){sub 1}. These two approaches take the SF-CAS wavefunction as the reference, and then perturbatively includes the effect of single excitations. For the quasidegenerate perturbation theory method, SF-CAS(S){sub 1}, the subscripted “1” in the acronym indicates that a truncated denominator expansion is used to obtain an energy-independent down-folded Hamiltonian. We also show how this can alternatively be formulated in terms of an extended Lagrangian, by introducing an orthonormality constraint on the first-order wavefunction. Several numerical examples are provided, which demonstrate the ability of SF-CAS(S) and SF-CAS(S){sub 1} to describe bond dissociations, singlet-triplet gaps of organic molecules, and exchange coupling parameters for binuclear transition metal complexes.

  18. Hydride stretch infrared spectra in the excited electronic states of indole and its derivatives: Direct evidence for the 1πσ* state

    NASA Astrophysics Data System (ADS)

    Dian, Brian C.; Longarte, Asier; Zwier, Timothy S.

    2003-02-01

    The hydride stretch infrared spectra of indole, indole-H2O, 3-methyl indole, 3-methyl indole-H2O, the main conformer of tryptamine (TRA), two conformers of N-acetyl tryptophan amide (NATA), and three conformers of N-acetyl tryptophan methyl amide (NATMA), have been recorded in the electronically excited singlet states using excited-state fluorescence-dip infrared spectroscopy. NATA and NATMA are methyl-capped dipeptides of tryptophan that have conformational flexibility and exhibit sensitivity in their electronic spectra to the conformation of the dipeptide backbone. In the indole monomer, the indole NH stretch fundamental at the S1 origin is shifted from its ground-state value (3525 cm-1) to 3478 cm-1. The corresponding band in the indole-H2O complex appears at 3387 cm-1, shifted by a similar amount from its ground-state position (3436 cm-1). Higher vibronic levels within 1500 cm-1 of the S1 origin, which have been identified previously [B. J. Fender et al., Chem. Phys. Lett. 239, 31 (1995)] as being 1Lb or 1La in character, all show similar excited state indole NH stretch absorptions. The corresponding spectra in 3-methyl indole, 3-methyl indole-H2O, TRA, and in the C5 conformers of NATA and NATMA all are missing the indole NH stretch absorption. In its place, a broad background absorption appears, spread over the entire 2800-3800 cm-1 region. In these molecules, other CH stretch or amide NH stretch absorptions remain sharp, appearing in their expected frequency ranges. Finally, the C7 conformations of NATA and NATMA, which possess an intramolecular hydrogen bond in the dipeptide backbone, have all infrared transitions washed out, replaced by a stronger broad background absorption. The entire data set can be explained by the presence of an excited 1πσ* state which is dissociative along the indole NH stretch coordinate, as recently predicted by Sobolewski and Domcke [Chem. Phys. Lett. 315, 293 (1999)]. In the weak coupling case (indole, indole-H2O), the gap

  19. On the Estimation of Excited-State Dipole Moments from Solvatochromic Shifts of Absorption and Fluorescence Spectra

    NASA Astrophysics Data System (ADS)

    Kawski, A.

    2002-05-01

    The effect of the solvent polarity parameters f (Ɛ, n) and ᵩ(Ɛ, n) appearing in solvatochromic theories, and the effect of the molecular shape of the Onsager cavity (sphere, ellipsoid of revolution) on the determined electric dipole moments μe in the singlet excited state are studied. It is found that the shape of the solute does not exhibit a significant effect on the determined values of μe, but only on the solvent parameters f (Ɛ, n) and ᵩ(Ɛ, n) as well as on the Onsager radius a. Passing from a sphere to an ellipsoid leads to such a change in the scale that induces a proportional change in the slope coefficients m1 and m2. Also the effect of α/a3 (a and a are the mean isotropic polarizability of the solute and the Onsager cavity radius in a homogeneous dielectric, respectively) on the determined values of m e has been studied, and it is found that the assumption α/a3 = 1/2 is valid in many cases.

  20. The effects of general anesthetics on ESR spectra of spin labels in phosphatidylcholine vesicles containing purified Na,K-ATPase or microsomal protein

    NASA Astrophysics Data System (ADS)

    Shibuya, Makiko; Hiraoki, Toshifumi; Kimura, Kunie; Fukushima, Kazuaki; Suzuki, Kuniaki

    2012-12-01

    We investigated the effects of general anesthetics on liposome containing spin labels, 5-doxyl stearic acid (5-DSA) and 16-doxyl stearic acid (16-DSA), and purified Na,K-ATPase or membrane protein of microsome using an electron spin resonance (ESR) spectroscopy. The spectra of 16-DSA in liposomes with both proteins showed three sharp signals compared with 5-DSA. The difference in the order parameter S value of 5-DSA and 16-DSA suggested that the nitroxide radical location of 5-DSA and 16-DSA were different in the membrane bilayer. The results were almost the same as those obtained in liposomes without proteins. The addition of sevoflurane, isoflurane, halothane, ether, ethanol and propofol increased the intensity of the signals, but the clinical concentrations of anesthetics did not significantly alter the S and τ values, which are indices of the fluidity of the membrane. These results suggest that anesthetics remain on the surface of the lipid bilayer and do not act on both the inside hydrophobic area and the relatively hydrophilic area near the surface. These results and others also suggest that the existence of Na,K-ATPase and microsomal proteins did not affect the environment around the spin labels in the liposome and the effects of anesthetics on liposome as a model membrane.