Localized excitations at the Mott insulator-superfluid interfaces for confined Bose-Einstein condensates.

PubMed

Mariani, Eros; Stern, Ady

2005-12-31

In this Letter, we derive the dispersion relation of the surface waves at the interfaces between Mott-insulating and superfluid domains for a two-dimensional Bose-Einstein condensate in an optical lattice subjected to a confining potential. We then calculate their contribution to the heat capacity of the system and show how its low-temperature scaling allows an experimental test of the existence and properties of Mott insulator-superfluid domains.

Producing coherent excitations in pumped Mott antiferromagnetic insulators

NASA Astrophysics Data System (ADS)

Wang, Yao; Claassen, Martin; Moritz, B.; Devereaux, T. P.

2017-12-01

Nonequilibrium dynamics in correlated materials has attracted attention due to the possibility of characterizing, tuning, and creating complex ordered states. To understand the photoinduced microscopic dynamics, especially the linkage under realistic pump conditions between transient states and remnant elementary excitations, we performed nonperturbative simulations of various time-resolved spectroscopies. We used the Mott antiferromagnetic insulator as a model platform. The transient dynamics of multiparticle excitations can be attributed to the interplay between Floquet virtual states and a modification of the density of states, in which interactions induce a spectral weight transfer. Using an autocorrelation of the time-dependent spectral function, we show that resonance of the virtual states with the upper Hubbard band in the Mott insulator provides the route towards manipulating the electronic distribution and modifying charge and spin excitations. Our results link transient dynamics to the nature of many-body excitations and provide an opportunity to design nonequilibrium states of matter via tuned laser pulses.

Producing coherent excitations in pumped Mott antiferromagnetic insulators

DOE PAGES

Wang, Yao; Claassen, Martin; Moritz, B.; ...

2017-12-15

Nonequilibrium dynamics in correlated materials has attracted attention due to the possibility of characterizing, tuning, and creating complex ordered states. To understand the photoinduced microscopic dynamics, especially the linkage under realistic pump conditions between transient states and remnant elementary excitations, we performed nonperturbative simulations of various time-resolved spectroscopies. We used the Mott antiferromagnetic insulator as a model platform. The transient dynamics of multi-particle excitations can be attributed to the interplay between Floquet virtual states and a modification of the density of states, in which interactions induce a spectral weight transfer. Using an autocorrelation of the time-dependent spectral function, we showmore » that resonance of the virtual states with the upper Hubbard band in the Mott insulator provides the route towards manipulating the electronic distribution and modifying charge and spin excitations. In conclusion, our results link transient dynamics to the nature of many-body excitations and provide an opportunity to design nonequilibrium states of matter via tuned laser pulses.« less

Mott insulator-to-metal transition in yttrium-doped CaIrO₃.

PubMed

Gunasekera, J; Chen, Y; Kremenak, J W; Miceli, P F; Singh, D K

2015-02-11

We report on the study of insulator-to-metal transition in post-perovskite compound CaIrO3. It is discovered that a gradual chemical substitution of calcium by yttrium leads to the onset of strong metallic behavior in this compound. This observation is in stark contrast to BaIrO3, which preserves its Mott insulating behavior despite excess of the charge carriers due to yttrium doping. Magnetic measurements reveal that both compounds tend to exhibit magnetic character irrespective of the chemical substitution of Ca or Ba. We analyze these unusual observations in light of recent researches that suggest that CaIrO3 does not necessarily possess j = 1/2 ground state due to structural distortion. The insulator-to-metal transition in CaIrO3 will spur new researches to explore more exotic ground state, including superconductivity, in post-perovskite Mott insulators.

Breakdown of Strong Coupling Expansions for doped Mott Insulators

NASA Astrophysics Data System (ADS)

Phillips, Philip; Galanakis, Dimitrios; Stanescu, Tudor

2005-03-01

We show that doped Mott insulators, such as the copper-oxide superconductors, are asymptotically slaved in that the quasiparticle weight, Z, near half-filling depends critically on the existence of the high energy scale set by the upper Hubbard band. In particular, near half filling, the following dichotomy arises: Z0 when the high energy scale is integrated out but Z=0 in the thermodynamic limit when it is retained. Slavery to the high energy scale arises from quantum interference between electronic excitations across the Mott gap.

Mott metal-insulator transition in the doped Hubbard-Holstein model

NASA Astrophysics Data System (ADS)

Kurdestany, Jamshid Moradi; Satpathy, S.

2017-08-01

Motivated by the current interest in the understanding of the Mott insulators away from half-filling, observed in many perovskite oxides, we study the Mott metal-insulator transition in the doped Hubbard-Holstein model using the Hartree-Fock mean field theory. The Hubbard-Holstein model is the simplest model containing both the Coulomb and the electron-lattice interactions, which are important ingredients in the physics of the perovskite oxides. In contrast to the half-filled Hubbard model, which always results in a single phase (either metallic or insulating), our results show that away from half-filling, a mixed phase of metallic and insulating regions occurs. As the dopant concentration is increased, the metallic part progressively grows in volume, until it exceeds the percolation threshold, leading to percolative conduction. This happens above a critical dopant concentration δc, which, depending on the strength of the electron-lattice interaction, can be a significant fraction of unity. This means that the material could be insulating even for a substantial amount of doping, in contrast to the expectation that doped holes would destroy the insulating behavior of the half-filled Hubbard model. While effects of fluctuation beyond the mean field remain an open question, our results provide a starting point for the understanding of the density-driven metal-insulator transition observed in many complex oxides.

Hallmarks of Hunds coupling in the Mott insulator Ca2RuO4

PubMed Central

Sutter, D.; Fatuzzo, C. G.; Moser, S.; Kim, M.; Fittipaldi, R.; Vecchione, A.; Granata, V.; Sassa, Y.; Cossalter, F.; Gatti, G.; Grioni, M.; Rønnow, H. M.; Plumb, N. C.; Matt, C. E.; Shi, M.; Hoesch, M.; Kim, T. K.; Chang, T-R; Jeng, H-T; Jozwiak, C.; Bostwick, A.; Rotenberg, E.; Georges, A.; Neupert, T.; Chang, J.

2017-01-01

A paradigmatic case of multi-band Mott physics including spin-orbit and Hund's coupling is realized in Ca2RuO4. Progress in understanding the nature of this Mott insulating phase has been impeded by the lack of knowledge about the low-energy electronic structure. Here we provide—using angle-resolved photoemission electron spectroscopy—the band structure of the paramagnetic insulating phase of Ca2RuO4 and show how it features several distinct energy scales. Comparison to a simple analysis of atomic multiplets provides a quantitative estimate of the Hund's coupling J=0.4 eV. Furthermore, the experimental spectra are in good agreement with electronic structure calculations performed with Dynamical Mean-Field Theory. The crystal field stabilization of the dxy orbital due to c-axis contraction is shown to be essential to explain the insulating phase. These results underscore the importance of multi-band physics, Coulomb interaction and Hund's coupling that together generate the Mott insulating state of Ca2RuO4. PMID:28474681

Large Fermi Surface of Heavy Electrons at the Border of Mott Insulating State in NiS 2

DOE PAGES

Friedemann, S.; Chang, H.; Gamża, M. B.; ...

2016-05-12

One early triumph of quantum physics is the explanation why some materials are metallic whereas others are insulating. While a treatment based on single electron states is correct for most materials this approach can fail spectacularly, when the electrostatic repulsion between electrons causes strong correlations. Not only can these favor new and subtle forms of matter, such as magnetism or superconductivity, they can even cause the electrons in a half-filled energy band to lock into position, producing a correlated, or Mott insulator. The transition into the Mott insulating state raises important fundamental questions. Foremost among these is the fate ofmore » the electronic Fermi surface and the associated charge carrier mass, as the Mott transition is approached. We report the first direct observation of the Fermi surface on the metallic side of a Mott insulating transition by high pressure quantum oscillatory measurements in NiS 2. We find our results point at a large Fermi surface consistent with Luttinger's theorem and a strongly enhanced quasiparticle effective mass. These two findings are in line with central tenets of the Brinkman-Rice picture of the correlated metal near the Mott insulating state and rule out alternative scenarios in which the carrier concentration vanishes continuously at the metal-insulator transition.« less

Response of the Lattice across the Filling-Controlled Mott Metal-Insulator Transition of a Rare Earth Titanate

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

Kim, Honggyu; Marshall, Patrick B.; Ahadi, Kaveh

The lattice response of a prototype Mott insulator, SmTiO 3, to hole doping is investigated with atomic-scale spatial resolution. SmTiO 3 films are doped with Sr on the Sm site with concentrations that span the insulating and metallic sides of the filling-controlled Mott metal-insulator transition (MIT). The GdFeO 3-type distortions are investigated using an atomic resolution scanning transmission electron microscopy technique that can resolve small lattice distortions with picometer precision. We show that these distortions are gradually and uniformly reduced as the Sr concentration is increased without any phase separation. Significant distortions persist into the metallic state. In conclusion, themore » results present a new picture of the physics of this prototype filling-controlled MIT, which is discussed.« less

Response of the Lattice across the Filling-Controlled Mott Metal-Insulator Transition of a Rare Earth Titanate

DOE PAGES

Kim, Honggyu; Marshall, Patrick B.; Ahadi, Kaveh; ...

2017-11-02

The lattice response of a prototype Mott insulator, SmTiO 3, to hole doping is investigated with atomic-scale spatial resolution. SmTiO 3 films are doped with Sr on the Sm site with concentrations that span the insulating and metallic sides of the filling-controlled Mott metal-insulator transition (MIT). The GdFeO 3-type distortions are investigated using an atomic resolution scanning transmission electron microscopy technique that can resolve small lattice distortions with picometer precision. We show that these distortions are gradually and uniformly reduced as the Sr concentration is increased without any phase separation. Significant distortions persist into the metallic state. In conclusion, themore » results present a new picture of the physics of this prototype filling-controlled MIT, which is discussed.« less

Volume-wise destruction of the antiferromagnetic Mott insulating state through quantum tuning

DOE PAGES

B. A. Frandsen; Liu, L.; Cheung, S. C.; ...

2016-08-17

RENiO 3 (RE=rare-earth element) and V 2O 3 are archetypal Mott insulator systems. When tuned by chemical substitution (RENiO 3) or pressure (V 2O 3), they exhibit a quantum phase transition (QPT) between an antiferromagnetic Mott insulating state and a paramagnetic metallic state. Because novel physics often appears near a Mott QPT, the details of this transition, such as whether it is first or second order, are important. Here, we demonstrate through muon spin relaxation/rotation (μSR) experiments that the QPT in RENiO 3 and V 2O 3 is first order: the magnetically ordered volume fraction decreases to zero at themore » QPT, resulting in a broad region of intrinsic phase separation, while the ordered magnetic moment retains its full value until it is suddenly destroyed at the QPT. These findings bring to light a surprising universality of the pressure-driven Mott transition, revealing the importance of phase separation and calling for further investigation into the nature of quantum fluctuations underlying the transition.« less

Volume-wise destruction of the antiferromagnetic Mott insulating state through quantum tuning.

PubMed

Frandsen, Benjamin A; Liu, Lian; Cheung, Sky C; Guguchia, Zurab; Khasanov, Rustem; Morenzoni, Elvezio; Munsie, Timothy J S; Hallas, Alannah M; Wilson, Murray N; Cai, Yipeng; Luke, Graeme M; Chen, Bijuan; Li, Wenmin; Jin, Changqing; Ding, Cui; Guo, Shengli; Ning, Fanlong; Ito, Takashi U; Higemoto, Wataru; Billinge, Simon J L; Sakamoto, Shoya; Fujimori, Atsushi; Murakami, Taito; Kageyama, Hiroshi; Alonso, Jose Antonio; Kotliar, Gabriel; Imada, Masatoshi; Uemura, Yasutomo J

2016-08-17

RENiO3 (RE=rare-earth element) and V2O3 are archetypal Mott insulator systems. When tuned by chemical substitution (RENiO3) or pressure (V2O3), they exhibit a quantum phase transition (QPT) between an antiferromagnetic Mott insulating state and a paramagnetic metallic state. Because novel physics often appears near a Mott QPT, the details of this transition, such as whether it is first or second order, are important. Here, we demonstrate through muon spin relaxation/rotation (μSR) experiments that the QPT in RENiO3 and V2O3 is first order: the magnetically ordered volume fraction decreases to zero at the QPT, resulting in a broad region of intrinsic phase separation, while the ordered magnetic moment retains its full value until it is suddenly destroyed at the QPT. These findings bring to light a surprising universality of the pressure-driven Mott transition, revealing the importance of phase separation and calling for further investigation into the nature of quantum fluctuations underlying the transition.

Volume-wise destruction of the antiferromagnetic Mott insulating state through quantum tuning

PubMed Central

Frandsen, Benjamin A.; Liu, Lian; Cheung, Sky C.; Guguchia, Zurab; Khasanov, Rustem; Morenzoni, Elvezio; Munsie, Timothy J. S.; Hallas, Alannah M.; Wilson, Murray N.; Cai, Yipeng; Luke, Graeme M.; Chen, Bijuan; Li, Wenmin; Jin, Changqing; Ding, Cui; Guo, Shengli; Ning, Fanlong; Ito, Takashi U.; Higemoto, Wataru; Billinge, Simon J. L.; Sakamoto, Shoya; Fujimori, Atsushi; Murakami, Taito; Kageyama, Hiroshi; Alonso, Jose Antonio; Kotliar, Gabriel; Imada, Masatoshi; Uemura, Yasutomo J.

2016-01-01

RENiO3 (RE=rare-earth element) and V2O3 are archetypal Mott insulator systems. When tuned by chemical substitution (RENiO3) or pressure (V2O3), they exhibit a quantum phase transition (QPT) between an antiferromagnetic Mott insulating state and a paramagnetic metallic state. Because novel physics often appears near a Mott QPT, the details of this transition, such as whether it is first or second order, are important. Here, we demonstrate through muon spin relaxation/rotation (μSR) experiments that the QPT in RENiO3 and V2O3 is first order: the magnetically ordered volume fraction decreases to zero at the QPT, resulting in a broad region of intrinsic phase separation, while the ordered magnetic moment retains its full value until it is suddenly destroyed at the QPT. These findings bring to light a surprising universality of the pressure-driven Mott transition, revealing the importance of phase separation and calling for further investigation into the nature of quantum fluctuations underlying the transition. PMID:27531192

Volume-wise destruction of the antiferromagnetic Mott insulating state through quantum tuning

NASA Astrophysics Data System (ADS)

Frandsen, Benjamin A.; Liu, Lian; Cheung, Sky C.; Guguchia, Zurab; Khasanov, Rustem; Morenzoni, Elvezio; Munsie, Timothy J. S.; Hallas, Alannah M.; Wilson, Murray N.; Cai, Yipeng; Luke, Graeme M.; Chen, Bijuan; Li, Wenmin; Jin, Changqing; Ding, Cui; Guo, Shengli; Ning, Fanlong; Ito, Takashi U.; Higemoto, Wataru; Billinge, Simon J. L.; Sakamoto, Shoya; Fujimori, Atsushi; Murakami, Taito; Kageyama, Hiroshi; Alonso, Jose Antonio; Kotliar, Gabriel; Imada, Masatoshi; Uemura, Yasutomo J.

2016-08-01

RENiO3 (RE=rare-earth element) and V2O3 are archetypal Mott insulator systems. When tuned by chemical substitution (RENiO3) or pressure (V2O3), they exhibit a quantum phase transition (QPT) between an antiferromagnetic Mott insulating state and a paramagnetic metallic state. Because novel physics often appears near a Mott QPT, the details of this transition, such as whether it is first or second order, are important. Here, we demonstrate through muon spin relaxation/rotation (μSR) experiments that the QPT in RENiO3 and V2O3 is first order: the magnetically ordered volume fraction decreases to zero at the QPT, resulting in a broad region of intrinsic phase separation, while the ordered magnetic moment retains its full value until it is suddenly destroyed at the QPT. These findings bring to light a surprising universality of the pressure-driven Mott transition, revealing the importance of phase separation and calling for further investigation into the nature of quantum fluctuations underlying the transition.

Tailoring Materials for Mottronics: Excess Oxygen Doping of a Prototypical Mott Insulator.

PubMed

Scheiderer, Philipp; Schmitt, Matthias; Gabel, Judith; Zapf, Michael; Stübinger, Martin; Schütz, Philipp; Dudy, Lenart; Schlueter, Christoph; Lee, Tien-Lin; Sing, Michael; Claessen, Ralph

2018-05-07

The Mott transistor is a paradigm for a new class of electronic devices-often referred to by the term Mottronics-which are based on charge correlations between the electrons. Since correlation-induced insulating phases of most oxide compounds are usually very robust, new methods have to be developed to push such materials right to the boundary to the metallic phase in order to enable the metal-insulator transition to be switched by electric gating. Here, it is demonstrated that thin films of the prototypical Mott insulator LaTiO 3 grown by pulsed laser deposition under oxygen atmosphere are readily tuned by excess oxygen doping across the line of the band-filling controlled Mott transition in the electronic phase diagram. The detected insulator to metal transition is characterized by a strong change in resistivity of several orders of magnitude. The use of suitable substrates and capping layers to inhibit oxygen diffusion facilitates full control of the oxygen content and renders the films stable against exposure to ambient conditions. These achievements represent a significant advancement in control and tuning of the electronic properties of LaTiO 3+ x thin films making it a promising channel material in future Mottronic devices. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Metallic Interface at the Boundary Between Band and Mott Insulators

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

Kancharla, Srivenkateswara S; Dagotto, Elbio R

2006-01-01

Motivated by experiments on atomically smooth layers of LaTiO3, a Mott insulator, sandwiched between layers of SrTiO3, a band insulator, a simple model for such heterostructures is studied using quasi one-dimensional lattices and the Lanczos method. Taking both the local and long-range Coulomb interactions into account, and computing the layer dependent local density of states, a metallic state was found at the interface whose extent strongly depends on the dielectric constant of the material. We also observed that the antiferromagnetic correlations in the bulk Mott phase persist into the metallic region. Our conclusions are in excellent agreement with recently reportedmore » results for this model in the opposite limit of infinite dimensions6,7, thus providing an alternative tool to study electronic reconstruction effects in heterostructures.« less

High-density Two-Dimensional Small Polaron Gas in a Delta-Doped Mott Insulator

PubMed Central

Ouellette, Daniel G.; Moetakef, Pouya; Cain, Tyler A.; Zhang, Jack Y.; Stemmer, Susanne; Emin, David; Allen, S. James

2013-01-01

Heterointerfaces in complex oxide systems open new arenas in which to test models of strongly correlated material, explore the role of dimensionality in metal-insulator-transitions (MITs) and small polaron formation. Close to the quantum critical point Mott MITs depend on band filling controlled by random disordered substitutional doping. Delta-doped Mott insulators are potentially free of random disorder and introduce a new arena in which to explore the effect of electron correlations and dimensionality. Epitaxial films of the prototypical Mott insulator GdTiO3 are delta-doped by substituting a single (GdO)+1 plane with a monolayer of charge neutral SrO to produce a two-dimensional system with high planar doping density. Unlike metallic SrTiO3 quantum wells in GdTiO3 the single SrO delta-doped layer exhibits thermally activated DC and optical conductivity that agree in a quantitative manner with predictions of small polaron transport but with an extremely high two-dimensional density of polarons, ~7 × 1014 cm−2. PMID:24257578

Influence of magnetism and correlation on the spectral properties of doped Mott insulators

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

Wang, Yao; Moritz, Brian; Chen, Cheng-Chien

Unraveling the nature of the doping-induced transition between a Mott insulator and a weakly correlated metal is crucial to understanding novel emergent phases in strongly correlated materials. Here, for this purpose, we study the evolution of spectral properties upon doping Mott insulating states by utilizing the cluster perturbation theory on the Hubbard and t – J -like models. Specifically, a quasifree dispersion crossing the Fermi level develops with small doping, and it eventually evolves into the most dominant feature at high doping levels. Although this dispersion is related to the free-electron hopping, our study shows that this spectral feature is,more » in fact, influenced inherently by both electron-electron correlation and spin-exchange interaction: the correlation destroys coherence, while the coupling between spin and mobile charge restores it in the photoemission spectrum. Due to the persistent impact of correlations and spin physics, the onset of gaps or the high-energy anomaly in the spectral functions can be expected in doped Mott insulators.« less

Influence of magnetism and correlation on the spectral properties of doped Mott insulators

DOE PAGES

Wang, Yao; Moritz, Brian; Chen, Cheng-Chien; ...

2018-03-01

Unraveling the nature of the doping-induced transition between a Mott insulator and a weakly correlated metal is crucial to understanding novel emergent phases in strongly correlated materials. Here, for this purpose, we study the evolution of spectral properties upon doping Mott insulating states by utilizing the cluster perturbation theory on the Hubbard and t – J -like models. Specifically, a quasifree dispersion crossing the Fermi level develops with small doping, and it eventually evolves into the most dominant feature at high doping levels. Although this dispersion is related to the free-electron hopping, our study shows that this spectral feature is,more » in fact, influenced inherently by both electron-electron correlation and spin-exchange interaction: the correlation destroys coherence, while the coupling between spin and mobile charge restores it in the photoemission spectrum. Due to the persistent impact of correlations and spin physics, the onset of gaps or the high-energy anomaly in the spectral functions can be expected in doped Mott insulators.« less

Multiple crossovers and coherent states in a Mott-Peierls insulator

NASA Astrophysics Data System (ADS)

Nájera, O.; Civelli, M.; Dobrosavljević, V.; Rozenberg, M. J.

2018-01-01

We consider the dimer Hubbard model within dynamical mean-field theory to study the interplay and competition between Mott and Peierls physics. We describe the various metal-insulator transition lines of the phase diagram and the breakdown of the different solutions that occur along them. We focus on the specific issue of the debated Mott-Peierls insulator crossover and describe the systematic evolution of the electronic structure across the phase diagram. We found that at low intradimer hopping, the emerging local magnetic moments can unbind above a characteristic singlet temperature T*. Upon increasing the interdimer hopping, subtle changes occur in the electronic structure. Notably, we find Hubbard bands of a mix character with coherent and incoherent excitations. We argue that this state might be relevant for materials such as VO2 and its signatures may be observed in spectroscopic studies, and possibly through pump-probe experiments.

Angle-resolved photoemission spectroscopy studies of the Mott insulator to superconductor evolution in calcium-sodium-copper-chloride

NASA Astrophysics Data System (ADS)

Shen, Kyle Michael

The parent compounds of the high-temperature cuprate superconductors are antiferromagnetic Mott insulators. To explain the microscopic mechanism behind high-temperature superconductivity, it is first necessary to understand how the electronic states evolve from the parent Mott insulator into the superconducting compounds. This dissertation presents angle-resolved photoemission spectroscopy (ARPES) studies of one particular family of the cuprate superconductors, Ca 2-xNaxCuO 2Cl2, to investigate how the single-electron excitations develop throughout momentum space as the system is hole doped from the Mott insulator into a superconductor with a transition temperature of 22 K. These measurements indicate that, due to very strong electron-boson interactions, the quasiparticle residue, Z, approaches zero in the parent Mott insulator due to the formation of small lattice polarons. As a result, many fundamental quantities such as the chemical potential, quasiparticle excitations, and the Fermi surface evolve in manners wholly unexpected from conventional weakly-interacting theories. In addition, highly anisotropic interactions have been observed in momentum space where quasiparticle-like excitations persist to low doping levels along the nodal direction of the d-wave super-conducting gap, in contrast to the unusual excitations near the d-wave antinode. This anisotropy may reflect the propensity of the lightly doped cuprates towards forming a competing, charge-ordered state. These results provide a novel and logically consistent explanation of the hole doping evolution of the lineshape, spectral weight, chemical potential, quasiparticle dispersion, and Fermi surface as Ca2- xNaxCuO2Cl2 evolves from the parent Mott insulator into a high-temperature superconductor.

Superconductivity and bandwidth-controlled Mott metal-insulator transition in 1T-TaS2-xSex

NASA Astrophysics Data System (ADS)

Ang, R.; Miyata, Y.; Ieki, E.; Nakayama, K.; Sato, T.; Liu, Y.; Lu, W. J.; Sun, Y. P.; Takahashi, T.

2013-09-01

We have performed high-resolution angle-resolved photoemission spectroscopy (ARPES) of layered chalcogenide 1T-TaS2-xSex to elucidate the electronic states especially relevant to the occurrence of superconductivity. We found a direct evidence for a Ta-5d-derived electron pocket associated with the superconductivity, which is fragile against a Mott-gap opening observed in the insulating ground state for S-rich samples. In particular, a strong electron-electron interaction-induced Mott gap driven by a Ta 5d orbital also exists in the metallic ground state for Se-rich samples, while finite ARPES intensity near the Fermi level likely originating from a Se 4p orbital survives, indicative of the orbital-selective nature of the Mott transition. Present results suggest that effective electron correlation and p-d hybridization play a crucial role to tune the superconductivity and Mott metal-insulator transition.

Quantum phase transitions and local magnetism in Mott insulators: A local probe investigation using muons, neutrons, and photons

NASA Astrophysics Data System (ADS)

Frandsen, Benjamin A.

Mott insulators are materials in which strong correlations among the electrons induce an unconventional insulating state. Rich interplay between the structural, magnetic, and electronic degrees of freedom resulting from the electron correlation can lead to unusual complexity of Mott materials on the atomic scale, such as microscopically heterogeneous phases or local structural correlations that deviate significantly from the average structure. Such behavior must be studied by suitable experimental techniques, i.e. "local probes", that are sensitive to this local behavior rather than just the bulk, average properties. In this thesis, I will present results from our studies of multiple families of Mott insulators using two such local probes: muon spin relaxation (muSR), a probe of local magnetism; and pair distribution function (PDF) analysis of x-ray and neutron total scattering, a probe of local atomic structure. In addition, I will present the development of magnetic pair distribution function analysis, a novel method for studying local magnetic correlations that is highly complementary to the muSR and atomic PDF techniques. We used muSR to study the phase transition from Mott insulator to metal in two archetypal Mott insulating systems: RENiO3 (RE = rare earth element) and V2O3. In both of these systems, the Mott insulating state can be suppressed by tuning a nonthermal parameter, resulting in a "quantum" phase transition at zero temperature from the Mott insulating state to a metallic state. In RENiO3, this occurs through variation of the rare-earth element in the chemical composition; in V 2O3, through the application of hydrostatic pressure. Our results show that the metallic and Mott insulating states unexpectedly coexist in phase-separated regions across a large portion of parameter space near the Mott quantum phase transition and that the magnitude of the ordered antiferromagnetic moment remains constant across the phase diagram until it is abruptly

Strongly enhanced thermal transport in a lightly doped Mott insulator at low temperature.

PubMed

Zlatić, V; Freericks, J K

2012-12-28

We show how a lightly doped Mott insulator has hugely enhanced electronic thermal transport at low temperature. It displays universal behavior independent of the interaction strength when the carriers can be treated as nondegenerate fermions and a nonuniversal "crossover" region where the Lorenz number grows to large values, while still maintaining a large thermoelectric figure of merit. The electron dynamics are described by the Falicov-Kimball model which is solved for arbitrary large on-site correlation with a dynamical mean-field theory algorithm on a Bethe lattice. We show how these results are generic for lightly doped Mott insulators as long as the renormalized Fermi liquid scale is pushed to very low temperature and the system is not magnetically ordered.

Volume-wise destruction of the antiferromagnetic Mott insulating state through quantum tuning.

NASA Astrophysics Data System (ADS)

Uemura, Yasutomo

RENiO3 (RE = rare-earth element) and V2O3 are archetypal Mott insulator systems. When tuned by chemical substitution (RENiO3) or hydrostatic pressure (V2O3) , they exhibit a quantum phase transition (QPT) between an antiferromagnetic Mott insulating state and a paramagnetic metallic state. We demonstrate through muon spin relaxation/rotation (μSR) experiments that the QPT in RENiO3 and V2O3 is first order: the magnetically ordered volume fraction decreases to zero at the QPT, resulting in a broad region of intrinsic phase separation, while the ordered magnetic moment retains its full value until it is suddenly destroyed at the QPT. These two cases correspond to the band-width tuning of Mott transitions, and also associated with structural phase transitions, Volume evolutions of antiferromagnetic transition from μSR will be compared to those of structure by x-ray and metallicity by nano optics, in first-order thermal Mott transition in a V2O3 film at ambient pressure. These results will be compared to the process of destruction of magnetic order in another Mott transition system Ba(Co,Ni)S2 in ``filling control'' without structural transition, and in parent compounds of high-Tc cuprates and Fe-based superconductors. We will also discuss roles of first-order quantum transition in generating soft modes relevant to magnetic resonance mode in unconventional superconductors. Work performed in collaboration with the groups of: J.A. Alonso (Madrid), H. Kageyama (Kyoto). E. Morenzoni (PSI), G.M. Luke (McMaster), C.Q. Jin (IOP Beijing), F.L. Ning (Zhejian), S.J.L. Billinge (Columbia), S. Shamoto, W. Higemoto (JAEA), A. Fujimori (Tokyo), A. Gauzzi (Paris), R. de Renzi (Parma), G. Kotliar (Rutgers), M. Imada (Tokyo), D. Basov (UCSD), I, Schuller (UCSD). supported by NSF DMR-1610633 and DMR-1436095 (DMREF).

Photoinduced Hund excitons in the breakdown of a two-orbital Mott insulator

NASA Astrophysics Data System (ADS)

Rincón, Julián; Dagotto, Elbio; Feiguin, Adrian E.

2018-06-01

We study the photoinduced breakdown of a two-orbital Mott insulator and resulting metallic state. Using time-dependent density matrix renormalization group, we scrutinize the real-time dynamics of the half-filled two-orbital Hubbard model interacting with a resonant radiation field pulse. The breakdown, caused by production of doublon-holon pairs, is enhanced by Hund's exchange, which dynamically activates large orbital fluctuations. The melting of the Mott insulator is accompanied by a high to low spin transition with a concomitant reduction of antiferromagnetic spin fluctuations. Most notably, the overall time response is driven by the photogeneration of excitons with orbital character that are stabilized by Hund's coupling. These unconventional "Hund excitons" correspond to bound spin-singlet orbital-triplet doublon-holon pairs. We study exciton properties such as bandwidth, binding potential, and size within a semiclassical approach. The photometallic state results from a coexistence of Hund excitons and doublon-holon plasma.

An Angle Resolved Photoemission Study of a Mott Insulator and Its Evolution to a High Temperature Superconductor

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

Ronning, Filip

2002-03-19

One of the most remarkable facts about the high temperature superconductors is their close proximity to an antiferromagnetically ordered Mott insulating phase. This fact suggests that to understand superconductivity in the cuprates we must first understand the insulating regime. Due to material properties the technique of angle resolved photoemission is ideally suited to study the electronic structure in the cuprates. Thus, a natural starting place to unlocking the secrets of high Tc would appears to be with a photoemission investigation of insulating cuprates. This dissertation presents the results of precisely such a study. In particular, we have focused on themore » compound Ca{sub 2-x}Na{sub x}CuO{sub 2}Cl{sub 2}. With increasing Na content this system goes from an antiferromagnetic Mott insulator with a Neel transition of 256K to a superconductor with an optimal transition temperature of 28K. At half filling we have found an asymmetry in the integrated spectral weight, which can be related to the occupation probability, n(k). This has led us to identify a d-wave-like dispersion in the insulator, which in turn implies that the high energy pseudogap as seen by photoemission is a remnant property of the insulator. These results are robust features of the insulator which we found in many different compounds and experimental conditions. By adding Na we were able to study the evolution of the electronic structure across the insulator to metal transition. We found that the chemical potential shifts as holes are doped into the system. This picture is in sharp contrast to the case of La{sub 2-x}Sr{sub x}CuO{sub 4} where the chemical potential remains fixed and states are created inside the gap. Furthermore, the low energy excitations (ie the Fermi surface) in metallic Ca{sub 1.9}Na{sub 0.1}CuO{sub 2}Cl{sub 2} is most well described as a Fermi arc, although the high binding energy features reveal the presence of shadow bands. Thus, the results in this dissertation

Disorder effect on the Friedel oscillations in a one-dimensional Mott insulator

NASA Astrophysics Data System (ADS)

Weiss, Y.; Goldstein, M.; Berkovits, R.

2007-07-01

The Friedel oscillations resulting from coupling a quantum dot to one edge of a disordered one-dimensional wire in the Mott insulator regime are calculated numerically using the density matrix renormalization group method. By investigating the influence of a constant weak disorder on the Friedel oscillations decay we find that the effect of disorder is reduced by increasing the interaction strength. This behavior is opposite to the recently reported influence of disorder in the Anderson insulator regime.

First-order melting of a weak spin-orbit mott insulator into a correlated metal

DOE PAGES

Hogan, Tom; Yamani, Z.; Walkup, D.; ...

2015-06-25

Herein, the electronic phase diagram of the weak spin-orbit Mott insulator (Sr 1-xLa x) 3Ir 2O 7 is determined via an exhaustive experimental study. Upon doping electrons via La substitution, an immediate collapse in resistivity occurs along with a narrow regime of nanoscale phase separation comprised of antiferromagnetic, insulating regions and paramagnetic, metallic puddles persisting until x≈0.04. Continued electron doping results in an abrupt, first-order phase boundary where the Néel state is suppressed and a homogenous, correlated, metallic state appears with an enhanced spin susceptibility and local moments. In conclusion, as the metallic state is stabilized, a weak structural distortionmore » develops and suggests a competing instability with the parent spin-orbit Mott state.« less

Photoinduced Hund excitons in the breakdown of a two-orbital Mott insulator

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

Rincon, Julian; Dagotto, Elbio R.; Feiguin, Adrian E.

We study the photoinduced breakdown of a two-orbital Mott insulator and resulting metallic state. Using time-dependent density matrix renormalization group, we scrutinize the real-time dynamics of the half-filled two-orbital Hubbard model interacting with a resonant radiation field pulse. The breakdown, caused by production of doublon-holon pairs, is enhanced by Hund's exchange, which dynamically activates large orbital fluctuations. The melting of the Mott insulator is accompanied by a high to low spin transition with a concomitant reduction of antiferromagnetic spin fluctuations. Most notably, the overall time response is driven by the photogeneration of excitons with orbital character that are stabilized bymore » Hund's coupling. These unconventional “Hund excitons” correspond to bound spin-singlet orbital-triplet doublon-holon pairs. We study exciton properties such as bandwidth, binding potential, and size within a semiclassical approach. In conclusion, the photometallic state results from a coexistence of Hund excitons and doublon-holon plasma.« less

Photoinduced Hund excitons in the breakdown of a two-orbital Mott insulator

DOE PAGES

Rincon, Julian; Dagotto, Elbio R.; Feiguin, Adrian E.

2018-06-05

We study the photoinduced breakdown of a two-orbital Mott insulator and resulting metallic state. Using time-dependent density matrix renormalization group, we scrutinize the real-time dynamics of the half-filled two-orbital Hubbard model interacting with a resonant radiation field pulse. The breakdown, caused by production of doublon-holon pairs, is enhanced by Hund's exchange, which dynamically activates large orbital fluctuations. The melting of the Mott insulator is accompanied by a high to low spin transition with a concomitant reduction of antiferromagnetic spin fluctuations. Most notably, the overall time response is driven by the photogeneration of excitons with orbital character that are stabilized bymore » Hund's coupling. These unconventional “Hund excitons” correspond to bound spin-singlet orbital-triplet doublon-holon pairs. We study exciton properties such as bandwidth, binding potential, and size within a semiclassical approach. In conclusion, the photometallic state results from a coexistence of Hund excitons and doublon-holon plasma.« less

Filling-driven Mott transition in SU(N ) Hubbard models

NASA Astrophysics Data System (ADS)

Lee, Seung-Sup B.; von Delft, Jan; Weichselbaum, Andreas

2018-04-01

We study the filling-driven Mott transition involving the metallic and paramagnetic insulating phases in SU (N ) Fermi-Hubbard models, using the dynamical mean-field theory and the numerical renormalization group as its impurity solver. The compressibility shows a striking temperature dependence: near the critical end-point temperature, it is strongly enhanced in the metallic phase close to the insulating phase. We demonstrate that this compressibility enhancement is associated with the thermal suppression of the quasiparticle peak in the local spectral functions. We also explain that the asymmetric shape of the quasiparticle peak originates from the asymmetry in the dynamics of the generalized doublons and holons.

Fabrication and Measurement of Electroluminescence and Electrical Properties of Organic Light-Emitting Diodes Containing Mott Insulator Nanocrystals.

PubMed

Nozoe, Soichiro; Kinoshita, Nobuaki; Matsuda, Masaki

2016-04-01

By using the short-time electrocrystallization technique, phthalocyanine (Pc)-based Mott insulator Co(Pc)(CN)2 . 2CHCl3 nanocrystals were fabricated and applied to organic light-emiting diodes (OLEDs). The fabricated device having the configuration ITO/Co(Pc)(CN)2 . 2CHCl3/Alq3/Al, in which ITO is indium-tin oxide and Alq3 is tris(8-hydroxyquinolinato)aluminum, showed clear emission from Alq3, suggesting the Mott insulator Co(Pc)(CN)2 . 2CHCl3 can work as useful hole-injection and transport material in OLEDs.

Nanoscale orbital excitations and the infrared spectrum of a molecular Mott insulator: A15-Cs3C60.

PubMed

Naghavi, S S; Fabrizio, M; Qin, T; Tosatti, E

2016-10-14

The quantum physics of ions and electrons behind low-energy spectra of strongly correlated molecular conductors, superconductors and Mott insulators is poorly known, yet fascinating especially in orbitally degenerate cases. The fulleride insulator Cs 3 C 60 (A15), one such system, exhibits infrared (IR) spectra with low temperature peak features and splittings suggestive of static Jahn-Teller distortions with a breakdown of orbital symmetry in the molecular site. That is puzzling, since there is no detectable static distortion, and because the features and splittings disappear upon modest heating, which they should not. Taking advantage of the Mott-induced collapse of electronic wavefunctions from lattice-extended to nanoscale localized inside a caged molecular site, we show that the unbroken spin and orbital symmetry of the ion multiplets explains the IR spectrum without adjustable parameters. This demonstrates the importance of a fully quantum treatment of nuclear positions and orbital momenta in the Mott insulator sites, dynamically but not statically distorted. The observed demise of these features with temperature is explained by the thermal population of a multiplet term whose nuclear positions are essentially undistorted, but whose energy is very low-lying. That term is in fact a scaled-down orbital excitation analogous to that of other Mott insulators, with the same spin 1/2 as the ground state, but with a larger orbital momentum of two instead of one.

Site-resolved imaging of a bosonic Mott insulator using ytterbium atoms

NASA Astrophysics Data System (ADS)

Miranda, Martin; Inoue, Ryotaro; Tambo, Naoki; Kozuma, Mikio

2017-10-01

We demonstrate site-resolved imaging of a strongly correlated quantum system without relying on laser cooling techniques during fluorescence imaging. We observe the formation of Mott shells in the insulating regime and realize thermometry in an atomic cloud. This work proves the feasibility of the noncooled approach and opens the door to extending the detection technology to new atomic species.

Absence of Asymptotic Freedom in Doped Mott Insulators: Breakdown of Strong Coupling Expansions

NASA Astrophysics Data System (ADS)

Phillips, Philip; Galanakis, Dimitrios; Stanescu, Tudor D.

2004-12-01

We show that doped Mott insulators such as the copper-oxide superconductors are asymptotically slaved in that the quasiparticle weight Z near half-filling depends critically on the existence of the high-energy scale set by the upper Hubbard band. In particular, near half-filling, the following dichotomy arises: Z≠0 when the high-energy scale is integrated out but Z=0 in the thermodynamic limit when it is retained. Slavery to the high-energy scale arises from quantum interference between electronic excitations across the Mott gap. Broad spectral features seen in photoemission in the normal state of the cuprates are argued to arise from high-energy slavery.

Realization of a Hole-Doped Mott Insulator on a Triangular Silicon Lattice

NASA Astrophysics Data System (ADS)

Ming, Fangfei; Johnston, Steve; Mulugeta, Daniel; Smith, Tyler S.; Vilmercati, Paolo; Lee, Geunseop; Maier, Thomas A.; Snijders, Paul C.; Weitering, Hanno H.

2017-12-01

The physics of doped Mott insulators is at the heart of some of the most exotic physical phenomena in materials research including insulator-metal transitions, colossal magnetoresistance, and high-temperature superconductivity in layered perovskite compounds. Advances in this field would greatly benefit from the availability of new material systems with a similar richness of physical phenomena but with fewer chemical and structural complications in comparison to oxides. Using scanning tunneling microscopy and spectroscopy, we show that such a system can be realized on a silicon platform. The adsorption of one-third monolayer of Sn atoms on a Si(111) surface produces a triangular surface lattice with half filled dangling bond orbitals. Modulation hole doping of these dangling bonds unveils clear hallmarks of Mott physics, such as spectral weight transfer and the formation of quasiparticle states at the Fermi level, well-defined Fermi contour segments, and a sharp singularity in the density of states. These observations are remarkably similar to those made in complex oxide materials, including high-temperature superconductors, but highly extraordinary within the realm of conventional s p -bonded semiconductor materials. It suggests that exotic quantum matter phases can be realized and engineered on silicon-based materials platforms.

Inhomogeneous field induced magnetoelectric effect in Mott insulators

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

Boulaevskii, Lev N; Batista, Cristian D

2008-01-01

We consider a Mott insulator like HoMnO{sub 3} whose magnetic lattice is geometrically frustrated and comprises a 3D array of triangular layers with magnetic moments ordered in a 120{sup o} structure. We show that the effect of a uniform magnetic field gradient, {gradient}H, is to redistribute the electronic charge of the magnetically ordered phase leading to a unfirom electric field gradient. The resulting voltage difference between the crystal edges is proportional to the square of the crystal thickness, or inter-edge distance, L. It can reach values of several volts for |{gradient}H| {approx} 0.01 T/cm and L {approx_equal} 1mm, as longmore » as the crystal is free of antiferromagnetic domain walls.« less

Mott transition between a spin-liquid insulator and a metal in three dimensions.

PubMed

Podolsky, Daniel; Paramekanti, Arun; Kim, Yong Baek; Senthil, T

2009-05-08

We study a bandwidth controlled Mott metal-insulator transition (MIT) from a Fermi-liquid metal to a quantum spin-liquid insulator in three dimensions. Using a slave rotor approach including gauge fluctuations, we obtain a continuous MIT and discuss finite temperature crossovers in its vicinity. We show that the specific heat C approximately Tlnln(1/T) at the MIT and that the metallic state near the MIT should exhibit a "conductivity minimum" as a function of temperature. We suggest Na4Ir3O8 as a candidate to test our predictions and compute its electron spectral function at the MIT.

Observation of the Mott insulator to superfluid crossover of a driven-dissipative Bose-Hubbard system

PubMed Central

Tomita, Takafumi; Nakajima, Shuta; Danshita, Ippei; Takasu, Yosuke; Takahashi, Yoshiro

2017-01-01

Dissipation is ubiquitous in nature and plays a crucial role in quantum systems such as causing decoherence of quantum states. Recently, much attention has been paid to an intriguing possibility of dissipation as an efficient tool for the preparation and manipulation of quantum states. We report the realization of successful demonstration of a novel role of dissipation in a quantum phase transition using cold atoms. We realize an engineered dissipative Bose-Hubbard system by introducing a controllable strength of two-body inelastic collision via photoassociation for ultracold bosons in a three-dimensional optical lattice. In the dynamics subjected to a slow ramp-down of the optical lattice, we find that strong on-site dissipation favors the Mott insulating state: The melting of the Mott insulator is delayed, and the growth of the phase coherence is suppressed. The controllability of the dissipation is highlighted by quenching the dissipation, providing a novel method for investigating a quantum many-body state and its nonequilibrium dynamics. PMID:29291246

Dynamical time-reversal symmetry breaking and photo-induced chiral spin liquids in frustrated Mott insulators

DOE PAGES

Claassen, Martin; Jiang, Hong -Chen; Moritz, Brian; ...

2017-10-30

The search for quantum spin liquids in frustrated quantum magnets recently has enjoyed a surge of interest, with various candidate materials under intense scrutiny. However, an experimental confirmation of a gapped topological spin liquid remains an open question. Here, we show that circularly polarized light can provide a knob to drive frustrated Mott insulators into a chiral spin liquid, realizing an elusive quantum spin liquid with topological order. We find that the dynamics of a driven Kagome Mott insulator is well-captured by an effective Floquet spin model, with heating strongly suppressed, inducing a scalar spin chirality S i · (Smore » j × S k) term which dynamically breaks time-reversal while preserving SU(2) spin symmetry. We fingerprint the transient phase diagram and find a stable photo-induced chiral spin liquid near the equilibrium state. Furthermore, the results presented suggest employing dynamical symmetry breaking to engineer quantum spin liquids and access elusive phase transitions that are not readily accessible in equilibrium.« less

Geometrically frustrated trimer-based Mott insulator

NASA Astrophysics Data System (ADS)

Nguyen, Loi T.; Halloran, T.; Xie, Weiwei; Kong, Tai; Broholm, C. L.; Cava, R. J.

2018-05-01

The crystal structure of B a4NbR u3O12 is based on triangular planes of elongated R u3O12 trimers oriented perpendicular to the plane. We report that it is semiconducting, that its Weiss temperature and effective magnetic moment are -155 K and 2.59 μB/f .u . , respectively, and that the magnetic susceptibility and specific-heat data indicate that it exhibits magnetic ordering near 4 K. The presence of a high density of low energy states is evidenced by a substantial Sommerfeld-like T-linear term [ γ =31 (2 ) mJ mo l-1K-2 ] in the specific heat. Electronic-structure calculations reveal that the electronic states at the Fermi energy reside on the R u3O12 trimers and that the calculated density of electronic states is high and continuous around the Fermi energy—in other words density functional theory calculates the material to be a metal. The results imply that B a4NbR u3O12 is a geometrically frustrated trimer-based Mott insulator.

Spin-Orbital Excitation Continuum and Anomalous Electron-Phonon Interaction in the Mott Insulator LaTiO3

NASA Astrophysics Data System (ADS)

Ulrich, C.; Khaliullin, G.; Guennou, M.; Roth, H.; Lorenz, T.; Keimer, B.

2015-10-01

Raman scattering experiments on stoichiometric, Mott-insulating LaTiO3 over a wide range of excitation energies reveal a broad electronic continuum which is featureless in the paramagnetic state, but develops a gap of ˜800 cm-1 upon cooling below the Néel temperature TN=146 K . In the antiferromagnetic state, the spectral weight below the gap is transferred to well-defined spectral features due to spin and orbital excitations. Low-energy phonons exhibit pronounced Fano anomalies indicative of strong interaction with the electron system for T >TN , but become sharp and symmetric for T Mott insulators and indicate liquidlike correlations between spins and orbitals.

Self-energy behavior away from the Fermi surface in doped Mott insulators.

PubMed

Merino, J; Gunnarsson, O; Kotliar, G

2016-02-03

We analyze self-energies of electrons away from the Fermi surface in doped Mott insulators using the dynamical cluster approximation to the Hubbard model. For large onsite repulsion, U, and hole doping, the magnitude of the self-energy for imaginary frequencies at the top of the band ([Formula: see text]) is enhanced with respect to the self-energy magnitude at the bottom of the band ([Formula: see text]). The self-energy behavior at these two [Formula: see text]-points is switched for electron doping. Although the hybridization is much larger for (0, 0) than for [Formula: see text], we demonstrate that this is not the origin of this difference. Isolated clusters under a downward shift of the chemical potential, [Formula: see text], at half-filling reproduce the overall self-energy behavior at (0, 0) and [Formula: see text] found in low hole doped embedded clusters. This happens although there is no change in the electronic structure of the isolated clusters. Our analysis shows that a downward shift of the chemical potential which weakly hole dopes the Mott insulator can lead to a large enhancement of the [Formula: see text] self-energy for imaginary frequencies which is not associated with electronic correlation effects, even in embedded clusters. Interpretations of the strength of electronic correlations based on self-energies for imaginary frequencies are, in general, misleading for states away from the Fermi surface.

Unusual Mott transition in multiferroic PbCrO 3

DOE PAGES

Wang, Shanmin; Zhu, Jinlong; Zhang, Yi; ...

2015-11-24

The Mott insulator in correlated electron systems arises from classical Coulomb repulsion between carriers to provide a powerful force for electron localization. When turning such an insulator into a metal, the so-called Mott transition, is commonly achieved by "bandwidth" control or "band filling." However, both mechanisms deviate from the original concept of Mott, which attributes such a transition to the screening of Coulomb potential and associated lattice contraction. We report a pressure-induced isostructural Mott transition in cubic perovskite PbCrO3. At the transition pressure of similar to 3 GPa, PbCrO3 exhibits significant collapse in both lattice volume and Coulomb potential. Concurrentmore » with the collapse, it transforms from a hybrid multiferroic insulator to a metal. For the first time to our knowledge, these findings validate the scenario conceived by Mott. Close to the Mott criticality at similar to 300 K, fluctuations of the lattice and charge give rise to elastic anomalies and Laudau critical behaviors resembling the classic liquid-gas transition. Moreover, the anomalously large lattice volume and Coulomb potential in the low-pressure insulating phase are largely associated with the ferroelectric distortion, which is substantially suppressed at high pressures, leading to the first-order phase transition without symmetry breaking.« less

Unusual Mott transition in multiferroic PbCrO3

PubMed Central

Wang, Shanmin; Zhu, Jinlong; Zhang, Yi; Yu, Xiaohui; Zhang, Jianzhong; Wang, Wendan; Bai, Ligang; Qian, Jiang; Yin, Liang; Sullivan, Neil S.; Jin, Changqing; He, Duanwei; Xu, Jian; Zhao, Yusheng

2015-01-01

The Mott insulator in correlated electron systems arises from classical Coulomb repulsion between carriers to provide a powerful force for electron localization. Turning such an insulator into a metal, the so-called Mott transition, is commonly achieved by “bandwidth” control or “band filling.” However, both mechanisms deviate from the original concept of Mott, which attributes such a transition to the screening of Coulomb potential and associated lattice contraction. Here, we report a pressure-induced isostructural Mott transition in cubic perovskite PbCrO3. At the transition pressure of ∼3 GPa, PbCrO3 exhibits significant collapse in both lattice volume and Coulomb potential. Concurrent with the collapse, it transforms from a hybrid multiferroic insulator to a metal. For the first time to our knowledge, these findings validate the scenario conceived by Mott. Close to the Mott criticality at ∼300 K, fluctuations of the lattice and charge give rise to elastic anomalies and Laudau critical behaviors resembling the classic liquid–gas transition. The anomalously large lattice volume and Coulomb potential in the low-pressure insulating phase are largely associated with the ferroelectric distortion, which is substantially suppressed at high pressures, leading to the first-order phase transition without symmetry breaking. PMID:26604314

Incipient 2D Mott insulators in extreme high electron density, ultra-thin GdTiO3/SrTiO3/GdTiO3 quantum wells

NASA Astrophysics Data System (ADS)

Allen, S. James; Ouellette, Daniel G.; Moetakef, Pouya; Cain, Tyler; Chen, Ru; Balents, Leon; Stemmer, Susanne

2013-03-01

By reducing the number of SrO planes in a GdTiO3 /SrTiO3/ GdTiO3 quantum well heterostructure, an electron gas with ~ fixed 2D electron density can be driven close to the Mott metal insulator transition - a quantum critical point at ~1 electron per unit cell. A single interface between the Mott insulator GdTiO3 and band insulator SrTiO3 has been shown to introduce ~ 1/2 electron per interface unit cell. Two interfaces produce a quantum well with ~ 7 1014 cm-2 electrons: at the limit of a single SrO layer it may produce a 2D magnetic Mott insulator. We use temperature and frequency dependent (DC - 3eV) conductivity and temperature dependent magneto-transport to understand the relative importance of electron-electron interactions, electron-phonon interactions, and surface roughness scattering as the electron gas is compressed toward the quantum critical point. Terahertz time-domain and FTIR spectroscopies, measure the frequency dependent carrier mass and scattering rate, and the mid-IR polaron absorption as a function of quantum well thickness. At the extreme limit of a single SrO plane, we observe insulating behavior with an optical gap substantially less than that of the surrounding GdTiO3, suggesting a novel 2D Mott insulator. MURI program of the Army Research Office - Grant No. W911-NF-09-1-0398

Spin-orbit coupling, strong correlation, and insulator-metal transitions: The J eff = 3 2 ferromagnetic Dirac-Mott insulator Ba 2 NaOsO 6

DOE PAGES

Gangopadhyay, Shruba; Pickett, Warren E.

2015-01-15

The double perovskite Ba 2NaOsO 6 (BNOO), an exotic example of a very high oxidation state (heptavalent) osmium d1 compound and also uncommon by being a ferromagnetic open d-shell (Mott) insulator without Jahn-Teller (JT) distortion, is modeled using a density functional theory based hybrid functional incorporating exact exchange for correlated electronic orbitals and including the large spin-orbit coupling (SOC). The experimentally observed narrow-gap ferromagnetic insulating ground state is obtained, but only when including spin-orbit coupling, making this a Dirac-Mott insulator. The calculated easy axis along [110] is in accord with experiment, providing additional support that this approach provides a realisticmore » method for studying this system. The predicted spin density for [110] spin orientation is nearly cubic (unlike for other directions), providing an explanation for the absence of JT distortion. An orbital moment of –0.4μ B strongly compensates the +0.5μ B spin moment on Os, leaving a strongly compensated moment more in line with experiment. Remarkably, the net moment lies primarily on the oxygen ions. An insulator-metal transition, by rotating the magnetization direction with an external field under moderate pressure, is predicted as one consequence of strong SOC, and metallization under moderate pressure is predicted. In conclusion, a comparison is made with the isostructural, isovalent insulator Ba 2LiOsO 6, which, however, orders antiferromagnetically.« less

Ultrafast hopping dynamics of 5f electrons in the Mott insulator UO₂ studied by femtosecond pump-probe spectroscopy.

PubMed

An, Yong Q; Taylor, Antoinette J; Conradson, Steven D; Trugman, Stuart A; Durakiewicz, Tomasz; Rodriguez, George

2011-05-20

We describe a femtosecond pump-probe study of ultrafast hopping dynamics of 5f electrons in the Mott insulator UO₂ following Mott-gap excitation at temperatures of 5-300 K. Hopping-induced response of the lattice and electrons is probed by transient reflectivity at mid- and above-gap photon energies, respectively. These measurements show an instantaneous hop, subsequent picosecond lattice deformation, followed by acoustic phonon emission and microsecond relaxation. Temperature-dependent studies indicate that the slow relaxation results from Hubbard excitons formed by U³⁺-U⁵⁺ pairs.

Mott criticality and multiferroicity in organic κ-(BEDT-TTF)2X salts

NASA Astrophysics Data System (ADS)

Lang, Michael

2014-03-01

Layered organic charge-transfer (CT) salts of the κ-(BEDT-TTF)2X family show a wealth of electronic phases resulting from the interplay of strong electron-electron correlations, reduced dimensions and magnetic frustration. Of particular interest has been the bandwidth-controlled Mott transition, separating an antiferromagnetic (afm) insulating state from a correlated metallic and superconducting state. Whereas the hydrogenated X = Cu[N(CN)2]Br salt is located on the metallic side, the deuterated variant, denoted κ-D8, is situated in splitting distance to the Mott transition, enabling the s-shaped transition line TMI to be crossed via temperature sweeps. The talk will address the following aspects: 1) Thermal expansion measurements on single crystalline κ-D8 reveal discontinuous changes of the lattice parameters on crossing the Mott transition line and a huge anomaly close to the second-order critical end point of TMI. By elaborating on a scaling theory, we found that (i) the latter effect is a consequence of an almost divergence of the Grüneisen parameter Γ at the finite- T critical end point, and (ii) that the expansivity data of are in excellent agreement with the Mott criticality lying within the 2D Ising universality class, at variance with results from conductivity measurements. Thermal expansion measurements under Helium-gas pressure are underway for providing thermodynamic information at variable pressure. 2) Surprisingly, for the isostructural X = Cu[N(CN)2]Cl salt, located close to the Mott transition on the insulating side, we found that besides the well-established afm order at TN ~ 27 K, the system also reveals a ferroelectric transition at TFE, making this material the first multiferroic CT salt. Most remarkably, the measurements reveal TFE ~TN , suggesting a close interrelation between both types of ferroic order. Work was supported by Deutsche Forschungsgemeinschaft through the Collaborative Research Centers TRR 49 and TRR 80.

Tunable and low-loss correlated plasmons in Mott-like insulating oxides

NASA Astrophysics Data System (ADS)

Asmara, Teguh Citra; Wan, Dongyang; Zhao, Yongliang; Majidi, Muhammad Aziz; Nelson, Christopher T.; Scott, Mary C.; Cai, Yao; Yan, Bixing; Schmidt, Daniel; Yang, Ming; Zhu, Tao; Trevisanutto, Paolo E.; Motapothula, Mallikarjuna R.; Feng, Yuan Ping; Breese, Mark B. H.; Sherburne, Matthew; Asta, Mark; Minor, Andrew; Venkatesan, T.; Rusydi, Andrivo

2017-05-01

Plasmonics has attracted tremendous interests for its ability to confine light into subwavelength dimensions, creating novel devices with unprecedented functionalities. New plasmonic materials are actively being searched, especially those with tunable plasmons and low loss in the visible-ultraviolet range. Such plasmons commonly occur in metals, but many metals have high plasmonic loss in the optical range, a main issue in current plasmonic research. Here, we discover an anomalous form of tunable correlated plasmons in a Mott-like insulating oxide from the Sr1-xNb1-yO3+δ family. These correlated plasmons have multiple plasmon frequencies and low loss in the visible-ultraviolet range. Supported by theoretical calculations, these plasmons arise from the nanometre-spaced confinement of extra oxygen planes that enhances the unscreened Coulomb interactions among charges. The correlated plasmons are tunable: they diminish as extra oxygen plane density or film thickness decreases. Our results open a path for plasmonics research in previously untapped insulating and strongly-correlated materials.

Tunable and low-loss correlated plasmons in Mott-like insulating oxides.

PubMed

Asmara, Teguh Citra; Wan, Dongyang; Zhao, Yongliang; Majidi, Muhammad Aziz; Nelson, Christopher T; Scott, Mary C; Cai, Yao; Yan, Bixing; Schmidt, Daniel; Yang, Ming; Zhu, Tao; Trevisanutto, Paolo E; Motapothula, Mallikarjuna R; Feng, Yuan Ping; Breese, Mark B H; Sherburne, Matthew; Asta, Mark; Minor, Andrew; Venkatesan, T; Rusydi, Andrivo

2017-05-12

Plasmonics has attracted tremendous interests for its ability to confine light into subwavelength dimensions, creating novel devices with unprecedented functionalities. New plasmonic materials are actively being searched, especially those with tunable plasmons and low loss in the visible-ultraviolet range. Such plasmons commonly occur in metals, but many metals have high plasmonic loss in the optical range, a main issue in current plasmonic research. Here, we discover an anomalous form of tunable correlated plasmons in a Mott-like insulating oxide from the Sr 1-x Nb 1-y O 3+δ family. These correlated plasmons have multiple plasmon frequencies and low loss in the visible-ultraviolet range. Supported by theoretical calculations, these plasmons arise from the nanometre-spaced confinement of extra oxygen planes that enhances the unscreened Coulomb interactions among charges. The correlated plasmons are tunable: they diminish as extra oxygen plane density or film thickness decreases. Our results open a path for plasmonics research in previously untapped insulating and strongly-correlated materials.

Tunable and low-loss correlated plasmons in Mott-like insulating oxides

PubMed Central

Asmara, Teguh Citra; Wan, Dongyang; Zhao, Yongliang; Majidi, Muhammad Aziz; Nelson, Christopher T.; Scott, Mary C.; Cai, Yao; Yan, Bixing; Schmidt, Daniel; Yang, Ming; Zhu, Tao; Trevisanutto, Paolo E.; Motapothula, Mallikarjuna R.; Feng, Yuan Ping; Breese, Mark B. H.; Sherburne, Matthew; Asta, Mark; Minor, Andrew; Venkatesan, T.; Rusydi, Andrivo

2017-01-01

Plasmonics has attracted tremendous interests for its ability to confine light into subwavelength dimensions, creating novel devices with unprecedented functionalities. New plasmonic materials are actively being searched, especially those with tunable plasmons and low loss in the visible–ultraviolet range. Such plasmons commonly occur in metals, but many metals have high plasmonic loss in the optical range, a main issue in current plasmonic research. Here, we discover an anomalous form of tunable correlated plasmons in a Mott-like insulating oxide from the Sr1−xNb1−yO3+δ family. These correlated plasmons have multiple plasmon frequencies and low loss in the visible–ultraviolet range. Supported by theoretical calculations, these plasmons arise from the nanometre-spaced confinement of extra oxygen planes that enhances the unscreened Coulomb interactions among charges. The correlated plasmons are tunable: they diminish as extra oxygen plane density or film thickness decreases. Our results open a path for plasmonics research in previously untapped insulating and strongly-correlated materials. PMID:28497786

Orbital liquid in three-dimensional mott insulator: LaTiO3

PubMed

Khaliullin; Maekawa

2000-10-30

We present a theory of spin and orbital states in Mott insulator LaTiO3. The spin-orbital superexchange interaction between d(1)(t(2g)) ions in cubic crystal suffers from a pathological degeneracy of orbital states at the classical level. Quantum effects remove this degeneracy and result in the formation of the coherent ground state, in which the orbital moment of t(2g) level is fully quenched. We find a finite gap for orbital excitations. Such a disordered state of local degrees of freedom on unfrustrated, simple cubic lattice is highly unusual. Orbital liquid state naturally explains observed anomalies of LaTiO3.

Spin Andreev-like Reflection in Metal-Mott Insulator Heterostructures

DOE PAGES

Al-Hassanieh, K. A.; Rincón, Julián; Alvarez, G.; ...

2015-02-09

Here we used the time-dependent density-matrix renormalization group (tDMRG) to study the time evolution of electron wave packets in one-dimensional (1D) metal-superconductor heterostructures. The results show Andreev reflection at the interface, as expected. By combining these results with the well-known single- spin-species electron-hole transformation in the Hubbard model, we predict an analogous spin Andreev reflection in metal-Mott insulator heterostructures. This effect is numerically confirmed using 1D tDMRG, but it is expected to also be present in higher dimensions, as well as in more general Hamiltonians. We present an intuitive picture of the spin reflection, analogous to that of Andreev reflectionmore » at metal- superconductor interfaces. This allows us to discuss a novel antiferromagnetic proximity effect. Possible experimental realizations are discussed.« less

Two-dimensional superconductivity at a Mott insulator/band insulator interface LaTiO3/SrTiO3.

PubMed

Biscaras, J; Bergeal, N; Kushwaha, A; Wolf, T; Rastogi, A; Budhani, R C; Lesueur, J

2010-10-05

Transition metal oxides show a great variety of quantum electronic behaviours where correlations often have an important role. The achievement of high-quality epitaxial interfaces involving such materials gives a unique opportunity to engineer artificial structures where new electronic orders take place. One of the most striking result in this area is the recent observation of a two-dimensional electron gas at the interface between a strongly correlated Mott insulator LaTiO(3) and a band insulator SrTiO(3). The mechanism responsible for such a behaviour is still under debate. In particular, the influence of the nature of the insulator has to be clarified. In this article, we show that despite the expected electronic correlations, LaTiO(3)/SrTiO(3) heterostructures undergo a superconducting transition at a critical temperature T(c)(onset)~300 mK. We have found that the superconducting electron gas is confined over a typical thickness of 12 nm and is located mostly on the SrTiO(3) substrate.

Raman scattering in the Mott insulators LaTiO3 and YTiO3: evidence for orbital excitations.

PubMed

Ulrich, C; Gössling, A; Grüninger, M; Guennou, M; Roth, H; Cwik, M; Lorenz, T; Khaliullin, G; Keimer, B

2006-10-13

Raman scattering is used to observe pronounced electronic excitations around 230 meV--well above the two-phonon range--in the Mott insulators LaTiO3 and YTiO3. Based on the temperature, polarization, and photon energy dependence, the modes are identified as orbital excitations. The observed profiles bear a striking resemblance to magnetic Raman modes in the insulating parent compounds of the superconducting cuprates, indicating an unanticipated universality of the electronic excitations in transition metal oxides.

Towards Mott design by δ-doping of strongly correlated titanates

NASA Astrophysics Data System (ADS)

Lechermann, Frank; Obermeyer, Michael

2015-04-01

Doping the distorted-perovskite Mott insulators LaTiO3 and GdTiO3 with a single SrO layer along the [001] direction gives rise to a rich correlated electronic structure. A realistic superlattice study by means of the charge self-consistent combination of density functional theory with dynamical mean-field theory reveals layer- and temperature-dependent multi-orbital metal-insulator transitions. An orbital-selective metallic layer at the interface dissolves via an orbital-polarized doped-Mott state into an orbital-ordered insulating regime beyond the two conducting TiO2 layers. We find large differences in the scattering behavior within the latter. Breaking the spin symmetry in δ-doped GdTiO3 results in blocks of ferromagnetic itinerant and ferromagnetic Mott-insulating layers that are coupled antiferromagnetically.

The Statistical Fragmentation Theory of N. F. Mott

NASA Astrophysics Data System (ADS)

Grady, Dennis

2004-07-01

For a brief period during the height of World War II, Neville F. Mott left his position at the University of Bristol and headed up a concerted theoretical effort at Fort Halstead, UK, to investigate the operational science of weapons and armor technology. The seminal achievements resulting from the efforts of the participating scientists are extraordinary and have provided the basis for much of the continuing research in this field over the intervening six decades. N. F. Mott chose to study the phenomenon of the explosive-driven fragmentation of exploding shell cases. The approaches pursued by Mott are documented in several interim reports and open literature publications and offer a fascinating look into the insightful thinking and scientific methods of one of the preeminent physicists of the last century. This presentation offers a perspective into the several theoretical approaches pursued by Mott. In particular, the hallmark relation for the representation of exploding munitions fragmentation data to the present day is the Mott distribution. The efforts of Mott leading to this distribution are explored and a judgment is offered as to whether Mott himself would use this distribution today.

Polymorphous band structure model of gapping in the antiferromagnetic and paramagnetic phases of the Mott insulators MnO, FeO, CoO, and NiO

NASA Astrophysics Data System (ADS)

Trimarchi, Giancarlo; Wang, Zhi; Zunger, Alex

2018-01-01

The existence of band gaps in both the antiferromagnetic (AFM) and paramagnetic (PM) phases of the classic NaCl-structure Mott insulators MnO, FeO, CoO, and NiO is traditionally viewed and taught as a manifestation of strong correlation whereby insulation results from electrons moving across the lattice forming states with doubly occupied d orbitals on certain atomic sites and empty d orbitals on other sites. Within such theories, the gap of the AFM and PM phases of these oxides emerges even in the absence of spatial symmetry breaking. The need for such a correlated picture is partially based on the known failure of the commonly used band models for the PM phase that assume for such a spin disordered state the macroscopically averaged NaCl structure, where all transition metal (TM) sites are symmetry-equivalent (a monomorphous description), producing a gapless PM state with zero magnetic moments, in sharp conflict with experiment. Here, we seek to understand the minimum theoretical description needed to capture the leading descriptors of ground state Mott insulation in the classic, 3 d monoxide Mott systems—gapping and moment formation in the AFM and PM phase. As noted by previous authors, the spin-ordered AFM phase in these materials already shows in band theory a significant band gap when one doubles the NaCl unit cell by permitting different potentials for transition-metal atoms with different spins. For the spin-disordered PM phase, we allow analogously larger NaCl-type supercells where each TM site can have different spin direction and local bonding environments (i.e., disordered), yet the total spin is zero. Such a polymorphous description has the flexibility to acquire symmetry-breaking energy-lowering patterns that can lift the degeneracy of the d orbitals and develop large on-site magnetic moments without violating the global, averaged NaCl symmetry. Electrons are exchanged between spin-up and spin-down bands to create closed-shell insulating

Designing a Spin-one Mott Insulator: Complete Charge Transfer in Nickelate-Titanate Heterostructures

NASA Astrophysics Data System (ADS)

Chen, Hanghui; Marianetti, Chris; Millis, Andrew

2013-03-01

Ab initio calculations are performed to show that complete charge transfer may occur from the TiO2 to the NiO2 layers in (LaTiO3)1/(LaNiO3)1 superlattices. Although the two component materials are an S = 1 / 2 Mott insulator and a weakly correlated paramagnetic metal, strong correlation effects on Ni d states can render the superlattice an unusual S = 1 charge transfer insulator, with the Ti- d band empty, the Ni in the d8 state and the oxygen bands filled. The charge transfer gap is set by the Ti/Ni d level splitting. Magnetic, photoemission and x-ray scattering experiments are suggested to test the theory. The results show that heterostructuring can lead to very high levels of electron doping of oxides. This research was supported by the Army Research Office under ARO-Ph 56032 and DOE-ER-046169.

Rapid generation of Mott insulators from arrays of noncondensed atoms

NASA Astrophysics Data System (ADS)

Sturm, M. R.; Schlosser, M.; Birkl, G.; Walser, R.

2018-06-01

We theoretically analyze a scheme for a fast adiabatic transfer of cold atoms from the atomic limit of isolated traps to a Mott insulator close to the superfluid phase. This gives access to the Bose-Hubbard physics without the need of a prior Bose-Einstein condensate. The initial state can be prepared by combining the deterministic assembly of atomic arrays with resolved Raman-sideband cooling. In the subsequent transfer the trap depth is reduced significantly. We derive conditions for the adiabaticity of this process and calculate optimal adiabatic ramp shapes. Using available experimental parameters, we estimate the impact of heating due to photon scattering and compute the fidelity of the transfer scheme. Finally, we discuss the particle number scaling behavior of the method for preparing low-entropy states. Our findings demonstrate the feasibility of the proposed scheme with state-of-the-art technology.

Electronic structure of Mott-insulator CaCu3Ti4O12: Photoemission and inverse photoemission study

NASA Astrophysics Data System (ADS)

Im, H. J.; Iwataki, M.; Yamazaki, S.; Usui, T.; Adachi, S.; Tsunekawa, M.; Watanabe, T.; Takegahara, K.; Kimura, S.; Matsunami, M.; Sato, H.; Namatame, H.; Taniguchi, M.

2015-09-01

We have performed the photoemission and inverse photoemission experiments to elucidate the origin of Mott insulating states in A-site ordered perovskite CaCu3Ti4O12 (CCTO). Experimental results have revealed that Cu 3d-O 2p hybridized bands, which are located around the Fermi level in the prediction of the local-density approximation (LDA) band calculations, are actually separated into the upper Hubbard band at ~1.5 eV and the lower Hubbard band at ~-1.7 eV with a band gap of ~1.5-1.8 eV. We also observed that Cu 3d peak at ~-3.8 eV and Ti 3d peak at ~3.8 eV are further away from each other than as indicated in the LDA calculations. In addition, it is found that the multiplet structure around -9 eV includes a considerable number of O 2p states. These observations indicate that the Cu 3d and Ti 3d electrons hybridized with the O 2p states are strongly correlated, which originates in the Mott-insulating states of CCTO.

Mott glass from localization and confinement

NASA Astrophysics Data System (ADS)

Chou, Yang-Zhi; Nandkishore, Rahul M.; Radzihovsky, Leo

2018-05-01

We study a system of fermions in one spatial dimension with linearly confining interactions and short-range disorder. We focus on the zero-temperature properties of this system, which we characterize using bosonization and the Gaussian variational method. We compute the static compressibility and ac conductivity, and thereby demonstrate that the system is incompressible, but exhibits gapless optical conductivity. This corresponds to a "Mott glass" state, distinct from an Anderson and a fully gapped Mott insulator, arising due to the interplay of disorder and charge confinement. We argue that this Mott glass phenomenology should persist to nonzero temperatures.

Anderson localization and Mott insulator phase in the time domain

PubMed Central

Sacha, Krzysztof

2015-01-01

Particles in space periodic potentials constitute standard models for investigation of crystalline phenomena in solid state physics. Time periodicity of periodically driven systems is a close analogue of space periodicity of solid state crystals. There is an intriguing question if solid state phenomena can be observed in the time domain. Here we show that wave-packets localized on resonant classical trajectories of periodically driven systems are ideal elements to realize Anderson localization or Mott insulator phase in the time domain. Uniform superpositions of the wave-packets form stationary states of a periodically driven particle. However, an additional perturbation that fluctuates in time results in disorder in time and Anderson localization effects emerge. Switching to many-particle systems we observe that depending on how strong particle interactions are, stationary states can be Bose-Einstein condensates or single Fock states where definite numbers of particles occupy the periodically evolving wave-packets. Our study shows that non-trivial crystal-like phenomena can be observed in the time domain. PMID:26074169

Mott metal-insulator transition on compressible lattices.

PubMed

Zacharias, Mario; Bartosch, Lorenz; Garst, Markus

2012-10-26

The critical properties of the finite temperature Mott end point are drastically altered by a coupling to crystal elasticity, i.e., whenever it is amenable to pressure tuning. Similar as for critical piezoelectric ferroelectrics, the Ising criticality of the electronic system is preempted by an isostructural instability, and long-range shear forces suppress microscopic fluctuations. As a result, the end point is governed by Landau criticality. Its hallmark is, thus, a breakdown of Hooke's law of elasticity with a nonlinear strain-stress relation characterized by a mean-field exponent. Based on a quantitative estimate, we predict critical elasticity to dominate the temperature range ΔT*/T(c)≃8%, close to the Mott end point of κ-(BEDT-TTF)(2)X.

Size and symmetry of the superconducting gap in the f.c.c. Cs3C60 polymorph close to the metal-Mott insulator boundary.

PubMed

Potočnik, Anton; Krajnc, Andraž; Jeglič, Peter; Takabayashi, Yasuhiro; Ganin, Alexey Y; Prassides, Kosmas; Rosseinsky, Matthew J; Arčon, Denis

2014-03-03

The alkali fullerides, A(3)C(60) (A = alkali metal) are molecular superconductors that undergo a transition to a magnetic Mott-insulating state at large lattice parameters. However, although the size and the symmetry of the superconducting gap, Δ, are both crucial for the understanding of the pairing mechanism, they are currently unknown for superconducting fullerides close to the correlation-driven magnetic insulator. Here we report a comprehensive nuclear magnetic resonance (NMR) study of face-centred-cubic (f.c.c.) Cs(3)C(60) polymorph, which can be tuned continuously through the bandwidth-controlled Mott insulator-metal/superconductor transition by pressure. When superconductivity emerges from the insulating state at large interfullerene separations upon compression, we observe an isotropic (s-wave) Δ with a large gap-to-superconducting transition temperature ratio, 2Δ0/k(B)T(c) = 5.3(2) [Δ0 = Δ(0 K)]. 2Δ0/k(B)T(c) decreases continuously upon pressurization until it approaches a value of ~3.5, characteristic of weak-coupling BCS theory of superconductivity despite the dome-shaped dependence of Tc on interfullerene separation. The results indicate the importance of the electronic correlations for the pairing interaction as the metal/superconductor-insulator boundary is approached.

Size and symmetry of the superconducting gap in the f.c.c. Cs3C60 polymorph close to the metal-Mott insulator boundary

PubMed Central

Potočnik, Anton; Krajnc, Andraž; Jeglič, Peter; Takabayashi, Yasuhiro; Ganin, Alexey Y.; Prassides, Kosmas; Rosseinsky, Matthew J.; Arčon, Denis

2014-01-01

The alkali fullerides, A3C60 (A = alkali metal) are molecular superconductors that undergo a transition to a magnetic Mott-insulating state at large lattice parameters. However, although the size and the symmetry of the superconducting gap, Δ, are both crucial for the understanding of the pairing mechanism, they are currently unknown for superconducting fullerides close to the correlation-driven magnetic insulator. Here we report a comprehensive nuclear magnetic resonance (NMR) study of face-centred-cubic (f.c.c.) Cs3C60 polymorph, which can be tuned continuously through the bandwidth-controlled Mott insulator-metal/superconductor transition by pressure. When superconductivity emerges from the insulating state at large interfullerene separations upon compression, we observe an isotropic (s-wave) Δ with a large gap-to-superconducting transition temperature ratio, 2Δ0/kBTc = 5.3(2) [Δ0 = Δ(0 K)]. 2Δ0/kBTc decreases continuously upon pressurization until it approaches a value of ~3.5, characteristic of weak-coupling BCS theory of superconductivity despite the dome-shaped dependence of Tc on interfullerene separation. The results indicate the importance of the electronic correlations for the pairing interaction as the metal/superconductor-insulator boundary is approached. PMID:24584087

Universality and critical behavior of the dynamical Mott transition in a system with long-range interactions

DOE PAGES

Rademaker, Louk; Vinokur, Valerii M.; Galda, Alexey

2017-03-16

Here, we study numerically the voltage-induced breakdown of a Mott insulating phase in a system of charged classical particles with long-range interactions. At half-filling on a square lattice this system exhibits Mott localization in the form of a checkerboard pattern. We find universal scaling behavior of the current at the dynamic Mott insulator-metal transition and calculate scaling exponents corresponding to the transition. Our results are in agreement, up to a difference in universality class, with recent experimental evidence of a dynamic Mott transition in a system of interacting superconducting vortices.

Universality and critical behavior of the dynamical Mott transition in a system with long-range interactions.

PubMed

Rademaker, Louk; Vinokur, Valerii M; Galda, Alexey

2017-03-16

We study numerically the voltage-induced breakdown of a Mott insulating phase in a system of charged classical particles with long-range interactions. At half-filling on a square lattice this system exhibits Mott localization in the form of a checkerboard pattern. We find universal scaling behavior of the current at the dynamic Mott insulator-metal transition and calculate scaling exponents corresponding to the transition. Our results are in agreement, up to a difference in universality class, with recent experimental evidence of a dynamic Mott transition in a system of interacting superconducting vortices.

Designing Quantum Spin-Orbital Liquids in Artificial Mott Insulators

PubMed Central

Dou, Xu; Kotov, Valeri N.; Uchoa, Bruno

2016-01-01

Quantum spin-orbital liquids are elusive strongly correlated states of matter that emerge from quantum frustration between spin and orbital degrees of freedom. A promising route towards the observation of those states is the creation of artificial Mott insulators where antiferromagnetic correlations between spins and orbitals can be designed. We show that Coulomb impurity lattices on the surface of gapped honeycomb substrates, such as graphene on SiC, can be used to simulate SU(4) symmetric spin-orbital lattice models. We exploit the property that massive Dirac fermions form mid-gap bound states with spin and valley degeneracies in the vicinity of a Coulomb impurity. Due to electronic repulsion, the antiferromagnetic correlations of the impurity lattice are driven by a super-exchange interaction with SU(4) symmetry, which emerges from the bound states degeneracy at quarter filling. We propose that quantum spin-orbital liquids can be engineered in artificially designed solid-state systems at vastly higher temperatures than achievable in optical lattices with cold atoms. We discuss the experimental setup and possible scenarios for candidate quantum spin-liquids in Coulomb impurity lattices of various geometries. PMID:27553516

Designing Quantum Spin-Orbital Liquids in Artificial Mott Insulators

DOE PAGES

Dou, Xu; Kotov, Valeri N.; Uchoa, Bruno

2016-08-24

Quantum spin-orbital liquids are elusive strongly correlated states of matter that emerge from quantum frustration between spin and orbital degrees of freedom. A promising route towards the observation of those states is the creation of artificial Mott insulators where antiferromagnetic correlations between spins and orbitals can be designed. We show that Coulomb impurity lattices on the surface of gapped honeycomb substrates, such as graphene on SiC, can be used to simulate SU(4) symmetric spin-orbital lattice models. We exploit the property that massive Dirac fermions form mid-gap bound states with spin and valley degeneracies in the vicinity of a Coulomb impurity.more » Due to electronic repulsion, the antiferromagnetic correlations of the impurity lattice are driven by a super-exchange interaction with SU(4) symmetry, which emerges from the bound states degeneracy at quarter filling. We propose that quantum spin-orbital liquids can be engineered in artificially designed solid-state systems at vastly higher temperatures than achievable in optical lattices with cold atoms. Lastly, we discuss the experimental setup and possible scenarios for candidate quantum spin-liquids in Coulomb impurity lattices of various geometries.« less

Parity-time symmetry-breaking mechanism of dynamic Mott transitions in dissipative systems

DOE PAGES

Tripathi, Vikram; Galda, Alexey; Barman, Himadri; ...

2016-07-05

Here, we describe the critical behavior of the electric field-driven (dynamic) Mott insulator-to-metal transitions in dissipative Fermi and Bose systems in terms of non-Hermitian Hamiltonians invariant under simultaneous parity (P) and time-reversal (T) operations. The dynamic Mott transition is identified as a PT symmetry-breaking phase transition, with the Mott insulating state corresponding to the regime of unbroken PT symmetry with a real energy spectrum. We also established that the imaginary part of the Hamiltonian arises from the combined effects of the driving field and inherent dissipation. We derive the renormalization and collapse of the Mott gap at the dielectric breakdownmore » and describe the resulting critical behavior of transport characteristics. The critical exponent we obtained is in an excellent agreement with experimental findings.« less

Quantum phase transition modulation in an atomtronic Mott switch

NASA Astrophysics Data System (ADS)

McLain, Marie A.; Carr, Lincoln D.

2018-07-01

Mott insulators provide stable quantum states and long coherence times due to small number fluctuations, making them good candidates for quantum memory and atomic circuits. We propose a proof-of-principle for a 1D Mott switch using an ultracold Bose gas and optical lattice. With time-evolving block decimation simulations—efficient matrix product state methods—we design a means for transient parameter characterization via a local excitation for ease of engineering into more complex atomtronics. We perform the switch operation by tuning the intensity of the optical lattice, and thus the interaction strength through a conductance transition due to the confined modifications of the ‘wedding cake’ Mott structure. We demonstrate the time-dependence of Fock state transmission and fidelity of the excitation as a means of tuning up the device in a double well and as a measure of noise performance. Two-point correlations via the g (2) measure provide additional information regarding superfluid fragments on the Mott insulating background due to the confinement of the potential.

Mott-Hubbard transition and Anderson localization: A generalized dynamical mean-field theory approach

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

Kuchinskii, E. Z.; Nekrasov, I. A.; Sadovskii, M. V.

The DOS, the dynamic (optical) conductivity, and the phase diagram of a strongly correlated and strongly disordered paramagnetic Anderson-Hubbard model are analyzed within the generalized dynamical mean field theory (DMFT + {sigma} approximation). Strong correlations are taken into account by the DMFT, and disorder is taken into account via an appropriate generalization of the self-consistent theory of localization. The DMFT effective single-impurity problem is solved by a numerical renormalization group (NRG); we consider the three-dimensional system with a semielliptic DOS. The correlated metal, Mott insulator, and correlated Anderson insulator phases are identified via the evolution of the DOS and dynamicmore » conductivity, demonstrating both the Mott-Hubbard and Anderson metal-insulator transition and allowing the construction of the complete zero-temperature phase diagram of the Anderson-Hubbard model. Rather unusual is the possibility of a disorder-induced Mott insulator-to-metal transition.« less

Transient carrier dynamics in a Mott insulator with antiferromagnetic order

NASA Astrophysics Data System (ADS)

Iyoda, Eiki; Ishihara, Sumio

2014-03-01

We study transient dynamics of hole carriers injected into a Mott insulator with antiferromagnetic long-range order. This "dynamical hole doping" contrasts with chemical hole doping. The theoretical framework for the transient carrier dynamics is presented based on the two-dimensional t-J model. The time dependencies of the optical conductivity spectra, as well as the one-particle excitation spectra, are calculated based on the Keldysh Green's function formalism at zero temperature combined with the self-consistent Born approximation. In the early stage after dynamical hole doping, the Drude component appears, and then incoherent components originating from hole-magnon scattering start to grow. Fast oscillatory behavior owing to coherent magnon and slow relaxation dynamics are confirmed in the spectra. The time profiles are interpreted as doped bare holes being dressed by magnon clouds and relaxed into spin polaron quasiparticle states. The characteristic relaxation times for Drude and incoherent peaks strongly depend on the momentum of the dynamically doped hole and the exchange constant. Implications for recent pump-probe experiments are discussed.

Importance of counter-rotating coupling in the superfluid-to-Mott-insulator quantum phase transition of light in the Jaynes-Cummings lattice

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

Zheng Hang; Takada, Yasutami

2011-10-15

The quantum phase transition between Mott insulator and superfluid is studied in the two-dimensional Jaynes-Cummings square lattice in which the counter-rotating coupling (CRC) is included. Both the ground state and the spectra of low-lying excitations are obtained with use of a sophisticated unitary transformation. This CRC is shown not only to induce a long-range interaction between cavities, favoring the long-range superfluid order, but also to break the conservation of local polariton number at each site, leading to the absence of the Mott lobes in the phase diagram, in sharp contrast with the case without the CRC as well as thatmore » of the Bose-Hubbard model.« less

Ultrafast energy- and momentum-resolved dynamics of magnetic correlations in the photo-doped Mott insulator Sr2IrO4.

PubMed

Dean, M P M; Cao, Y; Liu, X; Wall, S; Zhu, D; Mankowsky, R; Thampy, V; Chen, X M; Vale, J G; Casa, D; Kim, Jungho; Said, A H; Juhas, P; Alonso-Mori, R; Glownia, J M; Robert, A; Robinson, J; Sikorski, M; Song, S; Kozina, M; Lemke, H; Patthey, L; Owada, S; Katayama, T; Yabashi, M; Tanaka, Yoshikazu; Togashi, T; Liu, J; Rayan Serrao, C; Kim, B J; Huber, L; Chang, C-L; McMorrow, D F; Först, M; Hill, J P

2016-06-01

Measuring how the magnetic correlations evolve in doped Mott insulators has greatly improved our understanding of the pseudogap, non-Fermi liquids and high-temperature superconductivity. Recently, photo-excitation has been used to induce similarly exotic states transiently. However, the lack of available probes of magnetic correlations in the time domain hinders our understanding of these photo-induced states and how they could be controlled. Here, we implement magnetic resonant inelastic X-ray scattering at a free-electron laser to directly determine the magnetic dynamics after photo-doping the Mott insulator Sr2IrO4. We find that the non-equilibrium state, 2 ps after the excitation, exhibits strongly suppressed long-range magnetic order, but hosts photo-carriers that induce strong, non-thermal magnetic correlations. These two-dimensional (2D) in-plane Néel correlations recover within a few picoseconds, whereas the three-dimensional (3D) long-range magnetic order restores on a fluence-dependent timescale of a few hundred picoseconds. The marked difference in these two timescales implies that the dimensionality of magnetic correlations is vital for our understanding of ultrafast magnetic dynamics.

Ultrafast energy- and momentum-resolved dynamics of magnetic correlations in the photo-doped Mott insulator Sr 2IrO 4

DOE PAGES

Dean, M. P. M.; Cao, Y.; Liu, X.; ...

2016-05-09

Measuring how the magnetic correlations evolve in doped Mott insulators has greatly improved our understanding of the pseudogap, non-Fermi liquids and high-temperature superconductivity 1, 2, 3, 4. Recently, photo-excitation has been used to induce similarly exotic states transiently 5, 6, 7. However, the lack of available probes of magnetic correlations in the time domain hinders our understanding of these photo-induced states and how they could be controlled. Here, we implement magnetic resonant inelastic X-ray scattering at a free-electron laser to directly determine the magnetic dynamics after photo-doping the Mott insulator Sr 2IrO 4. We find that the non-equilibrium state, 2more » ps after the excitation, exhibits strongly suppressed long-range magnetic order, but hosts photo-carriers that induce strong, non-thermal magnetic correlations. These two-dimensional (2D) in-plane Néel correlations recover within a few picoseconds, whereas the three-dimensional (3D) long-range magnetic order restores on a fluence-dependent timescale of a few hundred picoseconds. In conclusion, the marked difference in these two timescales implies that the dimensionality of magnetic correlations is vital for our understanding of ultrafast magnetic dynamics.« less

Upper critical field reaches 90 tesla near the Mott transition in fulleride superconductors

DOE PAGES

Kasahara, Y.; Takeuchi, Y.; Zadik, R. H.; ...

2017-02-17

Controlled access to the border of the Mott insulating state by variation of control parameters offers exotic electronic states such as anomalous and possibly high-transition-temperature (T c) superconductivity. The alkali-doped fullerides show a transition from a Mott insulator to a superconductor for the first time in three-dimensional materials, but the impact of dimensionality and electron correlation on superconducting properties has remained unclear. Here we show that, near the Mott insulating phase, the upper critical field H c2 of the fulleride superconductors reaches values as high as ~90 T—the highest among cubic crystals. This is accompanied by a crossover from weak-more » to strong-coupling superconductivity and appears upon entering the metallic state with the dynamical Jahn–Teller effect as the Mott transition is approached. Lastly, these results suggest that the cooperative interplay between molecular electronic structure and strong electron correlations plays a key role in realizing robust superconductivity with high-T c and high-H c2.« less

Upper critical field reaches 90 tesla near the Mott transition in fulleride superconductors

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

Kasahara, Y.; Takeuchi, Y.; Zadik, R. H.

Controlled access to the border of the Mott insulating state by variation of control parameters offers exotic electronic states such as anomalous and possibly high-transition-temperature (T c) superconductivity. The alkali-doped fullerides show a transition from a Mott insulator to a superconductor for the first time in three-dimensional materials, but the impact of dimensionality and electron correlation on superconducting properties has remained unclear. Here we show that, near the Mott insulating phase, the upper critical field H c2 of the fulleride superconductors reaches values as high as ~90 T—the highest among cubic crystals. This is accompanied by a crossover from weak-more » to strong-coupling superconductivity and appears upon entering the metallic state with the dynamical Jahn–Teller effect as the Mott transition is approached. Lastly, these results suggest that the cooperative interplay between molecular electronic structure and strong electron correlations plays a key role in realizing robust superconductivity with high-T c and high-H c2.« less

Fine-tuning the Mott metal-insulator transition and critical charge carrier dynamics in molecular conductors

NASA Astrophysics Data System (ADS)

Müller, Jens; Hartmann, Benedikt; Sasaki, Takahiko

2017-12-01

The unique possibilities of fine-tuning their physical properties in the vicinity of the Mott metal-insulator transition make the quasi-two-dimensional organic charge-transfer salts ?-(BEDT-TTF)?X unprecedented model systems for studying the fundamentals of electron-electron correlations and the coupling between charge, spin and lattice degrees of freedom in reduced dimensions. The critical properties and the universality class of the Mott transition, however, are controversially debated for these materials, and information on the low-frequency dynamical properties of the correlated electrons is rather limited. By introducing fluctuation (noise) spectroscopy as a powerful new tool for studying the slow dynamics of charge carriers, in the past years we have been able to extract spectroscopic information on the coupling of charge carriers to the vibrational degrees of freedom of the crystal lattice. This is related to a glassy freezing of the BEDT-TTF molecules' ethylene end-group (EEG) rotations at elevated temperatures, which (i) results in a small amount of (intrinsic) disorder and (ii) crucially influences the ratio of bandwidth to on-site Coulomb repulsion (W / U) and therefore the samples' position in the phase diagram, i.e. the electronic ground state. The low-frequency resistance fluctuations show a dramatic enhancement and divergent behaviour when tuning the sample close to the critical point of the Mott transition, accompanied by a strong shift of spectral weight to low frequencies and the onset of non-Gaussian behaviour. This indicates the critical slowing down of the order-parameter (doublon density) fluctuations and suggests a collective dynamics of the correlated electrons. In order to enable detailed investigations of this hypothesis in future experiments, by exploiting the structural EEG relaxation, a 'warming cycle' protocol can be established that allows for fine-tuning the sample across the Mott transition and therefore precisely accessing the

Electric double-layer transistor using layered iron selenide Mott insulator TlFe1.6Se2

PubMed Central

Katase, Takayoshi; Hiramatsu, Hidenori; Kamiya, Toshio; Hosono, Hideo

2014-01-01

A1–xFe2–ySe2 (A = K, Cs, Rb, Tl) are recently discovered iron-based superconductors with critical temperatures (Tc) ranging up to 32 K. Their parent phases have unique properties compared with other iron-based superconductors; e.g., their crystal structures include ordered Fe vacancies, their normal states are antiferromagnetic (AFM) insulating phases, and they have extremely high Néel transition temperatures. However, control of carrier doping into the parent AFM insulators has been difficult due to their intrinsic phase separation. Here, we fabricated an Fe-vacancy-ordered TlFe1.6Se2 insulating epitaxial film with an atomically flat surface and examined its electrostatic carrier doping using an electric double-layer transistor (EDLT) structure with an ionic liquid gate. The positive gate voltage gave a conductance modulation of three orders of magnitude at 25 K, and further induced and manipulated a phase transition; i.e., delocalized carrier generation by electrostatic doping is the origin of the phase transition. This is the first demonstration, to the authors' knowledge, of an EDLT using a Mott insulator iron selenide channel and opens a way to explore high Tc superconductivity in iron-based layered materials, where carrier doping by conventional chemical means is difficult. PMID:24591598

Two-Magnon Scattering in Spin-Orbital Mott Insulator Ba2IrO4

NASA Astrophysics Data System (ADS)

Tsuda, Shunsuke; Okabe, Hirotaka; Isobe, Masaaki; Uji, Shinya

2016-02-01

A spin-orbit induced Mott insulator Ba2IrO4 with the pseudo-spin Jeff = 1/2, showing an antiferromagnetic order (TN = 240 K), has been investigated by Raman spectroscopy. A broad peak with the B1g symmetry is found in a wide temperature region up to 400 K, which is ascribed to the two-magnon scattering. From the peak position and width, the exchange coupling and the antiferromagnetic correlation length are estimated to be 590 cm-1 and 45 Å at 90 K, respectively. The results are compared with the antiferromagnet La2CuO4 with the spin S = 1/2. We conclude that there is no significant difference in the short wavelength spin-excitation between the S = 1/2 and Jeff = 1/2 systems.

Prospect of quantum anomalous Hall and quantum spin Hall effect in doped kagome lattice Mott insulators.

PubMed

Guterding, Daniel; Jeschke, Harald O; Valentí, Roser

2016-05-17

Electronic states with non-trivial topology host a number of novel phenomena with potential for revolutionizing information technology. The quantum anomalous Hall effect provides spin-polarized dissipation-free transport of electrons, while the quantum spin Hall effect in combination with superconductivity has been proposed as the basis for realizing decoherence-free quantum computing. We introduce a new strategy for realizing these effects, namely by hole and electron doping kagome lattice Mott insulators through, for instance, chemical substitution. As an example, we apply this new approach to the natural mineral herbertsmithite. We prove the feasibility of the proposed modifications by performing ab-initio density functional theory calculations and demonstrate the occurrence of the predicted effects using realistic models. Our results herald a new family of quantum anomalous Hall and quantum spin Hall insulators at affordable energy/temperature scales based on kagome lattices of transition metal ions.

Electronic Griffiths Phases and Quantum Criticality at Disordered Mott Transitions

NASA Astrophysics Data System (ADS)

Dobrosavljevic, Vladimir

2012-02-01

The effects of disorder are investigated in strongly correlated electronic systems near the Mott metal-insulator transition. Correlation effects are foundootnotetextE. C. Andrade, E. Miranda, and V. Dobrosavljevic, Phys. Rev. Lett., 102, 206403 (2009). to lead to strong disorder screening, a mechanism restricted to low-lying electronic states, very similar to what is observed in underdoped cuprates. These results suggest, however, that this effect is not specific to disordered d-wave superconductors, but is a generic feature of all disordered Mott systems. In addition, the resulting spatial inhomogeneity rapidly increasesootnotetextE. C. Andrade, E. Miranda, and V. Dobrosavljevic, Phys. Rev. Lett., 104 (23), 236401 (2010). as the Mott insulator is approached at fixed disorder strength. This behavior, which can be described as an Electronic Griffiths Phase, displays all the features expected for disorder-dominated Infinite-Randomness Fixed Point scenario of quantum criticality.

Scaling universality at the dynamic vortex Mott transition

NASA Astrophysics Data System (ADS)

Lankhorst, M.; Poccia, N.; Stehno, M. P.; Galda, A.; Barman, H.; Coneri, F.; Hilgenkamp, H.; Brinkman, A.; Golubov, A. A.; Tripathi, V.; Baturina, T. I.; Vinokur, V. M.

2018-01-01

The cleanest way to observe a dynamic Mott insulator-to-metal transition (DMT) without the interference from disorder and other effects inherent to electronic and atomic systems, is to employ the vortex Mott states formed by superconducting vortices in a regular array of pinning sites. Here, we report the critical behavior of the vortex system as it crosses the DMT line, driven by either current or temperature. We find universal scaling with respect to both, expressed by the same scaling function and characterized by a single critical exponent coinciding with the exponent for the thermodynamic Mott transition. We develop a theory for the DMT based on the parity reflection-time reversal (P T ) symmetry breaking formalism and find that the nonequilibrium-induced Mott transition has the same critical behavior as the thermal Mott transition. Our findings demonstrate the existence of physical systems in which the effect of a nonequilibrium drive is to generate an effective temperature and hence the transition belonging in the thermal universality class.

Impact ionization processes in the steady state of a driven Mott-insulating layer coupled to metallic leads

NASA Astrophysics Data System (ADS)

Sorantin, Max E.; Dorda, Antonius; Held, Karsten; Arrigoni, Enrico

2018-03-01

We study a simple model of photovoltaic energy harvesting across a Mott-insulating gap consisting of a correlated layer connected to two metallic leads held at different chemical potentials. We address, in particular, the issue of impact ionization, whereby a particle photoexcited to the high-energy part of the upper Hubbard band uses its extra energy to produce a second particle-hole excitation. We find a drastic increase of the photocurrent upon entering the frequency regime where impact ionization is possible. At large values of the Mott gap, where impact ionization is energetically not allowed, we observe a suppression of the current and a piling up of charge in the high-energy part of the upper Hubbard band. Our study is based on a Floquet dynamical mean-field theory treatment of the steady state with the so-called auxiliary master equation approach as impurity solver. We verify that an additional approximation, taking the self-energy diagonal in the Floquet indices, is appropriate for the parameter range we are considering.

Equilibration dynamics of a many-body quantum system across the superfluid to Mott insulator phase transition

NASA Astrophysics Data System (ADS)

Mullers, Andreas; Baals, Christian; Santra, Bodhaditya; Labouvie, Ralf; Mertz, Thomas; Dhar, Arya; Vasic, Ivana; Cichy, Agnieszka; Hofstetter, Walter; Ott, Herwig

2017-04-01

We report on the center-of-mass motion of ultracold 87Rb atoms on displacing an underlying potential. The atoms are adiabatically loaded into an optical lattice superimposed onto an optical dipole trap. The CO2 laser beam forming the dipole trap is then shifted by 1 μm which forces the system out of equilibrium. The subsequent motion of the atoms center-of mass is imaged with a scanning electron microscope for various depths of the optical lattice spanning the superfluid to Mott-insulator phase transition. The observed dynamics range from fast oscillations in the superfluid regime to a steady exponential movement towards the new equilibrium position for higher lattice depths. By piecewise analysis of the system, we can also identify a thermal phase at the edges which moves with velocities in between those of the superfluid and the insulating phase. We will present the experiment and the results of theoretical modelling currently in progress.

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

NASA Astrophysics Data System (ADS)

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

2017-10-01

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

Fingerprints of spin-orbital polarons and of their disorder in the photoemission spectra of doped Mott insulators with orbital degeneracy

NASA Astrophysics Data System (ADS)

Avella, Adolfo; Oleś, Andrzej M.; Horsch, Peter

2018-04-01

We explore the effects of disordered charged defects on the electronic excitations observed in the photoemission spectra of doped transition metal oxides in the Mott insulating regime by the example of the R1 -xCaxVO3 perovskites, where R = La, ⋯, Lu. A fundamental characteristic of these vanadium d2 compounds with partly filled t2 g valence orbitals is the persistence of spin and orbital order up to high doping, in contrast to the loss of magnetic order in high-Tc cuprates at low defect concentration. We study the disordered electronic structure of such doped Mott-Hubbard insulators within the unrestricted Hartree-Fock approximation and, as a result, manage to explain the spectral features that occur in photoemission and inverse photoemission. In particular, (i) the atomic multiplet excitations in the inverse photoemission spectra and the various defect-related states and satellites are qualitatively well reproduced, (ii) a robust Mott gap survives up to large doping, and (iii) we show that the defect states inside the Mott gap develop a soft gap at the Fermi energy. The soft defect-states gap, which separates the highest occupied from the lowest unoccupied states, can be characterized by a shape and a scale parameter extracted from a Weibull statistical sampling of the density of states near the chemical potential. These parameters provide a criterion and a comprehensive schematization for the insulator-metal transition in disordered systems. Our results provide clear indications that doped holes are bound to charged defects and form small spin-orbital polarons whose internal kinetic energy is responsible for the opening of the soft defect-states gap. We show that this kinetic gap survives disorder fluctuations of defects and is amplified by the long-range electron-electron interactions, whereas we observe a Coulomb singularity in the atomic limit. The small size of spin-orbital polarons is inferred by an analysis of the inverse participation ratio and by

Scaling universality at the dynamic vortex Mott transition

DOE PAGES

Lankhorst, M.; Poccia, N.; Stehno, M. P.; ...

2018-01-17

The cleanest way to observe a dynamic Mott insulator-to-metal transition (DMT) without the interference from disorder and other effects inherent to electronic and atomic systems, is to employ the vortex Mott states formed by superconducting vortices in a regular array of pinning sites. Here, we report the critical behavior of the vortex system as it crosses the DMT line, driven by either current or temperature. We find universal scaling with respect to both, expressed by the same scaling function and characterized by a single critical exponent coinciding with the exponent for the thermodynamic Mott transition. We develop a theory formore » the DMT based on the parity reflection-time reversal (PT) symmetry breaking formalism and find that the nonequilibrium-induced Mott transition has the same critical behavior as the thermal Mott transition. Our findings demonstrate the existence of physical systems in which the effect of a nonequilibrium drive is to generate an effective temperature and hence the transition belonging in the thermal universality class.« less

Observation of a Pseudogap in the Vicinity of the Metal-Insulator Transition in the Perovskite-type Vanadium Oxides Nd1-xSrxVO3

NASA Astrophysics Data System (ADS)

Yamamoto, Shintaro; Ootsuki, Daiki; Shimonaka, Daiya; Shibata, Daisuke; Kodera, Kenjiro; Okawa, Mario; Saitoh, Tomohiko; Horio, Masafumi; Fujimori, Atsushi; Kumigashira, Hiroshi; Ono, Kanta; Ikenaga, Eiji; Miyasaka, Shigeki; Tajima, Setsuko; Yoshida, Teppei

2018-02-01

We have performed a photoemission study of the Mott-Hubbard system Nd1-xSrxVO3 (x = 0.20 and 0.30) to investigate the electronic structure in the vicinity of the metal-insulator transition. By using bulk sensitive hard X-ray photoemission spectroscopy, we have observed a large coherent spectral weight near the Fermi level compared to those observed with surface-sensitive low photons. In particular, a pseudogap with an energy of ˜0.2 eV has been observed near the Fermi level, which is consistent with a prediction with a dynamical cluster approximation calculation. In order to understand the characteristic features in the Mott-Hubbard-type metal-insulator transition, particularly the pseudogap opening at x = 0.2 and 0.3, a phenomenological model of the self-energy has been proposed.

Superfluid-Mott insulator transition of spin-1 bosons in an optical lattice

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

Tsuchiya, Shunji; Department of Physics, University of Toronto, Toronto, Ontario, M5S 1A7; Kurihara, Susumu

2004-10-01

We study the superfluid-Mott insulator (SF-MI) transition of spin-1 bosons interacting antiferromagnetically in an optical lattice. Starting from a Bose-Hubbard tight-binding model for spin-1 bosons, we obtain the zero-temperature phase diagram by a mean-field approximation. We find that the MI phase with an even number of atoms per site is a spin singlet state, while the MI phase with an odd number of atoms per site has spin 1 at each site in the limit of t=0, where t is the hopping matrix element. We also show that the superfluid phase is a polar state as in the case formore » a spin-1 Bose condensate in a harmonic trap. It is found that the MI phase is strongly stabilized against the SF-MI transition when the number of atoms per site is even, due to the formation of singlet pairs. We derive the effective spin Hamiltonian for the MI phase with one atom per site and briefly discuss the spin order in the MI phase.« less

What is the origin of anomalous dielectric response in 2D organic dimer Mott insulators κ-(BEDT-TTF)2Cu[N(CN)2]Cl and κ-(BEDT-TTF)2Cu2(CN)3

NASA Astrophysics Data System (ADS)

Pinterić, M.; Ivek, T.; Čulo, M.; Milat, O.; Basletić, M.; Korin-Hamzić, B.; Tafra, E.; Hamzić, A.; Dressel, M.; Tomić, S.

2015-03-01

Novel forms of the low-temperature phases in the two-dimensional molecular solids with competing interactions between charges, spins and lattice, in particular those featuring anomalous dielectric relaxation, have been the focus of intense activity in recent years. Open issues concern the nature of collective charge excitations as well as their coupling to applied ac and dc electric fields. The charge response is reasonably well understood by now in the charge-ordered phase with the formation of ferroelectric-like domains below the metal-to-insulator phase transition. Conversely, the dielectric response observed in dimer Mott insulator phases with no complete evidence for charge ordering is rather intriguing. We overview our recent results of anisotropic complex conductivity (dc - MHz) in the magnetic phase of κ-(BEDT - TTF) 2 Cu [ N(CN)2 ] Cl and in the spin-liquid phase of κ-(BEDT - TTF) 2Cu2(CN)3. We discuss possible explanations for the observed dynamics within current theoretical models and compare them with the well-known fingerprints of the spin density wave response to ac electric fields.

Non-destructive reversible resistive switching in Cr doped Mott insulator Ca2RuO4: Interface vs bulk effects

NASA Astrophysics Data System (ADS)

Shen, Shida; Williamson, Morgan; Cao, Gang; Zhou, Jianshi; Goodenough, John; Tsoi, Maxim

2017-12-01

A non-destructive reversible resistive switching is demonstrated in single crystals of Cr-doped Mott insulator Ca2RuO4. An applied electrical bias was shown to reduce the DC resistance of the crystal by as much as 75%. The original resistance of the sample could be restored by applying an electrical bias of opposite polarity. We have studied this resistive switching as a function of the bias strength, applied magnetic field, and temperature. A combination of 2-, 3-, and 4-probe measurements provide a means to distinguish between bulk and interfacial contributions to the switching and suggests that the switching is mostly an interfacial effect. The switching was tentatively attributed to electric-field driven lattice distortions which accompany the impurity-induced Mott transition. This field effect was confirmed by temperature-dependent resistivity measurements which show that the activation energy of this material can be tuned by an applied DC electrical bias. The observed resistance switching can potentially be used for building non-volatile memory devices like resistive random access memory.

Raman scattering in the RTiO3 family of Mott-Hubbard insulators

NASA Astrophysics Data System (ADS)

Reedyk, M.; Crandles, D. A.; Cardona, M.; Garrett, J. D.; Greedan, J. E.

1997-01-01

Raman-scattering measurements have been carried out for crystals of the RTiO3 (R=La,Ce,Pr,Nd,Sm,Gd) system whose members are Mott-Hubbard insulators. RTiO3 has an orthorhombically distorted perovskite unit cell. The distortion increases systematically from LaTiO3 to GdTiO3 and is accompanied by changes in electronic structure (decreasing W/U ratio). As a consequence of the changing electronic properties, the Raman spectrum shows an interesting evolution of both the phonon features and the electronic continuum. Most notable are (1) a redistribution in the spectral shape of the electronic background, (2) a systematic change in line shape, and a dramatic increase in the center frequency of one of the phonon modes from 287 cm-1 in LaTiO3 to 385 cm-1 in GdTiO3, and (3) the observation of resonance effects in the most insulating members of the series. The appearance of a free-carrier component in the electronic-scattering background, which seems to be related to systematic self-energy effects of the phonon near 300 cm-1, is unexpected. It is likely the result of increased doping due to a greater facility for rare-earth vacancies to form in large R3+ ionic radius members of the series. A systematic increase in the continuum scattering rate is also observed and indicates that the free carriers are not scattering off rare-earth vacancies but rather that the scattering mechanism originates from changes in electronic structure.

Spectral properties near the Mott transition in the two-dimensional Hubbard model

NASA Astrophysics Data System (ADS)

Kohno, Masanori

2013-03-01

Single-particle excitations near the Mott transition in the two-dimensional (2D) Hubbard model are investigated by using cluster perturbation theory. The Mott transition is characterized by the loss of the spectral weight from the dispersing mode that leads continuously to the spin-wave excitation of the Mott insulator. The origins of the dominant modes of the 2D Hubbard model near the Mott transition can be traced back to those of the one-dimensional Hubbard model. Various anomalous spectral features observed in cuprate high-temperature superconductors, such as the pseudogap, Fermi arc, flat band, doping-induced states, hole pockets, and spinon-like and holon-like branches, as well as giant kink and waterfall in the dispersion relation, are explained in a unified manner as properties near the Mott transition in a 2D system.

Breakdown of Hooke's law of elasticity at the Mott critical endpoint in an organic conductor.

PubMed

Gati, Elena; Garst, Markus; Manna, Rudra S; Tutsch, Ulrich; Wolf, Bernd; Bartosch, Lorenz; Schubert, Harald; Sasaki, Takahiko; Schlueter, John A; Lang, Michael

2016-12-01

The Mott metal-insulator transition, a paradigm of strong electron-electron correlations, has been considered as a source of intriguing phenomena. Despite its importance for a wide range of materials, fundamental aspects of the transition, such as its universal properties, are still under debate. We report detailed measurements of relative length changes Δ L / L as a function of continuously controlled helium-gas pressure P for the organic conductor κ-(BEDT-TTF) 2 Cu[N(CN) 2 ]Cl across the pressure-induced Mott transition. We observe strongly nonlinear variations of Δ L / L with pressure around the Mott critical endpoint, highlighting a breakdown of Hooke's law of elasticity. We assign these nonlinear strain-stress relations to an intimate, nonperturbative coupling of the critical electronic system to the lattice degrees of freedom. Our results are fully consistent with mean-field criticality, predicted for electrons in a compressible lattice with finite shear moduli. We argue that the Mott transition for all systems that are amenable to pressure tuning shows the universal properties of an isostructural solid-solid transition.

Dynamical cluster approximation plus semiclassical approximation study for a Mott insulator and d-wave pairing

NASA Astrophysics Data System (ADS)

Kim, SungKun; Lee, Hunpyo

2017-06-01

Via a dynamical cluster approximation with N c = 4 in combination with a semiclassical approximation (DCA+SCA), we study the doped two-dimensional Hubbard model. We obtain a plaquette antiferromagnetic (AF) Mott insulator, a plaquette AF ordered metal, a pseudogap (or d-wave superconductor) and a paramagnetic metal by tuning the doping concentration. These features are similar to the behaviors observed in copper-oxide superconductors and are in qualitative agreement with the results calculated by the cluster dynamical mean field theory with the continuous-time quantum Monte Carlo (CDMFT+CTQMC) approach. The results of our DCA+SCA differ from those of the CDMFT+CTQMC approach in that the d-wave superconducting order parameters are shown even in the high doped region, unlike the results of the CDMFT+CTQMC approach. We think that the strong plaquette AF orderings in the dynamical cluster approximation (DCA) with N c = 4 suppress superconducting states with increasing doping up to strongly doped region, because frozen dynamical fluctuations in a semiclassical approximation (SCA) approach are unable to destroy those orderings. Our calculation with short-range spatial fluctuations is initial research, because the SCA can manage long-range spatial fluctuations in feasible computational times beyond the CDMFT+CTQMC tool. We believe that our future DCA+SCA calculations should supply information on the fully momentum-resolved physical properties, which could be compared with the results measured by angle-resolved photoemission spectroscopy experiments.

Emergent Phenomena at Mott Interfaces

DTIC Science & Technology

2016-11-03

from a two-dimensional electron gas at a Mott/band insulator interface, Applied Physics Letters, (10 2012): 151604. doi: 10.1063/1.4758989...coefficient of a quantum confined, high-electron-density electron gas in SrTiO3, Applied Physics Letters, (04 2012): 161601. doi: 10.1063...Jalan, Susanne Stemmer, Shawn Mack, S. James Allen. Two-dimensional electron gas in delta- doped SrTiO3, Physical Review B, (08 2010): . doi: A

Insulating phases of vanadium dioxide are Mott-Hubbard insulators

DOE PAGES

Huffman, T. J.; Hendriks, C.; Walter, E. J.; ...

2017-02-15

Here, we present comprehensive broadband optical spectroscopy data on two insulating phases of vanadium dioxide (VO 2): monoclinic M 2 and triclinic. The main result of our work is that the energy gap and the electronic structure are essentially unaltered by the first-order structural phase transition between the M 2 and triclinic phases. Moreover, the optical interband features in the M 2 and triclinic phases are remarkably similar to those observed in the well-studied monoclinic M 1 insulating phase of VO 2. As the energy gap is insensitive to the different lattice structures of the three insulating phases, we rulemore » out vanadium-vanadium pairing (the Peierls component) as the dominant contributor to the opening of the gap. Rather, the energy gap arises primarily from intra-atomic Coulomb correlations.« less

Breakdown of Hooke’s law of elasticity at the Mott critical endpoint in an organic conductor

PubMed Central

Gati, Elena; Garst, Markus; Manna, Rudra S.; Tutsch, Ulrich; Wolf, Bernd; Bartosch, Lorenz; Schubert, Harald; Sasaki, Takahiko; Schlueter, John A.; Lang, Michael

2016-01-01

The Mott metal-insulator transition, a paradigm of strong electron-electron correlations, has been considered as a source of intriguing phenomena. Despite its importance for a wide range of materials, fundamental aspects of the transition, such as its universal properties, are still under debate. We report detailed measurements of relative length changes ΔL/L as a function of continuously controlled helium-gas pressure P for the organic conductor κ-(BEDT-TTF)2Cu[N(CN)2]Cl across the pressure-induced Mott transition. We observe strongly nonlinear variations of ΔL/L with pressure around the Mott critical endpoint, highlighting a breakdown of Hooke’s law of elasticity. We assign these nonlinear strain-stress relations to an intimate, nonperturbative coupling of the critical electronic system to the lattice degrees of freedom. Our results are fully consistent with mean-field criticality, predicted for electrons in a compressible lattice with finite shear moduli. We argue that the Mott transition for all systems that are amenable to pressure tuning shows the universal properties of an isostructural solid-solid transition. PMID:27957540

Putting competing orders in their place near the Mott transition

NASA Astrophysics Data System (ADS)

Balents, Leon; Bartosch, Lorenz; Burkov, Anton; Sachdev, Subir; Sengupta, Krishnendu

2005-04-01

We describe the localization transition of superfluids on two-dimensional lattices into commensurate Mott insulators with average particle density p/q ( p,q relatively prime integers) per lattice site. For bosons on the square lattice, we argue that the superfluid has at least q degenerate species of vortices which transform under a projective representation of the square-lattice space group (a PSG). The formation of a single-vortex condensate produces the Mott insulator, which is required by the PSG to have density wave order at wavelengths of q/n lattice sites ( n integer) along the principle axes; such a second-order transition is forbidden in the Landau-Ginzburg-Wilson frame-work. We also discuss the superfluid-insulator transition in the direct boson representation and find that an interpretation of the quantum criticality in terms of deconfined fractionalized bosons is only permitted at special values of q for which a permutative representation of the PSG exists. We argue [and demonstrate in detail in a companion paper: L. Balents , following paper, Phys. Rev. B 71, 144509 (2005)] that our results apply essentially unchanged to electronic systems with short-range pairing, with the PSG determined by the particle density of Cooper pairs. We also describe the effect of static impurities in the superfluid: the impurities locally break the degeneracy between the q vortex species, and this induces density-wave order near each vortex. We suggest that such a theory offers an appealing rationale for the local density-of-states modulations observed by Hoffman [Science 295, 466 (2002)], in scanning tunneling microscopy (STM) studies of the vortex lattice of Bi2Sr2CaCu2O8+δ and allows a unified description of the nucleation of density-wave order in zero and finite magnetic fields. We note signatures of our theory that may be tested by future STM experiments.

Phase diagram of Ba 2 NaOsO 6, a Mott insulator with strong spin orbit interactions

NASA Astrophysics Data System (ADS)

Liu, W.; Cong, R.; Garcia, E.; Reyes, A. P.; Lee, H. O.; Fisher, I. R.; Mitrović, V. F.

2018-05-01

We report 23Na nuclear magnetic resonance (NMR) measurements of the Mott insulator with strong spin-orbit interaction Ba2NaOsO6 as a function of temperature in different magnetic fields ranging from 7 T to 29 T. The measurements, intended to concurrently probe spin and orbital/lattice degrees of freedom, are an extension of our work at lower fields reported in Lu et al. (2017) [1]. We have identified clear quantitative NMR signatures that display the appearance of a canted ferromagnetic phase, which is preceded by local point symmetry breaking. We have compiled the field temperature phase diagram extending up to 29 T. We find that the broken local point symmetry phase extends over a wider temperature range as magnetic field increases.

Insulating phase in Sr2IrO4: An investigation using critical analysis and magnetocaloric effect

NASA Astrophysics Data System (ADS)

Bhatti, Imtiaz Noor; Pramanik, A. K.

2017-01-01

The nature of insulating phase in 5d based Sr2IrO4 is quite debated as the theoretical as well as experimental investigations have put forward evidences in favor of both magnetically driven Slater-type and interaction driven Mott-type insulator. To understand this insulating behavior, we have investigated the nature of magnetic state in Sr2IrO4 through studying critical exponents, low temperature thermal demagnetization and magnetocaloric effect. The estimated critical exponents do not exactly match with any universality class, however, the values obey the scaling behavior. The exponent values suggest that spin interaction in present material is close to mean-field model. The analysis of low temperature thermal demagnetization data, however, shows dual presence of localized- and itinerant-type of magnetic interaction. Moreover, field dependent change in magnetic entropy indicates magnetic interaction is close to mean-field type. While this material shows an insulating behavior across the magnetic transition, yet a distinct change in slope in resistivity is observed around Tc. We infer that though the insulating phase in Sr2IrO4 is more close to be Slater-type but the simultaneous presence of both Slater- and Mott-type is the likely scenario for this material.

Mott physics beyond the Brinkman-Rice scenario

NASA Astrophysics Data System (ADS)

Wysokiński, Marcin M.; Fabrizio, Michele

2017-04-01

The main flaw of the well-known Brinkman-Rice description, obtained through the Gutzwiller approximation, of the paramagnetic Mott transition in the Hubbard model is in neglecting high-energy virtual processes that generate, for instance, the antiferromagnetic exchange J ˜t2/U . Here, we propose a way to capture those processes by combining the Brinkman-Rice approach with a variational Schrieffer-Wolff transformation, and apply this method to study the single-band metal-to-insulator transition in a Bethe lattice with infinite coordination number, where the Gutzwiller approximation becomes exact. We indeed find for the Mott transition a description very close to the real one provided by the dynamical mean-field theory, an encouraging result in view of possible applications to more involved models.

Analytical slave-spin mean-field approach to orbital selective Mott insulators

NASA Astrophysics Data System (ADS)

Komijani, Yashar; Kotliar, Gabriel

2017-09-01

We use the slave-spin mean-field approach to study particle-hole symmetric one- and two-band Hubbard models in the presence of Hund's coupling interaction. By analytical analysis of the Hamiltonian, we show that the locking of the two orbitals vs orbital selective Mott transition can be formulated within a Landau-Ginzburg framework. By applying the slave-spin mean field to impurity problems, we are able to make a correspondence between impurity and lattice. We also consider the stability of the orbital selective Mott phase to the hybridization between the orbitals and study the limitations of the slave-spin method for treating interorbital tunnelings in the case of multiorbital Bethe lattices with particle-hole symmetry.

On the possibility of many-body localization in a doped Mott insulator

PubMed Central

He, Rong-Qiang; Weng, Zheng-Yu

2016-01-01

Many-body localization (MBL) is currently a hot issue of interacting systems, in which quantum mechanics overcomes thermalization of statistical mechanics. Like Anderson localization of non-interacting electrons, disorders are usually crucial in engineering the quantum interference in MBL. For translation invariant systems, however, the breakdown of eigenstate thermalization hypothesis due to a pure many-body quantum effect is still unclear. Here we demonstrate a possible MBL phenomenon without disorder, which emerges in a lightly doped Hubbard model with very strong interaction. By means of density matrix renormalization group numerical calculation on a two-leg ladder, we show that whereas a single hole can induce a very heavy Nagaoka polaron, two or more holes will form bound pair/droplets which are all localized excitations with flat bands at low energy densities. Consequently, MBL eigenstates of finite energy density can be constructed as composed of these localized droplets spatially separated. We further identify the underlying mechanism for this MBL as due to a novel ‘Berry phase’ of the doped Mott insulator, and show that by turning off this Berry phase either by increasing the anisotropy of the model or by hand, an eigenstate transition from the MBL to a conventional quasiparticle phase can be realized. PMID:27752064

Quench of paramagnetic orbital selective Mott phase and appearance of antiferromagnetic orbital selective slater phase in multiorbital correlated systems

NASA Astrophysics Data System (ADS)

Quan, Ya-Min; Liu, Da-Yong; Lin, Hai-Qing; Zou, Liang-Jian

2018-06-01

We present the modulation of magnetic order on the orbital selective Mott phases (OSMP) and the metal-insulator transitions (MIT) of multi-orbital Hubbard models by employing the rotationally invariant slave-boson methods. We show that at half filling, the well-known paramagnetic (PM) OSMP is completely covered by an antiferromagnetic (AFM) Slater insulator, and the PM Mott phase by an AFM Mott insulator when electron correlation strength varies from intermediate to strong both in two- and three-orbitals Hubbard systems. Away from half-filling, we find that a partial-polarized AFM orbital-selective Slater phase appears in the intermediate correlation regime, and an almost full-polarized AFM OSMP fully covers the paramagnetic OSMP. In addition, the ferromagnetic phase in the three-orbital case is more robust than that in the two-orbital case. These results demonstrate that the modulation of magnetic correlation to the quasiparticle spectra leads to much rich and more interesting MIT scenario in multiorbital correlated systems.

Mean-Field Scaling of the Superfluid to Mott Insulator Transition in a 2D Optical Superlattice.

PubMed

Thomas, Claire K; Barter, Thomas H; Leung, Tsz-Him; Okano, Masayuki; Jo, Gyu-Boong; Guzman, Jennie; Kimchi, Itamar; Vishwanath, Ashvin; Stamper-Kurn, Dan M

2017-09-08

The mean-field treatment of the Bose-Hubbard model predicts properties of lattice-trapped gases to be insensitive to the specific lattice geometry once system energies are scaled by the lattice coordination number z. We test this scaling directly by comparing coherence properties of ^{87}Rb gases that are driven across the superfluid to Mott insulator transition within optical lattices of either the kagome (z=4) or the triangular (z=6) geometries. The coherent fraction measured for atoms in the kagome lattice is lower than for those in a triangular lattice with the same interaction and tunneling energies. A comparison of measurements from both lattices agrees quantitatively with the scaling prediction. We also study the response of the gas to a change in lattice geometry, and observe the dynamics as a strongly interacting kagome-lattice gas is suddenly "hole doped" by introducing the additional sites of the triangular lattice.

Characteristics of the Mott transition and electronic states of high-temperature cuprate superconductors from the perspective of the Hubbard model

NASA Astrophysics Data System (ADS)

Kohno, Masanori

2018-04-01

A fundamental issue of the Mott transition is how electrons behaving as single particles carrying spin and charge in a metal change into those exhibiting separated spin and charge excitations (low-energy spin excitation and high-energy charge excitation) in a Mott insulator. This issue has attracted considerable attention particularly in relation to high-temperature cuprate superconductors, which exhibit electronic states near the Mott transition that are difficult to explain in conventional pictures. Here, from a new viewpoint of the Mott transition based on analyses of the Hubbard model, we review anomalous features observed in high-temperature cuprate superconductors near the Mott transition.

Mixed-pairing superconductivity in 5 d Mott insulators with antisymmetric exchange: Application to Sr2IrO4

NASA Astrophysics Data System (ADS)

Zare, Mohammad-Hossein; Biderang, Mehdi; Akbari, Alireza

2017-11-01

We study the symmetry of the potential superconducting order parameter in 5 d Mott insulators with an eye toward hole-doped Sr2IrO4 . Using a mean-field method, a mixed singlet-triplet superconductivity, d +p , is observed due to the antisymmetric exchange originating from a quasi-spin-orbit coupling. Our calculation on ribbon geometry shows the possible existence of the topologically protected edge states, because of the nodal structure of the superconducting gap. These edge modes are spin polarized and emerge as zero-energy flat bands, supporting a symmetry-protected Majorana state, verified by evaluation of the winding number and Z2 topological invariant. At the end, a possible experimental approach for observation of these edge states and determination of the superconducting gap symmetry is discussed based on the quasiparticle interference technique.

Direct observation of the M2 phase with its Mott transition in a VO2 film

NASA Astrophysics Data System (ADS)

Kim, Hoon; Slusar, Tetiana V.; Wulferding, Dirk; Yang, Ilkyu; Cho, Jin-Cheol; Lee, Minkyung; Choi, Hee Cheul; Jeong, Yoon Hee; Kim, Hyun-Tak; Kim, Jeehoon

2016-12-01

In VO2, the explicit origin of the insulator-to-metal transition is still disputable between Peierls and Mott insulators. Along with the controversy, its second monoclinic (M2) phase has received considerable attention due to the presence of electron correlation in undimerized vanadium ions. However, the origin of the M2 phase is still obscure. Here, we study a granular VO2 film using conductive atomic force microscopy and Raman scattering. Upon the structural transition from monoclinic to rutile, we observe directly an intermediate state showing the coexistence of monoclinic M1 and M2 phases. The conductivity near the grain boundary in this regime is six times larger than that of the grain core, producing a donut-like landscape. Our results reveal an intra-grain percolation process, indicating that VO2 with the M2 phase is a Mott insulator.

Spin-orbital fluctuations in the paramagnetic Mott insulator (V1-xCrx)2O3

NASA Astrophysics Data System (ADS)

Leiner, Jonathan; Stone, Matthew; Lumsden, Mark; Bao, Wei; Broholm, Collin

2015-03-01

The phase diagram of rhombohedral V2O3 features several distinct strongly correlated phases as a function of doping, pressure and temperature. When doped with chromium for 180 K Mott metal to insulator transition. Using the modern time-of-flight neutron scattering spectrometer SEQUOIA at the SNS, we have probed the excitation spectrum of (V0.96Cr0.04)2O3 in the PI phase and in the monoclinic commensurate anti-ferromagnet for T <180 K. An effective exchange Hamiltonian that accounts for the low T spin waves indicates alternating FM and AFM interactions for nearest neighbor spin pairs that are equivalent in the PI. We argue that the corresponding spin-orbital fluctuations are responsible for the extremely short-range dynamic spin correlations that we document in the PI phase. Research at the Spallation Neutron Source was sponsored by the Scientific User Facilities Division, Office of Basic Energy Sciences, U.S. Department of Energy. Research was also supported by ORNL LDRD funding.

Negligible carrier freeze-out facilitated by impurity band conduction in highly p-type GaN

NASA Astrophysics Data System (ADS)

Gunning, Brendan; Lowder, Jonathan; Moseley, Michael; Alan Doolittle, W.

2012-08-01

Highly p-type GaN films with hole concentrations exceeding 6 × 1019 cm-3 grown by metal-modulated epitaxy are electrically characterized. Temperature-dependent Hall effect measurements at cryogenic temperatures reveal minimal carrier freeze-out in highly doped samples, while less heavily doped samples exhibited high resistivity and donor-compensated conductivity as is traditionally observed. Effective activation energies as low as 43 meV were extracted, and a maximum Mg activation efficiency of 52% was found. In addition, the effective activation energy was found to be negatively correlated to the hole concentration. These results indicate the onset of the Mott-Insulator transition leading to impurity band conduction.

Sitewise manipulations and Mott insulator-superfluid transition of interacting photons using superconducting circuit simulators

DOE PAGES

Deng, Xiuhao; Jia, Chunjing; Chien, Chih-Chun

2015-02-23

We report that the Bose Hubbard model (BHM) of interacting bosons in a lattice has been a paradigm in many-body physics, and it exhibits a Mott insulator (MI)-superfluid (SF) transition at integer filling. Here a quantum simulator of the BHM using a superconducting circuit is proposed. Specifically, a superconducting transmission line resonator supporting microwave photons is coupled to a charge qubit to form one site of the BHM, and adjacent sites are connected by a tunable coupler. To obtain a mapping from the superconducting circuit to the BHM, we focus on the dispersive regime where the excitations remain photonlike. Standardmore » perturbation theory is implemented to locate the parameter range where the MI-SF transition may be simulated. This simulator allows single-site manipulations and we illustrate this feature by considering two scenarios where a single-site manipulation can drive a MI-SF transition. The transition can be analyzed by mean-field analyses, and the exact diagonalization was implemented to provide accurate results. The variance of the photon density and the fidelity metric clearly show signatures of the transition. Lastly, experimental realizations and other possible applications of this simulator are also discussed.« less

Nanotextured phase coexistence in the correlated insulator V2O3

NASA Astrophysics Data System (ADS)

McLeod, Alexander

The Mott insulator-metal transition remains among the most studied phenomena in correlated electron physics. However, the formation of spontaneous spatial patterns amidst coexisting insulating and metallic phases remains poorly explored on the meso- and nanoscales. Here we present real-space evolution of the insulator-metal transition in a thin film of V2O3, the ``canonical'' Mott insulator, imaged at high spatial resolution by cryogenic near-field infrared microscopy. We resolve spontaneously nanotextured coexistence of metal and correlated Mott insulator phases near the insulator-metal transition (T = 160-180 K) associated with percolation and an underlying structural phase transition. Augmented with macroscopic temperature-resolved X-ray diffraction measurements of the same film, a quantitative analysis of nano-infrared images acquired across the transition suggests decoupling of electronic and structural transformations. Persistent low-temperature metallicity is accompanied by unconventional dimensional scaling among metallic ``puddles,'' implicating relevance of a long-range Coulombic interaction through the film's first-order insulator-metal transition. The speaker and co-authors acknowledge support from DOE-DE-SC0012375, DOE-DE-SC0012592, and AFOSR Grant No. FA9550-12-1-0381. The speaker also acknowledges support from a US Dept. of Energy Office of Science Graduate Fellowship (DOE SCGF).

Superconductor to Mott insulator transition in YBa2Cu3O7/LaCaMnO3 heterostructures.

PubMed

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

2016-09-15

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

Strong lattice correlation of non-equilibrium quasiparticles in a pseudospin-1/2 Mott insulator Sr 2IrO 4

DOE PAGES

Li, Yuelin; Schaller, Richard D.; Zhu, Mengze; ...

2016-01-20

In correlated oxides the coupling of quasiparticles to other degrees of freedom such as spin and lattice plays critical roles in the emergence of symmetry-breaking quantum ordered states such as high temperature superconductivity. We report a strong lattice coupling of photon-induced quasiparticles in spin-orbital coupling Mott insulator Sr 2IrO 4 probed via optical excitation. Combining time-resolved x-ray diffraction and optical spectroscopy techniques, we reconstruct a spatiotemporal map of the diffusion of these quasiparticles. Lastly, due to the unique electronic configuration of the quasiparticles, the strong lattice correlation is unexpected but extends the similarity between Sr 2IrO 4 and cuprates tomore » a new dimension of electron-phonon coupling which persists under highly non-equilibrium conditions.« less

Ellen N. La Motte: the making of a nurse, writer, and activist.

PubMed

Williams, Lea M

2015-01-01

This article examines the early career of Ellen N. La Motte (1873-1961) to trace how her training at the Johns Hopkins Training School for Nurses and years spent as a tuberculosis nurse in Baltimore shaped her perception of tuberculosis prevention and women's suffrage. Although studies of tuberculosis have frequently alluded to her work, no sustained biocritical discussion of her development as a nurse and scholar exists. Between 1902, when she graduated from nursing school, and 1914, the start of the Great War, La Motte published a textbook and dozens of articles in journals devoted to nursing and social reform and delivered many speeches at local, regional, and national meetings. In addition, as her reputation as an expert in the field of tuberculosis nursing grew, her advocacy for the vote for women increased, and she used her writing and speaking skills on behalf of the suffrage cause. This article assesses how the skills La Motte acquired during these years helped mold her into a successful and respected nurse, writer, and activist.

Spectral evolution with doping of an antiferromagnetic Mott state

NASA Astrophysics Data System (ADS)

Wu, Huan-Kuang; Lee, Ting-Kuo

2017-01-01

Since the discovery of half-filled cuprate to be a Mott insulator, the excitation spectra above the chemical potential for the unoccupied states has attracted much research attention. There were many theoretical works using different numerical techniques to study this problem, but many have reached different conclusions. One of the reasons is the lack of very detailed high-resolution experimental results for the theories to be compared with. Recently, the scanning tunneling spectroscopy [P. Cai et al., Nat. Phys. 12, 1047 (2016), 10.1038/nphys3840; C. Ye et al., Nat. Commun. 4, 1365 (2013), 10.1038/ncomms2369] on lightly doped Mott insulator with an antiferromagnetic order found the presence of in-gap states with energy of order half an eV above the chemical potential. The measured spectral properties with doping are not quite consistent with earlier theoretical works. Although the experiment has disorder and localization effect, but for the energy scale we will study here, a model without disorder is sufficed to illustrate the underlying physics. We perform a diagonalization method on top of the variational Monte Carlo calculation to study the evolution of antiferromagnetic Mott state with doped hole concentration in the Hubbard model. Our results found in-gap states that behave similarly with ones reported by STS. These in-gap states acquire a substantial amount of dynamical spectral weight transferred from the upper Hubbard band. The in-gap states move toward chemical potential with increasing spectral weight as doping increases. Our result also provides information about the energy scale of these in-gap states in relation with the Coulomb coupling strength U .

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

DOE PAGES

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

2016-09-15

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

Metal insulator transitions in perovskite SrIrO{sub 3} thin films

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

Biswas, Abhijit; Jeong, Yoon Hee, E-mail: yhj@postech.ac.kr; Kim, Ki-Seok

Understanding of metal insulator transitions in a strongly correlated system, driven by Anderson localization (disorder) and/or Mott localization (correlation), is a long standing problem in condensed matter physics. The prevailing fundamental question would be how these two mechanisms contrive to accomplish emergent anomalous behaviors. Here, we have grown high quality perovskite SrIrO{sub 3} thin films, containing a strong spin orbit coupled 5d element Ir, on various substrates such as GdScO{sub 3} (110), DyScO{sub 3} (110), SrTiO{sub 3} (001), and NdGaO{sub 3} (110) with increasing lattice mismatch, in order to carry out a systematic study on the transport properties. We foundmore » that metal insulator transitions can be induced in this system; by either reducing thickness (on best lattice matched substrate) or changing degree of lattice strain (by lattice mismatch between film and substrates) of films. Surprisingly these two pathways seek two distinct types of metal insulator transitions; the former falls into disorder driven Anderson type whereas the latter turns out to be of unconventional Mott-Anderson type with the interplay of disorder and correlation. More interestingly, in the metallic phases of SrIrO{sub 3}, unusual non-Fermi liquid characteristics emerge in resistivity as Δρ ∝ T{sup ε} with ε evolving from 4/5 to 1 to 3/2 with increasing lattice strain. We discuss theoretical implications of these phenomena to shed light on the metal insulator transitions.« less

Mott-metal transition in layered perovskite iridate thin films via field-effect doping

NASA Astrophysics Data System (ADS)

Cheema, Suraj; Turcaud, Jeremy; Nelson, Chris; Salahuddin, Sayeef; Ramesh, Ramamoorthy

We report on electrostatic gating of spin-orbit coupled Mott insulator Sr2IrO4 (Sr214) via ferroelectric field effect doping. Field effect doping has been used to modulate electronic phenomena in emerging 2D systems and strongly correlated oxides, but 5 d systems with large spin-orbit coupling have yet to be explored. Upon switching the polarization field of ferroelectric Pb(Zr20Ti80)O3 (PZT) to the down-poled (electron-accumulation) state, temperature-dependent resistivity measurements indicate extremely metallic behavior in the ultrathin Sr214 channel. This work successfully closes the Mott gap in Sr214 in a ''clean'' doping environment free of chemical disorder, thereby strengthening the link to the isostrucutral high-Tc cuprates, as Sr214 has been predicted to host d-wave superconductivity upon electron doping the parent antiferromagnetic insulating phase. Furthermore, the metallic behavior in Sr214 persists for thickness beyond the expected screening length, suggestive of a collective carrier delocalization mechanism. Electrostatically doped carriers prove to be a useful method for tuning the competition between spin-orbit and Coulomb interactions in order to trigger novel phase transitions, such as the Mott-metal crossover. This work was supported by the Office of Science, Office of Basic Energy Sciences, of the U.S. Department of Energy, under Contract No. DE-AC02-05CH11231.

Evidence of Mott physics in iron pnictides from x-ray spectroscopy

DOE PAGES

Lafuerza, S.; Gretarsson, H.; Hardy, F.; ...

2017-07-24

The existence of large instantaneous local magnetic moments in paramagnetic phases is a direct signature of Mott localization. In order to track the doping evolution of fluctuating local moments in iron-based superconductors, we jointly use two fast probes, x-ray emission and absorption spectroscopies. Exploring K- and Cr-hole-doped BaF e 2 A s 2 , we also find a systematic increase in the local moment with hole-doping, in contrast with inelastic neutron scattering measurements, which suggest an opposite trend. The results support the theoretical scenario in which a Mott insulating state that would be realized for half-filled conduction bands has anmore » influence throughout the phase diagram of these iron pnictides.« less

Mott-to-Goodenough insulator-insulator transition in LiVO2

NASA Astrophysics Data System (ADS)

Subedi, Alaska

2017-06-01

I critically examine Goodenough's explanation for the experimentally observed phase transition in LiVO2 using microscopic calculations based on density functional and dynamical mean field theories. The high-temperature rhombohedral phase exhibits both magnetic and dynamical instabilities. Allowing a magnetic solution for the rhombohedral structure does not open an insulating gap, and an explicit treatment of the on-site Coulomb U interaction is needed to stabilize an insulating rhombohedral phase. The non-spin-polarized phonon dispersions of the rhombohedral phase show two unstable phonon modes at the wave vector (1/3 ,-1/3 ,0 ) that corresponds to the experimentally observed trimer forming instability. A full relaxation of the supercell corresponding to this instability yields a nonmagnetic state containing V3 trimers. These results are consistent with Goodenough's suggestion that the high-temperature phase is in the localized-electron regime and the transition to the low-temperature phase in the itinerant-electron regime is driven by V-V covalency.

Resolving the chicken-and-egg problem in VO2: a new paradigm for the Mott transition

NASA Astrophysics Data System (ADS)

Najera, Oscar; Civelli, Marcello; Dobrosavljevi, Vladimir; Rozenberg, Marcelo

We consider a minimal model to investigate the metal-insulator transition in VO2. We adopt a Hubbard model with two orbital per unit cell, which captures the competition between Mott and singlet-dimer localization. We solve the model within Dynamical Mean Field Theory, characterizing in detail the metal-insulator transition and finding new features in the electronic states. We compare our results with available experimental data obtaining good agreement in the relevant model parameter range. Crucially, we can account for puzzling optical conductivity data obtained within the hysteresis region, which we associate to a novel metallic state characterized by a split heavy quasiparticle band. Our results show that the thermal-driven insulator-to-metal transition in VO2 is entirely compatible with a Mott electronic mechanism, solving a long standing ''chicken-and-egg'' debate and calling for further research of ``Mottronics'' applications of this system. This work was partially supported by public Grants from the French National Research Agency (ANR), project LACUNES No ANR-13-BS04-0006-01, the NSF DMR-1005751 and DMR-1410132.

Superfluid-insulator transitions of two-species bosons in an optical lattice

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

Isacsson, A.; Department of Physics, Yale University, P.O. Box 208120, New Haven, Connecticut 06520-8120; Cha, M.-C.

2005-11-01

We consider the two-species bosonic Hubbard model with variable interspecies interaction and hopping strength in the grand canonical ensemble with a common chemical potential. We analyze the superfluid-insulator (SI) transition for the relevant parameter regimes and compute the ground state phase diagram in the vicinity of odd filling Mott states. We find that the superfluid-insulator transition occurs with (a) simultaneous onset of superfluidity of both species or (b) coexistence of Mott insulating state of one species and superfluidity of the other or, in the case of unit filling (c) complete depopulation of one species. The superfluid-insulator transition can be firstmore » order in a large region of the phase diagram. We develop a variational mean-field method which takes into account the effect of second order quantum fluctuations on the superfluid-insulator transition and corroborate the mean-field phase diagram using a quantum Monte Carlo study.« less

Various topological Mott insulators and topological bulk charge pumping in strongly-interacting boson system in one-dimensional superlattice

NASA Astrophysics Data System (ADS)

Kuno, Yoshihito; Shimizu, Keita; Ichinose, Ikuo

2017-12-01

In this paper, we study a one-dimensional boson system in a superlattice potential. This system is experimentally feasible by using ultracold atomic gases, and attracts much attention these days. It is expected that the system has a topological phase called a topological Mott insulator (TMI). We show that in strongly-interacting cases, the competition between the superlattice potential and the on-site interaction leads to various TMIs with a non-vanishing integer Chern number. Compared to the hard-core case, the soft-core boson system exhibits rich phase diagrams including various non-trivial TMIs. By using the exact diagonalization, we obtain detailed bulk-global phase diagrams including the TMIs with high Chern numbers and also various non-topological phases. We also show that in adiabatic experimental setups, the strongly-interacting bosonic TMIs exhibit the topological particle transfer, i.e., the topological charge pumping phenomenon, similarly to weakly-interacting systems. The various TMIs are characterized by topological charge pumping as it is closely related to the Chern number, and therefore the Chern number is to be observed in feasible experiments.

Wide gap Chern Mott insulating phases achieved by design

NASA Astrophysics Data System (ADS)

Guo, Hongli; Gangopadhyay, Shruba; Köksal, Okan; Pentcheva, Rossitza; Pickett, Warren E.

2017-12-01

Quantum anomalous Hall insulators, which display robust boundary charge and spin currents categorized in terms of a bulk topological invariant known as the Chern number (Thouless et al Phys. Rev. Lett. 49, 405-408 (1982)), provide the quantum Hall anomalous effect without an applied magnetic field. Chern insulators are attracting interest both as a novel electronic phase and for their novel and potentially useful boundary charge and spin currents. Honeycomb lattice systems such as we discuss here, occupied by heavy transition-metal ions, have been proposed as Chern insulators, but finding a concrete example has been challenging due to an assortment of broken symmetry phases that thwart the topological character. Building on accumulated knowledge of the behavior of the 3d series, we tune spin-orbit and interaction strength together with strain to design two Chern insulator systems with bandgaps up to 130 meV and Chern numbers C = -1 and C = 2. We find, in this class, that a trade-off between larger spin-orbit coupling and strong interactions leads to a larger gap, whereas the stronger spin-orbit coupling correlates with the larger magnitude of the Hall conductivity. Symmetry lowering in the course of structural relaxation hampers obtaining quantum anomalous Hall character, as pointed out previously; there is only mild structural symmetry breaking of the bilayer in these robust Chern phases. Recent growth of insulating, magnetic phases in closely related materials with this orientation supports the likelihood that synthesis and exploitation will follow.

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

PubMed

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

2012-08-17

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

Metal-Insulator Transitions in Epitaxial LaVO(3) and LaTiO(3) Films

DTIC Science & Technology

2012-08-01

epitaxial films of LaVO3 and LaTiO3 can exhibit metallicity though their bulk counterparts are Mott insulators. When LaTiO3 films are compressively...secondarily to interface electronic reconstruction at the LaTiO3 /SrTiO3 interface. However, when LaVO3 films are compressively strained on SrTiO3...ABSTRACT We have demonstrated that epitaxial films of LaVO3 and LaTiO3 can exhibit metallicity though their bulk counterparts are Mott insulators. When

Optical Absorption in Degenerately Doped Semiconductors: Mott Transition or Mahan Excitons?

NASA Astrophysics Data System (ADS)

Schleife, André; Rödl, Claudia; Fuchs, Frank; Hannewald, Karsten; Bechstedt, Friedhelm

2011-12-01

Electron doping turns semiconductors conductive even when they have wide fundamental band gaps. The degenerate electron gas in the lowest conduction-band states, e.g., of a transparent conducting oxide, drastically modifies the Coulomb interaction between the electrons and, hence, the optical properties close to the absorption edge. We describe these effects by developing an ab initio technique which captures also the Pauli blocking and the Fermi-edge singularity at the optical-absorption onset, that occur in addition to quasiparticle and excitonic effects. We answer the question whether free carriers induce an excitonic Mott transition or trigger the evolution of Wannier-Mott excitons into Mahan excitons. The prototypical n-type zinc oxide is studied as an example.

Pertinence et limitations de la loi de Mott dans les isolants désordonnés

NASA Astrophysics Data System (ADS)

Ladieu, François; Sanquer, Marc

Twenty five years ago, Mott's law was established in order to describe electrical transport in disordered insulators at low temperature. In this review, we briefly summarize the different theoretical steps involved in the rigourous derivation of Mott's law. We stress upon the fact that Mott's law gives the mean conductance of an ensemble of macroscopic samples as long as electron-electron interactions remain negligible. We then study what happens when at least one of the key assumptions of Mott's law no longer holds. We first focus on systems whose size — at least in one dimension — is not macroscopic: the optimization involved in Mott's law is no longer relevant for the measured conductance. Eventually, we try to gather different works dealing with electron-electron interactions. It is now established that interactions generally produce a stronger divergence for the electrical resistance than the one predicted by Mott's law at the lowest temperatures. But the exact shape of this divergence, as well as its interpretation, remain debated. We try to make a link between Efros and Shklovskii 's work and their famous "Coulomb gap" and a more recent work about granular media. In this latter work, the size of the grains is the key parameter for the shape of the divergence of the resistance at low temperature. We suggest this could indicate a way for a model accounting for the different shapes of divergence of the electrical resistance at the lowest temperatures. Furthermore this framework of granular media allows us to deal with non linear regime: we explain the main differences between the predictions of the hot electrons model and the ones recently derived for a d -dimensional network of grains. Il y a déjà un quart de siècle que la loi de Mott a été établie afin de décrire le transport dans les milieux isolants désordonnés à basse température. Dans cet article de revue, nous rappelons brièvement les diverses étapes théoriques nécessaires à l

Wide gap Chern Mott insulating phases achieved by design

NASA Astrophysics Data System (ADS)

Guo, Hongli; Gangopadhyay, Shruba; Koeksal, Okan; Pentcheva, Rossitza; Pickett, Warren E.

Chern insulators are exciting both as a novel electronic phase and for their novel and potentially useful boundary transport properties. Honeycomb lattices occupied by heavy transition metal ions,have been proposed by Okamoto and coworkers as Chern insulators, but finding a concrete example has been challenging due to an assortment of broken symmetry phases that thwart the topological character. Building on accumulated knowledge of the behavior of the 3 d series, we tune spin-orbit and interaction strength together with strain to design two Chern insulator systems (one with Ru, one with Os) with bandgaps up to 130 meV and Chern numbers calC = - 1 and calC = 2 . We find, in this class, that a trade-off between larger spin-orbit coupling and strong interactions leads to a larger gap, whereas the stronger SOC correlates with the larger magnitude of the Hall conductivity. Symmetry lowering in the course of structural relaxation hampers retaining QAH character, as pointed out previously. Fortunately there is only mild structural symmetry breaking of the bilayer in these robust Chern phases.Recent (111) growth of insulating, magnetic phases in closely related materials with this orientation supports the likelihood that synthesis and exploitation will follow. Supported partially by the NSF DMREF program.

Finite-temperature dynamics of the Mott insulating Hubbard chain

NASA Astrophysics Data System (ADS)

Nocera, Alberto; Essler, Fabian H. L.; Feiguin, Adrian E.

2018-01-01

We study the dynamical response of the half-filled one-dimensional Hubbard model for a range of interaction strengths U and temperatures T by a combination of numerical and analytical techniques. Using time-dependent density matrix renormalization group computations we find that the single-particle spectral function undergoes a crossover to a spin-incoherent Luttinger liquid regime at temperatures T ˜J =4 t2/U for sufficiently large U >4 t . At smaller values of U and elevated temperatures the spectral function is found to exhibit two thermally broadened bands of excitations, reminiscent of what is found in the Hubbard-I approximation. The dynamical density-density response function is shown to exhibit a finite-temperature resonance at low frequencies inside the Mott gap, with a physical origin similar to the Villain mode in gapped quantum spin chains. We complement our numerical computations by developing an analytic strong-coupling approach to the low-temperature dynamics in the spin-incoherent regime.

Magnetic fluctuations driven insulator-to-metal transition in Ca(Ir(1-x)Rux)O3.

PubMed

Gunasekera, J; Harriger, L; Dahal, A; Heitmann, T; Vignale, G; Singh, D K

2015-12-09

Magnetic fluctuations in transition metal oxides are a subject of intensive research because of the key role they are expected to play in the transition from the Mott insulator to the unconventional metallic phase of these materials, and also as drivers of superconductivity. Despite much effort, a clear link between magnetic fluctuations and the insulator-to-metal transition has not yet been established. Here we report the discovery of a compelling link between magnetic fluctuations and the insulator-to-metal transition in Ca(Ir1-xRux)O3 perovskites as a function of the substitution coefficient x. We show that when the material turns from insulator to metal, at a critical value of x ~ 0.3, magnetic fluctuations tend to change their character from antiferromagnetic, a Mott insulator phase, to ferromagnetic, an itinerant electron state with Hund's orbital coupling. These results are expected to have wide-ranging implications for our understanding of the unconventional properties of strongly correlated electrons systems.

Chaotic dynamics in nanoscale NbO2 Mott memristors for analogue computing

NASA Astrophysics Data System (ADS)

Kumar, Suhas; Strachan, John Paul; Williams, R. Stanley

2017-08-01

At present, machine learning systems use simplified neuron models that lack the rich nonlinear phenomena observed in biological systems, which display spatio-temporal cooperative dynamics. There is evidence that neurons operate in a regime called the edge of chaos that may be central to complexity, learning efficiency, adaptability and analogue (non-Boolean) computation in brains. Neural networks have exhibited enhanced computational complexity when operated at the edge of chaos, and networks of chaotic elements have been proposed for solving combinatorial or global optimization problems. Thus, a source of controllable chaotic behaviour that can be incorporated into a neural-inspired circuit may be an essential component of future computational systems. Such chaotic elements have been simulated using elaborate transistor circuits that simulate known equations of chaos, but an experimental realization of chaotic dynamics from a single scalable electronic device has been lacking. Here we describe niobium dioxide (NbO2) Mott memristors each less than 100 nanometres across that exhibit both a nonlinear-transport-driven current-controlled negative differential resistance and a Mott-transition-driven temperature-controlled negative differential resistance. Mott materials have a temperature-dependent metal-insulator transition that acts as an electronic switch, which introduces a history-dependent resistance into the device. We incorporate these memristors into a relaxation oscillator and observe a tunable range of periodic and chaotic self-oscillations. We show that the nonlinear current transport coupled with thermal fluctuations at the nanoscale generates chaotic oscillations. Such memristors could be useful in certain types of neural-inspired computation by introducing a pseudo-random signal that prevents global synchronization and could also assist in finding a global minimum during a constrained search. We specifically demonstrate that incorporating such

Magnetic fluctuations driven insulator-to-metal transition in Ca(Ir1−xRux)O3

PubMed Central

Gunasekera, J.; Harriger, L.; Dahal, A.; Heitmann, T.; Vignale, G.; Singh, D. K.

2015-01-01

Magnetic fluctuations in transition metal oxides are a subject of intensive research because of the key role they are expected to play in the transition from the Mott insulator to the unconventional metallic phase of these materials, and also as drivers of superconductivity. Despite much effort, a clear link between magnetic fluctuations and the insulator-to-metal transition has not yet been established. Here we report the discovery of a compelling link between magnetic fluctuations and the insulator-to-metal transition in Ca(Ir1−xRux)O3 perovskites as a function of the substitution coefficient x. We show that when the material turns from insulator to metal, at a critical value of x ~ 0.3, magnetic fluctuations tend to change their character from antiferromagnetic, a Mott insulator phase, to ferromagnetic, an itinerant electron state with Hund’s orbital coupling. These results are expected to have wide-ranging implications for our understanding of the unconventional properties of strongly correlated electrons systems. PMID:26647965

Tuning the metal-insulator transition in d1 and d2 perovskites by epitaxial strain: A first-principles-based study

NASA Astrophysics Data System (ADS)

Sclauzero, Gabriele; Dymkowski, Krzysztof; Ederer, Claude

2016-12-01

We investigate the effect of epitaxial strain on the Mott metal-insulator transition (MIT) in perovskite systems with d1 and d2 electron configurations of the transition metal (TM) cation. We first discuss the general trends expected from the changes in the crystal-field splitting and in the hopping parameters that are induced by epitaxial strain. We argue that the strain-induced crystal-field splitting generally favors the Mott-insulating state, whereas the strain-induced changes in the hopping parameters favor the metallic state under compressive strain and the insulating state under tensile strain. Thus the two effects can effectively cancel each other under compressive strain, while they usually cooperate under tensile strain, in this case favoring the insulating state. We then validate these general considerations by performing electronic structure calculations for several d1 and d2 perovskites, using a combination of density functional theory (DFT) and dynamical mean-field theory (DMFT). We isolate the individual effects of strain-induced changes in either hopping or crystal-field by performing DMFT calculations where we fix one type of parameter to the corresponding unstrained DFT values. These calculations confirm our general considerations for SrVO3 (d1) and LaVO3 (d2), whereas the case of LaTiO3 (d1) is distinctly different, due to the strong effect of the octahedral tilt distortion in the underlying perovskite crystal structure. Our results demonstrate the possibility to tune the electronic properties of correlated TM oxides by using epitaxial strain, which allows to control the strength of electronic correlations and the vicinity to the Mott MIT.

Magnetic states, correlation effects and metal-insulator transition in FCC lattice

NASA Astrophysics Data System (ADS)

Timirgazin, M. A.; Igoshev, P. A.; Arzhnikov, A. K.; Irkhin, V. Yu

2016-12-01

The ground-state magnetic phase diagram (including collinear and spiral states) of the single-band Hubbard model for the face-centered cubic lattice and related metal-insulator transition (MIT) are investigated within the slave-boson approach by Kotliar and Ruckenstein. The correlation-induced electron spectrum narrowing and a comparison with a generalized Hartree-Fock approximation allow one to estimate the strength of correlation effects. This, as well as the MIT scenario, depends dramatically on the ratio of the next-nearest and nearest electron hopping integrals {{t}\\prime}/t . In contrast with metallic state, possessing substantial band narrowing, insulator one is only weakly correlated. The magnetic (Slater) scenario of MIT is found to be superior over the Mott one. Unlike simple and body-centered cubic lattices, MIT is the first order transition (discontinuous) for most {{t}\\prime}/t . The insulator state is type-II or type-III antiferromagnet, and the metallic state is spin-spiral, collinear antiferromagnet or paramagnet depending on {{t}\\prime}/t . The picture of magnetic ordering is compared with that in the standard localized-electron (Heisenberg) model.

Extrapolation procedures in Mott electron polarimetry

NASA Technical Reports Server (NTRS)

Gay, T. J.; Khakoo, M. A.; Brand, J. A.; Furst, J. E.; Wijayaratna, W. M. K. P.; Meyer, W. V.; Dunning, F. B.

1992-01-01

In standard Mott electron polarimetry using thin gold film targets, extrapolation procedures must be used to reduce the experimentally measured asymmetries A to the values they would have for scattering from single atoms. These extrapolations involve the dependent of A on either the gold film thickness or the maximum detected electron energy loss in the target. A concentric cylindrical-electrode Mott polarimeter, has been used to study and compare these two types of extrapolations over the electron energy range 20-100 keV. The potential systematic errors which can result from such procedures are analyzed in detail, particularly with regard to the use of various fitting functions in thickness extrapolations, and the failure of perfect energy-loss discrimination to yield accurate polarizations when thick foils are used.

Travel funds for Stanford University to Host Mott MURI Annual Review and Oxide Workshop, August 6-8, 2013

DTIC Science & Technology

2016-02-25

Insulator REPORT DOCUMENTATION PAGE 11. SPONSOR/MONITOR’S REPORT NUMBER(S) 10. SPONSOR/MONITOR’S ACRONYM(S) ARO 8. PERFORMING ORGANIZATION REPORT...THz electric‐field‐induced  insulator ‐to‐metal transition in VO2  4:10 – 4:35 pm  Adam Kajdos  Santosh Raghavan  UC Santa Barbara  A modulation doped...breakfast  9:00 – 9:40 am  Leon Balents  UC Santa Barbara  Doped Mott  insulators  – theoretical  perspectives  9:40 – 10:20 am  Shahal Ilani  Weizmann

Electric field-triggered metal-insulator transition resistive switching of bilayered multiphasic VOx

NASA Astrophysics Data System (ADS)

Won, Seokjae; Lee, Sang Yeon; Hwang, Jungyeon; Park, Jucheol; Seo, Hyungtak

2018-01-01

Electric field-triggered Mott transition of VO2 for next-generation memory devices with sharp and fast resistance-switching response is considered to be ideal but the formation of single-phase VO2 by common deposition techniques is very challenging. Here, VOx films with a VO2-dominant phase for a Mott transition-based metal-insulator transition (MIT) switching device were successfully fabricated by the combined process of RF magnetron sputtering of V metal and subsequent O2 annealing to form. By performing various material characterizations, including scanning transmission electron microscopy-electron energy loss spectroscopy, the film is determined to have a bilayer structure consisting of a VO2-rich bottom layer acting as the Mott transition switching layer and a V2O5/V2O3 mixed top layer acting as a control layer that suppresses any stray leakage current and improves cyclic performance. This bilayer structure enables excellent electric field-triggered Mott transition-based resistive switching of Pt-VOx-Pt metal-insulator-metal devices with a set/reset current ratio reaching 200, set/reset voltage of less than 2.5 V, and very stable DC cyclic switching upto 120 cycles with a great set/reset current and voltage distribution less than 5% of standard deviation at room temperature, which are specifications applicable for neuromorphic or memory device applications. [Figure not available: see fulltext.

Electron transport near the Mott transition in n-GaAs and n-GaN

NASA Astrophysics Data System (ADS)

Romanets, P. N.; Sachenko, A. V.

2016-01-01

In this paper, we study the temperature dependence of the conductivity and the Hall coefficient near the metal-insulator phase transition. A theoretical investigation is performed within the effective mass approximation. The variational method is used to calculate the eigenvalues and eigenfunctions of the impurity states. Unlike previous studies, we have included nonlinear corrections to the screened impurity potential, because the Thomas-Fermi approximation is incorrect for the insulator phase. It is also shown that near the phase transition the exchange interaction is essential. The obtained temperature dependencies explain several experimental measurements in gallium arsenide (GaAs) and gallium nitride (GaN).

Finite temperature quantum critical transport near the Mott transition

NASA Astrophysics Data System (ADS)

Terletska, Hanna; Dobrosavljevic, Vladimir

2010-03-01

We use Dynamical Mean-Field Theory to study incoherent transport above the critical end-point temperature Tc of the single band Hubbard model at half-filling. By employing an eigenvalue analysis for the free energy functional, we are able to precisely identify the crossover temperature T*(U) separating the Fermi liquid and the Mott insulating regimes. Our calculations demonstrate that a broad parameter range exist around the crossover line, where the family of resistivity curves displays simple scaling behavior. This is interpreted as a manifestation of quantum criticality controlled by the T=0 Mott transition, which is ``interrupted'' by the emergence of the coexistence dome at T < Tc . We argue that in situations where the critical temperature Tc is significantly reduced, so that the coexistence region is reduced or even absent (as in two-band, particle-hole asymmetric models, where this is found even in the clean d->∞ limit [1, 2]), similar critical scaling properties should persist down to much lower temperatures, resembling quantum critical transport similar to that found in a number of experiments [2]. [1] A. Amaricci, G. Sordi, and M. J. Rosenberg, Phys. Rev. Lett. 101, 146403 (2008) [2] A. Camjayi, K. Haule, V. Dobrosavljevic, and G. Kotliar, Nature Physics, 4, 932 (2008)

Low-threshold voltage ultraviolet light-emitting diodes based on (Al,Ga)N metal-insulator-semiconductor structures

NASA Astrophysics Data System (ADS)

Liang, Yu-Han; Towe, Elias

2017-12-01

Al-rich III-nitride-based deep-ultraviolet (UV) (275-320 nm) light-emitting diodes are plagued with a low emission efficiency and high turn-on voltages. We report Al-rich (Al,Ga)N metal-insulator-semiconductor UV light-emitting Schottky diodes with low turn-on voltages of <3 V, which are about half those of typical (Al,Ga)N p-i-n diodes. Our devices use a thin AlN film as the insulator and an n-type Al0.58Ga0.42N film as the semiconductor. To improve the efficiency, we inserted a GaN quantum-well structure between the AlN insulator and the n-type Al x Ga1- x N semiconductor. The benefits of the quantum-well structure include the potential to tune the emission wavelength and the capability to confine carriers for more efficient radiative recombination.

Field effect transistor with HfO2/Parylene-C bilayer hybrid gate insulator

NASA Astrophysics Data System (ADS)

Kumar, Neeraj; Kito, Ai; Inoue, Isao

2015-03-01

We have investigated the electric field control of the carrier density and the mobility at the surface of SrTiO3, a well known transition-metal oxide, in a field effect transistor (FET) geometry. We have used a Parylene-C (8 nm)/HfO2 (20 nm) double-layer gate insulator (GI), which can be a potential candidate for a solid state GI for the future Mott FETs. So far, only examples of the Mott FET used liquid electrolyte or ferroelectric oxides for the GI. However, possible electrochemical reaction at the interface causes damage to the surface of the Mott insulator. Thus, an alternative GI has been highly desired. We observed that even an ultra thin Parylene-C layer is effective for keeping the channel surface clean and free from oxygen vacancies. The 8 nm Parylene-C film has a relatively low resistance and consequentially its capacitance does not dominate the total capacitance of the Parylene-C/HfO2 GI. The breakdown gate voltage at 300 K is usually more than 10 V (~ 3.4 MV/cm). At gate voltage of 3 V the carrier density measured by the Hall effect is about 3 ×1013 cm-2, competent to cause the Mott transition. Moreover, the field effect mobility reaches in the range of 10 cm2/Vs indicating the Parylene-C passivated surface is actually very clean.

Optical absorption in degenerately doped semiconductors: Mott transition or Mahan excitons?

NASA Astrophysics Data System (ADS)

Schleife, André.; Rödl, Claudia; Hannewald, Karsten; Bechstedt, Friedhelm

2012-02-01

In the exploration of material properties, parameter-free calculations are a modern, sophisticated complement to cutting-edge experimental techniques. Ab-initio calculations are now capable of providing a deep understanding of the interesting physics underlying the electronic structure and optical absorption, e.g., of the transparent conductive oxides. Due to electron doping, these materials are conductive even though they have wide fundamental band gaps. The degenerate electron gas in the lowest conduction-band states drastically modifies the Coulomb interaction between the electrons and, hence, the optical properties close to the absorption edge. We describe these effects by developing an ab-initio technique which captures also the Pauli blocking and the Fermi-edge singularity at the optical absorption onset, that occur in addition to quasiparticle and excitonic effects. We answer the question whether free carriers induce an excitonic Mott transition or trigger the evolution of Wannier-Mott excitons into Mahan excitons. The prototypical n-type zinc oxide is studied as an example.

Disappearance of nodal gap across the insulator-superconductor transition in a copper-oxide superconductor.

PubMed

Peng, Yingying; Meng, Jianqiao; Mou, Daixiang; He, Junfeng; Zhao, Lin; Wu, Yue; Liu, Guodong; Dong, Xiaoli; He, Shaolong; Zhang, Jun; Wang, Xiaoyang; Peng, Qinjun; Wang, Zhimin; Zhang, Shenjin; Yang, Feng; Chen, Chuangtian; Xu, Zuyan; Lee, T K; Zhou, X J

2013-01-01

The parent compound of the copper-oxide high-temperature superconductors is a Mott insulator. Superconductivity is realized by doping an appropriate amount of charge carriers. How a Mott insulator transforms into a superconductor is crucial in understanding the unusual physical properties of high-temperature superconductors and the superconductivity mechanism. Here we report high-resolution angle-resolved photoemission measurement on heavily underdoped Bi₂Sr₂-xLaxCuO(₆+δ) system. The electronic structure of the lightly doped samples exhibit a number of characteristics: existence of an energy gap along the nodal direction, d-wave-like anisotropic energy gap along the underlying Fermi surface, and coexistence of a coherence peak and a broad hump in the photoemission spectra. Our results reveal a clear insulator-superconductor transition at a critical doping level of ~0.10 where the nodal energy gap approaches zero, the three-dimensional antiferromagnetic order disappears, and superconductivity starts to emerge. These observations clearly signal a close connection between the nodal gap, antiferromagnetism and superconductivity.

Phase diagram of the ultrafast photoinduced insulator-metal transition in vanadium dioxide

NASA Astrophysics Data System (ADS)

Cocker, T. L.; Titova, L. V.; Fourmaux, S.; Holloway, G.; Bandulet, H.-C.; Brassard, D.; Kieffer, J.-C.; El Khakani, M. A.; Hegmann, F. A.

2012-04-01

We use time-resolved terahertz spectroscopy to probe the ultrafast dynamics of the insulator-metal phase transition induced by femtosecond laser pulses in a nanogranular vanadium dioxide (VO2) film. Based on the observed thresholds for characteristic transient terahertz dynamics, a phase diagram of critical pump fluence versus temperature for the insulator-metal phase transition in VO2 is established for the first time over a broad range of temperatures down to 17 K. We find that both Mott and Peierls mechanisms are present in the insulating state and that the photoinduced transition is nonthermal. We propose a critical-threshold model for the ultrafast photoinduced transition based on a critical density of electrons and a critical density of coherently excited phonons necessary for the structural transition to the metallic state. As a result, evidence is found at low temperatures for an intermediate metallic state wherein the Mott state is melted but the Peierls distortion remains intact, consistent with recent theoretical predictions. Finally, the observed terahertz conductivity dynamics above the photoinduced transition threshold reveal nucleation and growth of metallic nanodomains over picosecond time scales.

Magnetism and electronic structure at the interface of a metal CaRuO3 and Mott insulator CaMnO3.

NASA Astrophysics Data System (ADS)

Boris, Alexander; Freeland, John; Kavich, Jerald; Lee, Ho Nyung; Yordanov, Petar; Khaliullin, Giniyat; Keimer, Bernhard; Chakhalian, Jak

2007-03-01

Recent advances in fabrication of ultra-thin complex oxide heterostructures have opened new opportunities to investigate possible novel quantum states at the correlated interfaces. With this aim we fabricated ultra-thin superlattices of CaMnO3(CMO)/CaRuO3(CRO) with the thickness of CRO layers from 1 to 12 unit cells by laser MBE. Electronic properties of CRO/CMO were investigated by soft x-ray spectroscopies at the L-edges of Mn and Ru. SQUID and optical reflectivity revealed a ferromagnetic thickness-independent transition at Tc 100K and CRO thickness-dependent negative magnetoresistance. This behavior is in marked contrast to the individual layers. At the interface we found a clear sign of net magnetic moment on Mn, which saturates only at magnetic field of 5T. Unlike CMO, similar measurements at the Ru L3-edge showed no detectable magnetism in the field up to 5T. Comparison with Ru references confirmed Ru(IV) oxidation state. These findings are in the sharp contrast with previously suggested models involving Ru(IV-V) valency exchange and thus reveal intricate nature of the interface between a metal and Mott insulator.

Metal-insulator-superconductor transition of spin-3/2 atoms on optical lattices

NASA Astrophysics Data System (ADS)

De Silva, Theja N.

2018-01-01

We use a slave-rotor approach within a mean-field theory to study the competition of metallic, Mott-insulating, and superconducting phases of spin-3/2 fermions subjected to a periodic optical lattice potential. In addition to the metallic, the Mott-insulating, and the superconducting phases that are associated with the gauge symmetry breaking of the spinon field, we identify an emerging superconducting phase that breaks both roton and spinon field gauge symmetries. This superconducting phase emerges as a result of the competition between spin-0 singlet and spin-2 quintet interaction channels naturally available for spin-3/2 systems. The two superconducting phases can be distinguished from each other by quasiparticle weight. We further discuss the properties of these phases for both two-dimensional square and three-dimensional cubic lattices at zero and finite temperatures.

Theory of metal-insulator transition in the family of perovskite iridium oxides

NASA Astrophysics Data System (ADS)

Carter, Jean-Michel; Shankar V., Vijay; Kee, Hae-Young

2013-07-01

Perovskite iridium oxides Srn+1IrnO3n+1 exhibit fascinating phenomena due to the combined effects of spin-orbit coupling (SOC) and electronic interactions. It was suggested that electronic correlation amplified via the strong SOC leads to a spin-orbit Mott insulator for n=1 and 2, while three-dimensional (3D) SrIrO3 remains metallic because of the large bandwidth from the 3D structure. However, this bandwidth-controlled metal-insulator transition (MIT) is only valid when SOC is large enough to split Jeff=1/2 and 3/2 bands, while the mixing of 1/2 and 3/2 bands is conspicuous among the occupied bands. Here, we investigate the MIT as a function of n using weak-coupling theory. In this approach, the magnetic instability is determined by the states near the Fermi level rather than the entire band structure. Starting from t2g tight-binding models for n=1, 2, and ∞, the states near the Fermi level are found to be predominantly Jeff=1/2 allowing an effective single-band model. Supplementing this effective Jeff=1/2 model with Hubbard-type interactions, transitions from a metal to magnetically ordered states are obtained. Strong-coupling spin models are derived to compare the magnetic ordering patterns obtained in the weak- and strong-coupling limits. We find that they are identical, indicating that these iridates are likely in an intermediate-coupling regime.

Finite mass enhancement across bandwidth controlled Mott transition in NiS2-xSex

NASA Astrophysics Data System (ADS)

Han, Garam; Kyung, W. S.; Kim, Y. K.; Cheng, C. M.; Tsuei, K. D.; Lee, K. D.; Hur, N.; Kim, H.-D.; Kim, C.

One of the most important and still debated issues in the strongly correlated electron systems is on the metal insulator transition (MIT) mechanism. In the bandwidth controlled Mott transition (BCMT) scenario, which Mott originally proposed, MIT occurs through a mass divergence in which the effective mass of the quasi-particle (QP) diverges approaching the MIT. The interpretation is supported by dynamic mean field theory (DMFT) model calculations. However, few direct observations have been made yet due to various experimental restrictions. In this talk, I present systematic angle resolved photoemission studies on the MIT in NiS2-xSex, which is a well-known BCMT material. We observed not only the bandwidth shrinkage but also the coherent quasi-particle peak (QP) which is not of the surface origin. In addition, we experimentally showed the mass of the QP remains finite approaching the MIT. This work was supported by IBS-R009-D1.

Photoinduced coherent acoustic phonon dynamics inside Mott insulator Sr2IrO4 films observed by femtosecond X-ray pulses

NASA Astrophysics Data System (ADS)

Zhang, Bing-Bing; Liu, Jian; Wei, Xu; Sun, Da-Rui; Jia, Quan-Jie; Li, Yuelin; Tao, Ye

2017-04-01

We investigate the transient photoexcited lattice dynamics in a layered perovskite Mott insulator Sr2IrO4 film by femtosecond X-ray diffraction using a laser plasma-based X-ray source. The ultrafast structural dynamics of Sr2IrO4 thin films are determined by observing the shift and broadening of (0012) Bragg diffraction after excitation by 1.5 eV and 3.0 eV pump photons for films with different thicknesses. The observed transient lattice response can be well interpreted as a distinct three-step dynamics due to the propagation of coherent acoustic phonons generated by photoinduced quasiparticles (QPs). Employing a normalized phonon propagation model, we found that the photoinduced angular shifts of the Bragg peak collapse into a universal curve after introducing normalized coordinates to account for different thicknesses and pump photon energies, pinpointing the origin of the lattice distortion and its early evolution. In addition, a transient photocurrent measurement indicates that the photoinduced QPs are charge neutral excitons. Mapping the phonon propagation and correlating its dynamics with the QP by ultrafast X-ray diffraction (UXRD) establish a powerful way to study electron-phonon coupling and uncover the exotic physics in strongly correlated systems under nonequilibrium conditions.

Nature of the insulating ground state of the 5d postperovskite CaIrO 3

DOE PAGES

Kim, Sun -Woo; Liu, Chen; Kim, Hyun -Jung; ...

2015-08-26

In this study, the insulating ground state of the 5d transition metal oxide CaIrO 3 has been classified as a Mott-type insulator. Based on a systematic density functional theory (DFT) study with local, semilocal, and hybrid exchange-correlation functionals, we reveal that the Ir t 2g states exhibit large splittings and one-dimensional electronic states along the c axis due to a tetragonal crystal field. Our hybrid DFT calculation adequately describes the antiferromagnetic (AFM) order along the c direction via a superexchange interaction between Ir 4+ spins. Furthermore, the spin-orbit coupling (SOC) hybridizes the t 2g states to open an insulating gap.more » These results indicate that CaIrO 3 can be represented as a spin-orbit Slater insulator, driven by the interplay between a long-range AFM order and the SOC. Such a Slater mechanism for the gap formation is also demonstrated by the DFT + dynamical mean field theory calculation, where the metal-insulator transition and the paramagnetic to AFM phase transition are concomitant with each other.« less

Interplay of long-range and short-range Coulomb interactions in an Anderson-Mott insulator

NASA Astrophysics Data System (ADS)

Baćani, Mirko; Novak, Mario; Orbanić, Filip; Prša, Krunoslav; Kokanović, Ivan; Babić, Dinko

2017-07-01

In this paper, we tackle the complexity of coexisting disorder and Coulomb electron-electron interactions (CEEIs) in solids by addressing a strongly disordered system with intricate CEEIs and a screening that changes both with charge carrier doping level Q and temperature T . We report on an experimental comparative study of the T dependencies of the electrical conductivity σ and magnetic susceptibility χ of polyaniline pellets doped with dodecylbenzenesulfonic acid over a wide range. This material is special within the class of doped polyaniline by exhibiting in the electronic transport a crossover between a low-T variable range hopping (VRH) and a high-T nearest-neighbor hopping (NNH) well below room temperature. Moreover, there is evidence of a soft Coulomb gap ΔC in the disorder band, which implies the existence of a long-range CEEI. Simultaneously, there is an onsite CEEI manifested as a Hubbard gap U and originating in the electronic structure of doped polyaniline, which consists of localized electron states with dynamically varying occupancy. Therefore, our samples represent an Anderson-Mott insulator in which long-range and short-range CEEIs coexist. The main result of the study is the presence of a crossover between low- and high-T regimes not only in σ (T ) but also in χ (T ) , the crossover temperature T* being essentially the same for both observables over the entire doping range. The relatively large electron localization length along the polymer chains results in U being small, between 12 and 20 meV for the high and low Q , respectively. Therefore, the thermal energy at T* is sufficiently large to lead to an effective closing of the Hubbard gap and the consequent appearance of NNH in the electronic transport within the disorder band. ΔC is considerably larger than U , decreasing from 190 to 30 meV as Q increases, and plays the role of an activation energy in the NNH.

Reliability of the one-crossing approximation in describing the Mott transition

NASA Astrophysics Data System (ADS)

Vildosola, V.; Pourovskii, L. V.; Manuel, L. O.; Roura-Bas, P.

2015-12-01

We assess the reliability of the one-crossing approximation (OCA) approach in a quantitative description of the Mott transition in the framework of the dynamical mean field theory (DMFT). The OCA approach has been applied in conjunction with DMFT to a number of heavy-fermion, actinide, transition metal compounds and nanoscale systems. However, several recent studies in the framework of impurity models pointed out serious deficiencies of OCA and raised questions regarding its reliability. Here we consider a single band Hubbard model on the Bethe lattice at finite temperatures and compare the results of OCA to those of a numerically exact quantum Monte Carlo (QMC) method. The temperature-local repulsion U phase diagram for the particle-hole symmetric case obtained by OCA is in good agreement with that of QMC, with the metal-insulator transition captured very well. We find, however, that the insulator to metal transition is shifted to higher values of U and, simultaneously, correlations in the metallic phase are significantly overestimated. This counter-intuitive behaviour is due to simultaneous underestimations of the Kondo scale in the metallic phase and the size of the insulating gap. We trace the underestimation of the insulating gap to that of the second moment of the high-frequency expansion of the impurity spectral density. Calculations of the system away from the particle-hole symmetric case are also presented and discussed.

Metal-insulator transition in CaVO3 thin films: Interplay between epitaxial strain, dimensional confinement, and surface effects

NASA Astrophysics Data System (ADS)

Beck, Sophie; Sclauzero, Gabriele; Chopra, Uday; Ederer, Claude

2018-02-01

We use density functional theory plus dynamical mean-field theory (DFT+DMFT) to study multiple control parameters for tuning the metal-insulator transition (MIT) in CaVO3 thin films. We focus on separating the effects resulting from substrate-induced epitaxial strain from those related to the reduced thickness of the film. We show that tensile epitaxial strain of around 3%-4% is sufficient to induce a transition to a paramagnetic Mott-insulating phase. This corresponds to the level of strain that could be achieved on a SrTiO3 substrate. Using free-standing slab models, we then demonstrate that reduced film thickness can also cause a MIT in CaVO3, however, only for thicknesses of less than 4 perovskite units. Our calculations indicate that the MIT in such ultrathin films results mainly from a surface-induced crystal-field splitting between the t2 g orbitals, favoring the formation of an orbitally polarized Mott insulator. This surface-induced crystal-field splitting is of the same type as the one resulting from tensile epitaxial strain, and thus the two effects can also cooperate. Furthermore, our calculations confirm an enhancement of correlation effects at the film surface, resulting in a reduced quasiparticle spectral weight in the outermost layer, whereas bulklike properties are recovered within only a few layers away from the surface.

Dielectric evidence for possible type-II multiferroicity in α-RuCl3

NASA Astrophysics Data System (ADS)

Zheng, JiaCheng; Cui, Yi; Li, TianRun; Ran, KeJing; Wen, JinSheng; Yu, WeiQiang

2018-05-01

$\\alpha$-RuCl$_3$ is a Mott insulator with a honeycomb lattice with strong spin-orbit coupling. We report dielectric measurements on $\\alpha$-RuCl$_3$ single crystals under field. At zero field, the dielectric constant, $\\epsilon$, drops rapidly when cooled through the magnetic transition temperature T$_N$. With increasing field, the onset of the drop in $\\epsilon$ tracks the T$_N$. Such behavior is absent with field above a critical value H$_c$ ~ 7.5 T, indicating the onset of a quantum phase transition. Our data suggest that the dielectric constant can be used as a probe of magnetic ordering in $\\alpha$-RuCl$_3$, and $\\alpha$-RuCl$_3$ is a possible type-II multiferroics.

Semiconductor of spinons: from Ising band insulator to orthogonal band insulator.

PubMed

Farajollahpour, T; Jafari, S A

2018-01-10

We use the ionic Hubbard model to study the effects of strong correlations on a two-dimensional semiconductor. The spectral gap in the limit where on-site interactions are zero is set by the staggered ionic potential, while in the strong interaction limit it is set by the Hubbard U. Combining mean field solutions of the slave spin and slave rotor methods, we propose two interesting gapped phases in between: (i) the insulating phase before the Mott phase can be viewed as gapping a non-Fermi liquid state of spinons by the staggered ionic potential. The quasi-particles of underlying spinons are orthogonal to physical electrons, giving rise to the 'ARPES-dark' state where the ARPES gap will be larger than the optical and thermal gap. (ii) The Ising insulator corresponding to ordered phase of the Ising variable is characterized by single-particle excitations whose dispersion is controlled by Ising-like temperature and field dependences. The temperature can be conveniently employed to drive a phase transition between these two insulating phases where Ising exponents become measurable by ARPES and cyclotron resonance. The rare earth monochalcogenide semiconductors where the magneto-resistance is anomalously large can be a candidate system for the Ising band insulator. We argue that the Ising and orthogonal insulating phases require strong enough ionic potential to survive the downward renormalization of the ionic potential caused by Hubbard U.

Semiconductor of spinons: from Ising band insulator to orthogonal band insulator

NASA Astrophysics Data System (ADS)

Farajollahpour, T.; Jafari, S. A.

2018-01-01

We use the ionic Hubbard model to study the effects of strong correlations on a two-dimensional semiconductor. The spectral gap in the limit where on-site interactions are zero is set by the staggered ionic potential, while in the strong interaction limit it is set by the Hubbard U. Combining mean field solutions of the slave spin and slave rotor methods, we propose two interesting gapped phases in between: (i) the insulating phase before the Mott phase can be viewed as gapping a non-Fermi liquid state of spinons by the staggered ionic potential. The quasi-particles of underlying spinons are orthogonal to physical electrons, giving rise to the ‘ARPES-dark’ state where the ARPES gap will be larger than the optical and thermal gap. (ii) The Ising insulator corresponding to ordered phase of the Ising variable is characterized by single-particle excitations whose dispersion is controlled by Ising-like temperature and field dependences. The temperature can be conveniently employed to drive a phase transition between these two insulating phases where Ising exponents become measurable by ARPES and cyclotron resonance. The rare earth monochalcogenide semiconductors where the magneto-resistance is anomalously large can be a candidate system for the Ising band insulator. We argue that the Ising and orthogonal insulating phases require strong enough ionic potential to survive the downward renormalization of the ionic potential caused by Hubbard U.

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

Zhu, M.; Peng, J.; Zou, T.

Here, we present a new type of colossal magnetoresistance (CMR) arising from an anomalous collapse of the Mott insulating state via a modest magnetic field in a bilayer ruthenate, Ti-doped Ca 3Ru 2O 7. Such an insulator-metal transition is accompanied by changes in both lattice and magnetic structures. Our findings have important implications because a magnetic field usually stabilizes the insulating ground state in a Mott-Hubbard system, thus calling for a deeper theoretical study to reexamine the magnetic field tuning of Mott systems with magnetic and electronic instabilities and spin-lattice-charge coupling. This study further provides a model approach to searchmore » for CMR systems other than manganites, such as Mott insulators in the vicinity of the boundary between competing phases.« less

Foundations of heavy-fermion superconductivity: lattice Kondo effect and Mott physics

NASA Astrophysics Data System (ADS)

Steglich, Frank; Wirth, Steffen

2016-08-01

This article overviews the development of heavy-fermion superconductivity, notably in such rare-earth-based intermetallic compounds which behave as Kondo-lattice systems. Heavy-fermion superconductivity is of unconventional nature in the sense that it is not mediated by electron-phonon coupling. Rather, in most cases the attractive interaction between charge carriers is apparently magnetic in origin. Fluctuations associated with an antiferromagnetic (AF) quantum critical point (QCP) play a major role. The first heavy-fermion superconductor CeCu2Si2 turned out to be the prototype of a larger group of materials for which the underlying, often pressure-induced, AF QCP is likely to be of a three-dimensional (3D) spin-density-wave (SDW) variety. For UBe13, the second heavy-fermion superconductor, a magnetic-field-induced 3D SDW QCP inside the superconducting phase can be conjectured. Such a ‘conventional’, itinerant QCP can be well understood within Landau’s paradigm of order-parameter fluctuations. In contrast, the low-temperature normal-state properties of a few heavy-fermion superconductors are at odds with the Landau framework. They are characterized by an ‘unconventional’, local QCP which may be considered a zero-temperature 4 f-orbital selective Mott transition. Here, as concluded for YbRh2Si2, the breakdown of the Kondo effect concurring with the AF instability gives rise to an abrupt change of the Fermi surface. Very recently, superconductivity was discovered for this compound at ultra-low temperatures. Therefore, YbRh2Si2 along with CeRhIn5 under pressure provide a natural link between the large group of about fifty low-temperature heavy-fermion superconductors and other families of unconventional superconductors with substantially higher T c, e.g. the doped Mott insulators of the perovskite-type cuprates and the organic charge-transfer salts.

Foundations of heavy-fermion superconductivity: lattice Kondo effect and Mott physics.

PubMed

Steglich, Frank; Wirth, Steffen

2016-08-01

This article overviews the development of heavy-fermion superconductivity, notably in such rare-earth-based intermetallic compounds which behave as Kondo-lattice systems. Heavy-fermion superconductivity is of unconventional nature in the sense that it is not mediated by electron-phonon coupling. Rather, in most cases the attractive interaction between charge carriers is apparently magnetic in origin. Fluctuations associated with an antiferromagnetic (AF) quantum critical point (QCP) play a major role. The first heavy-fermion superconductor CeCu2Si2 turned out to be the prototype of a larger group of materials for which the underlying, often pressure-induced, AF QCP is likely to be of a three-dimensional (3D) spin-density-wave (SDW) variety. For UBe13, the second heavy-fermion superconductor, a magnetic-field-induced 3D SDW QCP inside the superconducting phase can be conjectured. Such a 'conventional', itinerant QCP can be well understood within Landau's paradigm of order-parameter fluctuations. In contrast, the low-temperature normal-state properties of a few heavy-fermion superconductors are at odds with the Landau framework. They are characterized by an 'unconventional', local QCP which may be considered a zero-temperature 4 f-orbital selective Mott transition. Here, as concluded for YbRh2Si2, the breakdown of the Kondo effect concurring with the AF instability gives rise to an abrupt change of the Fermi surface. Very recently, superconductivity was discovered for this compound at ultra-low temperatures. Therefore, YbRh2Si2 along with CeRhIn5 under pressure provide a natural link between the large group of about fifty low-temperature heavy-fermion superconductors and other families of unconventional superconductors with substantially higher T c, e.g. the doped Mott insulators of the perovskite-type cuprates and the organic charge-transfer salts.

Holographic superconductor on a novel insulator

NASA Astrophysics Data System (ADS)

Ling, Yi; Liu, Peng; Wu, Jian-Pin; Wu, Meng-He

2018-01-01

We construct a holographic superconductor model, based on a gravity theory, which exhibits novel metal-insulator transitions. We investigate the condition for the condensation of the scalar field over the parameter space, and then focus on the superconductivity over the insulating phase with a hard gap, which is supposed to be Mott-like. It turns out that the formation of the hard gap in the insulating phase benefits the superconductivity. This phenomenon is analogous to the fact that the pseudogap phase can promote the pre-pairing of electrons in high {T}{{c}} cuprates. We expect that this work can shed light on understanding the mechanism of high {T}{{c}} superconductivity from the holographic side. Supported by Natural Science Foundation of China (11575195, 11775036, 11305018), Y.L. also acknowledges the support from Jiangxi young scientists (JingGang Star) program and 555 talent project of Jiangxi Province. J. P. Wu is also supported by Natural Science Foundation of Liaoning Province (201602013)

Tuning metal-insulator behavior in LaTiO3/SrTiO3 heterostructures integrated directly on Si(100) through control of atomic layer thickness

NASA Astrophysics Data System (ADS)

Ahmadi-Majlan, Kamyar; Chen, Tongjie; Lim, Zheng Hui; Conlin, Patrick; Hensley, Ricky; Chrysler, Matthew; Su, Dong; Chen, Hanghui; Kumah, Divine P.; Ngai, Joseph H.

2018-05-01

We present electrical and structural characterization of epitaxial LaTiO3/SrTiO3 heterostructures integrated directly on Si(100). By reducing the thicknesses of the heterostructures, an enhancement in carrier-carrier scattering is observed in the Fermi liquid behavior, followed by a metal to insulator transition in the electrical transport. The insulating behavior is described by activated transport, and its onset occurs near an occupation of 1 electron per Ti site within the SrTiO3, providing evidence for a Mott driven transition. We also discuss the role that structure and gradients in strain could play in enhancing the carrier density. The manipulation of Mott metal-insulator behavior in oxides grown directly on Si opens the pathway to harnessing strongly correlated phenomena in device technologies.

A Review on Disorder-Driven Metal-Insulator Transition in Crystalline Vacancy-Rich GeSbTe Phase-Change Materials.

PubMed

Wang, Jiang-Jing; Xu, Ya-Zhi; Mazzarello, Riccardo; Wuttig, Matthias; Zhang, Wei

2017-07-27

Metal-insulator transition (MIT) is one of the most essential topics in condensed matter physics and materials science. The accompanied drastic change in electrical resistance can be exploited in electronic devices, such as data storage and memory technology. It is generally accepted that the underlying mechanism of most MITs is an interplay of electron correlation effects (Mott type) and disorder effects (Anderson type), and to disentangle the two effects is difficult. Recent progress on the crystalline Ge₁Sb₂Te₄ (GST) compound provides compelling evidence for a disorder-driven MIT. In this work, we discuss the presence of strong disorder in GST, and elucidate its effects on electron localization and transport properties. We also show how the degree of disorder in GST can be reduced via thermal annealing, triggering a disorder-driven metal-insulator transition. The resistance switching by disorder tuning in crystalline GST may enable novel multilevel data storage devices.

A difference in using atomic layer deposition or physical vapour deposition TiN as electrode material in metal-insulator-metal and metal-insulator-silicon capacitors.

PubMed

Groenland, A W; Wolters, R A M; Kovalgin, A Y; Schmitz, J

2011-09-01

In this work, metal-insulator-metal (MIM) and metal-insulator-silicon (MIS) capacitors are studied using titanium nitride (TiN) as the electrode material. The effect of structural defects on the electrical properties on MIS and MIM capacitors is studied for various electrode configurations. In the MIM capacitors the bottom electrode is a patterned 100 nm TiN layer (called BE type 1), deposited via sputtering, while MIS capacitors have a flat bottom electrode (called BE type 2-silicon substrate). A high quality 50-100 nm thick SiO2 layer, made by inductively-coupled plasma CVD at 150 degrees C, is deposited as a dielectric on top of both types of bottom electrodes. BE type 1 (MIM) capacitors have a varying from low to high concentration of structural defects in the SiO2 layer. BE type 2 (MIS) capacitors have a low concentration of structural defects and are used as a reference. Two sets of each capacitor design are fabricated with the TiN top electrode deposited either via physical vapour deposition (PVD, i.e., sputtering) or atomic layer deposition (ALD). The MIM and MIS capacitors are electrically characterized in terms of the leakage current at an electric field of 0.1 MV/cm (I leak) and for different structural defect concentrations. It is shown that the structural defects only show up in the electrical characteristics of BE type 1 capacitors with an ALD TiN-based top electrode. This is due to the excellent step coverage of the ALD process. This work clearly demonstrates the sensitivity to process-induced structural defects, when ALD is used as a step in process integration of conductors on insulation materials.

Magnetically driven metal-insulator transition in NaOsO3

NASA Astrophysics Data System (ADS)

Calder, Stuart

2013-03-01

The metal-insulator transition (MIT) is one of the most dramatic manifestations of electron correlations in materials, enjoying interest both for its fundamental nature and technological application. Various mechanisms producing MITs have been extensively considered over the years, including the Mott (electron localization via Coulomb repulsion), Anderson (localization via disorder) and Peierls (localization via distortion of a periodic one-dimensional lattice). One additional route to a MIT proposed by Slater in 1951, in which long-range magnetic order in a three dimensional system drives the MIT, has received relatively little attention, particularly from an experimental viewpoint. Using neutron and x-ray scattering we have shown that the MIT in NaOsO3 is coincident with the onset of long-range commensurate magnetic order at 410 K. Whilst candidate materials have been suggested, our experimental methodology allows the first definitive demonstration of the long predicted Slater MIT. We discuss our results in light of recent work on other 5d systems that contrastingly have been predicted to host a Mott spin-orbit insulating state. Work was supported by the Scientific User Facilities Division, Office of Basic Energy Sciences, U.S. Department of Energy (DOE).

Ambipolar surface state thermoelectric power of topological insulator Bi2Se3.

PubMed

Kim, Dohun; Syers, Paul; Butch, Nicholas P; Paglione, Johnpierre; Fuhrer, Michael S

2014-01-01

We measure gate-tuned thermoelectric power of mechanically exfoliated Bi2Se3 thin films in the topological insulator regime. The sign of the thermoelectric power changes across the charge neutrality point as the majority carrier type switches from electron to hole, consistent with the ambipolar electric field effect observed in conductivity and Hall effect measurements. Near the charge neutrality point and at low temperatures, the gate-dependent thermoelectric power follows the semiclassical Mott relation using the expected surface state density of states but is larger than expected at high electron doping, possibly reflecting a large density of states in the bulk gap. The thermoelectric power factor shows significant enhancement near the electron-hole puddle carrier density ∼0.5 × 10(12) cm(-2) per surface at all temperatures. Together with the expected reduction of lattice thermal conductivity in low-dimensional structures, the results demonstrate that nanostructuring and Fermi level tuning of three-dimensional topological insulators can be promising routes to realize efficient thermoelectric devices.

Electronic correlation in the infrared optical properties of the quasi-two-dimensional κ-type BEDT-TTF dimer system

NASA Astrophysics Data System (ADS)

Sasaki, T.; Ito, I.; Yoneyama, N.; Kobayashi, N.; Hanasaki, N.; Tajima, H.; Ito, T.; Iwasa, Y.

2004-02-01

The polarized optical reflectance spectra of the quasi-two-dimensional organic correlated electron system κ-(BEDT-TTF)2Cu[N(CN)2]Y, Y=Br and Cl are measured in the infrared region. The former shows the superconductivity at Tc≃11.6 K and the latter does the antiferromagnetic insulator transition at TN≃28 K. Both the specific molecular vibration mode ν3(ag) of the BEDT-TTF molecule and the optical conductivity hump in the mid-infrared region change correlatively at T*≃38 K of κ-(BEDT-TTF)2Cu[N(CN)2]Br, although no indication of T* but the insulating behavior below Tins≃50 60 K are found in κ-(BEDT-TTF)2Cu[N(CN)2]Cl. The results suggest that the electron-molecular vibration coupling on the ν3(ag) mode becomes weak due to the enhancement of the itinerant nature of the carriers on the dimer of the BEDT-TTF molecules below T*, while it does strong below Tins because of the localized carriers on the dimer. These changes are in agreement with the reduction and the enhancement of the mid-infrared conductivity hump below T* and Tins, respectively, which originates from the transitions between the upper and lower Mott-Hubbard bands. The present observations demonstrate that two different metallic states of κ-(BEDT-TTF)2Cu[N(CN)2]Br are regarded as a correlated good metal below T* including the superconducting state and a half filling bad metal above T*. In contrast the insulating state of κ-(BEDT-TTF)2Cu[N(CN)2]Cl below Tins is the Mott insulator.

Superfluid and Insulating Phases of Fermion Mixtures in Optical Lattices

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

Iskin, M.; Sa de Melo, C. A. R.

2007-08-24

The ground state phase diagram of fermion mixtures in optical lattices is analyzed as a function of interaction strength, fermion filling factor, and tunneling parameters. In addition to standard superfluid, phase-separated or coexisting superfluid-excess-fermion phases found in homogeneous or harmonically trapped systems, fermions in optical lattices have several insulating phases, including a molecular Bose-Mott insulator (BMI), a Fermi-Pauli (band) insulator (FPI), a phase-separated BMI-FPI mixture or a Bose-Fermi checkerboard (BFC). The molecular BMI phase is the fermion mixture counterpart of the atomic BMI found in atomic Bose systems, the BFC or BMI-FPI phases exist in Bose-Fermi mixtures, and lastly themore » FPI phase is particular to the Fermi nature of the constituent atoms of the mixture.« less

Superfluid-insulator transition in a disordered two-dimensional quantum rotor model with random on-site interactions

NASA Astrophysics Data System (ADS)

An, Taeyang; Cha, Min-Chul

2013-03-01

We study the superfluid-insulator quantum phase transition in a disordered two-dimensional quantum rotor model with random on-site interactions in the presence of particle-hole symmetry. Via worm-algorithm Monte Carlo calculations of superfluid density and compressibility, we find the dynamical critical exponent z ~ 1 . 13 (2) and the correlation length critical exponent 1 / ν ~ 1 . 1 (1) . These exponents suggest that the insulating phase is a incompressible Mott glass rather than a Bose glass.

A Review on Disorder-Driven Metal–Insulator Transition in Crystalline Vacancy-Rich GeSbTe Phase-Change Materials

PubMed Central

Wang, Jiang-Jing; Xu, Ya-Zhi; Mazzarello, Riccardo; Wuttig, Matthias; Zhang, Wei

2017-01-01

Metal–insulator transition (MIT) is one of the most essential topics in condensed matter physics and materials science. The accompanied drastic change in electrical resistance can be exploited in electronic devices, such as data storage and memory technology. It is generally accepted that the underlying mechanism of most MITs is an interplay of electron correlation effects (Mott type) and disorder effects (Anderson type), and to disentangle the two effects is difficult. Recent progress on the crystalline Ge1Sb2Te4 (GST) compound provides compelling evidence for a disorder-driven MIT. In this work, we discuss the presence of strong disorder in GST, and elucidate its effects on electron localization and transport properties. We also show how the degree of disorder in GST can be reduced via thermal annealing, triggering a disorder-driven metal–insulator transition. The resistance switching by disorder tuning in crystalline GST may enable novel multilevel data storage devices. PMID:28773222

Origin of positive fixed charge at insulator/AlGaN interfaces and its control by AlGaN composition

NASA Astrophysics Data System (ADS)

Matys, M.; Stoklas, R.; Blaho, M.; Adamowicz, B.

2017-06-01

The key feature for the precise tuning of Vth in GaN-based metal-insulator-semiconductor (MIS) high electron mobility transistors is the control of the positive fixed charge (Qf) at the insulator/III-N interfaces, whose amount is often comparable to the negative surface polarization charge ( Qp o l -). In order to clarify the origin of Qf, we carried out a comprehensive capacitance-voltage (C-V) characterization of SiO2/AlxGa1-xN/GaN and SiN/AlxGa1-xN/GaN structures with Al composition (x) varying from 0.15 to 0.4. For both types of structures, we observed a significant Vth shift in C-V curves towards the positive gate voltage with increasing x. On the contrary, the Schottky gate structures exhibited Vth shift towards the more negative biases. From the numerical simulations of C-V curves using the Poisson's equation supported by the analytical calculations of Vth, we showed that the Vth shift in the examined MIS structures is due to a significant decrease in the positive Qf with rising x. Finally, we examined this result with respect to various hypotheses developed in the literature to explain the origin of the positive Qf at insulator/III-N interfaces.

Nonlocal correlations in the orbital selective Mott phase of a one-dimensional multiorbital Hubbard model

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

Li, S.; Kaushal, N.; Wang, Y.

Here, we study nonlocal correlations in a three-orbital Hubbard model defined on an extended one-dimensional chain using determinant quantum Monte Carlo and density matrix renormalization group methods. We focus on a parameter regime with robust Hund's coupling, which produces an orbital selective Mott phase (OSMP) at intermediate values of the Hubbard U, as well as an orbitally ordered ferromagnetic insulating state at stronger coupling. An examination of the orbital- and spin-correlation functions indicates that the orbital ordering occurs before the onset of magnetic correlations in this parameter regime as a function of temperature. In the OSMP, we find that themore » self-energy for the itinerant electrons is momentum dependent, indicating a degree of nonlocal correlations while the localized electrons have largely momentum independent self-energies. These nonlocal correlations also produce relative shifts of the holelike and electronlike bands within our model. The overall momentum dependence of these quantities is strongly suppressed in the orbitally ordered insulating phase.« less

Nonlocal correlations in the orbital selective Mott phase of a one-dimensional multiorbital Hubbard model

DOE PAGES

Li, S.; Kaushal, N.; Wang, Y.; ...

2016-12-12

Here, we study nonlocal correlations in a three-orbital Hubbard model defined on an extended one-dimensional chain using determinant quantum Monte Carlo and density matrix renormalization group methods. We focus on a parameter regime with robust Hund's coupling, which produces an orbital selective Mott phase (OSMP) at intermediate values of the Hubbard U, as well as an orbitally ordered ferromagnetic insulating state at stronger coupling. An examination of the orbital- and spin-correlation functions indicates that the orbital ordering occurs before the onset of magnetic correlations in this parameter regime as a function of temperature. In the OSMP, we find that themore » self-energy for the itinerant electrons is momentum dependent, indicating a degree of nonlocal correlations while the localized electrons have largely momentum independent self-energies. These nonlocal correlations also produce relative shifts of the holelike and electronlike bands within our model. The overall momentum dependence of these quantities is strongly suppressed in the orbitally ordered insulating phase.« less

B a2NiOs O6 : A Dirac-Mott insulator with ferromagnetism near 100 K

NASA Astrophysics Data System (ADS)

Feng, Hai L.; Calder, Stuart; Ghimire, Madhav Prasad; Yuan, Ya-Hua; Shirako, Yuichi; Tsujimoto, Yoshihiro; Matsushita, Yoshitaka; Hu, Zhiwei; Kuo, Chang-Yang; Tjeng, Liu Hao; Pi, Tun-Wen; Soo, Yun-Liang; He, Jianfeng; Tanaka, Masahiko; Katsuya, Yoshio; Richter, Manuel; Yamaura, Kazunari

2016-12-01

The ferromagnetic semiconductor B a2NiOs O6 (Tmag˜100 K ) was synthesized at 6 GPa and 1500 °C. It crystallizes into a double perovskite structure [F m -3 m ; a =8.0428 (1 )Å ], where the N i2 + and O s6 + ions are perfectly ordered at the perovskite B site. We show that the spin-orbit coupling of O s6 + plays an essential role in opening the charge gap. The magnetic state was investigated by density functional theory calculations and powder neutron diffraction. The latter revealed a collinear ferromagnetic order in a >21 kOe magnetic field at 5 K. The ferromagnetic gapped state is fundamentally different from that of known dilute magnetic semiconductors such as (Ga,Mn)As and (Cd,Mn)Te (Tmag<180 K ), the spin-gapless semiconductor M n2CoAl (Tmag˜720 K ), and the ferromagnetic insulators EuO (Tmag˜70 K ) and B i3C r3O11 (Tmag˜220 K ). It is also qualitatively different from known ferrimagnetic insulators and semiconductors, which are characterized by an antiparallel spin arrangement. Our finding of the ferromagnetic semiconductivity of B a2NiOs O6 should increase interest in the platinum group oxides, because this alternative class of materials should be useful in the development of spintronic, quantum magnetic, and related devices.

Dynamic Jahn-Teller effect in the parent insulating state of the molecular superconductor Cs₃C₆₀.

PubMed

Klupp, Gyöngyi; Matus, Péter; Kamarás, Katalin; Ganin, Alexey Y; McLennan, Alec; Rosseinsky, Matthew J; Takabayashi, Yasuhiro; McDonald, Martin T; Prassides, Kosmas

2012-06-19

The 'expanded fulleride' Cs(3)C(60) is an antiferromagnetic insulator in its normal state and becomes a molecular superconductor with T(c) as high as 38 K under pressure. There is mounting evidence that superconductivity is not of the conventional BCS type and electron-electron interactions are essential for its explanation. Here we present evidence for the dynamic Jahn-Teller effect as the source of the dramatic change in electronic structure occurring during the transition from the metallic to the localized state. We apply infrared spectroscopy, which can detect subtle changes in the shape of the C(60)3- ion due to the Jahn-Teller distortion. The temperature dependence of the spectra in the insulating phase can be explained by the gradual transformation from two temperature-dependent solid-state conformers to a single one, typical and unique for Jahn-Teller systems. These results unequivocally establish the relevance of the dynamic Jahn-Teller effect to overcoming Hund's rule and forming a low-spin state, leading to a magnetic Mott-Jahn-Teller insulator.

Electronic localization in an extreme 1-D conductor: the organic salt (TTDM-TTF) Type="Bold"/> [Au(mnt) Type="Bold"/>

NASA Astrophysics Data System (ADS)

Lopes, E. B.; Alves, H.; Ribera, E.; Mas-Torrent, M.; Auban-Senzier, P.; Canadell, E.; Henriques, R. T.; Almeida, M.; Molins, E.; Veciana, J.; Rovira, C.; Jérome, D.

2002-09-01

This article reports the investigation of a new low-dimensional organic salt, (TTDM-TTF)2 [ Au(mnt)2] , by single crystal X-ray diffraction, static magnetic susceptibility, EPR, thermopower, electrical resistivity measurements under pressure up to 25 kbar and band structure calculations. The crystal structure consists in a dimerized head to tail stacking of TTDM-TTF molecules separated by layers of orthogonal Au(mnt)2 anions. The absence of overlap between neighboring chains coming from this particular crystal structure leads to an extreme one-dimensionality (1-D) for which the carriers of the half-filled conduction band become strongly localized in a Mott-Hubbard insulating state. This material is the first 1-D conductor in which the Mott-Hubbard insulating character cannot be suppressed under pressure.

Strain-induced insulator-to-metal transition in LaTiO3 within DFT + DMFT

NASA Astrophysics Data System (ADS)

Dymkowski, Krzysztof; Ederer, Claude

2014-04-01

We present results of combined density functional theory plus dynamical mean-field theory (DFT + DMFT) calculations, which show that the Mott insulator LaTiO3 undergoes an insulator-to-metal transition under compressive epitaxial strain of about -2%. This transition is driven by strain-induced changes in the crystal-field splitting between the Ti t2g orbitals, which in turn are intimately related to the collective tilts and rotations of the oxygen octahedra in the orthorhombically distorted Pbnm perovskite structure. An accurate treatment of the underlying crystal structure is therefore crucial for a correct description of the observed metal-insulator transition. Our theoretical results are consistent with recent experimental observations and demonstrate that metallic behavior in heterostructures of otherwise insulating materials can emerge also from mechanisms other than genuine interface effects.

Semi-insulating 4H-SiC layers formed by the implantation of high-energy (53 MeV) argon ions into n-type epitaxial films

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

Ivanov, P. A., E-mail: Pavel.Ivanov@mail.ioffe.ru; Kudoyarov, M. F.; Kozlovski, M. A.

It is shown that 9-μm-thick semi-insulating surface layers can be formed in moderately doped n-type silicon carbide (donor concentration 2 × 10{sup 16} cm{sup –3}) via the comparatively low-dose (7 × 10{sup 11} cm{sup –2}) implantation of high-energy (53 MeV) argon ions. The free-carrier removal rate is estimated at ~10{sup 4} cm{sup –1}. The resistivity of the semi-insulator is no less than 7 × 10{sup 12} Ω cm. Analysis of the monopolar current of electron injection into the semi-insulator shows that the impurity-conductivity compensation is due to radiation induced defects pinning the equilibrium Fermi level at a depth of 1.16more » eV below the conduction-band bottom. The density of defect states at the Fermi level is 2.7 × 10{sup 16} cm{sup 2} eV{sup –1}.« less

Engineered Mott ground state in a LaTiO3+δ/LaNiO3 heterostructure

NASA Astrophysics Data System (ADS)

Cao, Yanwei; Liu, Xiaoran; Kareev, M.; Choudhury, D.; Middey, S.; Meyers, D.; Kim, J.-W.; Ryan, P. J.; Freeland, J. W.; Chakhalian, J.

2016-01-01

In pursuit of creating cuprate-like electronic and orbital structures, artificial heterostructures based on LaNiO3 have inspired a wealth of exciting experimental and theoretical results. However, to date there is a very limited experimental understanding of the electronic and orbital states emerging from interfacial charge transfer and their connections to the modified band structure at the interface. Towards this goal, we have synthesized a prototypical superlattice composed of a correlated metal LaNiO3 and a doped Mott insulator LaTiO3+δ, and investigated its electronic structure by resonant X-ray absorption spectroscopy combined with X-ray photoemission spectroscopy, electrical transport and theory calculations. The heterostructure exhibits interfacial charge transfer from Ti to Ni sites, giving rise to an insulating ground state with orbital polarization and eg orbital band splitting. Our findings demonstrate how the control over charge at the interface can be effectively used to create exotic electronic, orbital and spin states.

Engineered Mott ground state in a LaTiO3+δ/LaNiO3 heterostructure

PubMed Central

Cao, Yanwei; Liu, Xiaoran; Kareev, M.; Choudhury, D.; Middey, S.; Meyers, D.; Kim, J.-W.; Ryan, P. J.; Freeland, J.W.; Chakhalian, J.

2016-01-01

In pursuit of creating cuprate-like electronic and orbital structures, artificial heterostructures based on LaNiO3 have inspired a wealth of exciting experimental and theoretical results. However, to date there is a very limited experimental understanding of the electronic and orbital states emerging from interfacial charge transfer and their connections to the modified band structure at the interface. Towards this goal, we have synthesized a prototypical superlattice composed of a correlated metal LaNiO3 and a doped Mott insulator LaTiO3+δ, and investigated its electronic structure by resonant X-ray absorption spectroscopy combined with X-ray photoemission spectroscopy, electrical transport and theory calculations. The heterostructure exhibits interfacial charge transfer from Ti to Ni sites, giving rise to an insulating ground state with orbital polarization and eg orbital band splitting. Our findings demonstrate how the control over charge at the interface can be effectively used to create exotic electronic, orbital and spin states. PMID:26791402

Engineered Mott ground state in a LaTiO 3+δ/LaNiO 3 heterostructure

DOE PAGES

Cao, Yanwei; Liu, Xiaoran; Kareev, M.; ...

2016-01-21

In pursuit of creating cuprate-like electronic and orbital structures, artificial heterostructures based on LaNiO 3 have inspired a wealth of exciting experimental and theoretical results. However, to date there is a very limited experimental understanding of the electronic and orbital states emerging from interfacial charge transfer and their connections to the modified band structure at the interface. Towards this goal, we have synthesized a prototypical superlattice composed of a correlated metal LaNiO 3 and a doped Mott insulator LaTiO 3+δ, and investigated its electronic structure by resonant X-ray absorption spectroscopy combined with X-ray photoemission spectroscopy, electrical transport and theory calculations.more » The heterostructure exhibits interfacial charge transfer from Ti to Ni sites, giving rise to an insulating ground state with orbital polarization and e g orbital band splitting. Here, our findings demonstrate how the control over charge at the interface can be effectively used to create exotic electronic, orbital and spin states.« less

Quantum fluctuations and the closing of the Coulomb gap in a correlated insulator.

PubMed

Roy, A S; Hoekstra, A F Th; Rosenbaum, T F; Griessen, R

2002-12-30

The "switchable mirror" yttrium hydride is one of the few strongly correlated systems with a continuous Mott-Hubbard metal-insulator transition. We systematically map out the low temperature electrical transport from deep in the insulator to the quantum critical point using persistent photoconductivity as a drive parameter. Both activated hopping over a Coulomb gap and power-law quantum fluctuations must be included to describe the data. Collapse of the data onto a universal curve within a dynamical scaling framework (with corrections) requires znu=6.0+/-0.5, where nu and z are the static and dynamical critical exponents, respectively.

Carrier and photon dynamics in a topological insulator Bi{sub 2}Te{sub 3}/GaN type II staggered heterostructure

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

Chaturvedi, P.; Chouksey, S.; Banerjee, D.

2015-11-09

We have demonstrated a type-II band-aligned heterostructure between pulsed laser deposited topological insulator bismuth telluride and metal organic-chemical-vapour deposited GaN on a sapphire substrate. The heterostructure shows a large valence band-offset of 3.27 eV as determined from x-ray photoelectron spectroscopy, which is close to the bandgap of GaN (3.4 eV). Further investigation using x-ray diffraction, Raman spectroscopy, and energy-dispersive x-ray spectrum reveals the stoichiometric and material properties of bismuth telluride on GaN. Steady state photon emission from GaN is found to be modulated by the charge transfer process due to diffusion across the junction. The time constant involved with the charge transfermore » process is found to be 0.6 ns by transient absorption spectroscopy. The heterostructure can be used for designing devices with different functionalities and improving the performance of the existing devices on GaN.« less

Understanding Metal-Insulator transitions in ultra-thin films of LaNiO3

NASA Astrophysics Data System (ADS)

Ravichandran, Jayakanth; King, Philip D. C.; Schlom, Darrell G.; Shen, Kyle M.; Kim, Philip

2014-03-01

LaNiO3 (LNO) is a bulk paramagnetic metal and a member of the family of RENiO3 Nickelates (RE = Rare Earth Metals), which is on the verge of the metal-insulator transition. Ultra-thin films of LNO has been studied extensively in the past and due to its sensitivity to disorder, the true nature of the metal-insulator transition in these films have been hard to decipher. We grow high quality ultra-thin films of LNO using reactive molecular beam epitaxy (MBE) and use a combination of ionic liquid gating and magneto-transport measurements to understand the nature and tunability of metal-insulator transition as a function of thickness for LNO. The underlying mechanisms for the transition are discussed in the framework of standard transport models. These results are discussed in the light of other Mott insulators such as Sr2IrO4, where we have performed similar measurements around the insulating state.

Electronic structure properties of UO2 as a Mott insulator

NASA Astrophysics Data System (ADS)

Sheykhi, Samira; Payami, Mahmoud

2018-06-01

In this work using the density functional theory (DFT), we have studied the structural, electronic and magnetic properties of uranium dioxide with antiferromagnetic 1k-, 2k-, and 3k-order structures. Ordinary approximations in DFT, such as the local density approximation (LDA) or generalized gradient approximation (GGA), usually predict incorrect metallic behaviors for this strongly correlated electron system. Using Hubbard term correction for f-electrons, LDA+U method, as well as using the screened Heyd-Scuseria-Ernzerhof (HSE) hybrid functional for the exchange-correlation (XC), we have obtained the correct ground-state behavior as an insulator, with band gaps in good agreement with experiment.

Evaluation of the density of the charge trapped in organic ferroelectric capacitors based on the Mott-Schottky model

NASA Astrophysics Data System (ADS)

Kim, Won-Ho; Kwon, Jin-Hyuk; Park, Gyeong-Tae; Kim, Jae-Hyun; Bae, Jin-Hyuk; Zhang, Xue; Park, Jaehoon

2014-09-01

Organic ferroelectric capacitors were fabricated using pentacene and poly(vinylidene fluoride-trifluoroethylene) (PVDF-TrFE) as an organic semiconductor and a ferroelectric material, respectively. A paraelectric poly(vinyl cinnamate) layer was adopted as an interlayer between the PVDF-TrFE layer and the bottom electrode. The paraelectric interlayer induced a depolarization field opposite to the direction of the polarization formed in the ferroelectric PVDF-TrFE insulator, thereby suppressing spontaneous polarization. As a result, the Mott-Schottky model could be used to evaluate, from the extracted flat-band voltages, the density of the charge trapped in the organic ferroelectric capacitors.

Tuning metal-insulator behavior in LaTiO 3/SrTiO 3 heterostructures integrated directly on Si(100) through control of atomic layer thickness

DOE PAGES

Ahmadi-Majlan, Kamyar; Chen, Tongjie; Lim, Zheng Hui; ...

2018-05-07

Here, we present electrical and structural characterization of epitaxial LaTiO 3/SrTiO 3 heterostructures integrated directly on Si(100). By reducing the thicknesses of the heterostructures, an enhancement in carrier-carrier scattering is observed in the Fermi liquid behavior, followed by a metal to insulator transition in the electrical transport. The insulating behavior is described by activated transport, and its onset occurs near 1 electron per Ti occupation within the SrTiO 3 well, providing evidence for a Mott driven transition. We also discuss the role that structure and gradients in strain could play in enhancing the carrier density. The manipulation of Mott metal-insulatormore » behavior in oxides grown directly on Si opens the pathway to harnessing strongly correlated phenomena in device technologies.« less

Tuning metal-insulator behavior in LaTiO 3/SrTiO 3 heterostructures integrated directly on Si(100) through control of atomic layer thickness

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

Ahmadi-Majlan, Kamyar; Chen, Tongjie; Lim, Zheng Hui

Here, we present electrical and structural characterization of epitaxial LaTiO 3/SrTiO 3 heterostructures integrated directly on Si(100). By reducing the thicknesses of the heterostructures, an enhancement in carrier-carrier scattering is observed in the Fermi liquid behavior, followed by a metal to insulator transition in the electrical transport. The insulating behavior is described by activated transport, and its onset occurs near 1 electron per Ti occupation within the SrTiO 3 well, providing evidence for a Mott driven transition. We also discuss the role that structure and gradients in strain could play in enhancing the carrier density. The manipulation of Mott metal-insulatormore » behavior in oxides grown directly on Si opens the pathway to harnessing strongly correlated phenomena in device technologies.« less

Two-Dimensional Jeff=1 /2 Antiferromagnetic Insulator Unraveled from Interlayer Exchange Coupling in Artificial Perovskite Iridate Superlattices

NASA Astrophysics Data System (ADS)

Hao, Lin; Meyers, D.; Frederick, Clayton; Fabbris, Gilberto; Yang, Junyi; Traynor, Nathan; Horak, Lukas; Kriegner, Dominik; Choi, Yongseong; Kim, Jong-Woo; Haskel, Daniel; Ryan, Phil J.; Dean, M. P. M.; Liu, Jian

2017-07-01

We report an experimental investigation of the two-dimensional Jeff=1 /2 antiferromagnetic Mott insulator by varying the interlayer exchange coupling in [(SrIrO3)1 , (SrTiO3)m ] (m =1 , 2 and 3) superlattices. Although all samples exhibited an insulating ground state with long-range magnetic order, temperature-dependent resistivity measurements showed a stronger insulating behavior in the m =2 and m =3 samples than the m =1 sample which displayed a clear kink at the magnetic transition. This difference indicates that the blocking effect of the excessive SrTiO3 layer enhances the effective electron-electron correlation and strengthens the Mott phase. The significant reduction of the Néel temperature from 150 K for m =1 to 40 K for m =2 demonstrates that the long-range order stability in the former is boosted by a substantial interlayer exchange coupling. Resonant x-ray magnetic scattering revealed that the interlayer exchange coupling has a switchable sign, depending on the SrTiO3 layer number m , for maintaining canting-induced weak ferromagnetism. The nearly unaltered transition temperature between the m =2 and the m =3 demonstrated that we have realized a two-dimensional antiferromagnet at finite temperatures with diminishing interlayer exchange coupling.

Two-Dimensional J eff = 1 / 2 Antiferromagnetic Insulator Unraveled from Interlayer Exchange Coupling in Artificial Perovskite Iridate Superlattices

DOE PAGES

Hao, Lin; Meyers, D.; Frederick, Clayton; ...

2017-07-14

We report an experimental investigation of the two-dimensional J eff=1/2 antiferromagnetic Mott insulator by varying the interlayer exchange coupling in [(SrIrO 3) 1, (SrTiO 3) m] (m=1, 2 and 3) superlattices. Although all samples exhibited an insulating ground state with long-range magnetic order, temperature-dependent resistivity measurements showed a stronger insulating behavior in the m = 2 and m = 3 samples than the m = 1 sample which displayed a clear kink at the magnetic transition. This difference indicates that the blocking effect of the excessive SrTiO 3 layer enhances the effective electron-electron correlation and strengthens the Mott phase. Themore » significant reduction of the Néel temperature from 150 K for m = 1 to 40 K for m = 2 demonstrates that the long-range order stability in the former is boosted by a substantial interlayer exchange coupling. Resonant x-ray magnetic scattering revealed that the interlayer exchange coupling has a switchable sign, depending on the SrTiO 3 layer number m, for maintaining canting-induced weak ferromagnetism. In conclusion, the nearly unaltered transition temperature between the m = 2 and the m = 3 demonstrated that we have realized a two-dimensional antiferromagnet at finite temperatures with diminishing interlayer exchange coupling.« less

Two-Dimensional J eff = 1 / 2 Antiferromagnetic Insulator Unraveled from Interlayer Exchange Coupling in Artificial Perovskite Iridate Superlattices

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

Hao, Lin; Meyers, D.; Frederick, Clayton

We report an experimental investigation of the two-dimensional J eff=1/2 antiferromagnetic Mott insulator by varying the interlayer exchange coupling in [(SrIrO 3) 1, (SrTiO 3) m] (m=1, 2 and 3) superlattices. Although all samples exhibited an insulating ground state with long-range magnetic order, temperature-dependent resistivity measurements showed a stronger insulating behavior in the m = 2 and m = 3 samples than the m = 1 sample which displayed a clear kink at the magnetic transition. This difference indicates that the blocking effect of the excessive SrTiO 3 layer enhances the effective electron-electron correlation and strengthens the Mott phase. Themore » significant reduction of the Néel temperature from 150 K for m = 1 to 40 K for m = 2 demonstrates that the long-range order stability in the former is boosted by a substantial interlayer exchange coupling. Resonant x-ray magnetic scattering revealed that the interlayer exchange coupling has a switchable sign, depending on the SrTiO 3 layer number m, for maintaining canting-induced weak ferromagnetism. In conclusion, the nearly unaltered transition temperature between the m = 2 and the m = 3 demonstrated that we have realized a two-dimensional antiferromagnet at finite temperatures with diminishing interlayer exchange coupling.« less

p-Type Doping of GaN Nanowires Characterized by Photoelectrochemical Measurements.

PubMed

Kamimura, Jumpei; Bogdanoff, Peter; Ramsteiner, Manfred; Corfdir, Pierre; Feix, Felix; Geelhaar, Lutz; Riechert, Henning

2017-03-08

GaN nanowires (NWs) doped with Mg as a p-type impurity were grown on Si(111) substrates by plasma-assisted molecular beam epitaxy. In a systematic series of experiments, the amount of Mg supplied during NW growth was varied. The incorporation of Mg into the NWs was confirmed by the observation of donor-acceptor pairs and acceptor-bound excitons in low-temperature photoluminescence spectroscopy. Quantitative information about the Mg concentrations was deduced from Raman scattering by local vibrational modes related to Mg. In order to study the type and density of charge carriers present in the NWs, we employed two photoelectrochemical techniques, open-circuit potential and Mott-Schottky measurements. Both methods showed the expected transition from n-type to p-type conductivity with increasing Mg doping level, and the latter characterization technique allowed us to quantify the charge carrier concentration. Beyond the quantitative information obtained for Mg doping of GaN NWs, our systematic and comprehensive investigation demonstrates the benefit of photoelectrochemical methods for the analysis of doping in semiconductor NWs in general.

Transformation from insulating p-type to semiconducting n-type conduction in CaCu3Ti4O12-related Na(Cu5/2Ti1/2)Ti4O12 ceramics

NASA Astrophysics Data System (ADS)

Li, Ming; Sinclair, Derek C.

2013-07-01

A double doping mechanism of Na+ + 1/2 Ti4+ → Ca2+ + 1/2 Cu2+ on the general formula Ca1-xNax(Cu3-x/2Tix/2)Ti4O12 has been used to prepare a series of isostructural CaCu3Ti4O12 (CCTO)-type perovskites. A complete solid solution exists for 0 ≤ x ≤ 1 and all compositions exhibit incipient ferroelectric behaviour with higher than expected intrinsic relative permittivity. Although CCTO ceramics typically exhibit n-type semiconductivity (room temperature, RT, resistivity of ˜10-100 Ω cm), Na(Cu5/2Ti1/2)Ti4O12 (NCTO) ceramics sintered at 950 °C consist of two insulating bulk phases (RT resistivity > 1 GΩ cm), one p-type and the other n-type. With increasing sintering temperature/period, the p-type phase transforms into the n-type phase. During the transformation, the resistivity and activation energy for electrical conduction (Ea ˜ 1.0 eV) of the p-type phase remain unchanged, whereas the n-type phase becomes increasingly conductive with Ea decreasing from ˜ 0.71 to 0.11 eV with increasing sintering temperature. These changes are attributed to small variations in stoichiometry that occur during high temperature ceramic processing with oxygen-loss playing a crucial role.

Superconductor-Insulator Transition in NbTiN Films

NASA Astrophysics Data System (ADS)

Burdastyh, M. V.; Postolova, S. V.; Baturina, T. I.; Proslier, T.; Vinokur, V. M.; Mironov, A. Yu.

2017-12-01

Experimental results indicating a direct disorder-induced superconductor-insulator transition in NbTiN thin films have been reported. It has been shown that an increase in the resistance per square in the normal state is accompanied by the suppression of the critical temperature of the superconducting transition T c according to the fermion mechanism of suppression of superconductivity by disorder. At the same time, the temperature of the Berezinskii-Kosterlitz-Thouless transition is completely suppressed at a nonzero critical temperature and, then, the ground state changes to insulating, which is characteristic of the boson model of suppression of superconductivity by disorder. It has been shown that the temperature dependences of the resistance of insulating films follow the Arrhenius activation law.

Economics of PPP-insulated pipe-type cable: Final report

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

Ernst, A.

1987-10-01

This study has been designed to establish the economic range of application and the potential cost advantage of PPP-insulated pipe-type cable compared with presently utilized paper-insulated designs. The study is in two parts. In the first part the electrical and thermal characteristics of a range of cable sizes are tabulated. This data can be utilized for planning and economic comparison purposes. In the second part 12 transmission load scenarios are studied to determine the relative cost of various designs considering materials, installation and the losses over a wide range of assumptions.

Insulator-semiconductor interface fixed charges in AlGaN/GaN metal-insulator-semiconductor devices with Al2O3 or AlTiO gate dielectrics

NASA Astrophysics Data System (ADS)

Le, Son Phuong; Nguyen, Duong Dai; Suzuki, Toshi-kazu

2018-01-01

We have investigated insulator-semiconductor interface fixed charges in AlGaN/GaN metal-insulator-semiconductor (MIS) devices with Al2O3 or AlTiO (an alloy of Al2O3 and TiO2) gate dielectrics obtained by atomic layer deposition on AlGaN. Analyzing insulator-thickness dependences of threshold voltages for the MIS devices, we evaluated positive interface fixed charges, whose density at the AlTiO/AlGaN interface is significantly lower than that at the Al2O3/AlGaN interface. This and a higher dielectric constant of AlTiO lead to rather shallower threshold voltages for the AlTiO gate dielectric than for Al2O3. The lower interface fixed charge density also leads to the fact that the two-dimensional electron concentration is a decreasing function of the insulator thickness for AlTiO, whereas being an increasing function for Al2O3. Moreover, we discuss the relationship between the interface fixed charges and interface states. From the conductance method, it is shown that the interface state densities are very similar at the Al2O3/AlGaN and AlTiO/AlGaN interfaces. Therefore, we consider that the lower AlTiO/AlGaN interface fixed charge density is not owing to electrons trapped at deep interface states compensating the positive fixed charges and can be attributed to a lower density of oxygen-related interface donors.

Metal-insulator transitions

NASA Astrophysics Data System (ADS)

Imada, Masatoshi; Fujimori, Atsushi; Tokura, Yoshinori

1998-10-01

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

Emergent Bloch excitations in Mott matter

DOE PAGES

Lanata, Nicola; Lee, Tsung -Han; Yao, Yong -Xin; ...

2017-11-14

Here, we develop a unified theoretical picture for excitations in Mott systems, portraying both the heavy quasiparticle excitations and the Hubbard bands as features of an emergent Fermi liquid state formed in an extended Hilbert space, which is nonperturbatively connected to the physical system. This observation sheds light on the fact that even the incoherent excitations in strongly correlated matter often display a well-defined Bloch character, with pronounced momentum dispersion. Furthermore, it indicates that the Mott point can be viewed as a topological transition, where the number of distinct dispersing bands displays a sudden change at the critical point. Ourmore » results, obtained from an appropriate variational principle, display also remarkable quantitative accuracy. This opens an exciting avenue for fast realistic modeling of strongly correlated materials.« less

Development of 72/84kV Dry Air Insulated Dead Tank Type VCB

NASA Astrophysics Data System (ADS)

Saito, Hitoshi; Nagatake, Kazuhiro; Komatsu, Hideki; Takeshita, Yukihiro; Matsui, Yoshihiko; Katsumata, Kiyohito; Sakaki, Masayuki

As a circuit breaker for over 84kV, SF6 gas circuit breaker (GCB) has been used for a long time, in virtue of its excellent characteristics as arc extinction and insulating medium. Although, SF6 gas has very high global warming potential (GWP) of 23,900, and it was designated to regulation object in COP3 in Kyoto in 1997. A lot of efforts have been done to reduce the amount of SF6 gas usage and emission from conventional equipments. On the other hand, SF6 gas free equipment has been researching and one strong candidate is air-insulated type switchgears with vacuum interrupters. In last few years, air-insulated switchgears, which include GIS, Cubicle type GIS (C-GIS) and dead tank type VCB, have been developed in succession. So far, we have already more than three years operation record for the air-insulated dead tank type VCB, and over 100 units is in-service in power systems. Recently, VCB technology, that is essential for SF6 gas-free equipments, has been advanced in the field of high-voltage, large current interruption and environment-conscious design. In this paper, the advanced dead tank type VCB and its technology is descried.

Composite Behavior of a Novel Insulated Concrete Sandwich Wall Panel Reinforced with GFRP Shear Grids: Effects of Insulation Types.

PubMed

Kim, JunHee; You, Young-Chan

2015-03-03

A full-scale experimental program was used in this study to investigate the structural behavior of novel insulated concrete sandwich wall panels (SWPs) reinforced with grid-type glass-fiber-reinforced polymer (GFRP) shear connectors. Two kinds of insulation-expanded polystyrene (EPS) and extruded polystyrene (XPS) with 100 mm thickness were incased between the two concrete wythes to meet the increasing demand for the insulation performance of building envelope. One to four GFRP shear grids were used to examine the degree of composite action of the two concrete wythes. Ten specimens of SWPs were tested under displacement control subjected to four-point concentrated loads. The test results showed that the SWPs reinforced with GFRP grids as shear connectors developed a high degree of composite action resulting in high flexural strength. The specimens with EPS foam exhibited an enhanced load-displacement behavior compared with the specimens with XPS because of the relatively stronger bond between insulation and concrete. In addition, the ultimate strength of the test results was compared to the analytical prediction with the mechanical properties of only GRFP grids. The specimens with EPS insulation presented higher strength-based composite action than the ones with XPS insulation.

Composite Behavior of a Novel Insulated Concrete Sandwich Wall Panel Reinforced with GFRP Shear Grids: Effects of Insulation Types

PubMed Central

Kim, JunHee; You, Young-Chan

2015-01-01

A full-scale experimental program was used in this study to investigate the structural behavior of novel insulated concrete sandwich wall panels (SWPs) reinforced with grid-type glass-fiber-reinforced polymer (GFRP) shear connectors. Two kinds of insulation-expanded polystyrene (EPS) and extruded polystyrene (XPS) with 100 mm thickness were incased between the two concrete wythes to meet the increasing demand for the insulation performance of building envelope. One to four GFRP shear grids were used to examine the degree of composite action of the two concrete wythes. Ten specimens of SWPs were tested under displacement control subjected to four-point concentrated loads. The test results showed that the SWPs reinforced with GFRP grids as shear connectors developed a high degree of composite action resulting in high flexural strength. The specimens with EPS foam exhibited an enhanced load-displacement behavior compared with the specimens with XPS because of the relatively stronger bond between insulation and concrete. In addition, the ultimate strength of the test results was compared to the analytical prediction with the mechanical properties of only GRFP grids. The specimens with EPS insulation presented higher strength-based composite action than the ones with XPS insulation. PMID:28787978

DFT with larger supercells explains the band gap formation in the antiferromagnetic and paramagnetic phases of the Mott insulators MnO, FeO, CoO, and NiO

NASA Astrophysics Data System (ADS)

Zunger, Alex; Trimarchi, Giancarlo

The existence of large band gaps both in the antiferromagnetic (AFM) and the paramagnetic (PM) phases of the classic Mott insulators MnO, FeO, CoO, and NiO has traditionally been discussed in terms of theoretical methods requiring both (i) simple (often primitive) unit cells and (ii) correlated-electron methodologies. We show that if condition (i) is avoided (by using supercells, such as PM special quasi-random structures, in which chemically identical atoms can have different local environments), then even without condition (ii) one can describe the gaps and moments within a single-determinant DFT band structure approach. In this approach gapping is caused by basic structure, magnetism, and bonding effects underlying DFT, not via dynamic correlation (absent from DFT). As long as correlation is simplistically considered as ``anything that DFT does not get right'', gap formation in the AFM and PM phases is not due to correlation. This result defines the minimal theoretical methods needed to explain gapping and points to the possibility that some transition-metal oxides generally considered to have localized electrons detrimental to transport, could, in fact, rejoin the family of electronic semiconductors, to the benefit of a carrier transport technologies. A. Z. supported by DOE-OS-BES-MSE, Grant DE-FG02-13ER46959.

Wannier-Mott Excitons in Nanoscale Molecular Ices

NASA Astrophysics Data System (ADS)

Chen, Y.-J.; Muñoz Caro, G. M.; Aparicio, S.; Jiménez-Escobar, A.; Lasne, J.; Rosu-Finsen, A.; McCoustra, M. R. S.; Cassidy, A. M.; Field, D.

2017-10-01

The absorption of light to create Wannier-Mott excitons is a fundamental feature dictating the optical and photovoltaic properties of low band gap, high permittivity semiconductors. Such excitons, with an electron-hole separation an order of magnitude greater than lattice dimensions, are largely limited to these semiconductors but here we find evidence of Wannier-Mott exciton formation in solid carbon monoxide (CO) with a band gap of >8 eV and a low electrical permittivity. This is established through the observation that a change of a few degrees K in deposition temperature can shift the electronic absorption spectra of solid CO by several hundred wave numbers, coupled with the recent discovery that deposition of CO leads to the spontaneous formation of electric fields within the film. These so-called spontelectric fields, here approaching 4 ×107 V m-1 , are strongly temperature dependent. We find that a simple electrostatic model reproduces the observed temperature dependent spectral shifts based on the Stark effect on a hole and electron residing several nm apart, identifying the presence of Wannier-Mott excitons. The spontelectric effect in CO simultaneously explains the long-standing enigma of the sensitivity of vacuum ultraviolet spectra to the deposition temperature.

Ba2NiOsO6: a Dirac-Mott insulator with ferromagnetism near 100 K

NASA Astrophysics Data System (ADS)

Feng, Hl; Calder, S.; Ghimire, M.; Yuan, Yh; Shirako, Y.; Tsujimoto, Y.; Matsushita, Y.; Hu, Z.; Kuo, Cy; Tjeng, Lh; Pi, Tw; Soo, Yl; He, Jf; Tanaka, M.; Katsuya, Y.; Richte, M.; Yamaura, Kazunari

The ferromagnetic semiconductor Ba2NiOsO6(Tmag 100 K) was synthesized at 6 GPa and 1500 ° C. It crystallizes into a double perovskite structure [Fm-3 m; a = 8.0428(1)], where the Ni2+ and Os6+ ions are perfectly ordered at the perovskite B-site. We show that the spin-orbit coupling of Os6+ plays an essential role in opening the charge gap. The magnetic state was investigated by density functional theory calculations and powder neutron diffraction. The latter revealed a collinear ferromagnetic order in a >21-kOe magnetic field at 5 K. The ferromagnetic gapped state is fundamentally different from that of known dilute magnetic semiconductors such as (Ga,Mn)As and (Cd,Mn)Te (Tmag<180 K), the spin-gapless semiconductor Mn2CoAl (Tmag 720 K), and the ferromagnetic insulators EuO (Tmag 70 K) and Bi3Cr3O11(Tmag 220 K). It is also qualitatively different from known ferrimagnetic insulator/semiconductors, which are characterized by an antiparallel spin arrangement. Our report of cubic Ba2NiOsO6 heralds a new class of FM insulator oxides, which may be useful in developing a practical magnetic semiconductor that can be employed in spintronic and quantum magnetic devices.

Probing the spin-orbit Mott state in Sr3Ir2O7 by electron doping

NASA Astrophysics Data System (ADS)

Hogan, Thomas C.

Iridium-based members of the Ruddlesden-Popper family of oxide compounds are characterized by a unique combination of energetically comparable effects: crystal-field splitting, spin-orbit coupling, and electron-electron interactions are all present, and the combine to produce a Jeff = 1/2 ground state. In the bilayer member of this series, Sr3Ir2O7, this state manifests as electrically insulating, with unpaired Ir4+ spins aligned along the long axis of the unit cell to produce a G-type antiferromagnet with an ordered moment of 0.36 uB. In this work, this Mott state is destabilized by electron doping via La3+ substitution on the Sr-site to produce (Sr1-x Lax)3Ir2O7. The introduction of carriers initially causes nano-scale phase-separated regions to develop before driving a global insulator-to-metal transition at x=0.04. Coinciding with this transition is the disappearance of evidence of magnetic order in the system in either bulk magnetization or magnetic scattering experiments. The doping also enhances a structural order parameter observed in the parent compound at forbidden reciprocal lattice vectors. A more complete structural solution is proposed to account for this previously unresolved distortion, and also offers an explanation as to the anomalous net ferromagnetism seen prior in bulk measurements. Finally, spin dynamics are probed via a resonant x-ray technique to reveal evidence of spin-dimer-like behavior dominated by inter-plane interactions. This result supports a bond-operator treatment of the interaction Hamiltonian, and also explains the doping dependence of high temperature magnetic susceptibility.

Orbital-selective Mott phase in multiorbital models for iron pnictides and chalcogenides

NASA Astrophysics Data System (ADS)

Yu, Rong; Si, Qimiao

2017-09-01

There is increasing recognition that the multiorbital nature of the 3 d electrons is important to the proper description of the electronic states in the normal state of the iron-based superconductors. Earlier studies of the pertinent multiorbital Hubbard models identified an orbital-selective Mott phase, which anchors the orbital-selective behavior seen in the overall phase diagram. An important characteristics of the models is that the orbitals are kinetically coupled, i.e., hybridized, to each other, which makes the orbital-selective Mott phase especially nontrivial. A U (1 ) slave-spin method was used to analyze the model with nonzero orbital-level splittings. Here we develop a Landau free-energy functional to shed further light on this issue. We put the microscopic analysis from the U (1 ) slave-spin approach in this perspective, and show that the intersite spin correlations are crucial to the renormalization of the bare hybridization amplitude towards zero and the concomitant realization of the orbital-selective Mott transition. Based on this insight, we discuss additional ways to study the orbital-selective Mott physics from a dynamical competition between the interorbital hybridization and collective spin correlations. Our results demonstrate the robustness of the orbital-selective Mott phase in the multiorbital models appropriate for the iron-based superconductors.

Fermi surface in the absence of a Fermi liquid in the Kondo insulator SmB6

NASA Astrophysics Data System (ADS)

Hartstein, M.; Toews, W. H.; Hsu, Y.-T.; Zeng, B.; Chen, X.; Hatnean, M. Ciomaga; Zhang, Q. R.; Nakamura, S.; Padgett, A. S.; Rodway-Gant, G.; Berk, J.; Kingston, M. K.; Zhang, G. H.; Chan, M. K.; Yamashita, S.; Sakakibara, T.; Takano, Y.; Park, J.-H.; Balicas, L.; Harrison, N.; Shitsevalova, N.; Balakrishnan, G.; Lonzarich, G. G.; Hill, R. W.; Sutherland, M.; Sebastian, Suchitra E.

2018-02-01

The search for a Fermi surface in the absence of a conventional Fermi liquid has thus far yielded very few potential candidates. Among promising materials are spin-frustrated Mott insulators near the insulator-metal transition, where theory predicts a Fermi surface associated with neutral low-energy excitations. Here we reveal another route to experimentally realize a Fermi surface in the absence of a Fermi liquid by the experimental study of a Kondo insulator SmB6 positioned close to the insulator-metal transition. We present experimental signatures down to low temperatures (<<1 K) associated with a Fermi surface in the bulk, including a sizeable linear specific heat coefficient, and on the application of a finite magnetic field, bulk magnetic quantum oscillations, finite quantum oscillatory entropy, and substantial enhancement in thermal conductivity well below the charge gap energy scale. Thus, the weight of evidence indicates that despite an extreme instance of Fermi liquid breakdown in Kondo insulating SmB6, a Fermi surface arises from novel itinerant low-energy excitations that couple to magnetic fields, but not weak DC electric fields.

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

Song, Yu; Yamani, Zahra; Cao, Chongde

Iron-based superconductivity develops near an antiferromagnetic order and out of a bad-metal normal state, which has been interpreted as originating from a proximate Mott transition. Whether an actual Mott insulator can be realized in the phase diagram of the iron pnictides remains an open question. Here we use transport, transmission electron microscopy, X-ray absorption spectroscopy, resonant inelastic X-ray scattering and neutron scattering to demonstrate that NaFe 1-xCu xAs near x≈0.5 exhibits real space Fe and Cu ordering, and are antiferromagnetic insulators with the insulating behaviour persisting above the Néel temperature, indicative of a Mott insulator. On decreasing x from 0.5,more » the antiferromagnetic-ordered moment continuously decreases, yielding to superconductivity ~x=0.05. Our discovery of a Mott-insulating state in NaFe 1-xCu xAs thus makes it the only known Fe-based material, in which superconductivity can be smoothly connected to the Mott-insulating state, highlighting the important role of electron correlations in the high-T c superconductivity.« less

On the nature of the Mott transition in multiorbital systems

NASA Astrophysics Data System (ADS)

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

2017-02-01

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

Strain-induced metal-insulator transitions in d1 perovskites within DFT+DMFT

NASA Astrophysics Data System (ADS)

Dymkowski, Krzysztof; Ederer, Claude

2014-03-01

We present results of combined density functional theory plus dynamical mean-field theory (DFT+DMFT) calculations, assessing the effect of epitaxial strain on the electronic properties of the Mott insulator LaTiO3 and the correlated metal SrVO3. In particular, we take into account the effect of strain on the collective tilts and rotations of the oxygen octahedra in the orthorhombically distorted Pbnm perovskite structure of LaTiO3. We find that LaTiO3 undergoes an insulator-to-metal transition under a compressive strain of about - 2 %, consistent with recent experimental observations. We show that this transition is driven mainly by strain-induced changes in the crystal-field splitting between the Ti t2 g orbitals, which in turn are related to changes in the octahedral tilt distortion. We compare this with the case of SrVO3, without octahedral tilts, where we find a metal-to-insulator transition under tensile epitaxial strain. Similar to LaTiO3, this metal-insulator transition is linked to the strain-induced change in the crystal-field splitting within the t2 g orbitals.

Low-frequency and multiple-bands sound insulation using hollow boxes with membrane-type faces

NASA Astrophysics Data System (ADS)

Yu, Wei-wei; Fan, Li; Ma, Ren-hao; Zhang, Hui; Zhang, Shu-yi

2018-04-01

Hollow boxes with their faces made up of elastic membranes are used to block acoustic waves. It is demonstrated that placing a cuboid membrane-type box inside a pipe can effectively insulate acoustic waves even if the box is smaller than the cross-section of the pipe. The sound insulation is achieved within multiple frequency-bands below 500 Hz based on different mechanisms, which originate from the coaction of the cavity, membrane-type faces, and the intervals between the box and pipe walls. Furthermore, by adjusting the structural parameters and establishing an array of boxes, we can achieve better sound insulation at more frequency-bands.

[Insulitis in type 1 diabetes].

PubMed

In't Veld, P; Klöppel, G

2016-05-01

Insulitis is considered to be the key morphological lesion of type 1 diabetes mellitus (T1DM) for which the diagnostic criteria were recently defined. From the immunophenotype of the lymphocytic infiltration, its frequency and extent during the course of T1DM and the presence of autoantibodies against beta cell proteins, it has been deduced that T1DM is a chronic autoimmune disease leading to gradual destruction of the insulin-producing cells of the islets of Langerhans in the pancreas, profound insulin deficiency and chronic hyperglycemia. This review article presents the morphological findings that support this hypothesis and addresses questions that need to be answered in order to further clarify the pathogenesis and to develop specific treatment options.

Note: A high-energy-density Tesla-type pulse generator with novel insulating oil

NASA Astrophysics Data System (ADS)

Liu, Sheng; Su, Jiancang; Fan, Xuliang

2017-09-01

A 10-GW high-energy-density Tesla-type pulse generator is developed with an improved insulating liquid based on a modified Tesla pulser—TPG700, of which the pulse forming line (PFL) is filled with novel insulating oil instead of transformer oil. Properties of insulating oil determining the stored energy density of the PFL are analyzed, and a criterion for appropriate oil is proposed. Midel 7131 is chosen as an application example. The results of insulating property experiment under tens-of-microsecond pulse charging demonstrate that the insulation capability of Midel 7131 is better than that of KI45X transformer oil. The application test in Tesla pulser TPG700 shows that the output power is increased to 10.5 GW with Midel 7131. The output energy density of TPG700 increases for about 60% with Midel 7131.

Note: A high-energy-density Tesla-type pulse generator with novel insulating oil.

PubMed

Liu, Sheng; Su, Jiancang; Fan, Xuliang

2017-09-01

A 10-GW high-energy-density Tesla-type pulse generator is developed with an improved insulating liquid based on a modified Tesla pulser-TPG700, of which the pulse forming line (PFL) is filled with novel insulating oil instead of transformer oil. Properties of insulating oil determining the stored energy density of the PFL are analyzed, and a criterion for appropriate oil is proposed. Midel 7131 is chosen as an application example. The results of insulating property experiment under tens-of-microsecond pulse charging demonstrate that the insulation capability of Midel 7131 is better than that of KI45X transformer oil. The application test in Tesla pulser TPG700 shows that the output power is increased to 10.5 GW with Midel 7131. The output energy density of TPG700 increases for about 60% with Midel 7131.

Superconducting dome in doped quasi-two-dimensional organic Mott insulators: A paradigm for strongly correlated superconductivity

NASA Astrophysics Data System (ADS)

Hébert, Charles-David; Sémon, Patrick; Tremblay, A.-M. S.

2015-11-01

Layered organic superconductors of the BEDT family are model systems for understanding the interplay of the Mott transition with superconductivity, magnetic order, and frustration, ingredients that are essential to understand superconductivity also in the cuprate high-temperature superconductors. Recent experimental studies on a hole-doped version of the organic compounds reveals an enhancement of superconductivity and a rapid crossover between two different conducting phases above the superconducting dome. One of these phases is a Fermi liquid, the other not. Using plaquette cellular dynamical mean field theory with state-of-the-art continuous-time quantum Monte Carlo calculations, we study this problem with the two-dimensional Hubbard model on the anisotropic triangular lattice. Phase diagrams as a function of temperature T and interaction strength U /t are obtained for anisotropy parameters t'=0.4 t ,t'=0.8 t and for various fillings. As in the case of the cuprates, we find, at finite doping, a first-order transition between two normal-state phases. One of theses phases has a pseudogap while the other does not. At temperatures above the critical point of the first-order transition, there is a Widom line where crossovers occur. The maximum (optimal) superconducting critical temperature Tcm at finite doping is enhanced by about 25% compared with its maximum at half filling and the range of U /t where superconductivity appears is greatly extended. These results are in broad agreement with experiment. Also, increasing frustration (larger t'/t ) significantly reduces magnetic ordering, as expected. This suggests that for compounds with intermediate to high frustration, very light doping should reveal the influence of the first-order transition and associated crossovers. These crossovers could possibly be even visible in the superconducting phase through subtle signatures. We also predict that destroying the superconducting phase by a magnetic field should reveal the

Spin-orbit driven magnetic insulating state with J eff=1/2 character in a 4d oxide

DOE PAGES

Calder, S.; Li, Ling; Okamoto, Satoshi; ...

2015-11-30

The unusual magnetic and electronic ground states of 5d iridates has been shown to be driven by intrinsically enhanced spin-orbit coupling (SOC). The influence of appreciable but reduced SOC in creating the manifested magnetic insulating states in 4d oxides is less clear, with one hurdle being the existence of such compounds. Here we present experimental and theoretical results on Sr 4RhO 6 that reveal SOC dominated behavior. Neutron measurements show the octahedra are both spatially separated and locally ideal, making the electronic ground state susceptible to alterations by SOC. Magnetic ordering is observed with a similar structure to an analogousmore » J eff=1/2 Mott iridate. We consider the underlying role of SOC in this rhodate with density functional theory and x-ray absorption spectroscopy and find a magnetic insulating ground state with J eff =1/2 character.The unusual magnetic and electronic ground states of 5d iridates have been shown to be driven by intrinsically enhanced spin-orbit coupling (SOC). The influence of appreciable but reduced SOC in creating the manifested magnetic insulating states in 4d oxides is less clear, with one hurdle being the existence of such compounds. Here, we present experimental and theoretical results on Sr 4RhO 6 that reveal SOC dominated behavior. Neutron measurements show the octahedra are both spatially separated and locally ideal, making the electronic ground state susceptible to alterations by SOC. Magnetic ordering is observed with a similar structure to an analogous J eff=1/2 Mott iridate. We consider the underlying role of SOC in this rhodate with density functional theory and x-ray absorption spectroscopy, and find a magnetic insulating ground state with J eff=12 character.« less

Topological insulator thin films starting from the amorphous phase-Bi{sub 2}Se{sub 3} as example

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

Barzola-Quiquia, J., E-mail: j.barzola@physik.uni-leipzig.de; Lehmann, T.; Stiller, M.

We present a new method to obtain topological insulator Bi{sub 2}Se{sub 3} thin films with a centimeter large lateral length. To produce amorphous Bi{sub 2}Se{sub 3} thin films, we have used a sequential flash-evaporation method at room temperature. Transmission electron microscopy has been used to verify that the prepared samples are in a pure amorphous state. During annealing, the samples transform into the rhombohedral Bi{sub 2}Se{sub 3} crystalline structure which was confirmed using X-ray diffraction and Raman spectroscopy. Resistance measurements of the amorphous films show the expected Mott variable range hopping conduction process with a high specific resistance compared tomore » the one obtained in the crystalline phase (metallic behavior). We have measured the magnetoresistance and the Hall effect at different temperatures between 2 K and 275 K. At temperatures T ≲ 50 K and fields B ≲ 1 T, we observe weak anti-localization in the MR; the Hall measurements confirm the n-type character of the samples. All experimental results of our films are in quantitative agreement with results from samples prepared using more sophisticated methods.« less

Ambipolar pentacene field-effect transistor with double-layer organic insulator

NASA Astrophysics Data System (ADS)

Kwak, Jeong-Hun; Baek, Heume-Il; Lee, Changhee

2006-08-01

Ambipolar conduction in organic field-effect transistor is very important feature to achieve organic CMOS circuitry. We fabricated an ambipolar pentacene field-effect transistors consisted of gold source-drain electrodes and double-layered PMMA (Polymethylmethacrylate) / PVA (Polyvinyl Alcohol) organic insulator on the ITO(Indium-tin-oxide)-patterned glass substrate. These top-contact geometry field-effect transistors were fabricated in the vacuum of 10 -6 Torr and minimally exposed to atmosphere before its measurement and characterized in the vacuum condition. Our device showed reasonable p-type characteristics of field-effect hole mobility of 0.2-0.9 cm2/Vs and the current ON/OFF ratio of about 10 6 compared to prior reports with similar configurations. For the n-type characteristics, field-effect electron mobility of 0.004-0.008 cm2/Vs and the current ON/OFF ratio of about 10 3 were measured, which is relatively high performance for the n-type conduction of pentacene field-effect transistors. We attributed these ambipolar properties mainly to the hydroxyl-free PMMA insulator interface with the pentacene active layer. In addition, an increased insulator capacitance due to double-layer insulator structure with high-k PVA layer also helped us to observe relatively good n-type characteristics.

Localized Vibrations of Bi Bilayer Leading to Ultralow Lattice Thermal Conductivity and High Thermoelectric Performance in Weak Topological Insulator n-Type BiSe.

PubMed

Samanta, Manisha; Pal, Koushik; Pal, Provas; Waghmare, Umesh V; Biswas, Kanishka

2018-05-02

Realization of high thermoelectric performance in n-type semiconductors is of imperative need on account of the dearth of efficient n-type thermoelectric materials compared to the p-type counterpart. Moreover, development of efficient thermoelectric materials based on Te-free compounds is desirable because of the scarcity of Te in the Earth's crust. Herein, we report the intrinsic ultralow thermal conductivity and high thermoelectric performance near room temperature in n-type BiSe, a Te-free solid, which recently has emerged as a weak topological insulator. BiSe possesses a layered structure consisting of a bismuth bilayer (Bi 2 ) sandwiched between two Bi 2 Se 3 quintuple layers [Se-Bi-Se-Bi-Se], resembling natural heterostructure. High thermoelectric performance of BiSe is realized through the ultralow lattice thermal conductivity (κ lat of ∼0.6 W/mK at 300 K), which is significantly lower than that of Bi 2 Se 3 (κ lat of ∼1.8 W/mK at 300 K), although both of them belong to the same layered homologous family (Bi 2 ) m (Bi 2 Se 3 ) n . Phonon dispersion calculated from first-principles and the experimental low-temperature specific heat data indicate that soft localized vibrations of bismuth bilayer in BiSe are responsible for its ultralow κ lat . These low energy optical phonon branches couple strongly with the heat carrying acoustic phonons, and consequently suppress the phonon mean free path leading to low κ lat . Further optimization of thermoelectric properties of BiSe through Sb substitution and spark plasma sintering (SPS) results in high ZT ∼ 0.8 at 425 K along the pressing direction, which is indeed remarkable among Te-free n-type thermoelectric materials near room temperature.

Temperature dependent electrical characterisation of Pt/HfO{sub 2}/n-GaN metal-insulator-semiconductor (MIS) Schottky diodes

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

Shetty, Arjun, E-mail: arjun@ece.iisc.ernet.in; Vinoy, K. J.; Roul, Basanta

2015-09-15

This paper reports an improvement in Pt/n-GaN metal-semiconductor (MS) Schottky diode characteristics by the introduction of a layer of HfO{sub 2} (5 nm) between the metal and semiconductor interface. The resulting Pt/HfO{sub 2}/n-GaN metal-insulator-semiconductor (MIS) Schottky diode showed an increase in rectification ratio from 35.9 to 98.9(@ 2V), increase in barrier height (0.52 eV to 0.63eV) and a reduction in ideality factor (2.1 to 1.3) as compared to the MS Schottky. Epitaxial n-type GaN films of thickness 300nm were grown using plasma assisted molecular beam epitaxy (PAMBE). The crystalline and optical qualities of the films were confirmed using high resolutionmore » X-ray diffraction and photoluminescence measurements. Metal-semiconductor (Pt/n-GaN) and metal-insulator-semiconductor (Pt/HfO{sub 2}/n-GaN) Schottky diodes were fabricated. To gain further understanding of the Pt/HfO{sub 2}/GaN interface, I-V characterisation was carried out on the MIS Schottky diode over a temperature range of 150 K to 370 K. The barrier height was found to increase (0.3 eV to 0.79 eV) and the ideality factor decreased (3.6 to 1.2) with increase in temperature from 150 K to 370 K. This temperature dependence was attributed to the inhomogeneous nature of the contact and the explanation was validated by fitting the experimental data into a Gaussian distribution of barrier heights.« less

Imaging of β-cell mass and insulitis in insulin-dependent (Type 1) diabetes mellitus.

PubMed

Di Gialleonardo, Valentina; de Vries, Erik F J; Di Girolamo, Marco; Quintero, Ana M; Dierckx, Rudi A J O; Signore, Alberto

2012-12-01

Insulin-dependent (type 1) diabetes mellitus is a metabolic disease with a complex multifactorial etiology and a poorly understood pathogenesis. Genetic and environmental factors cause an autoimmune reaction against pancreatic β-cells, called insulitis, confirmed in pancreatic samples obtained at autopsy. The possibility to noninvasively quantify β-cell mass in vivo would provide important biological insights and facilitate aspects of diagnosis and therapy, including follow-up of islet cell transplantation. Moreover, the availability of a noninvasive tool to quantify the extent and severity of pancreatic insulitis could be useful for understanding the natural history of human insulin-dependent (type 1) diabetes mellitus, to early diagnose children at risk to develop overt diabetes, and to select patients to be treated with immunotherapies aimed at blocking the insulitis and monitoring the efficacy of these therapies. In this review, we outline the imaging techniques currently available for in vivo, noninvasive detection of β-cell mass and insulitis. These imaging techniques include magnetic resonance imaging, ultrasound, computed tomography, bioluminescence and fluorescence imaging, and the nuclear medicine techniques positron emission tomography and single-photon emission computed tomography. Several approaches and radiopharmaceuticals for imaging β-cells and lymphocytic insulitis are reviewed in detail.

Hybridization wave as the cause of the metal-insulator transition in rare earth nickelates

NASA Astrophysics Data System (ADS)

Park, Hyowon; Marianetti, Chris A.; Millis, Andrew J.

2012-02-01

The metal-insulator transition driven by varying rare earth (Re) ion in ReNiO3 has been a longstanding challenge to materials theory. Experimental evidence suggesting charge order is seemingly incompatible with the strong Mott-Hubbard correlations characteristic of transition metals. We present density functional, Hartree-Fock and Dynamical Mean field calculations showing that the origin of the insulating phase is a hybridization wave, in which a two sublattice ordering of the oxygen breathing mode produces two Ni sites with almost identical Ni d-charge densities but very different magnetic moments and other properties. The high temperature crystal structure associated with smaller Re ions such as Lu is shown to be more susceptible to the distortion than the high temperature structure associated with larger Re ions such as La.

Spatiotemporal Dynamics of Insulitis in Human Type 1 Diabetes

PubMed Central

Wedgwood, Kyle C. A.; Richardson, Sarah J.; Morgan, Noel G.; Tsaneva-Atanasova, Krasimira

2016-01-01

Type 1 diabetes (T1D) is an auto-immune disease characterized by the selective destruction of the insulin secreting beta cells in the pancreas during an inflammatory phase known as insulitis. Patients with T1D are typically dependent on the administration of externally provided insulin in order to manage blood glucose levels. Whilst technological developments have significantly improved both the life expectancy and quality of life of these patients, an understanding of the mechanisms of the disease remains elusive. Animal models, such as the NOD mouse model, have been widely used to probe the process of insulitis, but there exist very few data from humans studied at disease onset. In this manuscript, we employ data from human pancreases collected close to the onset of T1D and propose a spatio-temporal computational model for the progression of insulitis in human T1D, with particular focus on the mechanisms underlying the development of insulitis in pancreatic islets. This framework allows us to investigate how the time-course of insulitis progression is affected by altering key parameters, such as the number of the CD20+ B cells present in the inflammatory infiltrate, which has recently been proposed to influence the aggressiveness of the disease. Through the analysis of repeated simulations of our stochastic model, which track the number of beta cells within an islet, we find that increased numbers of B cells in the peri-islet space lead to faster destruction of the beta cells. We also find that the balance between the degradation and repair of the basement membrane surrounding the islet is a critical component in governing the overall destruction rate of the beta cells and their remaining number. Our model provides a framework for continued and improved spatio-temporal modeling of human T1D. PMID:28082906

First-order metal-insulator transitions in the extended Hubbard model due to self-consistent screening of the effective interaction

NASA Astrophysics Data System (ADS)

Schüler, M.; van Loon, E. G. C. P.; Katsnelson, M. I.; Wehling, T. O.

2018-04-01

While the Hubbard model is the standard model to study Mott metal-insulator transitions, it is still unclear to what extent it can describe metal-insulator transitions in real solids, where nonlocal Coulomb interactions are always present. By using a variational principle, we clarify this issue for short- and long-range nonlocal Coulomb interactions for half-filled systems on bipartite lattices. We find that repulsive nonlocal interactions generally stabilize the Fermi-liquid regime. The metal-insulator phase boundary is shifted to larger interaction strengths to leading order linearly with nonlocal interactions. Importantly, nonlocal interactions can raise the order of the metal-insulator transition. We present a detailed analysis of how the dimension and geometry of the lattice as well as the temperature determine the critical nonlocal interaction leading to a first-order transition: for systems in more than two dimensions with nonzero density of states at the Fermi energy the critical nonlocal interaction is arbitrarily small; otherwise, it is finite.

Tuning bad metal and non-Fermi liquid behavior in a Mott material: Rare-earth nickelate thin films

PubMed Central

Mikheev, Evgeny; Hauser, Adam J.; Himmetoglu, Burak; Moreno, Nelson E.; Janotti, Anderson; Van de Walle, Chris G.; Stemmer, Susanne

2015-01-01

Resistances that exceed the Mott-Ioffe-Regel limit (known as bad metal behavior) and non-Fermi liquid behavior are ubiquitous features of the normal state of many strongly correlated materials. We establish the conditions that lead to bad metal and non-Fermi liquid phases in NdNiO3, which exhibits a prototype bandwidth-controlled metal-insulator transition. We show that resistance saturation is determined by the magnitude of Ni eg orbital splitting, which can be tuned by strain in epitaxial films, causing the appearance of bad metal behavior under certain conditions. The results shed light on the nature of a crossover to a non-Fermi liquid metal phase and provide a predictive criterion for Anderson localization. They elucidate a seemingly complex phase behavior as a function of film strain and confinement and provide guidelines for orbital engineering and novel devices. PMID:26601140

Covalency and the metal-insulator transition in titanate and vanadate perovskites

NASA Astrophysics Data System (ADS)

Dang, Hung T.; Millis, Andrew J.; Marianetti, Chris A.

2014-04-01

A combination of density functional and dynamical mean-field theory is applied to the perovskites SrVO3, LaTiO3, and LaVO3. We show that DFT + DMFT in conjunction with the standard fully localized-limit (FLL) double-counting predicts that LaTiO3 and LaVO3 are metals even though experimentally they are correlation-driven ("Mott") insulators. In addition, the FLL double counting implies a splitting between oxygen p and transition metal d levels, which differs from experiment. Introducing into the theory an ad hoc double counting correction, which reproduces the experimentally measured insulating gap leads also to a p-d splitting consistent with experiment if the on-site interaction U is chosen in a relatively narrow range (˜6±1 eV). The results indicate that these early transition metal oxides will serve as critical test for the formulation of a general ab initio theory of correlated electron metals.

Suppression of Structural Phase Transition in VO2 by Epitaxial Strain in Vicinity of Metal-insulator Transition

PubMed Central

Yang, Mengmeng; Yang, Yuanjun; Bin Hong; Wang, Liangxin; Hu, Kai; Dong, Yongqi; Xu, Han; Huang, Haoliang; Zhao, Jiangtao; Chen, Haiping; Song, Li; Ju, Huanxin; Zhu, Junfa; Bao, Jun; Li, Xiaoguang; Gu, Yueliang; Yang, Tieying; Gao, Xingyu; Luo, Zhenlin; Gao, Chen

2016-01-01

Mechanism of metal-insulator transition (MIT) in strained VO2 thin films is very complicated and incompletely understood despite three scenarios with potential explanations including electronic correlation (Mott mechanism), structural transformation (Peierls theory) and collaborative Mott-Peierls transition. Herein, we have decoupled coactions of structural and electronic phase transitions across the MIT by implementing epitaxial strain on 13-nm-thick (001)-VO2 films in comparison to thicker films. The structural evolution during MIT characterized by temperature-dependent synchrotron radiation high-resolution X-ray diffraction reciprocal space mapping and Raman spectroscopy suggested that the structural phase transition in the temperature range of vicinity of the MIT is suppressed by epitaxial strain. Furthermore, temperature-dependent Ultraviolet Photoelectron Spectroscopy (UPS) revealed the changes in electron occupancy near the Fermi energy EF of V 3d orbital, implying that the electronic transition triggers the MIT in the strained films. Thus the MIT in the bi-axially strained VO2 thin films should be only driven by electronic transition without assistance of structural phase transition. Density functional theoretical calculations further confirmed that the tetragonal phase across the MIT can be both in insulating and metallic states in the strained (001)-VO2/TiO2 thin films. This work offers a better understanding of the mechanism of MIT in the strained VO2 films. PMID:26975328

Spin-Orbital Excitations in Ca2 RuO4 Revealed by Resonant Inelastic X-Ray Scattering

NASA Astrophysics Data System (ADS)

Das, L.; Forte, F.; Fittipaldi, R.; Fatuzzo, C. G.; Granata, V.; Ivashko, O.; Horio, M.; Schindler, F.; Dantz, M.; Tseng, Yi; McNally, D. E.; Rønnow, H. M.; Wan, W.; Christensen, N. B.; Pelliciari, J.; Olalde-Velasco, P.; Kikugawa, N.; Neupert, T.; Vecchione, A.; Schmitt, T.; Cuoco, M.; Chang, J.

2018-01-01

The strongly correlated insulator Ca2 RuO4 is considered as a paradigmatic realization of both spin-orbital physics and a band-Mott insulating phase, characterized by orbitally selective coexistence of a band and a Mott gap. We present a high resolution oxygen K -edge resonant inelastic x-ray scattering study of the antiferromagnetic Mott insulating state of Ca2 RuO4 . A set of low-energy (about 80 and 400 meV) and high-energy (about 1.3 and 2.2 eV) excitations are reported, which show strong incident light polarization dependence. Our results strongly support a spin-orbit coupled band-Mott scenario and explore in detail the nature of its exotic excitations. Guided by theoretical modeling, we interpret the low-energy excitations as a result of composite spin-orbital excitations. Their nature unveils the intricate interplay of crystal-field splitting and spin-orbit coupling in the band-Mott scenario. The high-energy excitations correspond to intra-atomic singlet-triplet transitions at an energy scale set by Hund's coupling. Our findings give a unifying picture of the spin and orbital excitations in the band-Mott insulator Ca2 RuO4 .

Electronic evidence of an insulator-superconductor crossover in single-layer FeSe/SrTiO3 films.

PubMed

He, Junfeng; Liu, Xu; Zhang, Wenhao; Zhao, Lin; Liu, Defa; He, Shaolong; Mou, Daixiang; Li, Fangsen; Tang, Chenjia; Li, Zhi; Wang, Lili; Peng, Yingying; Liu, Yan; Chen, Chaoyu; Yu, Li; Liu, Guodong; Dong, Xiaoli; Zhang, Jun; Chen, Chuangtian; Xu, Zuyan; Chen, Xi; Ma, Xucun; Xue, Qikun; Zhou, X J

2014-12-30

In high-temperature cuprate superconductors, it is now generally agreed that superconductivity is realized by doping an antiferromagnetic Mott (charge transfer) insulator. The doping-induced insulator-to-superconductor transition has been widely observed in cuprates, which provides important information for understanding the superconductivity mechanism. In the iron-based superconductors, however, the parent compound is mostly antiferromagnetic bad metal, raising a debate on whether an appropriate starting point should go with an itinerant picture or a localized picture. No evidence of doping-induced insulator-superconductor transition (or crossover) has been reported in the iron-based compounds so far. Here, we report an electronic evidence of an insulator-superconductor crossover observed in the single-layer FeSe film grown on a SrTiO3 substrate. By taking angle-resolved photoemission measurements on the electronic structure and energy gap, we have identified a clear evolution of an insulator to a superconductor with increasing carrier concentration. In particular, the insulator-superconductor crossover in FeSe/SrTiO3 film exhibits similar behaviors to that observed in the cuprate superconductors. Our results suggest that the observed insulator-superconductor crossover may be associated with the two-dimensionality that enhances electron localization or correlation. The reduced dimensionality and the interfacial effect provide a new pathway in searching for new phenomena and novel superconductors with a high transition temperature.

A type of cylindrical Hall thruster with a magnetically insulated anode

NASA Astrophysics Data System (ADS)

Yongjie, Ding; Yu, Xu; Wuji, Peng; Liqiu, Wei; Hongbo, Su; Hezhi, Sun; Peng, Li; Hong, Li; Daren, Yu

2017-04-01

In this paper, a type of magnetically insulated anode structure is proposed for the design of a low-power cylindrical Hall thruster. The magnetic field distribution in the channel is guided by the magnetically insulated anode, altering the intersection status of the magnetic field line passing through the anode and wall. Experimental and simulation results show that a high potential is formed near the wall by the magnetically insulated anode. As the ionization moves towards the outlet, the energy and flux of the ions bombarding the channel wall can be reduced effectively. Due to the reduction in the bombardment of the wall from high-energy ions, the thrust and specific impulse greatly increase compared with those of the non-magnetically insulated anode. For anode mass flow rates of 0.3 and 0.35 mg s-1 and discharge voltages in the 100-200 V range, the thrust can be increased by more than 33% and the anode efficiency can be improved by more than 7%. Meanwhile, the length of the sputtering area is clearly reduced. The starting position of the sputtering area is in front of the magnetic pole, which can effectively prolong the service life of the thruster.

Insulation.

ERIC Educational Resources Information Center

Rhea, Dennis

This instructional unit is one of 10 developed by students on various energy-related areas that deals specifically with insulation. Its objective is for the student to be able to determine insulation needs of new or existing structures, select type to use, use installation techniques, calculate costs, and apply safety factors. Some topics covered…

Investigating compositional effects of atomic layer deposition ternary dielectric Ti-Al-O on metal-insulator-semiconductor heterojunction capacitor structure for gate insulation of InAlN/GaN and AlGaN/GaN

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

Colon, Albert; Stan, Liliana; Divan, Ralu

Gate insulation/surface passivation in AlGaN/GaN and InAlN/GaN heterojunction field-effect transistors is a major concern for passivation of surface traps and reduction of gate leakage current. However, finding the most appropriate gate dielectric materials is challenging and often involves a compromise of the required properties such as dielectric constant, conduction/valence band-offsets, or thermal stability. Creating a ternary compound such as Ti-Al-O and tailoring its composition may result in a reasonably good gate material in terms of the said properties. To date, there is limited knowledge of the performance of ternary dielectric compounds on AlGaN/GaN and even less on InAlN/GaN. To approachmore » this problem, the authors fabricated metal-insulator-semiconductor heterojunction (MISH) capacitors with ternary dielectrics Ti-Al-O of various compositions, deposited by atomic layer deposition (ALD). The film deposition was achieved by alternating cycles of TiO2 and Al2O3 using different ratios of ALD cycles. TiO2 was also deposited as a reference sample. The electrical characterization of the MISH capacitors shows an overall better performance of ternary compounds compared to the pure TiO2. The gate leakage current density decreases with increasing Al content, being similar to 2-3 orders of magnitude lower for a TiO2:Al2O3 cycle ratio of 2:1. Although the dielectric constant has the highest value of 79 for TiO2 and decreases with increasing the number of Al2O3 cycles, it is maintaining a relatively high value compared to an Al2O3 film. Capacitance voltage sweeps were also measured in order to characterize the interface trap density. A decreasing trend in the interface trap density was found while increasing Al content in the film. In conclusion, our study reveals that the desired high-kappa properties of TiO2 can be adequately maintained while improving other insulator performance factors. The ternary compounds may be an excellent choice as a gate material

Orbital disc insulator for SF.sub.6 gas-insulated bus

DOEpatents

Bacvarov, Dosio C.; Gomarac, Nicholas G.

1977-01-01

An insulator for supporting a high voltage conductor within a gas-filled grounded housing consists of radially spaced insulation rings fitted to the exterior of the bus and the interior of the grounded housing respectively, and the spaced rings are connected by trefoil type rings which are integrally formed with the spaced insulation rings.

The comprehensive study and the reduction of contact resistivity on the n-InGaAs M-I-S contact system with different inserted insulators

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

Liao, M.-H., E-mail: mhliaoa@ntu.edu.tw; Lien, C.

2015-05-15

Five different kinds of insulators including BaTiO{sub 3}, TiO{sub 2}, Al{sub 2}O{sub 3}, CdO and ZnO on the n-type InGaAs metal-insulator-semiconductor (M-I-S) ohmic contact structure are studied. The effect for the dielectric constant (ε) of inserted insulator and the conduction band offset (CBO) between an insulator and semiconductor substrate is analyzed by a unified M-I-S contact model. Based on the theoretical model and experimental data, we demonstrates that the inserted ZnO insulator with the high electron affinity and the low CBO (∼0.1 eV) to the InGaAs substrate results in ∼10 times contact resistivity reduction, even the ε of ZnO ismore » not pretty high (∼10)« less

Polymorphism control of superconductivity and magnetism in Cs(3)C(60) close to the Mott transition.

PubMed

Ganin, Alexey Y; Takabayashi, Yasuhiro; Jeglic, Peter; Arcon, Denis; Potocnik, Anton; Baker, Peter J; Ohishi, Yasuo; McDonald, Martin T; Tzirakis, Manolis D; McLennan, Alec; Darling, George R; Takata, Masaki; Rosseinsky, Matthew J; Prassides, Kosmas

2010-07-08

The crystal structure of a solid controls the interactions between the electronically active units and thus its electronic properties. In the high-temperature superconducting copper oxides, only one spatial arrangement of the electronically active Cu(2+) units-a two-dimensional square lattice-is available to study the competition between the cooperative electronic states of magnetic order and superconductivity. Crystals of the spherical molecular C(60)(3-) anion support both superconductivity and magnetism but can consist of fundamentally distinct three-dimensional arrangements of the anions. Superconductivity in the A(3)C(60) (A = alkali metal) fullerides has been exclusively associated with face-centred cubic (f.c.c.) packing of C(60)(3-) (refs 2, 3), but recently the most expanded (and thus having the highest superconducting transition temperature, T(c); ref. 4) composition Cs(3)C(60) has been isolated as a body-centred cubic (b.c.c.) packing, which supports both superconductivity and magnetic order. Here we isolate the f.c.c. polymorph of Cs(3)C(60) to show how the spatial arrangement of the electronically active units controls the competing superconducting and magnetic electronic ground states. Unlike all the other f.c.c. A(3)C(60) fullerides, f.c.c. Cs(3)C(60) is not a superconductor but a magnetic insulator at ambient pressure, and becomes superconducting under pressure. The magnetic ordering occurs at an order of magnitude lower temperature in the geometrically frustrated f.c.c. polymorph (Néel temperature T(N) = 2.2 K) than in the b.c.c.-based packing (T(N) = 46 K). The different lattice packings of C(60)(3-) change T(c) from 38 K in b.c.c. Cs(3)C(60) to 35 K in f.c.c. Cs(3)C(60) (the highest found in the f.c.c. A(3)C(60) family). The existence of two superconducting packings of the same electronically active unit reveals that T(c) scales universally in a structure-independent dome-like relationship with proximity to the Mott metal-insulator transition

Fundamental Insulation Characteristics of Air, N2, CO2, N2/O2 and SF6/N2 Mixed Gases

NASA Astrophysics Data System (ADS)

Rokunohe, Toshiaki; Yagihashi, Yoshitaka; Endo, Fumihiro; Oomori, Takashi

SF6 gas has excellent dielectric strength and interruption performance. For these reasons, it has been widely used for gas insulated switchgear (GIS). However, use of SF6 gas has become regulated under agreements set at the 1997 COP3. Presently, development of a gas circuit breaker (GCB) using CO2 gas and development of a high voltage vacuum circuit breaker (VCB) are being pursued. GIS consists of disconnectors (DS), earthing switches (ES) and buses in addition to GCB. Since the interruption performance is not an important requirement for DS, ES and BUS, use of a gas with high dielectric strength is better than use of a gas with good interruption performance. Air and N2 are not greenhouse gases, and their dielectric strengths are higher than those of other SF6 alternative gases, but only about one-third of the dielectric strength of SF6 gas. This paper deals with a suitable insulation gas which has no greenhouse effect as an SF6 alternative gas. The N2/O2 mixed gas was investigated by changing the ratio of O2. Moreover, the effect of an insulation coating was investigated and compared with the dielectric strength of SF6/N2 mixed gas. The dielectric strength of air under the coating condition was equal to that of 10%SF6/N2 mixed gas.

Lucretia Mott: Friend of Justice. With a Message from Rosalynn Carter. Picture-book Biography Series.

ERIC Educational Resources Information Center

Sawyer, Kem Knapp

An illustrated biography for children features Lucretia Mott, one of the pioneers of the movement for womens' rights. Born in 1793, Lucretia Mott was raised a Quaker; her strong spiritual beliefs underlay her outspoken advocacy of equal rights for women and blacks, and against war. Lucretia became a leader among those who wished to abolish…

Hubbard physics in the PAW GW approximation

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

Booth, J. M., E-mail: jamie.booth@rmit.edu.au; Smith, J. S.; Russo, S. P.

It is demonstrated that the signatures of the Hubbard Model in the strongly interacting regime can be simulated by modifying the screening in the limit of zero wavevector in Projector-Augmented Wave GW calculations for systems without significant nesting. This modification, when applied to the Mott insulator CuO, results in the opening of the Mott gap by the splitting of states at the Fermi level into upper and lower Hubbard bands, and exhibits a giant transfer of spectral weight upon electron doping. The method is also employed to clearly illustrate that the M{sub 1} and M{sub 2} forms of vanadium dioxidemore » are fundamentally different types of insulator. Standard GW calculations are sufficient to open a gap in M{sub 1} VO{sub 2}, which arise from the Peierls pairing filling the valence band, creating homopolar bonds. The valence band wavefunctions are stabilized with respect to the conduction band, reducing polarizability and pushing the conduction band eigenvalues to higher energy. The M{sub 2} structure, however, opens a gap from strong on-site interactions; it is a Mott insulator.« less

High-carrier-density phase in LaTiO3/SrTiO3 superlattices

NASA Astrophysics Data System (ADS)

Park, Se Young; Rabe, Karin; Millis, Andrew

2015-03-01

We investigate superlattices composed of alternating layers of Mott insulating LaTiO3 and band insulating SrTiO3 from first principles, using the density functional theory plus U (DFT+U) method. For values of U above a critical threshold, we find that melting of the Mott-insulating phase can extend from the interface into the LaTiO3 layer, resulting in a sheet carrier density exceeding the density of 0.5 electrons per in-plane unit cell found in previous studies. The critical U for the melting transition is larger than the critical Coulomb correlation required for the insulating LaTiO3, suggesting the existence of a high sheet carrier density phase in LaTiO3/SrTiO3 superlattices. The effects of in-plane strain and varying layer thickness on the melting transition are discussed. For insulating superlattices, we study the strain and thickness dependence of the polarization and its relation to near-interface local atomic distortions. Support: DOE ER 046169, ONR N00014-11-0666.

Localization to delocalization crossover in a driven nonlinear cavity array

NASA Astrophysics Data System (ADS)

Brown, Oliver T.; Hartmann, Michael J.

2018-05-01

We study nonlinear cavity arrays where the particle relaxation rate in each cavity increases with the excitation number. We show that coherent parametric inputs can drive such arrays into states with commensurate filling that form non-equilibrium analogs of Mott insulating states. We explore the boundaries of the Mott insulating phase and the crossover to a delocalized phase with spontaneous first order coherence. While sharing many similarities with the Mott insulator to superfluid transition in equilibrium, the phase diagrams we find also show marked differences. Particularly the off diagonal order does not become long range since the influence of dephasing processes increases with increasing tunneling rates.

Uniaxial-Strain-Orientation Dependence of the Competition between Mott and Charge Ordered Phases and their Corresponding Superconductivity of β-(BDA-TTP)2I3

NASA Astrophysics Data System (ADS)

Nuruzzaman, Md.; Yokogawa, Keiichi; Yoshino, Harukazu; Yoshimoto, Haruo; Kikuchi, Koichi; Kaihatsu, Takayuki; Yamada, Jun-ichi; Murata, Keizo

2012-12-01

We studied the electronic transport properties of the charge transfer salt β-(BDA-TTP)2I3 [BDA-TTP: 2,5-bis(1,3-dithian-2-ylidene)-1,3,4,6-tetrathiapentalene] by applying uniaxial strains along the three crystallographic axes, and obtained three corresponding temperature-pressure phase diagrams. Three phase diagrams were quite dependent on the direction of compression. Following the preceding paper by Kikuchi et al., we speculate that the insulating states are of 1/2-filled Mott insulators for the a- and b-axes compressions, and of 1/4-filled charge ordered states for the c-axis compression as well as hydrostatic pressure. The superconducting phase under uniaxial strain was realized with Tc = 5 K at 1.9 GPa along the a-axis and with Tc = 5.6 K at 1.75 GPa along the b-axis. Superconductivity was also reproduced with a Tc of 9.5 K at 1.0 GPa for the c-axis compressions in the range of 0.85 to 1.53 GPa as previously reported. We studied tentative measurement on upper critical fields, Bc2's of these superconductivities and found that the extrapolated values, Bc2(0)'s, exceeded Pauli-limit by about 2--3 times. However, at least in terms of Bc2, the difference in superconductivity associated with two different insulating states was not clear.

Andreev Reflection in an s-Type Superconductor Proximized 3D Topological Insulator.

PubMed

Tikhonov, E S; Shovkun, D V; Snelder, M; Stehno, M P; Huang, Y; Golden, M S; Golubov, A A; Brinkman, A; Khrapai, V S

2016-09-30

We investigate transport and shot noise in lateral normal-metal-3D topological-insulator-superconductor contacts, where the 3D topological insulator (TI) is based on Bi. In the normal state, the devices are in the elastic diffusive transport regime, as demonstrated by a nearly universal value of the shot noise Fano factor F_{N}≈1/3 in magnetic field and in a reference normal-metal contact. In the absence of magnetic field, we identify the Andreev reflection (AR) regime, which gives rise to the effective charge doubling in shot noise measurements. Surprisingly, the Fano factor F_{AR}≈0.22±0.02 is considerably reduced in the AR regime compared to F_{N}, in contrast to previous AR experiments in normal metals and semiconductors. We suggest that this effect is related to a finite thermal conduction of the proximized, superconducting TI owing to a residual density of states at low energies.

Real-space visualization of remnant Mott gap and magnon excitations.

PubMed

Wang, Y; Jia, C J; Moritz, B; Devereaux, T P

2014-04-18

We demonstrate the ability to visualize real-space dynamics of charge gap and magnon excitations in the Mott phase of the single-band Hubbard model and the remnants of these excitations with hole or electron doping. At short times, the character of magnetic and charge excitations is maintained even for large doping away from the Mott and antiferromagnetic phases. Doping influences both the real-space patterns and long timescales of these excitations with a clear carrier asymmetry attributable to particle-hole symmetry breaking in the underlying model. Further, a rapidly oscillating charge-density-wave-like pattern weakens, but persists as a visible demonstration of a subleading instability at half-filling which remains upon doping. The results offer an approach to analyzing the behavior of systems where momentum space is either inaccessible or poorly defined.

Origins of Persistent Photoconductivity in GaAsN Alloys

NASA Astrophysics Data System (ADS)

Field, R. L., III; Wang, Y. Q.; Kurdak, C.; Goldman, R. S.

2013-03-01

In GaAs1-xNx alloys, we observe significant persistent photoconductivity (PPC) at cryogenic temperatures for x > 0.006, with the PPC strength increasing with increasing x and decreasing upon rapid-thermal annealing (RTA). Since the RTA-induced suppression is accompanied by a reduction of the interstitial N fraction, the N-induced donor state is likely associated with N pairs. PPC is attributed to the promotion of carriers from a ground N-pair state to the conduction band edge, inducing modifications in the N-pair molecular bond configuration. When illumination is terminated, an energy barrier hinders the return of carriers to the N-pair induced complex. With the addition of thermal energy, the original N-pair configuration is restored and the N-pair induced complex is then able to accept carriers. We use PPC at cryogenic temperatures to go through a metal-insulator transition in GaAsN by increasing the carrier density with illumination. For different illumination durations we determine the minimum metallic conductivity, giving us the critical carrier density, nc, at the transition point. We then determine the effective mass, m * , using the Mott criterion nc1 / 3 aH = 0.26 where aH = (4 πɛ h2) /(e2 m *) is the Bohr radius. We use PPC to induce a metal-insulator transition in GaAsN. We will discuss the effective mass as a function of N concentration and compare to the predictions of the band anticrossing model.

A lightweight low-frequency sound insulation membrane-type acoustic metamaterial

NASA Astrophysics Data System (ADS)

Lu, Kuan; Wu, Jiu Hui; Guan, Dong; Gao, Nansha; Jing, Li

2016-02-01

A novel membrane-type acoustic metamaterial with a high sound transmission loss (STL) at low frequencies (⩽500Hz) was designed and the mechanisms were investigated by using negative mass density theory. This metamaterial's structure is like a sandwich with a thin (thickness=0.25mm) lightweight flexible rubber material within two layers of honeycomb cell plates. Negative mass density was demonstrated at frequencies below the first natural frequency, which results in the excellent low-frequency sound insulation. The effects of different structural parameters of the membrane on the sound-proofed performance at low frequencies were investigated by using finite element method (FEM). The numerical results show that, the STL can be modulated to higher value by changing the structural parameters, such as the membrane surface density, the unite cell film shape, and the membrane tension. The acoustic metamaterial proposed in this study could provide a potential application in the low-frequency noise insulation.

Engineering three-dimensional topological insulators in Rashba-type spin-orbit coupled heterostructures

PubMed Central

Das, Tanmoy; Balatsky, A. V.

2013-01-01

Topological insulators represent a new class of quantum phase defined by invariant symmetries and spin-orbit coupling that guarantees metallic Dirac excitations at its surface. The discoveries of these states have sparked the hope of realizing non-trivial excitations and novel effects such as a magnetoelectric effect and topological Majorana excitations. Here we develop a theoretical formalism to show that a three-dimensional topological insulator can be designed artificially via stacking bilayers of two-dimensional Fermi gases with opposite Rashba-type spin-orbit coupling on adjacent layers, and with interlayer quantum tunneling. We demonstrate that in the stack of bilayers grown along a (001)-direction, a non-trivial topological phase transition occurs above a critical number of Rashba bilayers. In the topological phase, we find the formation of a single spin-polarized Dirac cone at the -point. This approach offers an accessible way to design artificial topological insulators in a set up that takes full advantage of the atomic layer deposition approach. This design principle is tunable and also allows us to bypass limitations imposed by bulk crystal geometry. PMID:23739724

Spin-Orbit Coupled Bose-Einstein Condensates

DTIC Science & Technology

2016-11-03

generalized the new concepts to interacting spin-1/2 bosons in optical lattices and described a superfluid-to-Mott insulator transition in spin-orbit...and quantum phase transitions in topological insulators , Physical Review B, (09 2010): 0. doi: 10.1103/PhysRevB.82.115125 Christopher Varney, Kai...109.235308 J. Radi?, A. Di Ciolo, K. Sun, V. Galitski. Exotic Quantum Spin Models in Spin-Orbit-Coupled Mott Insulators , Physical Review Letters

Low-frequency noise in AlN/AlGaN/GaN metal-insulator-semiconductor devices: A comparison with Schottky devices

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

Le, Son Phuong; Nguyen, Tuan Quy; Shih, Hong-An

2014-08-07

We have systematically investigated low-frequency noise (LFN) in AlN/AlGaN/GaN metal-insulator-semiconductor (MIS) devices, where the AlN gate insulator layer was sputtering-deposited on the AlGaN surface, in comparison with LFN in AlGaN/GaN Schottky devices. By measuring LFN in ungated two-terminal devices and heterojunction field-effect transistors (HFETs), we extracted LFN characteristics in the intrinsic gated region of the HFETs. Although there is a bias regime of the Schottky-HFETs in which LFN is dominated by the gate leakage current, LFN in the MIS-HFETs is always dominated by only the channel current. Analyzing the channel-current-dominated LFN, we obtained Hooge parameters α for the gated regionmore » as a function of the sheet electron concentration n{sub s} under the gate. In a regime of small n{sub s}, both the MIS- and Schottky-HFETs exhibit α∝n{sub s}{sup −1}. On the other hand, in a middle n{sub s} regime of the MIS-HFETs, α decreases rapidly like n{sub s}{sup −ξ} with ξ ∼ 2-3, which is not observed for the Schottky-HFETs. In addition, we observe strong increase in α∝n{sub s}{sup 3} in a large n{sub s} regime for both the MIS- and Schottky-HFETs.« less

Mott Time Crystal: Models and Realizations in Cold Atoms

NASA Astrophysics Data System (ADS)

Huang, Biao; Wu, Ying-Hai; Liu, W. Vincent

2017-04-01

Time crystals, a phase showing spontaneously breaking of time-translation symmetry, has been an intriguing subject for systems far away from equilibrium. Recent experiments found such a phase both in the presence and absence of localization, while in theories localization is usually assumed a priori. In this work, we point out that time crystals can generally exist in systems without disorder and is not in a pre-thermal state. A series of driven interacting ladder models are proposed to demonstrate this unexpected result in principle. Robust time crystalline orders are found in the Mott regime due to the emergent integrals of motion in the dynamical system, which can be characterized by the out-of-time-order correlators (OTOC). We propose two cold atom experimental schemes to realize the Mott time crystals, one by making use of dipolar gases and another by synthetic dimensions. U.S. ARO (W911NF-11-1-0230), AFOSR (FA9550-16-1-0006).

The happy marriage between electron-phonon superconductivity and Mott physics in Cs3C60: A first-principle phase diagram

NASA Astrophysics Data System (ADS)

Capone, Massimo; Nomura, Yusuke; Sakai, Shiro; Giovannetti, Gianluca; Arita, Ryotaro

The phase diagram of doped fullerides like Cs3C60 as a function of the spacing between fullerene molecules is characterized by a first-order transition between a Mott insulator and an s-wave superconductor with a dome-shaped behavior of the critical temperature. By means of an ab-initio modeling of the bandstructure, the electron-phonon interaction and the interaction parameter and a Dynamical Mean-Field Theory solution, we reproduce the phase diagram and demonstrate that phonon superconductivity benefits from strong correlations confirming earlier model predictions. The role of correlations is manifest also in infrared measurements carried out by L. Baldassarre. The superconducting phase shares many similarities with ''exotic'' superconductors with electronic pairing, suggesting that the anomalies in the ''normal'' state, rather than the pairing glue, can be the real common element unifying a wide family of strongly correlated superconductors including cuprates and iron superconductors

Fermi surface in the absence of a Fermi liquid in the Kondo insulator SmB 6

DOE PAGES

Hartstein, M.; Toews, W. H.; Hsu, Y. -T.; ...

2017-10-23

The search for a Fermi surface in the absence of a conventional Fermi liquid has thus far yielded very few potential candidates. Among promising materials are spin-frustrated Mott insulators near the insulator–metal transition, where theory predicts a Fermi surface associated with neutral low-energy excitations. In this paper, we reveal another route to experimentally realize a Fermi surface in the absence of a Fermi liquid by the experimental study of a Kondo insulator SmB 6 positioned close to the insulator–metal transition. We present experimental signatures down to low temperatures (<<1 K) associated with a Fermi surface in the bulk, including amore » sizeable linear specific heat coefficient, and on the application of a finite magnetic field, bulk magnetic quantum oscillations, finite quantum oscillatory entropy, and substantial enhancement in thermal conductivity well below the charge gap energy scale. Finally, the weight of evidence indicates that despite an extreme instance of Fermi liquid breakdown in Kondo insulating SmB 6, a Fermi surface arises from novel itinerant low-energy excitations that couple to magnetic fields, but not weak DC electric fields.« less

The evolution of vacancy-type defects in silicon-on-insulator structures studied by positron annihilation spectroscopy

NASA Astrophysics Data System (ADS)

Coleman, P. G.; Nash, D.; Edwardson, C. J.; Knights, A. P.; Gwilliam, R. M.

2011-07-01

Variable-energy positron annihilation spectroscopy (VEPAS) has been applied to the study of the formation and evolution of vacancy-type defect structures in silicon (Si) and the 1.5 μm thick Si top layer of silicon-on-insulator (SOI) samples. The samples were implanted with 2 MeV Si ions at fluences between 1013 and 1015 cm-2, and probed in the as-implanted state and after annealing for 30 min at temperatures between 350 and 800 °C. In the case of SOI the ions were implanted such that their profile was predominantly in the insulating buried oxide layer, and thus their ability to combine with vacancies in the top Si layer, and that of other interstitials beyond the buried oxide, was effectively negated. No measurable differences in the positron response to the evolution of small clusters of n vacancies (Vn, n ˜ 3) in the top Si layer of the Si and SOI samples were observed after annealing up to 500 °C; at higher temperatures, however, this response persisted in the SOI samples as that in Si decreased toward zero. At 700 and 800 °C the damage in Si was below detectable levels, but the VEPAS response in the top Si layer in the SOI was consistent with the development of nanovoids.

16 CFR 460.18 - Insulation ads.

Code of Federal Regulations, 2010 CFR

2010-01-01

... 16 Commercial Practices 1 2010-01-01 2010-01-01 false Insulation ads. 460.18 Section 460.18... INSULATION § 460.18 Insulation ads. (a) If your ad gives an R-value, you must give the type of insulation and... the R-value, the greater the insulating power. Ask your seller for the fact sheet on R-values.” (b) If...

16 CFR 460.18 - Insulation ads.

Code of Federal Regulations, 2014 CFR

2014-01-01

... 16 Commercial Practices 1 2014-01-01 2014-01-01 false Insulation ads. 460.18 Section 460.18... INSULATION § 460.18 Insulation ads. (a) If your ad gives an R-value, you must give the type of insulation and... the R-value, the greater the insulating power. Ask your seller for the fact sheet on R-values.” (b) If...

16 CFR 460.18 - Insulation ads.

Code of Federal Regulations, 2013 CFR

2013-01-01

... 16 Commercial Practices 1 2013-01-01 2013-01-01 false Insulation ads. 460.18 Section 460.18... INSULATION § 460.18 Insulation ads. (a) If your ad gives an R-value, you must give the type of insulation and... the R-value, the greater the insulating power. Ask your seller for the fact sheet on R-values.” (b) If...

16 CFR 460.18 - Insulation ads.

Code of Federal Regulations, 2012 CFR

2012-01-01

... 16 Commercial Practices 1 2012-01-01 2012-01-01 false Insulation ads. 460.18 Section 460.18... INSULATION § 460.18 Insulation ads. (a) If your ad gives an R-value, you must give the type of insulation and... the R-value, the greater the insulating power. Ask your seller for the fact sheet on R-values.” (b) If...

16 CFR 460.18 - Insulation ads.

Code of Federal Regulations, 2011 CFR

2011-01-01

... 16 Commercial Practices 1 2011-01-01 2011-01-01 false Insulation ads. 460.18 Section 460.18... INSULATION § 460.18 Insulation ads. (a) If your ad gives an R-value, you must give the type of insulation and... the R-value, the greater the insulating power. Ask your seller for the fact sheet on R-values.” (b) If...

B a 2 NiOs O 6 : A Dirac-Mott insulator with ferromagnetism near 100 K

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

Feng, Hai L.; Calder, Stuart; Ghimire, Madhav Prasad

In this study, the ferromagnetic semiconductor Ba 2NiOsO 6 ( T mag ~ 100 K ) was synthesized at 6 GPa and 1500 °C. It crystallizes into a double perovskite structure [Fm - 3m ; a = 8.0428 ( 1 ) Å], where the Ni 2+ and Os 6+ ions are perfectly ordered at the perovskite B site. We show that the spin-orbit coupling of Os 6+ plays an essential role in opening the charge gap. The magnetic state was investigated by density functional theory calculations and powder neutron diffraction. The latter revealed a collinear ferromagnetic order in a >more » 21 kOe magnetic field at 5 K. The ferromagnetic gapped state is fundamentally different from that of known dilute magnetic semiconductors such as (Ga,Mn)As and (Cd,Mn)Te ( T mag < 180 K ), the spin-gapless semiconductor Mn 2 CoAl ( T mag ~ 720 K ), and the ferromagnetic insulators EuO ( T mag ~ 70 K ) and Bi 3Cr 3O 11 ( T mag ~ 220 K ). It is also qualitatively different from known ferrimagnetic insulators and semiconductors, which are characterized by an antiparallel spin arrangement. Our finding of the ferromagnetic semiconductivity of Ba 2NiOsO 6 should increase interest in the platinum group oxides, because this alternative class of materials should be useful in the development of spintronic, quantum magnetic, and related devices.« less

B a 2 NiOs O 6 : A Dirac-Mott insulator with ferromagnetism near 100 K

DOE PAGES

Feng, Hai L.; Calder, Stuart; Ghimire, Madhav Prasad; ...

2016-12-28

In this study, the ferromagnetic semiconductor Ba 2NiOsO 6 ( T mag ~ 100 K ) was synthesized at 6 GPa and 1500 °C. It crystallizes into a double perovskite structure [Fm - 3m ; a = 8.0428 ( 1 ) Å], where the Ni 2+ and Os 6+ ions are perfectly ordered at the perovskite B site. We show that the spin-orbit coupling of Os 6+ plays an essential role in opening the charge gap. The magnetic state was investigated by density functional theory calculations and powder neutron diffraction. The latter revealed a collinear ferromagnetic order in a >more » 21 kOe magnetic field at 5 K. The ferromagnetic gapped state is fundamentally different from that of known dilute magnetic semiconductors such as (Ga,Mn)As and (Cd,Mn)Te ( T mag < 180 K ), the spin-gapless semiconductor Mn 2 CoAl ( T mag ~ 720 K ), and the ferromagnetic insulators EuO ( T mag ~ 70 K ) and Bi 3Cr 3O 11 ( T mag ~ 220 K ). It is also qualitatively different from known ferrimagnetic insulators and semiconductors, which are characterized by an antiparallel spin arrangement. Our finding of the ferromagnetic semiconductivity of Ba 2NiOsO 6 should increase interest in the platinum group oxides, because this alternative class of materials should be useful in the development of spintronic, quantum magnetic, and related devices.« less

Quasi-continuous transition from a Fermi liquid to a spin liquid in κ-(ET)2Cu2(CN)3.

PubMed

Furukawa, Tetsuya; Kobashi, Kazuhiko; Kurosaki, Yosuke; Miyagawa, Kazuya; Kanoda, Kazushi

2018-01-22

The Mott metal-insulator transition-a manifestation of Coulomb interactions among electrons-is known as a discontinuous transition. Recent theoretical studies, however, suggest that the transition is continuous if the Mott insulator carries a spin liquid with a spinon Fermi surface. Here, we demonstrate the case of a quasi-continuous Mott transition from a Fermi liquid to a spin liquid in an organic triangular-lattice system κ-(ET) 2 Cu 2 (CN) 3 . Transport experiments performed under fine pressure tuning have found that as the Mott transition is approached, the Fermi liquid coherence temperature continuously falls to the scale of kelvins, with a divergent quasi-particle decay rate on the metal side, and the charge gap continuously closes on the insulator side. A Clausius-Clapeyron analysis provides thermodynamic evidence for the extremely weak first-order nature of the transition. These results provide additional support for the existence of a spinon Fermi surface, which becomes an electron Fermi surface when charges are delocalized.

High pressure induced crossover between metal and insulator conductivity type in low dimensionality electron systems

NASA Astrophysics Data System (ADS)

Dizhur, E.; Voronovskii, A.; Kostyleva, I.; Kotel'nikov, I.; Zaitsev-Zotov, S.

2011-12-01

We report the results of our recent experimental studies concerned with electron systems of lower dimensionality the conductivity of which may be toggled between metallic and insulating regime appliing high pressure. The objects under present study include: a) tunneling through Shottky barrier into two-dimension (2D) electron system formed in the δ-doped layer in GaAs under hydrostatic pressure up to 3 GPa in a cylinder-piston cell; b) quasi-one-dimension (1D) `insulator' crystals NbS3 which obtain metallic conductivity type at pressures above 5.5 GPa in `toroid' anvils.

Metastability and avalanche dynamics in strongly correlated gases with long-range interactions

NASA Astrophysics Data System (ADS)

Hruby, Lorenz; Dogra, Nishant; Landini, Manuele; Donner, Tobias; Esslinger, Tilman

2018-03-01

We experimentally study the stability of a bosonic Mott insulator against the formation of a density wave induced by long-range interactions and characterize the intrinsic dynamics between these two states. The Mott insulator is created in a quantum degenerate gas of 87-Rubidium atoms, trapped in a 3D optical lattice. The gas is located inside and globally coupled to an optical cavity. This causes interactions of global range, mediated by photons dispersively scattered between a transverse lattice and the cavity. The scattering comes with an atomic density modulation, which is measured by the photon flux leaking from the cavity. We initialize the system in a Mott-insulating state and then rapidly increase the global coupling strength. We observe that the system falls into either of two distinct final states. One is characterized by a low photon flux, signaling a Mott insulator, and the other is characterized by a high photon flux, which we associate with a density wave. Ramping the global coupling slowly, we observe a hysteresis loop between the two states—a further signature of metastability. A comparison with a theoretical model confirms that the metastability originates in the competition between short- and global-range interactions. From the increasing photon flux monitored during the switching process, we find that several thousand atoms tunnel to a neighboring site on the timescale of the single-particle dynamics. We argue that a density modulation, initially forming in the compressible surface of the trapped gas, triggers an avalanche tunneling process in the Mott-insulating region.

Extension of the Mott-Gurney Law for a Bilayer Gap

NASA Astrophysics Data System (ADS)

Dubinov, A. E.; Kitayev, I. N.

2018-04-01

Steady drift states of an electron flow in a planar gap filled with a bilayer dielectric have been considered. Exact mathematical formulas have been derived that describe the distributions of the electrostatic potential and space charge limited electron flow current (extended Mott-Gurney law for a bilayer diode).

Phase modulation in horizontal metal-insulator-silicon-insulator-metal plasmonic waveguides.

PubMed

Zhu, Shiyang; Lo, G Q; Kwong, D L

2013-04-08

An extremely compact Si phase modulator is proposed and validated, which relies on effective modulation of the real part of modal index of horizontal metal-insulator-Si-insulator-metal plasmonic waveguides by a voltage applied between the metal cover and the Si core. Proof-of-concept devices are fabricated on silicon-on-insulator substrates using standard complementary metal-oxide-semiconductor technology using copper as the metal and thermal silicon dioxide as the insulator. A modulator with a 1-μm-long phase shifter inserted in an asymmetric Si Mach-Zehnder interferometer exhibits 9-dB extinction ratio under a 6-V/10-kHz voltage swing. Numerical simulations suggest that high speed and low driving voltage could be achieved by shortening the distance between the Si core and the n(+)-contact and by using a high-κ dielectric as the insulator, respectively.

Flat-Band Potential of a Semiconductor: Using the Mott-Schottky Equation

ERIC Educational Resources Information Center

Gelderman, K.; L. Lee; Donne, S. W.

2007-01-01

An experiment is suitable for fourth-year undergraduate and graduate students in which the nature of the semiconductor materials through determination of flat-band potential using the Mott-Schottky equation is explored. The experiment confirms the soundness of the technique.

Materials for foam type insulation

NASA Technical Reports Server (NTRS)

Hill, W. E.

1971-01-01

An internal foam fabrication is one of the concepts being considered for cryogenic insulation on the hydrogen tanks of the shuttle vehicle. The three-dimensional polyurethane used on the S-4 B tanks failed to meet the higher temperature requirements of the shuttle vehicle, however, and other foams under consideration include polyisocyanurates, polyphenylene oxides, polyimides, and polybenzimidazoles. Improved adhesive systems for attaching the foams to the interior tank wall are under study.

n-Type Doping of Vapor-Liquid-Solid Grown GaAs Nanowires.

PubMed

Gutsche, Christoph; Lysov, Andrey; Regolin, Ingo; Blekker, Kai; Prost, Werner; Tegude, Franz-Josef

2011-12-01

In this letter, n-type doping of GaAs nanowires grown by metal-organic vapor phase epitaxy in the vapor-liquid-solid growth mode on (111)B GaAs substrates is reported. A low growth temperature of 400°C is adjusted in order to exclude shell growth. The impact of doping precursors on the morphology of GaAs nanowires was investigated. Tetraethyl tin as doping precursor enables heavily n-type doped GaAs nanowires in a relatively small process window while no doping effect could be found for ditertiarybutylsilane. Electrical measurements carried out on single nanowires reveal an axially non-uniform doping profile. Within a number of wires from the same run, the donor concentrations ND of GaAs nanowires are found to vary from 7 × 10(17) cm(-3) to 2 × 10(18) cm(-3). The n-type conductivity is proven by the transfer characteristics of fabricated nanowire metal-insulator-semiconductor field-effect transistor devices.

Competition entre supraconductivite et magnetisme au voisinage de la transition de Mott dans le conducteur organique quasi-bidimensionnel k-(BEDT-TTF)2copper[N(CN)2]bromine

NASA Astrophysics Data System (ADS)

Fournier, David

Les conducteurs organiques quasi-bidimensionnels kappa-ET2X presentent d'importantes similitudes avec les SCHT telles qu'une phase isolant de Mott, un regime de pseudogap et un etat supraconducteur. L'etude de leurs proprietes apparait donc complementaire. Parmi les interrogations persistantes concernant la physique de ces systemes, l'origine du (ou des) processus exotique d'appariement, responsable de la supraconductivite est le sujet suscitant l'interet le plus marque dans la communaute. L'hypothese d'un mecanisme lie a la proximite d'un etat antiferromagnetique est privilegiee. Une etape importante dans la resolution de cette problematique est l'identification de la symetrie du parametre d'ordre. D'apres de nombreux travaux sur les systemes fortement correles, la sonde ultrasonore, de par sa sensibilite aux excitations de quasiparticule a basse temperature, est consideree comme particulierement adaptee a l'etude de cette propriete. Cependant, son emploi necessite l'utilisation d'un compose metallique a basse temperature et completement supraconducteur. Le compose metallique organique kappa-ET 2Cu[N(CN)2]Br presente toutes les caracteristiques necessaires a l'etude de cette propriete. En effet, il est situe loin de la transition du premier ordre de Mott et est completement supraconducteur. De facon surprenante, ce systeme semble se coupler fortement avec le reseau ce qui augmente significativement la sensibilite de cette sonde aux proprietes du gaz electronique. Cependant, des difficultes techniques importantes, liees a la nature intrinseque de ce materiau, doivent etre surmontees pour proceder a des mesures suivant differentes polarisations. La presente etude a profondement modifie notre comprehension de ce systeme. En effet, ces mesures ont permis de constater que le kappa-ET2Cu[N(CN)2]Br est un compose qui est situe en bordure de la zone de coexistence entre la supraconductivite et le magnetisme, ce qui constitue un resultat totalement inattendu. De plus, la

Peierls instability as the insulating origin of the Na/Si(111)-(3 × 1) surface with a Na coverage of 2/3 monolayers

NASA Astrophysics Data System (ADS)

Kang, Myung Ho; Kwon, Se Gab; Jung, Sung Chul

2018-03-01

Density functional theory (DFT) calculations are used to investigate the insulating origin of the Na/Si(111)-(3 × 1) surface with a Na coverage of 2/3 monolayers. In the coverage definition, one monolayer refers to one Na atom per surface Si atom, so this surface contains an odd number of electrons (i.e., three Si dangling-bond electrons plus two Na electrons) per 3 × 1 unit cell. Interestingly, this odd-electron surface has been ascribed to a Mott-Hubbard insulator to account for the measured insulating band structure with a gap of about 0.8 eV. Here, we instead propose a Peierls instability as the origin of the experimental band gap. The concept of Peierls instability is fundamental in one-dimensional metal systems but has not been taken into account in previous studies of this surface. Our DFT calculations demonstrate that the linear chain structure of Si dangling bonds in this surface is energetically unstable with respect to a × 2 buckling modulation, and the buckling-induced band gap of 0.79 eV explains well the measured insulating nature.

Ultrathin silicon oxynitride layer on GaN for dangling-bond-free GaN/insulator interface.

PubMed

Nishio, Kengo; Yayama, Tomoe; Miyazaki, Takehide; Taoka, Noriyuki; Shimizu, Mitsuaki

2018-01-23

Despite the scientific and technological importance of removing interface dangling bonds, even an ideal model of a dangling-bond-free interface between GaN and an insulator has not been known. The formation of an atomically thin ordered buffer layer between crystalline GaN and amorphous SiO 2 would be a key to synthesize a dangling-bond-free GaN/SiO 2 interface. Here, we predict that a silicon oxynitride (Si 4 O 5 N 3 ) layer can epitaxially grow on a GaN(0001) surface without creating dangling bonds at the interface. Our ab initio calculations show that the GaN/Si 4 O 5 N 3 structure is more stable than silicon-oxide-terminated GaN(0001) surfaces. The electronic properties of the GaN/Si 4 O 5 N 3 structure can be tuned by modifying the chemical components near the interface. We also propose a possible approach to experimentally synthesize the GaN/Si 4 O 5 N 3 structure.

First-principles many-body investigation of δ-doped titanates

NASA Astrophysics Data System (ADS)

Lechermann, Frank; Obermeyer, Michael

2015-03-01

Studying oxide heterostructures provides the possibility for exploring novel composite materials beyond nature's original conception. In this respect, the doping of Mott-insulating distorted-perovskite titanates such as LaTiO3 and GdTiO3 with a single SrO layer gives rise to a very rich correlated electronic structure. A realistic superlattice survey by means of the charge self-consistent combination of density functional theory (DFT) with dynamical mean-field theory (DMFT) reveals layer- and temperature-dependent multi-orbital metal-insulator transitions. In [001] stacking, an orbital-selective metallic layer at the interface dissolves via an orbital-polarized doped-Mott state into an orbital-ordered insulating regime beyond the two conducting TiO2 layers. We find large differences in the scattering behavior within the latter. Breaking the spin symmetry in δ-doped GdTiO3 results in blocks of ferromagnetic itinerant and ferromagnetic Mott-insulating layers which are coupled antiferromagnetically. Support from the DFG-FOR1346 is acknowledged.

The Mott transition in the strong coupling perturbation theory

NASA Astrophysics Data System (ADS)

Sherman, A.

2015-01-01

Using the strong coupling diagram technique a self-consistent equation for the electron Green's function is derived for the repulsive Hubbard model. Terms of two lowest orders of the ratio of the bandwidth Δ to the Hubbard repulsion U are taken into account in the irreducible part of the Larkin equation. The obtained equation is shown to retain causality and reduces to Green's function of uncorrelated electrons in the limit U → 0. Calculations were performed for the semi-elliptical initial band. It is shown that the approximation describes the Mott transition, which occurs at Uc =√{ 3 } Δ / 2. This value coincides with that obtained in the Hubbard-III approximation. At half-filling, for 0 < U Uc the Mott gap disappears.

Estimation of dc transport dynamics in strongly correlated (La,Pr,Ca)MnO{sub 3} film using an insulator-metal composite model for terahertz conductivity

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

Nguyen, T. V. A.; Graduate School of Engineering Science, Osaka University, 1-3 Machikaneyama, Toyonaka, Osaka 560-8531; Hattori, A. N.

2014-07-14

Temperature-dependent conductivities at dc and terahertz (THz) frequency region (σ{sub THz}(ω,T)) were obtained for a strongly correlated (La{sub 0.275}Pr{sub 0.35}Ca{sub 0.375})MnO{sub 3} (LPCMO) film using THz time domain spectroscopy. A composite model that describes σ{sub THz}(ω,T) for LPCMO through the insulator-metal transition (IMT) was established by incorporating Austin-Mott model characterizing the hopping of localized electrons and Drude model explaining the behavior of free electrons. This model enables us to reliably investigate the dc transport dynamics from THz conductivity measurement, i.e., simultaneously evaluate the dc conductivity and the competing composition of metal and insulator phases through the IMT, reflecting the changesmore » in microscopic conductivity of these phases.« less

Metal-Insulator Transition of strained SmNiO3 Thin Films: Structural, Electrical and Optical Properties

PubMed Central

Torriss, B.; Margot, J.; Chaker, M.

2017-01-01

Samarium nickelate (SmNiO3) thin films were successfully synthesized on LaAlO3 and SrTiO3 substrates using pulsed-laser deposition. The Mott metal-insulator (MI) transition of the thin films is sensitive to epitaxial strain and strain relaxation. Once the strain changes from compressive to tensile, the transition temperature of the SmNiO3 samples shifts to slightly higher values. The optical conductivity reveals the strong dependence of the Drude spectral weight on the strain relaxation. Actually, compressive strain broadens the bandwidth. In contrast, tensile strain causes the effective number of free carriers to reduce which is consistent with the d-band narrowing. PMID:28098240

Double layered tailorable advanced blanket insulation

NASA Technical Reports Server (NTRS)

Falstrup, D.

1983-01-01

An advanced flexible reusable surface insulation material for future space shuttle flights was investigated. A conventional fly shuttle loom with special modifications to weave an integral double layer triangular core fabric from quartz yarn was used. Two types of insulating material were inserted into the cells of the fabric, and a procedure to accomplish this was developed. The program is follow up of a program in which single layer rectangular cell core fabrics are woven and a single type of insulating material was inserted into the cells.

Waveguide-integrated vertical pin photodiodes of Ge fabricated on p+ and n+ Si-on-insulator layers

NASA Astrophysics Data System (ADS)

Ito, Kazuki; Hiraki, Tatsurou; Tsuchizawa, Tai; Ishikawa, Yasuhiko

2017-04-01

Vertical pin structures of Ge photodiodes (PDs) integrated with Si optical waveguides are fabricated by depositing Ge epitaxial layers on Si-on-insulator (SOI) layers, and the performances of n+-Ge/i-Ge/p+-SOI PDs are compared with those of p+-Ge/i-Ge/n+-SOI PDs. Both types of PDs show responsivities as high as 1.0 A/W at 1.55 µm, while the dark leakage current is different, which is consistent with previous reports on free-space PDs formed on bulk Si wafers. The dark current of the p+-Ge/i-Ge/n+-SOI PDs is higher by more than one order of magnitude. Taking into account the activation energies for dark current as well as the dependence on PD area, the dark current of the n+-Ge/i-Ge/p+-SOI PDs is dominated by the thermal generation of carriers via mid-gap defect levels in Ge, while for the p+-Ge/i-Ge/n+-SOI PDs, the dark current is ascribed to not only thermal generation but also other mechanisms such as locally formed conduction paths.

Universal conductivity in a two-dimensional superfluid-to-insulator quantum critical system.

PubMed

Chen, Kun; Liu, Longxiang; Deng, Youjin; Pollet, Lode; Prokof'ev, Nikolay

2014-01-24

We compute the universal conductivity of the (2+1)-dimensional XY universality class, which is realized for a superfluid-to-Mott insulator quantum phase transition at constant density. Based on large-scale Monte Carlo simulations of the classical (2+1)-dimensional J-current model and the two-dimensional Bose-Hubbard model, we can precisely determine the conductivity on the quantum critical plateau, σ(∞) = 0.359(4)σQ with σQ the conductivity quantum. The universal conductivity curve is the standard example with the lowest number of components where the bottoms-up AdS/CFT correspondence from string theory can be tested and made to use [R. C. Myers, S. Sachdev, and A. Singh, Phys. Rev. D 83, 066017 (2011)]. For the first time, the shape of the σ(iω(n)) - σ(∞) function in the Matsubara representation is accurate enough for a conclusive comparison and establishes the particlelike nature of charge transport. We find that the holographic gauge-gravity duality theory for transport properties can be made compatible with the data if temperature of the horizon of the black brane is different from the temperature of the conformal field theory. The requirements for measuring the universal conductivity in a cold gas experiment are also determined by our calculation.

Understanding Mott-Schottky Measurements under Illumination in Organic Bulk Heterojunction Solar Cells

NASA Astrophysics Data System (ADS)

Zonno, Irene; Martinez-Otero, Alberto; Hebig, Jan-Christoph; Kirchartz, Thomas

2017-03-01

The Mott-Schottky analysis in the dark is a frequently used method to determine the doping concentration of semiconductors from capacitance-voltage measurements, even for such complex systems as polymer:fullerene blends used for organic solar cells. While the analysis of capacitance-voltage measurements in the dark is relatively well established, the analysis of data taken under illumination is currently not fully understood. Here, we present experiments and simulations to show which physical mechanisms affect the Mott-Schottky analysis under illumination. We show that the mobility of the blend has a major influence on the shape of the capacitance-voltage curve and can be obtained from data taken under reverse bias. In addition, we show that the apparent shift of the built-in voltage observed previously can be explained by a shift of the onset of space-charge-limited collection with illumination intensity.

Manganese-induced magnetic symmetry breaking and its correlation with the metal-insulator transition in bilayered S r 3 ( R u 1 - x M n x ) 2 O 7

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

Zhang, Qiang; Ye, Feng; Tian, Wei

Bilayered Sr 3Ru 2O 7 is an unusual metamagnetic metal with inherently antiferromagnetic (AFM) and ferromagnetic (FM) fluctuations. Partial substitution of Ru by Mn results in the establishment of a metal-insulator transition (MIT) at TMIT and AFM ordering at TM in Sr 3(Ru 1-xMn x) 2O 7. Using elastic neutron scattering, we investigated the effect of Mn doping on the magnetic structure, in-plane magnetic correlation lengths and their correlation to the MIT in Sr 3(Ru 1-xMn x) 2O 7 (x=0.06 and 0.12). With the increase of Mn doping (x) from 0.06 to 0.12 or the decrease of temperatures for x=0.12,more » an evolution from an in-plane short-range to long-range antiferromagnetic (AFM) ground state occurs. For both compounds, the magnetic ordering has a double-stripe configuration, and the onset of magnetic correlation with an anisotropic behavior coincides with the sharp rise in electrical resistivity and specific heat. Since it does not induce a measurable lattice distortion, the double-stripe antiferromagnetic order with anisotropic spin texture breaks symmetry from a C 4v crystal lattice to a C 2v magnetic sublattice. These observations shed light on an age-old question regarding the Slater versus Mott-type MIT.« less

Manganese-induced magnetic symmetry breaking and its correlation with the metal-insulator transition in bilayered S r 3 ( R u 1 - x M n x ) 2 O 7

DOE PAGES

Zhang, Qiang; Ye, Feng; Tian, Wei; ...

2017-06-12

Bilayered Sr 3Ru 2O 7 is an unusual metamagnetic metal with inherently antiferromagnetic (AFM) and ferromagnetic (FM) fluctuations. Partial substitution of Ru by Mn results in the establishment of a metal-insulator transition (MIT) at TMIT and AFM ordering at TM in Sr 3(Ru 1-xMn x) 2O 7. Using elastic neutron scattering, we investigated the effect of Mn doping on the magnetic structure, in-plane magnetic correlation lengths and their correlation to the MIT in Sr 3(Ru 1-xMn x) 2O 7 (x=0.06 and 0.12). With the increase of Mn doping (x) from 0.06 to 0.12 or the decrease of temperatures for x=0.12,more » an evolution from an in-plane short-range to long-range antiferromagnetic (AFM) ground state occurs. For both compounds, the magnetic ordering has a double-stripe configuration, and the onset of magnetic correlation with an anisotropic behavior coincides with the sharp rise in electrical resistivity and specific heat. Since it does not induce a measurable lattice distortion, the double-stripe antiferromagnetic order with anisotropic spin texture breaks symmetry from a C 4v crystal lattice to a C 2v magnetic sublattice. These observations shed light on an age-old question regarding the Slater versus Mott-type MIT.« less

Formation of an incoherent metallic state in Rh-doped Sr2IrO4

NASA Astrophysics Data System (ADS)

Louat, A.; Bert, F.; Serrier-Garcia, L.; Bertran, F.; Le Fèvre, P.; Rault, J.; Brouet, V.

2018-04-01

Sr2IrO4 is the archetype of the spin-orbit Mott insulator, but the nature of the metallic states that may emerge from this type of insulator is still not very well known. We study with angle-resolved photoemission the insulator-to-metal transition observed in Sr2Ir1 -xRhxO4 when Ir is substituted by Rh (0.02 Mott gap appears quite insensitive to the introduction of up to ˜20 % holes in this band. The metallic phase, which forms for x >0.07 , is not a Fermi liquid. It is characterized by the absence of quasiparticles, unrenormalized band dispersion compared to calculations, and an ˜30 -meV pseudogap on the entire Fermi surface.

Insulation Progress since the Mid-1950s

NASA Astrophysics Data System (ADS)

Timmerhaus, K. D.

Storage vessel and cryostat design for modern cryogenic systems has become rather routine as the result of the wide use of and application of cryogenic fluids. Such vessels for these fluids range in size from 1 L flasks used in the laboratory for liquid nitrogen to the more than 200,000 m3 double-walled tanks used for temporary storage of liquefied natural gas before being transported overseas to their final destination. These storage vessels for cryogenic fluids range in type from low-performance containers insulated with rigid foam or fibrous insulation to high-performance containers insulated with evacuated multilayer insulations. The overriding factors in the type of container selected normally are of economics and safety. This paper will consider various insulation concepts used in such cryogenic storage systems and will review the progress that has been made over the past 50 years in these insulation systems.

Electronic passivation of n- and p-type GaAs using chemical vapor deposited GaS

NASA Technical Reports Server (NTRS)

Tabib-Azar, Massood; Kang, Soon; Macinnes, Andrew N.; Power, Michael B.; Barron, Andrew R.; Jenkins, Phillip P.; Hepp, Aloysius F.

1993-01-01

We report on the electronic passivation of n- and p-type GaAs using CVD cubic GaS. Au/GaS/GaAs-fabricated metal-insulator-semiconductor (MIS) structures exhibit classical high-frequency capacitor vs voltage (C-V) behavior with well-defined accumulation and inversion regions. Using high- and low-frequency C-V, the interface trap densities of about 10 exp 11/eV per sq cm on both n- and p-type GaAs are determined. The electronic condition of GaS/GaAs interface did not show any deterioration after a six week time period.

Efficient Photothermoelectric Conversion in Lateral Topological Insulator Heterojunctions.

PubMed

Mashhadi, Soudabeh; Duong, Dinh Loc; Burghard, Marko; Kern, Klaus

2017-01-11

Tuning the electron and phonon transport properties of thermoelectric materials by nanostructuring has enabled improving their thermopower figure of merit. Three-dimensional topological insulators, including many bismuth chalcogenides, attract increasing attention for this purpose, as their topologically protected surface states are promising to further enhance the thermoelectric performance. While individual bismuth chalcogenide nanostructures have been studied with respect to their photothermoelectric properties, nanostructured p-n junctions of these compounds have not yet been explored. Here, we experimentally investigate the room temperature thermoelectric conversion capability of lateral heterostructures consisting of two different three-dimensional topological insulators, namely, the n-type doped Bi 2 Te 2 Se and the p-type doped Sb 2 Te 3 . Scanning photocurrent microscopy of the nanoplatelets reveals efficient thermoelectric conversion at the p-n heterojunction, exploiting hot carriers of opposite sign in the two materials. From the photocurrent data, a Seebeck coefficient difference of ΔS = 200 μV/K was extracted, in accordance with the best values reported for the corresponding bulk materials. Furthermore, it is in very good agreement with the value of ΔS = 185 μV/K obtained by DFT calculation taking into account the specific doping levels of the two nanostructured components.

Contact spectroscopy on S/TI/N devices: Induced pairing on the surface of a topological insulator

NASA Astrophysics Data System (ADS)

Stehno, Martin P.; Ngabonziza, Prosper; Snelder, Marieke; Myoren, Hiroaki; Pan, Yu; de Visser, Anne; Huang, Y.; Golden, Mark S.; Brinkman, Alexander

Translating concepts of topological quantum computation into applications requires fine-tuning of parameters in the model Hamiltonians of candidate systems. Such level of control has proven difficult to achieve in devices where superconductors are used to induce pairing in topological insulator (TI) materials. While local probe experiments have indicated features of p-wave superconducting correlations in TIs (as suggested by theory), results on extended devices often remain ambiguous. We present contact spectroscopy data on superconductor/topological insulator/normal metal devices with bulk-insulating TI material and compare these with bulk conducting samples. We discuss the magnitude of the induced gap and unusual features in the conductance traces of the bulk-insulating samples that may suggest the presence of p-wave type correlations in the TI. This work is financially supported by the Dutch Foundation for Fundamental Research on Matter (FOM), the Netherlands Organization for Scientific Research (NWO), and by the European Research Council (ERC).

Processing of n+/p-/p+ strip detectors with atomic layer deposition (ALD) grown Al2O3 field insulator on magnetic Czochralski silicon (MCz-si) substrates

NASA Astrophysics Data System (ADS)

Härkönen, J.; Tuovinen, E.; Luukka, P.; Gädda, A.; Mäenpää, T.; Tuominen, E.; Arsenovich, T.; Junkes, A.; Wu, X.; Li, Z.

2016-08-01

Detectors manufactured on p-type silicon material are known to have significant advantages in very harsh radiation environment over n-type detectors, traditionally used in High Energy Physics experiments for particle tracking. In p-type (n+ segmentation on p substrate) position-sensitive strip detectors, however, the fixed oxide charge in the silicon dioxide is positive and, thus, causes electron accumulation at the Si/SiO2 interface. As a result, unless appropriate interstrip isolation is applied, the n-type strips are short-circuited. Widely adopted methods to terminate surface electron accumulation are segmented p-stop or p-spray field implantations. A different approach to overcome the near-surface electron accumulation at the interface of silicon dioxide and p-type silicon is to deposit a thin film field insulator with negative oxide charge. We have processed silicon strip detectors on p-type Magnetic Czochralski silicon (MCz-Si) substrates with aluminum oxide (Al2O3) thin film insulator, grown with Atomic Layer Deposition (ALD) method. The electrical characterization by current-voltage and capacitance-voltage measurement shows reliable performance of the aluminum oxide. The final proof of concept was obtained at the test beam with 200 GeV/c muons. For the non-irradiated detector the charge collection efficiency (CCE) was nearly 100% with a signal-to-noise ratio (S/N) of about 40, whereas for the 2×1015 neq/cm2 proton irradiated detector the CCE was 35%, when the sensor was biased at 500 V. These results are comparable with the results from p-type detectors with the p-spray and p-stop interstrip isolation techniques. In addition, interestingly, when the aluminum oxide was irradiated with Co-60 gamma-rays, an accumulation of negative fixed oxide charge in the oxide was observed.

5 MeV Mott Polarimeter Development at Jefferson Lab

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

Price, J. S.; Sinclair, C. K.; Cardman, L. S.

1997-01-01

Low energy (E{sub k}=100 keV) Mott scattering polarimeters are ill- suited to support operations foreseen for the polarized electron injector at Jefferson Lab. One solution is to measure the polarization at 5 MeV where multiple and plural scattering are unimportant and precision beam monitoring is straightforward. The higher injector beam current offsets the lower cross-sections. Recent improvements in the CEBAF injector polarimeter scattering chamber have improved signal to noise.

Effect of dopant density on contact potential difference across n-type GaAs homojunctions using Kelvin Probe Force Microscopy

NASA Astrophysics Data System (ADS)

Boumenou, C. Kameni; Urgessa, Z. N.; Djiokap, S. R. Tankio; Botha, J. R.; Nel, J.

2018-04-01

In this study, cross-sectional surface potential imaging of n+/semi-insulating GaAs junctions is investigated by using amplitude mode kelvin probe force microscopy. The measurements have shown two different potential profiles, related to the difference in surface potential between the semi-insulating (SI) substrate and the epilayers. It is shown that the contact potential difference (CPD) between the tip and the sample is higher on the semi-insulating substrate side than on the n-type epilayer side. This change in CPD across the interface has been explained by means of energy band diagrams indicating the relative Fermi level positions. In addition, it has also been found that the CPD values across the interface are much smaller than the calculated values (on average about 25% of the theoretical values) and increase with the electron density. Therefore, the results presented in study are only in qualitative agreement with the theory.

Magnetic End States in a Strongly Interacting One-Dimensional Topological Kondo Insulator

DOE PAGES

Lobos, Alejandro M.; Dobry, Ariel O.; Galitski, Victor

2015-05-22

Topological Kondo insulators are strongly correlated materials where itinerant electrons hybridize with localized spins, giving rise to a topologically nontrivial band structure. Here, we use nonperturbative bosonization and renormalization-group techniques to study theoretically a one-dimensional topological Kondo insulator, described as a Kondo-Heisenberg model, where the Heisenberg spin-1/2 chain is coupled to a Hubbard chain through a Kondo exchange interaction in the p-wave channel (i.e., a strongly correlated version of the prototypical Tamm-Schockley model).We derive and solve renormalization-group equations at two-loop order in the Kondo parameter, and find that, at half filling, the charge degrees of freedom in the Hubbard chainmore » acquire a Mott gap, even in the case of a noninteracting conduction band (Hubbard parameter U = 0). Furthermore, at low enough temperatures, the system maps onto a spin-1/2 ladder with local ferromagnetic interactions along the rungs, effectively locking the spin degrees of freedom into a spin-1 chain with frozen charge degrees of freedom. This structure behaves as a spin-1 Haldane chain, a prototypical interacting topological spin model, and features two magnetic spin-1/2 end states for chains with open boundary conditions. In conclusion, our analysis allows us to derive an insightful connection between topological Kondo insulators in one spatial dimension and the well-known physics of the Haldane chain, showing that the ground state of the former is qualitatively different from the predictions of the naive mean-field theory.« less

Pluralism in Rhetorical Criticism: The Case of Lucretia Coffin Mott's "Discourse on Woman."

ERIC Educational Resources Information Center

Campbell, Karlyn Kohrs

1995-01-01

Investigates the issue of pluralistic readings and how they can be compared with each other, justified, and evaluated. Looks particularly at the five rhetorical analyses of Lucretia Coffin Mott's speech on women which follows this article. (TB)

Poole Frenkel current and Schottky emission in SiN gate dielectric in AlGaN/GaN metal insulator semiconductor heterostructure field effect transistors

NASA Astrophysics Data System (ADS)

Hanna, Mina J.; Zhao, Han; Lee, Jack C.

2012-10-01

We analyze the anomalous I-V behavior in SiN prepared by plasma enhanced chemical vapor deposition for use as a gate insulator in AlGaN/GaN metal insulator semiconductor heterostructure filed effect transistors (HFETs). We observe leakage current across the dielectric with opposite polarity with respect to the applied electric field once the voltage sweep reaches a level below a determined threshold. This is observed as the absolute minimum of the leakage current does not occur at minimum voltage level (0 V) but occurs earlier in the sweep interval. Curve-fitting analysis suggests that the charge-transport mechanism in this region is Poole-Frenkel current, followed by Schottky emission due to band bending. Despite the current anomaly, the sample devices have shown a notable reduction of leakage current of over 2 to 6 order of magnitudes compared to the standard Schottky HFET. We show that higher pressures and higher silane concentrations produce better films manifesting less trapping. This conforms to our results that we reported in earlier publications. We found that higher chamber pressure achieves higher sheet carrier concentration that was found to be strongly dependent on the trapped space charge at the SiN/GaN interface. This would suggest that a lower chamber pressure induces more trap states into the SiN/GaN interface.

Localized superconductivity in the quantum-critical region of the disorder-driven superconductor-insulator transition in TiN thin films.

PubMed

Baturina, T I; Mironov, A Yu; Vinokur, V M; Baklanov, M R; Strunk, C

2007-12-21

We investigate low-temperature transport properties of thin TiN superconducting films in the vicinity of the disorder-driven superconductor-insulator transition. In a zero magnetic field, we find an extremely sharp separation between superconducting and insulating phases, evidencing a direct superconductor-insulator transition without an intermediate metallic phase. At moderate temperatures, in the insulating films we reveal thermally activated conductivity with the magnetic field-dependent activation energy. At very low temperatures, we observe a zero-conductivity state, which is destroyed at some depinning threshold voltage V{T}. These findings indicate the formation of a distinct collective state of the localized Cooper pairs in the critical region at both sides of the transition.

First-order metal-insulator transition not accompanied by the structural phase transition observed in VO2-based devices

NASA Astrophysics Data System (ADS)

Kim, Hyun-Tak; Chae, Byung-Gyu; Kim, Bong-Jun; Lee, Yong-Wook; Yun, Sun-Jin; Kang, Kwang-Yong

2006-03-01

An abrupt first-order metal-insulator transition (MIT) is observed during the application of a switching pulse voltage to VO2-based two-terminal devices. When the abrupt MIT occurs, the structural phase transition (SPT) is investigated by a micro- Raman spectroscopy and a micro-XRD. The result shows that the MIT is not accompanied with the structural phase transition (SPT); the abrupt MIT is prior to the SPT. Moreover, any switching pulse over a threshold voltage of 7.1 V for the MIT enabled the device material to transform efficiently from an insulator to a metal. The measured delay time from the source switching pulse to an induced MIT pulse is an order of 20 nsec which is much less than a delay time of about one msec deduced by thermal model. This indicates that the first-order MIT does not occur due to thermal. We think this MIT is the Mott transition. (Reference: New J. Phys. 6 (1994) 52 (www.njp.org), Appl. Phys. Lett. 86 (2005) 242101, Physica B 369 (2005. December) xxxx)

Antifuse with a single silicon-rich silicon nitride insulating layer

DOEpatents

Habermehl, Scott D.; Apodaca, Roger T.

2013-01-22

An antifuse is disclosed which has an electrically-insulating region sandwiched between two electrodes. The electrically-insulating region has a single layer of a non-hydrogenated silicon-rich (i.e. non-stoichiometric) silicon nitride SiN.sub.X with a nitrogen content X which is generally in the range of 0N.sub.X layer. The SiN.sub.X layer thickness can also be made sufficiently large so that Poole-Frenkel emission will be the primary electrical conduction mechanism in the antifuse. Different types of electrodes are disclosed including electrodes formed of titanium silicide, aluminum and silicon. Arrays of antifuses can also be formed.

Tailorable advanced blanket insulation using aluminoborosilicate and alumina batting

NASA Technical Reports Server (NTRS)

Calamito, Dominic P.

1989-01-01

Two types of Tailorable Advanced Blanket Insulation (TABI) flat panels for Advanced Space Transportation Systems were produced. Both types consisted of integrally woven, 3-D fluted core having parallel faces and connecting ribs of Nicalon yarns. The triangular cross section flutes of one type was filled with mandrels of processed Ultrafiber (aluminoborosilicate) stitchbonded Nextel 440 fibrous felt, and the second type wall filled with Saffil alumina fibrous felt insulation. Weaving problems were minimal. Insertion of the fragile insulation mandrels into the fabric flutes was improved by using a special insertion tool. An attempt was made to weave fluted core fabrics from Nextel 440 yarns but was unsuccessful because of the yarn's fragility. A small sample was eventually produced by an unorthodox weaving process and then filled with Saffil insulation. The procedures for setting up and weaving the fabrics and preparing and inserting insulation mandrels are discussed. Characterizations of the panels produced are also presented.

Entanglement Entropy across the Superfluid-Insulator Transition: A Signature of Bosonic Criticality.

PubMed

Frérot, Irénée; Roscilde, Tommaso

2016-05-13

We study the entanglement entropy and entanglement spectrum of the paradigmatic Bose-Hubbard model, describing strongly correlated bosons on a lattice. The use of a controlled approximation-the slave-boson approach-allows us to study entanglement in all regimes of the model (and, most importantly, across its superfluid-Mott-insulator transition) at a minimal cost. We find that the area-law scaling of entanglement-verified in all the phases-exhibits a sharp singularity at the transition. The singularity is greatly enhanced when the transition is crossed at fixed, integer filling, due to a richer entanglement spectrum containing an additional gapless mode, which descends from the amplitude (Higgs) mode of the global excitation spectrum-while this mode remains gapped at the generic (commensurate-incommensurate) transition with variable filling. Hence, the entanglement properties contain a unique signature of the two different forms of bosonic criticality exhibited by the Bose-Hubbard model.

Cylindrical cryogenic calorimeter testing of six types of multilayer insulation systems

NASA Astrophysics Data System (ADS)

Fesmire, J. E.; Johnson, W. L.

2018-01-01

Extensive cryogenic thermal testing of more than 100 different multilayer insulation (MLI) specimens was performed over the last 20 years for the research and development of evacuated reflective thermal insulation systems. From this data library, 26 MLI systems plus several vacuum-only systems are selected for analysis and comparison. The test apparatus, methods, and results enabled the adoption of two new technical consensus standards under ASTM International. Materials tested include reflectors of aluminum foil or double-aluminized Mylar and spacers of fiberglass paper, polyester netting, silk netting, polyester fabric, or discrete polymer standoffs. The six types of MLI systems tested are listed as follows: Mylar/Paper, Foil/Paper, Mylar/Net, Mylar/Blanket, Mylar/Fabric, Mylar/Discrete. Also tested are vacuum-only systems with different cold surface materials/finishes including stainless steel, black, copper, and aluminum. Testing was performed between the boundary temperatures of 78 K and 293 K (and up to 350 K) using a thermally guarded one-meter-long cylindrical calorimeter (Cryostat-100) for absolute heat flow measurement. Cold vacuum pressures include the full range from 1 × 10-6 torr to 760 torr with nitrogen as the residual gas. System variations include number of layers from one to 80 layers, layer densities from 0.5 to 5 layers per millimeter, and installation techniques such layer-by-layer, blankets (multi-layer assemblies), sub-blankets, seaming, butt-joining, spiral wrapping, and roll-wrapping. Experimental thermal performance data for the different MLI systems are presented in terms of heat flux and effective thermal conductivity. Benchmark cryogenic-vacuum thermal performance curves for MLI are given for comparison with different insulation approaches for storage and transfer equipment, cryostats, launch vehicles, spacecraft, or science instruments.

Nonlinear Sensing With Collective States of Ultracold Atoms in Optical Lattices

DTIC Science & Technology

2015-04-02

20) E. Tiesinga, “Particle-hole Pair Coherence in Mott insulator quench dynamics” at the June 2014, Division of atomic, molecular, and optical...Jian, Philip R. Johnson, Eite Tiesinga. Particle-Hole Pair Coherence in Mott Insulator Quench Dynamics, P H Y S I C A L R E V I EW L E T T E R S (01...lattices. We focused on techniques that make use of the coherent superposition states in atom number. These state are not unlike the photon number

Ultracold fermions in a one-dimensional bipartite optical lattice: Metal-insulator transitions driven by shaking

NASA Astrophysics Data System (ADS)

Di Liberto, M.; Malpetti, D.; Japaridze, G. I.; Morais Smith, C.

2014-08-01

We theoretically investigate the behavior of a system of fermionic atoms loaded in a bipartite one-dimensional optical lattice that is under the action of an external time-periodic driving force. By using Floquet theory, an effective model is derived. The bare hopping coefficients are renormalized by zeroth-order Bessel functions of the first kind with different arguments for the nearest-neighbor and next-nearest-neighbor hopping. The insulating behavior characterizing the system at half filling in the absence of driving is dynamically suppressed, and for particular values of the driving parameter the system becomes either a standard metal or an unconventional metal with four Fermi points. The existence of the four-Fermi-point metal relies on the fact that, as a consequence of the shaking procedure, the next-nearest-neighbor hopping coefficients become significant compared to the nearest-neighbor ones. We use the bosonization technique to investigate the effect of on-site Hubbard interactions on the four-Fermi-point metal-insulator phase transition. Attractive interactions are expected to enlarge the regime of parameters where the unconventional metallic phase arises, whereas repulsive interactions reduce it. This metallic phase is known to be a Luther-Emery liquid (spin-gapped metal) for both repulsive and attractive interactions, contrary to the usual Hubbard model, which exhibits a Mott-insulator phase for repulsive interactions. Ultracold fermions in driven one-dimensional bipartite optical lattices provide an interesting platform for the realization of this long-studied four-Fermi-point unconventional metal.

Orbital-selective Mott phases of a one-dimensional three-orbital Hubbard model studied using computational techniques

DOE PAGES

Liu, Guangkun; Kaushal, Nitin; Liu, Shaozhi; ...

2016-06-24

A recently introduced one-dimensional three-orbital Hubbard model displays orbital-selective Mott phases with exotic spin arrangements such as spin block states [J. Rincón et al., Phys. Rev. Lett. 112, 106405 (2014)]. In this paper we show that the constrained-path quantum Monte Carlo (CPQMC) technique can accurately reproduce the phase diagram of this multiorbital one-dimensional model, paving the way to future CPQMC studies in systems with more challenging geometries, such as ladders and planes. The success of this approach relies on using the Hartree-Fock technique to prepare the trial states needed in CPQMC. In addition, we study a simplified version of themore » model where the pair-hopping term is neglected and the Hund coupling is restricted to its Ising component. The corresponding phase diagrams are shown to be only mildly affected by the absence of these technically difficult-to-implement terms. This is confirmed by additional density matrix renormalization group and determinant quantum Monte Carlo calculations carried out for the same simplified model, with the latter displaying only mild fermion sign problems. Lastly, we conclude that these methods are able to capture quantitatively the rich physics of the several orbital-selective Mott phases (OSMP) displayed by this model, thus enabling computational studies of the OSMP regime in higher dimensions, beyond static or dynamic mean-field approximations.« less

Correlated insulator behaviour at half-filling in magic-angle graphene superlattices

NASA Astrophysics Data System (ADS)

Cao, Yuan; Fatemi, Valla; Demir, Ahmet; Fang, Shiang; Tomarken, Spencer L.; Luo, Jason Y.; Sanchez-Yamagishi, Javier D.; Watanabe, Kenji; Taniguchi, Takashi; Kaxiras, Efthimios; Ashoori, Ray C.; Jarillo-Herrero, Pablo

2018-04-01

A van der Waals heterostructure is a type of metamaterial that consists of vertically stacked two-dimensional building blocks held together by the van der Waals forces between the layers. This design means that the properties of van der Waals heterostructures can be engineered precisely, even more so than those of two-dimensional materials. One such property is the ‘twist’ angle between different layers in the heterostructure. This angle has a crucial role in the electronic properties of van der Waals heterostructures, but does not have a direct analogue in other types of heterostructure, such as semiconductors grown using molecular beam epitaxy. For small twist angles, the moiré pattern that is produced by the lattice misorientation between the two-dimensional layers creates long-range modulation of the stacking order. So far, studies of the effects of the twist angle in van der Waals heterostructures have concentrated mostly on heterostructures consisting of monolayer graphene on top of hexagonal boron nitride, which exhibit relatively weak interlayer interaction owing to the large bandgap in hexagonal boron nitride. Here we study a heterostructure consisting of bilayer graphene, in which the two graphene layers are twisted relative to each other by a certain angle. We show experimentally that, as predicted theoretically, when this angle is close to the ‘magic’ angle the electronic band structure near zero Fermi energy becomes flat, owing to strong interlayer coupling. These flat bands exhibit insulating states at half-filling, which are not expected in the absence of correlations between electrons. We show that these correlated states at half-filling are consistent with Mott-like insulator states, which can arise from electrons being localized in the superlattice that is induced by the moiré pattern. These properties of magic-angle-twisted bilayer graphene heterostructures suggest that these materials could be used to study other exotic many

Metal-insulator transition, giant negative magnetoresistance, and ferromagnetism in LaCo1-yNiyO3

NASA Astrophysics Data System (ADS)

Hammer, D.; Wu, J.; Leighton, C.

2004-04-01

We have investigated the transport and magnetic properties of the perovskite LaCo1-yNiyO3, an alloy of LaCoO3 (a semiconductor that exhibits spin-state transitions) and LaNiO3 (a paramagnetic metal). The metal-insulator transition (MIT) was found to occur at y=0.40. On the insulating side of the transition the conductivity obeys Mott variable range hopping with a characteristic temperature (T0) that varies with y in a manner consistent with the predictions of the scaling theory of electron localization. On the metallic side the low temperature conductivity (down to 0.35 K) varies as T1/2 due to the effects of electron-electron interaction in the presence of disorder. The composition dependence of the low-temperature conductivity in the critical region fits the scaling theory of electron localization with a conductivity critical exponent close to unity, consistent with the scaling of T0 in the insulating phase. A large negative magnetoresistance is observed (up to 70% in 17 T) which increases monotonically with decreasing temperature and is smoothly decreased through the MIT. The magnetic properties show that doping LaCoO3 with Ni leads to a rapid destruction of the low spin-state for Co3+ ions, followed by the onset of distinct ferromagnetic interactions at higher Ni content. Similar to La1-xSrxCoO3, the system shows a smooth evolution from spin-glass to ferromagnetic ground states, which is interpreted in terms of the formation of ferromagnetic clusters. In contrast to La1-xSrxCoO3 further doping does not lead to a bulk ferromagnetlike state with a large TC, despite the clear existence of ferromagnetic interactions. We suggest that this is due to a limitation of the strength of the ferromagnetic interactions, which could be related to the fact that Ni rich clusters are not thermodynamically stable. The ferromagnetic clusters in LaCo1-yNiyO3 do not percolate with increasing y explaining the lack of a high-TC ferromagnetic state and the fact that the MIT is a simple

A dynamical mean-field study of orbital-selective Mott phase enhanced by next-nearest neighbor hopping

NASA Astrophysics Data System (ADS)

Niu, Yuekun; Sun, Jian; Ni, Yu; Song, Yun

2018-06-01

The dynamical mean-field theory is employed to study the orbital-selective Mott transition (OSMT) of the two-orbital Hubbard model with nearest neighbor hopping and next-nearest neighbor (NNN) hopping. The NNN hopping breaks the particle-hole symmetry at half filling and gives rise to an asymmetric density of states (DOS). Our calculations show that the broken symmetry of DOS benefits the OSMT, where the region of the orbital-selective Mott phase significantly extends with the increasing NNN hopping integral. We also find that Hund's rule coupling promotes OSMT by blocking the orbital fluctuations, but the influence of NNN hopping is more remarkable.

Observation of non-Fermi liquid behavior in hole-doped Eu2Ir2O7

NASA Astrophysics Data System (ADS)

Banerjee, A.; Sannigrahi, J.; Giri, S.; Majumdar, S.

2017-12-01

The Weyl semimetallic compound Eu2Ir2O7 and its hole-doped derivatives (which are achieved by substituting trivalent Eu by divalent Sr) are investigated through transport, magnetic, and calorimetric studies. The metal-insulator transition (MIT) temperature is found to get substantially reduced with hole doping, and for 10% Sr doping the composition is metallic down to temperature as low as 5 K. These doped compositions are found to violate the Mott-Ioffe-Regel condition for minimum electrical conductivity and show a distinct signature of non-Fermi liquid behavior at low temperature. The MIT in the doped compounds does not correlate with the magnetic transition point, and Anderson-Mott-type disorder-induced localization may be attributed to the ground-state insulating phase. The observed non-Fermi liquid behavior can be understood on the basis of disorder-induced distribution of the spin-orbit-coupling parameter, which is markedly different in the case of Ir4 + and Ir5 + ions.

Collective Kondo effect in the Anderson-Hubbard lattice

NASA Astrophysics Data System (ADS)

Fazekas, P.; Itai, K.

1997-02-01

The periodic Anderson model is extended by switching on a Hubbard U for the conduction electrons. We use the Gutzwiller variational method to study the nearly integral valent limit. The lattice Kondo energy contains the U-dependent chemical potential of the Hubbard subsystem in the exponent, and the correlation-induced band narrowing in the prefactor. Both effects tend to suppress the Kondo scale, which can be understood to result from the blocking of hybridization. At half-filling, we find a Brinkman-Rice-type transition from a Kondo insulator to a Mott insulator.

Effect of the Mott cross section on the determination of the charge of ultraheavy cosmic rays from emulsion tracks

NASA Technical Reports Server (NTRS)

Eby, P. B.; Morgan, S. H.; Parnell, T. A.

1978-01-01

Energy deposition due to secondary electrons is calculated as a function of distance from the axis of the track of a heavy ion. The calculation incorporates the empirical formulas of Kobetich and Katz (1968) for delta-ray energy dissipation. Both the Mott and Born-approximation expressions for the delta-ray energy distributions are used, and the results are compared. The energy deposition projected along a line perpendicular to the track is also calculated. These results are used to estimate the effect that the use of the Mott cross section would have in the interpretation of photometric measurements on emulsion tracks of trans-iron cosmic-ray particles. It is shown that the use of 50 keV as a characteristic track-formation electron energy to estimate the effect of the Mott cross section systematically overestimates charge as derived from emulsions for Z greater than 20.

Seebeck Effects in N-Type and P-Type Polymers Driven Simultaneously by Surface Polarization and Entropy Differences Based on Conductor/Polymer/Conductor Thin-Film Devices

DOE PAGES

Hu, Dehua; Liu, Qing; Tisdale, Jeremy; ...

2015-04-15

This paper reports Seebeck effects driven by both surface polarization difference and entropy difference by using intramolecular charge-transfer states in n-type and p-type conjugated polymers, namely IIDT and IIDDT, based on vertical conductor/polymer/conductor thin-film devices. Large Seebeck coefficients of -898 V/K and 1300 V/K from are observed from n-type IIDT p-type IIDDT, respectively, when the charge-transfer states are generated by a white light illumination of 100 mW/cm2. Simultaneously, electrical conductivities are increased from almost insulating states in dark condition to conducting states under photoexcitation in both n-type IIDT and p-type IIDDT devices. We find that the intramolecular charge-transfer states canmore » largely enhance Seebeck effects in the n-type IIDT and p-type IIDDT devices driven by both surface polarization difference and entropy difference. Furthermore, the Seebeck effects can be shifted between polarization and entropy regimes when electrical conductivities are changed. This reveals a new concept to develop Seebeck effects by controlling polarization and entropy regimes based on charge-transfer states in vertical conductor/polymer/conductor thin-film devices.« less

Metal-Insulator Transition in Copper Oxides Induced by Apex Displacements

NASA Astrophysics Data System (ADS)

Acharya, Swagata; Weber, Cédric; Plekhanov, Evgeny; Pashov, Dimitar; Taraphder, A.; Van Schilfgaarde, Mark

2018-04-01

High temperature superconductivity has been found in many kinds of compounds built from planes of Cu and O, separated by spacer layers. Understanding why critical temperatures are so high has been the subject of numerous investigations and extensive controversy. To realize high temperature superconductivity, parent compounds are either hole doped, such as La2 CuO4 (LCO) with Sr (LSCO), or electron doped, such as Nd2 CuO4 (NCO) with Ce (NCCO). In the electron-doped cuprates, the antiferromagnetic phase is much more robust than the superconducting phase. However, it was recently found that the reduction of residual out-of-plane apical oxygen dramatically affects the phase diagram, driving those compounds to a superconducting phase. Here we use a recently developed first-principles method to explore how displacement of the apical oxygen (AO) in LCO affects the optical gap, spin and charge susceptibilities, and superconducting order parameter. By combining quasiparticle self-consistent GW (QS GW) and dynamical mean-field theory (DMFT), we show that LCO is a Mott insulator, but small displacements of the apical oxygen drive the compound to a metallic state through a localization-delocalization transition, with a concomitant maximum in d -wave order parameter at the transition. We address the question of whether NCO can be seen as the limit of LCO with large apical displacements, and we elucidate the deep physical reasons why the behavior of NCO is so different from the hole-doped materials. We shed new light on the recent correlation observed between Tc and the charge transfer gap, while also providing a guide towards the design of optimized high-Tc superconductors. Further, our results suggest that strong correlation, enough to induce a Mott gap, may not be a prerequisite for high-Tc superconductivity.

Topological magnetic phase in LaMnO3 (111) bilayer

NASA Astrophysics Data System (ADS)

Weng, Yakui; Huang, Xin; Yao, Yugui; Dong, Shuai

Candidates for correlated topological insulators, originated from the spin-orbit coupling as well as Hubbard type correlation, are expected in the (111) bilayer of perovskite-structural transition-metal oxides. Based on the first-principles calculation and tight-binding model, the electronic structure of a LaMnO3 (111) bilayer sandwiched in LaScO3 barriers has been investigated. For the ideal undistorted perovskite structure, the Fermi energy of LaMnO3 (111) bilayer just stays at the Dirac point, rendering a semi-metal (graphene-like) which is also a half-metal (different from graphene nor previous studied LaNiO3 (111) bilayer). The Dirac cone can be opened by the spin-orbit coupling, giving rise to nontrivial topological bands corresponding to the (quantized) anomalous Hall effect. For the realistic orthorhombic distorted lattice, the Dirac point moves with increasing Hubbard repulsion (or equivalent Jahn-Teller distortion). Finally, a Mott gap opens, establishing a phase boundary between the Mott insulator and topological magnetic insulator. Our calculation finds that the gap opened by spin-orbit coupling is much smaller in the orthorhombic distorted lattice (~ 1 . 7 meV) than the undistorted one (~11 meV).

Spectral properties near the Mott transition in the two-dimensional t-J model with next-nearest-neighbor hopping

NASA Astrophysics Data System (ADS)

Kohno, Masanori

2018-05-01

The single-particle spectral properties of the two-dimensional t-J model with next-nearest-neighbor hopping are investigated near the Mott transition by using cluster perturbation theory. The spectral features are interpreted by considering the effects of the next-nearest-neighbor hopping on the shift of the spectral-weight distribution of the two-dimensional t-J model. Various anomalous features observed in hole-doped and electron-doped high-temperature cuprate superconductors are collectively explained in the two-dimensional t-J model with next-nearest-neighbor hopping near the Mott transition.

Disappearance of the metal-insulator transition in iridate pyrochlores on approaching the ideal R2Ir2O7 stoichiometry

NASA Astrophysics Data System (ADS)

Sleight, Arthur W.; Ramirez, Arthur P.

2018-07-01

Recently, rare earth iridates, R2Ir2O7, with the pyrochlore structure have been intensively investigated due to their promise as either topological Mott insulators or Weyl semimetals. Single crystals of such pyrochlores with R = Nd, Sm, Eu, and Dy were prepared hydrothermally in sealed gold tubes at 975 K and show significantly higher electrical resistivities than previously reported for either crystals or polycrystalline samples. Furthermore, none of the present crystals exhibit the metal-insulator transition found for some samples of these phases. Lower resistivities are ascribed to lack of control of x and y in R2-xIr2O7-y in other more commonly used synthesis methods, yielding uncertainty in the Ir oxidation state. We also report resistivity of R2Ru2O7 crystals for R = Yb, Gd, Eu, and Nd, prepared in the same manner. These results suggest that the observed charge transport in hydrothermally grown iridate crystals is that of essentially stoichiometric phases and is consistent a with the existence of Weyl nodes.

Mott localization in a pure stripe antiferromagnet Rb 1 - δ Fe 1.5 - σ S 2

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

Wang, Meng; Yi, Ming; Cao, Huibo

A combination of neutron diffraction and angle-resolved photoemission spectroscopy measurements on a pure antiferromagnetic stripe Rb 1-δFe 1.5-σS 2 is reported. A neutron diffraction experiment on a powder sample shows that a 98% volume fraction of the sample is in the antiferromagnetic stripe phase with rhombic iron vacancy order and a refined composition of Rb 0.66Fe 1.36S 2, and that only 2% of the sample is in the block antiferromagnetic phase with √5×√5 iron vacancy order. Furthermore, a neutron diffraction experiment on a single crystal shows that there is only a single phase with the stripe antiferromagnetic order with themore » refined composition of Rb 0.78Fe 1.35S 2, while the phase with block antiferromagnetic order is absent. Angle-resolved photoemission spectroscopy measurements on the same crystal with the pure stripe phase reveal that the electronic structure is gapped at the Fermi level with a gap larger than 0.325 eV. The data collectively demonstrate that the extra 10% iron vacancies in addition to the rhombic iron vacancy order effectively impede the formation of the block antiferromagnetic phase; the data also suggest that the stripe antiferromagnetic phase with rhombic iron vacancy order is a Mott insulator.« less

Sialons as high temperature insulators

NASA Technical Reports Server (NTRS)

Phillips, W. M.; Kuo, Y. S.

1978-01-01

Sialons were evaluated for application as high temperature electrical insulators in contact with molybdenum and tungsten components in hard vacuum applications. Both D.C. and variable frequency A.C. resistivity data indicate the sialons to have electrical resistivity similar to common oxide in the 1000 C or higher range. Metallographic evaluations indicate good bonding of the type 15R ALN polytype to molybdenum and tungsten. The beta prime or modified silicon nitride phase was unacceptable in terms of vacuum stability. Additives effect on electrical resistivity. Similar resistivity decreases were produced by additions of molybdenum or tungsten to form cermets. The use of hot pressing at 1800 C with ALN, Al2 O3 and Si3N4 starting powders produced a better product than did a combination of SiO2 and AIN staring powders. It was indicated that sialons will be suitable insulators in the 1600K range in contact with molybdenum or tungsten if they are produced as a pure ceramic and subsequently bonded to the metal components at temperatures in the 1600K range.

Fabrication of current confinement aperture structure by transforming a conductive GaN:Si epitaxial layer into an insulating GaOx layer.

PubMed

Lin, Chia-Feng; Lee, Wen-Che; Shieh, Bing-Cheng; Chen, Danti; Wang, Dili; Han, Jung

2014-12-24

We report here a simple and robust process to convert embedded conductive GaN epilayers into insulating GaOx and demonstrate its efficacy in vertical current blocking and lateral current steering in a working LED device. The fabrication processes consist of laser scribing, electrochemical (EC) wet-etching, photoelectrochemical (PEC) oxidation, and thermal oxidization of a sacrificial n(+)-GaN:Si layer. The conversion of GaN is made possible through an intermediate stage of porosification where the standard n-type GaN epilayers can be laterally and selectively anodized into a nanoporous (NP) texture while keeping the rest of the layers intact. The fibrous texture of NP GaN with an average wall thickness of less than 100 nm dramatically increases the surface-to-volume ratio and facilitates a rapid oxidation process of GaN into GaOX. The GaOX aperture was formed on the n-side of the LED between the active region and the n-type GaN layer. The wavelength blueshift phenomena of electroluminescence spectra is observed in the treated aperture-emission LED structure (441.5 nm) when compared to nontreated LED structure (443.7 nm) at 0.1 mA. The observation of aperture-confined electroluminescence from an InGaN LED structure suggests that the NP GaN based oxidation will play an enabling role in the design and fabrication of III-nitride photonic devices.

Window Insulation: How to Sort Through the Options.

ERIC Educational Resources Information Center

Miller, Barbara

This two-part report explores the efforts of businesses and individuals to improve the thermal performance of windows. Part I discusses the basics of what makes a window product insulate or save energy. Topic areas addressed include saving energy lost through windows, key components of window insulation, three basic types of window insulation,…

Quasistatic antiferromagnetism in the quantum wells of SmTiO3/SrTiO3 heterostructures

NASA Astrophysics Data System (ADS)

Need, Ryan F.; Marshall, Patrick B.; Kenney, Eric; Suter, Andreas; Prokscha, Thomas; Salman, Zaher; Kirby, Brian J.; Stemmer, Susanne; Graf, Michael J.; Wilson, Stephen D.

2018-03-01

High carrier density quantum wells embedded within a Mott insulating matrix present a rich arena for exploring unconventional electronic phase behavior ranging from non-Fermi-liquid transport and signatures of quantum criticality to pseudogap formation. Probing the proposed connection between unconventional magnetotransport and incipient electronic order within these quantum wells has however remained an enduring challenge due to the ultra-thin layer thicknesses required. Here we address this challenge by exploring the magnetic properties of high-density SrTiO3 quantum wells embedded within the antiferromagnetic Mott insulator SmTiO3 via muon spin relaxation and polarized neutron reflectometry measurements. The one electron per planar unit cell acquired by the nominal d0 band insulator SrTiO3 when embedded within a d1 Mott SmTiO3 matrix exhibits slow magnetic fluctuations that begin to freeze into a quasistatic spin state below a critical temperature T*. The appearance of this quasistatic well magnetism coincides with the previously reported opening of a pseudogap in the tunneling spectra of high carrier density wells inside this film architecture. Our data suggest a common origin of the pseudogap phase behavior in this quantum critical oxide heterostructure with those observed in bulk Mott materials close to an antiferromagnetic instability.

Switching adhesion forces by crossing the metal–insulator transition in Magnéli-type vanadium oxide crystals

PubMed Central

Klemm, Matthias; Horn, Siegfried; Woydt, Mathias

2011-01-01

Summary Magnéli-type vanadium oxides form the homologous series VnO2 n -1 and exhibit a temperature-induced, reversible metal–insulator first order phase transition (MIT). We studied the change of the adhesion force across the transition temperature between the cleavage planes of various vanadium oxide Magnéli phases (n = 3 … 7) and spherical titanium atomic force microscope (AFM) tips by systematic force–distance measurements with a variable-temperature AFM under ultrahigh vacuum conditions (UHV). The results show, for all investigated samples, that crossing the transition temperatures leads to a distinct change of the adhesion force. Low adhesion corresponds consistently to the metallic state. Accordingly, the ability to modify the electronic structure of the vanadium Magnéli phases while maintaining composition, stoichiometry and crystallographic integrity, allows for relating frictional and electronic material properties at the nano scale. This behavior makes the vanadium Magnéli phases interesting candidates for technology, e.g., as intelligent devices or coatings where switching of adhesion or friction is desired. PMID:21977416

Orthorhombic fulleride (CH3NH2)K3C60 close to Mott-Hubbard instability: Ab initio study

NASA Astrophysics Data System (ADS)

Potočnik, Anton; Manini, Nicola; Komelj, Matej; Tosatti, Erio; Arčon, Denis

2012-08-01

We study the electronic structure and magnetic interactions in methylamine-intercalated orthorhombic alkali-doped fullerene (CH3NH2)K3C60 within the density functional theory. As in the simpler ammonia intercalated compound (NH3)K3C60, the orthorhombic crystal-field anisotropy Δ lifts the t1u triple degeneracy at the Γ point and drives the system deep into the Mott-insulating phase. However, the computed Δ and conduction electron bandwidth W cannot alone account for the abnormally low experimental Néel temperature, TN=11 K, of the methylamine compound, compared to the much higher value TN=40 K of the ammonia one. Significant interactions between CH3NH2 and C603- are responsible for the stabilization of particular fullerene-cage distortions and the ensuing low-spin S=1/2 state. These interactions also seem to affect the magnetic properties, as interfullerene exchange interactions depend on the relative orientation of deformations of neighboring C603- molecules. For the ferro-orientational order of CH3NH2-K+ groups we find an apparent reduced dimensionality in magnetic exchange interactions, which may explain the suppressed Néel temperature. The disorder in exchange interactions caused by orientational disorder of CH3NH2-K+ groups could further contribute to this suppression.

High pressure electrical insulated feed thru connector

DOEpatents

Oeschger, Joseph E.; Berkeland, James E.

1979-11-13

A feed-thru type hermetic electrical connector including at least one connector pin feeding through an insulator block within the metallic body of the connector shell. A compression stop arrangement coaxially disposed about the insulator body is brazed to the shell, and the shoulder on the insulator block bears against this top in a compression mode, the high pressure or internal connector being at the opposite end of the shell. Seals between the pin and an internal bore at the high pressure end of the insulator block and between the insulator block and the metallic shell at the high pressure end are hermetically brazed in place, the first of these also functioning to transfer the axial compressive load without permitting appreciable shear action between the pin and insulator block.

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

Mcdonald, Ross David

The alkali-doped fullerides provide the first example of a transition from a three-dimensional Mott insulator to a superconductor, enabling the effects of both dimensionality and electron correlation on superconductivity to be explored. Chemically the alkali species tunes the superconductivity in the vicinity of the the Mott transition via sample volume. Measuring the relationship between the superconducting transition temperature and upper critical field reveals a crossover from weak- to strong-coupling associated with the dynamical Jahn–Teller effect as the Mott transition is approached. The use of pulsed magnets is required because the upper critical field is enhanced in the vicinity of themore » Mott insulating phase, reaching 90 T for RbxCs3-xC60 — the highest among cubic crystals. This required close collaboration between Prof Kasahara’s group and the Mag Lab to design rf-measurements compatible with sample encapsulation in an inert atmosphere. The concomitant increase of pairing strength with lattice volume near the Mott transition suggest that the cooperative interplay between molecular electronic structure and strong electron correlations plays a key role in realizing robust superconductivity (with high-T C and high-H C2).« less

Printable Top-Gate-Type Polymer Light-Emitting Transistors with Surfaces of Amorphous Fluoropolymer Insulators Modified by Vacuum Ultraviolet Light Treatment

NASA Astrophysics Data System (ADS)

Kajii, Hirotake; Terashima, Daiki; Kusumoto, Yusuke; Ikezoe, Ikuya; Ohmori, Yutaka

2013-04-01

We investigated the fabrication and electrical and optical properties of top-gate-type polymer light-emitting transistors with the surfaces of amorphous fluoropolymer insulators, CYTOP (Asahi Glass) modified by vacuum ultraviolet light (VUV) treatment. The surface energy of CYTOP, which has a good solution barrier property was increased by VUV irradiation, and the gate electrode was fabricated by solution processing on the CYTOP film using the Ag nano-ink. The influence of VUV irradiation on the optical properties of poly(9,9-dioctylfluorene-co-benzothiadiazole) (F8BT) films with various gate insulators was investigated to clarify the passivation effect of gate insulators. It was found that the poly(methyl methacrylate) (PMMA) film prevented the degradation of the F8BT layer under VUV irradiation because the PMMA film can absorb VUV. The solution-processed F8BT device with multilayer PMMA/CYTOP insulators utilizing a gate electrode fabricated using the Ag nano-ink exhibited both the ambipolar characteristics and yellow-green emission.

Slater insulator in iridate perovskites with strong spin-orbit coupling

DOE PAGES

Cui, Q.; Cheng, J. -G.; Fan, W.; ...

2016-10-20

The perovskite SrIrO 3 is an exotic narrow-band metal owing to a confluence of the strengths of the spin-orbit coupling (SOC) and the electron-electron correlations. It has been proposed that topological and magnetic insulating phases can be achieved by tuning the SOC, Hubbard interactions, and/or lattice symmetry. Here, we report that the substitution of nonmagnetic, isovalent Sn 4+ for Ir 4+ in the SrIr 1–xSn xO 3 perovskites synthesized under high pressure leads to a metal-insulator transition to an antiferromagnetic (AF) phase at T N ≥ 225 K. The continuous change of the cell volume as detected by x-ray diffractionmore » and the λ-shape transition of the specific heat on cooling through T N demonstrate that the metal-insulator transition is of second order. Neutron powder diffraction results indicate that the Sn substitution enlarges an octahedral-site distortion that reduces the SOC relative to the spin-spin exchange interaction and results in the type- G AF spin ordering below T N. Measurement of high-temperature magnetic susceptibility shows the evolution of magnetic coupling in the paramagnetic phase typical of weak itinerant-electron magnetism in the Sn-substituted samples. Furthermore, a reduced structural symmetry in the magnetically ordered phase leads to an electron gap opening at the Brillouin zone boundary below T N in the same way as proposed by Slater.« less

Slater Insulator in Iridate Perovskites with Strong Spin-Orbit Coupling.

PubMed

Cui, Q; Cheng, J-G; Fan, W; Taylor, A E; Calder, S; McGuire, M A; Yan, J-Q; Meyers, D; Li, X; Cai, Y Q; Jiao, Y Y; Choi, Y; Haskel, D; Gotou, H; Uwatoko, Y; Chakhalian, J; Christianson, A D; Yunoki, S; Goodenough, J B; Zhou, J-S

2016-10-21

The perovskite SrIrO_{3} is an exotic narrow-band metal owing to a confluence of the strengths of the spin-orbit coupling (SOC) and the electron-electron correlations. It has been proposed that topological and magnetic insulating phases can be achieved by tuning the SOC, Hubbard interactions, and/or lattice symmetry. Here, we report that the substitution of nonmagnetic, isovalent Sn^{4+} for Ir^{4+} in the SrIr_{1-x}Sn_{x}O_{3} perovskites synthesized under high pressure leads to a metal-insulator transition to an antiferromagnetic (AF) phase at T_{N}≥225  K. The continuous change of the cell volume as detected by x-ray diffraction and the λ-shape transition of the specific heat on cooling through T_{N} demonstrate that the metal-insulator transition is of second order. Neutron powder diffraction results indicate that the Sn substitution enlarges an octahedral-site distortion that reduces the SOC relative to the spin-spin exchange interaction and results in the type-G AF spin ordering below T_{N}. Measurement of high-temperature magnetic susceptibility shows the evolution of magnetic coupling in the paramagnetic phase typical of weak itinerant-electron magnetism in the Sn-substituted samples. A reduced structural symmetry in the magnetically ordered phase leads to an electron gap opening at the Brillouin zone boundary below T_{N} in the same way as proposed by Slater.

Urea formaldehyde foam: a dangerous insulation

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

Keough, C.

1980-12-01

Insulating a home with urea formaldehyde foam can lead to severe health problems due to poisoning from formaldehyde gas. Respiratory problems, allergies, memory loss, and mental problems can result from exposure to foam insulation fumes. Research is now under way at the Chemical Industry Inst., Univ. of Washington, and other institutions to learn more about the health effects of formaldehyde foam and to develop possible remedies to these problems. Several states are either banning or controlling the use of this type of home insulation.

Time-resolved nonlinear optics in strongly correlated insulators

NASA Astrophysics Data System (ADS)

Dodge, J. Steven

2000-03-01

Transition metal oxides form the basis for much of our understanding of Mott insulators, and have enjoyed a renaissance of interest since the discovery of high temperature superconductivity in the cuprates. They are characterized by complex interactions among spin, lattice, orbital and charge degrees of freedom, which lead to dynamical behavior on time scales ranging from femtoseconds to microseconds. We have applied time resolved nonlinear optical spectroscopy to probe these dynamics. In one well-studied antiferromagnetic insulator, Cr_2O_3, we observed spin-wave dynamics on a picosecond time scale by performing pump-probe spectroscopy of the exciton-magnon transition(J. S. Dodge, et al.), Phys. Rev. Lett. 83, 4650 (1999).. At excitation densities ~ 10-3/Cr, a lineshape associated with the exciton-magnon absorption appears in the pump-probe spectrum. We assign this nonlinearity to a time-dependent renormalization of the magnon band structure, which in turn modifies the lineshape of the exciton-magnon transition. At long time delays, this assignment agrees semiquantitatively with calculations based on spin-wave theory. However, the initial population at the zone-boundary induces surprisingly little renormalization effect, indicating that spin-wave theory is insufficient to describe our observations in this regime. The renormalization lineshape grows on a time scale of ~ 50 ps, which we associate with the decay of the photoexcited, nonequilibrium population of zone-boundary spin-waves into a thermalized population of zone-center spin-waves. We have also performed a study of the linear and nonlinear optical properties of Sr_2CuO_2Cl_2, an insulating, two-dimensional cuprate. In the nonlinear optical experiments, we have performed pump-probe spectroscopy over a 1 eV spectral range, varying both the pump and the probe energy. We observe a pump-probe lineshape which varies considerably as a function of pump energy and temperature, and which differs sharply from those

Insulation systems for liquid methane fuel tanks for supersonic cruise aircraft

NASA Technical Reports Server (NTRS)

Brady, H. F.; Delduca, D.

1972-01-01

Two insulation systems for tanks containing liquid methane in supersonic cruise-type aircraft were designed and tested after an extensive materials investigation. One system is an external insulation and the other is an internal wet-type insulation system. Tank volume was maximized by making the tank shape approach a rectangular parallelopiped. One tank was designed to use the external insulation and the other tank to use the internal insulation. Performance of the external insulation system was evaluated on a full-scale tank under the temperature environment of -320 F to 700 F and ambient pressures of ground-level atmospheric to 1 psia. Problems with installing the internal insulation on the test tank prevented full-scale evaluation of performance; however, small-scale testing verified thermal conductivity, temperature capability, and installed density.

Self-Aligned ALD AlOx T-gate Insulator for Gate Leakage Current Suppression in SiNx-Passivated AlGaN/GaN HEMTs

DTIC Science & Technology

2010-01-01

Heterostructure epitaxial material growth was performed by RF plasma-assisted molecular - beam epitaxy (MBE) on a 2-in. semi- insulating 4H SiC wafer. From... beam epitaxy of beryllium-doped GaN buffer layers for AlGaN/GaN HEMTs . J Cryst Growth 2003;251:481–6. [25] Storm DF, Katzer DS, Binari SC, Glaser ER...Shanabrook BV, Roussos JA. Reduction of buffer layer conduction near plasma-assisted molecular - beam epitaxy grown GaN/AlN interfaces by beryllium

Exploring the validity and limitations of the Mott-Gurney law for charge-carrier mobility determination of semiconducting thin-films.

PubMed

Röhr, Jason A; Moia, Davide; Haque, Saif A; Kirchartz, Thomas; Nelson, Jenny

2018-03-14

Using drift-diffusion simulations, we investigate the voltage dependence of the dark current in single carrier devices typically used to determine charge-carrier mobilities. For both low and high voltages, the current increases linearly with the applied voltage. Whereas the linear current at low voltages is mainly due to space charge in the middle of the device, the linear current at high voltage is caused by charge-carrier saturation due to a high degree of injection. As a consequence, the current density at these voltages does not follow the classical square law derived by Mott and Gurney, and we show that for trap-free devices, only for intermediate voltages, a space-charge-limited drift current can be observed with a slope that approaches a value of two. We show that, depending on the thickness of the semiconductor layer and the size of the injection barriers, the two linear current-voltage regimes can dominate the whole voltage range, and the intermediate Mott-Gurney regime can shrink or disappear. In this case, which will especially occur for thicknesses and injection barriers typical of single-carrier devices used to probe organic semiconductors, a meaningful analysis using the Mott-Gurney law will become unachievable, because a square-law fit can no longer be achieved, resulting in the mobility being substantially underestimated. General criteria for when to expect deviations from the Mott-Gurney law when used for analysis of intrinsic semiconductors are discussed.

Exploring the validity and limitations of the Mott-Gurney law for charge-carrier mobility determination of semiconducting thin-films

NASA Astrophysics Data System (ADS)

Röhr, Jason A.; Moia, Davide; Haque, Saif A.; Kirchartz, Thomas; Nelson, Jenny

2018-03-01

Using drift-diffusion simulations, we investigate the voltage dependence of the dark current in single carrier devices typically used to determine charge-carrier mobilities. For both low and high voltages, the current increases linearly with the applied voltage. Whereas the linear current at low voltages is mainly due to space charge in the middle of the device, the linear current at high voltage is caused by charge-carrier saturation due to a high degree of injection. As a consequence, the current density at these voltages does not follow the classical square law derived by Mott and Gurney, and we show that for trap-free devices, only for intermediate voltages, a space-charge-limited drift current can be observed with a slope that approaches a value of two. We show that, depending on the thickness of the semiconductor layer and the size of the injection barriers, the two linear current-voltage regimes can dominate the whole voltage range, and the intermediate Mott-Gurney regime can shrink or disappear. In this case, which will especially occur for thicknesses and injection barriers typical of single-carrier devices used to probe organic semiconductors, a meaningful analysis using the Mott-Gurney law will become unachievable, because a square-law fit can no longer be achieved, resulting in the mobility being substantially underestimated. General criteria for when to expect deviations from the Mott-Gurney law when used for analysis of intrinsic semiconductors are discussed.

Characterization of Textile-Insulated Capacitive Biosensors

PubMed Central

Ng, Charn Loong; Reaz, Mamun Bin Ibne

2017-01-01

Capacitive biosensors are an emerging technology revolutionizing wearable sensing systems and personal healthcare devices. They are capable of continuously measuring bioelectrical signals from the human body while utilizing textiles as an insulator. Different textile types have their own unique properties that alter skin-electrode capacitance and the performance of capacitive biosensors. This paper aims to identify the best textile insulator to be used with capacitive biosensors by analysing the characteristics of 6 types of common textile materials (cotton, linen, rayon, nylon, polyester, and PVC-textile) while evaluating their impact on the performance of a capacitive biosensor. A textile-insulated capacitive (TEX-C) biosensor was developed and validated on 3 subjects. Experimental results revealed that higher skin-electrode capacitance of a TEX-C biosensor yields a lower noise floor and better signal quality. Natural fabric such as cotton and linen were the two best insulating materials to integrate with a capacitive biosensor. They yielded the lowest noise floor of 2 mV and achieved consistent electromyography (EMG) signals measurements throughout the performance test. PMID:28287493

Ladder physics in the spin fermion model

NASA Astrophysics Data System (ADS)

Tsvelik, A. M.

2017-05-01

A link is established between the spin fermion (SF) model of the cuprates and the approach based on the analogy between the physics of doped Mott insulators in two dimensions and the physics of fermionic ladders. This enables one to use nonperturbative results derived for fermionic ladders to move beyond the large-N approximation in the SF model. It is shown that the paramagnon exchange postulated in the SF model has exactly the right form to facilitate the emergence of the fully gapped d -Mott state in the region of the Brillouin zone at the hot spots of the Fermi surface. Hence, the SF model provides an adequate description of the pseudogap.

Ladder physics in the spin fermion model

DOE PAGES

Tsvelik, A. M.

2017-05-01

A link is established between the spin fermion (SF) model of the cuprates and the approach based on the analogy between the physics of doped Mott insulators in two dimensions and the physics of fermionic ladders. This enables one to use nonperturbative results derived for fermionic ladders to move beyond the large-N approximation in the SF model. Here, it is shown that the paramagnon exchange postulated in the SF model has exactly the right form to facilitate the emergence of the fully gapped d-Mott state in the region of the Brillouin zone at the hot spots of the Fermi surface.more » Hence, the SF model provides an adequate description of the pseudogap.« less

High-Quality LaVO3 Films as Solar Energy Conversion Material.

PubMed

Zhang, Hai-Tian; Brahlek, Matthew; Ji, Xiaoyu; Lei, Shiming; Lapano, Jason; Freeland, John W; Gopalan, Venkatraman; Engel-Herbert, Roman

2017-04-12

Mott insulating oxides and their heterostructures have recently been identified as potential photovoltaic materials with favorable absorption properties and an intrinsic built-in electric field that can efficiently separate excited electron-hole pairs. At the same time, they are predicted to overcome the Shockley-Queisser limit due to strong electron-electron interaction present. Despite these premises a high concentration of defects commonly observed in Mott insulating films acting as recombination centers can derogate the photovoltaic conversion efficiency. With use of the self-regulated growth kinetics in hybrid molecular beam epitaxy, this obstacle can be overcome. High-quality, stoichiometric LaVO 3 films were grown with defect densities of in-gap states up to 2 orders of magnitude lower compared to the films in the literature, and a factor of 3 lower than LaVO 3 bulk single crystals. Photoconductivity measurements revealed a significant photoresponsivity increase as high as tenfold of stoichiometric LaVO 3 films compared to their nonstoichiometric counterparts. This work marks a critical step toward the realization of high-performance Mott insulator solar cells beyond conventional semiconductors.

Excitonic Order and Superconductivity in the Two-Orbital Hubbard Model: Variational Cluster Approach

NASA Astrophysics Data System (ADS)

Fujiuchi, Ryo; Sugimoto, Koudai; Ohta, Yukinori

2018-06-01

Using the variational cluster approach based on the self-energy functional theory, we study the possible occurrence of excitonic order and superconductivity in the two-orbital Hubbard model with intra- and inter-orbital Coulomb interactions. It is known that an antiferromagnetic Mott insulator state appears in the regime of strong intra-orbital interaction, a band insulator state appears in the regime of strong inter-orbital interaction, and an excitonic insulator state appears between them. In addition to these states, we find that the s±-wave superconducting state appears in the small-correlation regime, and the dx2 - y2-wave superconducting state appears on the boundary of the antiferromagnetic Mott insulator state. We calculate the single-particle spectral function of the model and compare the band gap formation due to the superconducting and excitonic orders.

One-dimensional anyons under three-body interactions.

NASA Astrophysics Data System (ADS)

Silva-Valencia, Jereson; Arcila-Forero, Julian; Franco, Roberto

Anyons are a third class of particles with nontrivial exchange statistics, particles carrying fractional statistics that interpolate between bosons and fermions. In the last years, it has been made some proposals to emulate an anyon gas by confining bosonic atoms in optical lattices [ Nat. Commun. 2, 361 (2011)]. In this work, we studied the ground state of anyons interacting through local three-body terms in one-dimension, motivated by recent experimental and theoretical studies about multi-body interactions in cold atoms setups. We used the density-matrix renormalization group method to find the phase diagram and the von Neumann block entropy to determinate the critical point position. The main quantum phases found are the superfluid and the Mott insulator ones. For the statistical angle θ = π /4, the phase diagram shows that the Mott lobes are surrounded by superfluid regions, the Mott lobes increase with the density and the first Mott lobe has two anyons per site. We found that a Mott lobe with one anyon per site, it is possible for larger statistical angles, a fact that it is impossible with bosons. DIBE- Universidad Nacional de Colombia and Departamento Administrativo de Ciencia, Tecnología e Innovación (COLCIENCAS) (Grant No. FP44842-057-2015).

Fabrication and Properties of a Metal-Insulator - Type Oxygen Sensor Using Lanthanum Trifluoride as the Sole Dielectric.

NASA Astrophysics Data System (ADS)

Mattingly, William Brashear, III

1995-01-01

Oxygen sensors were fabricated using a metal-insulator -semiconductor construction where the sole 'insulator' is a thin film of LaF_3, an ionic conductor. The typical oxide or nitride layers were eliminated producing a simple Pt/LaF_3/Si design. LaF_3 films, 200-300nm thick, were directly deposited on n-type Si(111) using a high temperature effusion cell in an ultra high vacuum MBE chamber. The film morphology could be controlled from polycrystalline to near single crystal epitaxy. Epitaxial films exhibited a single relaxed variant with the LaF _3 c-axis normal to the silicon surface and the in-plane LaF_3(10^ -10) parallel to Si(110). Polycrystalline films also showed a high degree of LaF_3 c-axis normal texture. Films doped with strontium were also produced. Polycrystalline films were more robust and fabricated into MIS (metal-insulator-semiconductor) capacitors. Capacitance voltage tests of the devices demonstrate nearly ideal MIS capacitor behavior. The flatband voltages were typically within 300mV of the calculated value. Bias challenge tests developed in the lab showed less than 70mV flatband voltage shift. The dielectric constant of undoped LaF_3 films measured close to 14. Doped films, rm Sr_{x}La_ {1-x}F_3 x =.06, showed a dielectric constant of 275, at 100kHz. Oxygen partial pressure tests were performed with mixtures of dry nitrogen and dry oxygen. Oxygen partial pressures were varied between 2.5 times 10^{-4} and 1.0 atmosphere. The steady state data are consistent with a Pt/LaF _3 interface adsorption mechanism, where the work function of the platinum gate metal is modulated. The mechanism is not a half-cell Nernst-type response. Langmiur isotherm fitted data indicate the response range for undoped devices is 0.3 V. Signal drift was less than 5 mV/day. The metal free-surface reactions and the dipole species at the Pt/LaF_3 interface are yet to be determined. Device kinetic studies show the time required for full equilibration after a step in oxygen

Interaction effect in the Kondo energy of the periodic Anderson-Hubbard model

NASA Astrophysics Data System (ADS)

Itai, K.; Fazekas, P.

1996-07-01

We extend the periodic Anderson model by switching on a Hubbard U for the conduction band. The nearly integral valent limit of the Anderson-Hubbard model is studied with the Gutzwiller variational method. The lattice Kondo energy shows U dependence both in the prefactor and the exponent. Switching on U reduces the Kondo scale, which can be understood to result from the blocking of hybridization. At half filling, we find a Brinkman-Rice-type transition from a Kondo insulator to a Mott insulator. Our findings should be relevant for a number of correlated two-band models of recent interest.

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

Mielke, Charles H.

The alkali-doped fullerides provide the first example of a transition from a three-dimensional Mott insulator to a superconductor, enabling the effects of both dimensionality and electron correlations on superconductivity to be explored. Chemically, the alkali species tunes the superconductivity in the vicinity of the Mott transition by varying the unit cell volume.

Neutron Scattering Studies on Correlated Transition-Metal Oxides

NASA Astrophysics Data System (ADS)

Zhu, Mengze

We have explored the collective phenomena of correlated electrons in two different transition-metal oxides, Ruddlesden-Popper type ruthenates (Sr,Ca) n+1RunO3n+1 and inverse-trirutile chromates Cr2MO6 (M = Te, Mo and W), using neutron scattering in combination with various material characterization methods. (Sr,Ca)n+1RunO 3n+1 are 4d transition-metal oxides exhibiting competing magnetic and electronic tendencies. The delicate balance among the competing states can be readily tuned by perturbations, such as chemical doping and magnetic field, which gives rise to emergent phenomena. We have investigated the effects of 3d transition-metal doping on the magnetic and electronic properties of layered ruthenates. For instance, the single-layer (n = 1) Sr2RuO4 is an unconventional superconductor possessing an incommensurate spin density wave instability with a wave vector qic= (0.3 0.3 L) driven by Fermi surface nesting. Upon Fe substitution, we have unveiled an unexpected commensurate spin density wave order with a propagation vector qc= (0.25 0.25 0) in Sr2Ru1-xFexO 4 (x = 0.03 and 0.05), despite the magnetic fluctuations persisting at qic. The latter feature is corroborated by the first principles calculations, which show that Fe doping barely changes the nesting vector of the Fermi surface. These results suggest that in addition to the known incommensurate magnetic instability, Sr2RuO4 is also in proximity to a commensurate magnetic tendency that can be stabilized via Fe doping. We have also studied the effects of a magnetic field. For example, the bilayer (n = 2) Ca3(Ru1-xTi x)2O7 (x = 0.03) is a G-type antiferromagnetic Mott insulator. We have revealed that a modest magnetic field can lead to colossal magnetoresistance arising from an anomalous collapse of the Mott insulating state. Such an insulator-to-metal transition is accompanied by magnetic and structural transitions. These findings call for deeper theoretical studies to reexamine the magnetic field tuning of

Distinct nature of orbital-selective Mott phases dominated by low-energy local spin fluctuations

NASA Astrophysics Data System (ADS)

Song, Ze-Yi; Jiang, Xiu-Cai; Lin, Hai-Qing; Zhang, Yu-Zhong

2017-12-01

Quantum orbital-selective Mott (OSM) transitions are investigated within dynamical mean-field theory based on a two-orbital Hubbard model with different bandwidth at half filling. We find two distinct OSM phases both showing coexistence of itinerant electrons and localized spins, dependent on whether the Hund's coupling is full or of Ising type. The critical values and the nature of the OSM transitions are efficiently determined by entanglement entropy. We reveal that vanishing of the Kondo energy scale evidenced by absence of local spin fluctuations at low frequency in local dynamical spin susceptibility is responsible for the appearance of non-Fermi-liquid OSM phase in Ising Hund's coupling case. We argue that this scenario can also be applied to account for emergent quantum non-Fermi liquid in the one-band Hubbard model when short-range antiferromagnetic order is considered.

Preparation and properties of the multi-layer aerogel thermal insulation composites

NASA Astrophysics Data System (ADS)

Wang, Miao; Feng, Junzong; Jiang, Yonggang; Zhang, Zhongming; Feng, Jian

2018-03-01

Multi-layer insulation materials possess low radiation thermal conductivity, and excellent thermal insulation property in a vacuum environment. However, the spacers of the traditional multi-layer insulation materials are mostly loose fibers, which lead to more sensitive to the vacuum environmental of serviced. With the vacuum degree declining, gas phases thermal convection increase obviously, and the reflective screen will be severe oxidation, all of these make the thermal insulation property of traditional multi-layer insulation deteriorate, thus limits its application scope. In this paper, traditional multi-layer insulation material is combined with aerogel and obtain a new multi-layer aerogel thermal insulation composite, and the effects of the number, thickness and type of the reflective screens on the thermal insulation properties of the multi-layer composites are also studied. The result is that the thermal insulation property of the new type multi-layer aerogel composites is better than the pure aerogel composites and the traditional multi-layer insulation composites. When the 0.01 mm stainless steel foil as the reflective screen, and the aluminum silicate fiber and silica aerogel as the spacer layer, the layer density of composite with the best thermal insulation property is one layer per millimeter at 1000 °C.

Electrical and carrier transport properties of the Au/Y2O3/n-GaN metal-insulator-semiconductor (MIS) diode with rare-earth oxide interlayer

NASA Astrophysics Data System (ADS)

Venkata Prasad, C.; Rajagopal Reddy, V.; Choi, Chel-Jong

2017-04-01

The electrical and transport properties of rare-earth Y2O3 on n-type GaN with Au electrode have been investigated by current-voltage and capacitance-voltage techniques at room temperature. The Au/Y2O3/n-GaN metal-insulator-semiconductor (MIS) diode shows a good rectification behavior compared to the Au/n-GaN metal-semiconductor (MS) diode. Statistical analysis showed that a mean barrier height (BH) and ideality factor are 0.78 eV and 1.93, and 0.96 eV and 2.09 for the Au/n-GaN MS and Au/Y2O3/n-GaN MIS diodes, respectively. Results indicate that the high BH is obtained for the MIS diode compared to the MS diode. The BH, ideality factor and series resistance are also estimated by Cheung's function and Norde method. From the forward current-voltage data, the interface state density ( N SS) is estimated for both the MS and MIS Schottky diodes, and found that the estimated N SS is lower for the MIS diode compared to the MS diode. The results reveal that the introduction of Y2O3 interlayer facilitated the reduction of N SS of the Au/n-GaN interface. Experimental results suggest that the Poole-Frenkel emission is a dominant conduction mechanism in the reverse bias region of both Au/n-GaN MS and Au/Y2O3/n-GaN MIS diodes.

Perovskite ThTaN3: A large-thermopower topological crystalline insulator

NASA Astrophysics Data System (ADS)

Jung, Myung-Chul; Lee, Kwan-Woo; Pickett, Warren E.

2018-03-01

ThTaN3, a rare cubic perovskite nitride semiconductor, has been studied using ab initio methods. Spin-orbit coupling (SOC) results in band inversion and a band gap of 150 meV at the zone center. Despite trivial Z2 indices, two pairs of spin-polarized surface bands cross the gap near the zone center, indicating that this system is a topological crystalline insulator with the mirror Chern number of | Cm|=2 protected by the mirror and C4 rotational symmetries. Additionally, SOC doubles the Seebeck coefficient, leading to a maximum of ˜400 μ V /K at 150 K for carrier-doping levels of several 1017/cm3.ThTaN3 combines excellent bulk thermopower with parallel conduction through topological surface states that may point toward new possibilities for platforms for engineering devices with larger figures of merit.

Negative Differential Resistance in Insulating Systems: From Molecules to Polymers

NASA Astrophysics Data System (ADS)

Pati, Swapan

2007-03-01

We have developed a microscopic theory to explain the negative differential resistance behavior in molecular bridges. This feature has been observed in many molecules with different on/off ratios, sharpness of the current peak and the critical bias. Our theory, based on simple dimer model (both Peierls and donor/acceptor) together with bias driven conformational/ electronic change, covers almost all the experimental characteristics for a large number of real molecular systems and encompasses all the theory that has been known till date. Similar argument is also extended to Mott insulator, where we find a large number of insulator/quasi-metal transitions in finite size chains and a thermodynamic insulator/metal transition in polymers due to the application of static electric field between two ends of the chain. The interplay between charge inhomogenities and electric field induced polarization will be discussed in a number of cases. We will also show that none of these transitions follow Landau-Zener mechanism. I shall also discuss our theoretical proposal for the experimental strategies to stabilize highly unstable and reactive metal clusters like Al4Li4 and their analogs. Reference: 1. S. Lakshmi and Swapan K. Pati, Phys. Rev. B 72, 193410 (2005). 2. S. Lakshmi, Ayan Datta and Swapan K. Pati, Phys. Rev. B 72, 045131 (2005). 3. S. Lakshmi and Swapan K. Pati, Spl on Nanosc and Tech, Pramana, 65, 593. (2005). 4. S. Sengupta, S. Lakshmi and Swapan K Pati, J. Phys. Cond. Mat. 18, 9189 (2006). 5. Swapan K. Pati and S. Ramasesha, J. Phys. Condens. Matter 16, 989 (2004). 6. S.Lakshmi and Swapan K. Pati, J. Chem. Phys. 121, 11998 (2004). 7. S. Dutta, S. Lakshmi and Swapan K Pati, Submitted (2006). 8. A. Datta and Swapan K. Pati, J. Am. Chem. Soc. 127, 3496 (2005). 9. Sairam S. M., A. Datta and Swapan K. Pati, J. Phys. Chem. B 110, 20098 (2006). 10. A. Datta, Sairam S. M. and Swapan K. Pati, Acc. Chem. Res. (to appear)

The Influence of Heat Treatment on the Electrical Characteristics of Semi-Insulating SiC Layers Obtained by Irradiating n-SiC with High-Energy Argon Ions

NASA Astrophysics Data System (ADS)

Ivanov, P. A.; Potapov, A. S.; Kudoyarov, M. F.; Kozlovskii, M. A.; Samsonova, T. P.

2018-03-01

Irradiation of crystalline n-type silicon carbide ( n-SiC) with high-energy (53-MeV) argon ions was used to create near-surface semi-insulating ( i-SiC) layers. The influence of subsequent heat treatment on the electrical characteristics of i-SiC layers has been studied. The most high-ohmic ion-irradiated i-SiC layers with room-temperature resistivity of no less than 1.6 × 1013 Ω cm were obtained upon the heat treatment at 600°C, whereas the resistivity of such layers heat-treated at 230°C was about 5 × 107 Ω cm.

Quench dynamics and nonequilibrium phase diagram of the bose-hubbard model.

PubMed

Kollath, Corinna; Läuchli, Andreas M; Altman, Ehud

2007-05-04

We investigate the time evolution of correlations in the Bose-Hubbard model following a quench from the superfluid to the Mott insulator. For large values of the final interaction strength the system approaches a distinctly nonequilibrium steady state that bears strong memory of the initial conditions. In contrast, when the final interaction strength is comparable to the hopping, the correlations are rather well approximated by those at thermal equilibrium. The existence of two distinct nonequilibrium regimes is surprising given the nonintegrability of the Bose-Hubbard model. We relate this phenomenon to the role of quasiparticle interactions in the Mott insulator.

Closure of the Mott gap and formation of a superthermal metal in the Fröhlich-type nonequilibrium polaron Bose-Einstein condensate in U O 2 + x

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

Conradson, Steven D.; Andersson, David A.; Boland, Kevin S.

Mixed valence O-doped UO 2+x and photoexcited UO 2 containing transitory U 3+ and U 5+ host a coherent polaronic quantum phase (CPQP) that exhibits the characteristics of a Fröhlich-type, nonequilibrium, phonon-coupled Bose-Einstein condensate whose stability and coherence are amplified by collective, anharmonic motions of atoms and charges. Complementary to the available, detailed, real space information from scattering and EXAFS, an outstanding question is the electronic structure. Mapping the Mott gap in UO 2, U 4O 9, and U 3O 7 with O XAS and NIXS and UM5 RIXS shows that O doping raises the peak of the U5f statesmore » of the valence band by ~0.4 eV relative to a calculated value of 0.25 eV. However, it lowers the edge of the conduction band by 1.5 eV vs the calculated 0.6 eV, a difference much larger than the experimental error. This 1.9 eV reduction in the gap width constitutes most of the 2–2.2 eV gap measured by optical absorption. In addition, the XAS spectra show a tail that will intersect the occupied U5f states and give a continuous density-of-states that increases rapidly above its constricted intersection. Femtosecond-resolved photoemission measurements of UO 2, coincident with the excitation pulse with 4.7 eV excitation, show the unoccupied U5f states of UO 2 and no hot electrons. 3.1 eV excitation, however, complements the O-doping results by giving a continuous population of electrons for several eV above the Fermi level. The CPQP in photoexcited UO 2 therefore fulfills the criteria for a nonequilibrium condensate. The electron distributions resulting from both excitations persist for 5–10 ps, indicating that they are the final state that therefore forms without passing through the initial continuous distribution of nonthermal electrons observed for other materials. Three exceptional findings are: (1) the direct formation of both of these long lived (>3–10 ps) excited states without the short lived nonthermal intermediate; (2) the

Wholly Aromatic Ether-Imides as n-Type Semiconductors

NASA Technical Reports Server (NTRS)

Weiser, Erik; St. Clair, Terry L.; Dingemans, Theo J.; Samulski, Edward T.; Irene, Gene

2006-01-01

Some wholly aromatic ether-imides consisting of rod-shaped, relatively-low-mass molecules that can form liquid crystals have been investigated for potential utility as electron-donor-type (ntype) organic semiconductors. It is envisioned that after further research to improve understanding of their physical and chemical properties, compounds of this type would be used to make thin film semiconductor devices (e.g., photovoltaic cells and field-effect transistors) on flexible electronic-circuit substrates. This investigation was inspired by several prior developments: Poly(ether-imides) [PEIs] are a class of engineering plastics that have been used extensively in the form of films in a variety of electronic applications, including insulating layers, circuit boards, and low-permittivity coatings. Wholly aromatic PEIs containing naphthalene and perylene moieties have been shown to be useful as electrochromic polymers. More recently, low-molecular-weight imides comprising naphthalene-based molecules with terminal fluorinated tails were shown to be useful as n-type organic semiconductors in such devices as field-effect transistors and Schottky diodes. Poly(etherimide)s as structural resins have been extensively investigated at NASA Langley Research Center for over 30 years. More recently, the need for multi-functional materials has become increasingly important. This n-type semiconductor illustrates the scope of current work towards new families of PEIs that not only can be used as structural resins for carbon-fiber reinforced composites, but also can function as sensors. Such a multi-functional material would permit so-called in-situ health monitoring of composite structures during service. The work presented here demonstrates that parts of the PEI backbone can be used as an n-type semiconductor with such materials being sensitive to damage, temperature, stress, and pressure. In the near future, multi-functional or "smart" composite structures are envisioned to be able

Progress of gas-insulated transformers

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

Togawa, Y.; Ikeda, M.; Toda, K.

The world`s first transformer was manufactured at Ganz in Hungary in 1885. Two years later in 1887 patents applications were made for about oil immersed transformers in the US. Since then, oil immersed types have predominated for medium- and large-capacity transformers, which are now giving way to gas insulated transformers in some areas. Behind such trends are plans to construct substations inside buildings or underground, because of the difficulty in acquiring land for substations in large cities where power demand is concentrated. Requirements are protection against accidents, compactness and overall economy. Total gas insulated substations combining GIS units and gasmore » insulated transformers these needs. Demand for gas insulated transformers has been increasing rapidly, particularly in Japan and Hong Kong. First, relatively small-capacity models below 20--30 MVA were put into practical use and today 275 kV, 300 MVa models are in use and 500kV, 1,500 MVA models are coming into use. Engineering is progressing very rapidly in these areas. This paper describes the design techniques and important maintenance techniques for the latest gas insulated transformers from 5,000 kVA to 300 MVA.« less

Topological Quantum Information Processing Mediated Via Hybrid Topological Insulator Structures

DTIC Science & Technology

2013-11-13

manipulation, entanglement and detection ofMajorana fermions in diamond-topological insulator - superconductor heterojunctions. Furthennore, we propose to...the formation, manipulation, entanglement and detection of Majorana fermions in diamond-topological insulator - superconductor heterojunctions...Interactions between Superconductors and Topological Insulators Recent advances have revealed a new type of information processing, topological quantum

Topological Quantum Information Processing Mediated Via Hybrid Topogical Insulator Structures

DTIC Science & Technology

2014-03-28

formation, manipulation, entanglement and detection of Majorana fermions in diamond-topological insulator - superconductor heterojunctions. Furthermore...between Superconductors and Topological Insulators Recent advances have revealed a new type of information processing, topological quantum...Topological Insulator - Superconductor Heterostructures," Physical Review B 84, 144507 (2011). 7 Hsiang-Hsuan Hung, Pouyan Ghaemi, Taylor L

Evaluation of propellant tank insulation concepts for low-thrust chemical propulsion systems

NASA Technical Reports Server (NTRS)

Kramer, T.; Brogren, E.; Seigel, B.

1984-01-01

An analytical evaluation of cryogenic propellant tank insulations for liquid oxygen/liquid hydrogen low-thrust 2224N (500 lbf) propulsion systems (LTPS) was conducted. The insulation studied consisted of combinations of N2-purged foam and multilayer insulation (MLI) as well as He-purged MLI-only. Heat leak and payload performance predictions were made for three Shuttle-launched LTPS designed for Shuttle bay packaged payload densities of 56 kg/cu m, 40 kg/cu m and 24 kg/cu m. Foam/MLI insulations were found to increase LTPS payload delivery capability when compared with He-purged MLI-only. An additional benefit of foam/MLI was reduced operational complexity because Orbiter cargo bay N2 purge gas could be used for MLI purging. Maximum payload mass benefit occurred when an enhanced convection, rather than natural convection, heat transfer was specified for the insulation purge enclosure. The enhanced convection environment allowed minimum insulation thickness to be used for the foam/MLI interface temperature selected to correspond to the moisture dew point in the N2 purge gas. Experimental verification of foam/MLI benefits was recommended. A conservative program cost estimate for testing a MLI-foam insulated tank was 2.1 million dollars. It was noted this cost could be reduced significantly without increasing program risk.

A Study of "Successful" Students at C. S. Mott Community College: 1979, Flint, Michigan.

ERIC Educational Resources Information Center

Reinertson, Jacquelyn

In 1979, a study was conducted at Charles Stewart Mott Community College (MCC) to draw a profile of "successful" students and determine the level of reading achievement necessary for successful college work. "Successful" students were defined as those who had completed most of their coursework and were nearing graduation; therefore, the sample was…

Optimation of cooled shields in insulations

NASA Technical Reports Server (NTRS)

Chato, J. C.; Khodadadi, J. M.; Seyed-Yagoobi, J.

1984-01-01

A method to optimize the location, temperature, and heat dissipation rate of each cooled shield inside an insulation layer was developed. The method is based on the minimization of the entropy production rate which is proportional to the heat leak across the insulation. It is shown that the maximum number of shields to be used in most practical applications is three. However, cooled shields are useful only at low values of the overall, cold wall to hot wall absolute temperature ratio. The performance of the insulation system is relatively insensitive to deviations from the optimum values of the temperature and location of the cooling shields. Design curves for rapid estimates of the locations and temperatures of cooling shields in various types of insulations, and an equation for calculating the cooling loads for the shields are presented.

Ceramic insulation/multifoil composite for thermal protection of reentry spacecraft

NASA Technical Reports Server (NTRS)

Pitts, W. C.; Kourtides, D. A.

1989-01-01

A new type of insulation blanket called Composite Flexible Blanket Insulation is proposed for thermal protection of advanced spacecraft in regions where the maximum temperature is not excessive. The blanket is a composite of two proven insulation materials: ceramic insulation blankets from Space Shuttle technology and multilayer insulation blankets from spacecraft thermal control technology. A potential heatshield weight saving of up to 500 g/sq m is predicted. The concept is described; proof of concept experimental data are presented; and a spaceflight experiment to demonstrate its actual performance is discussed.

Fabrication of Multilayer-Type Mn-Si Thermoelectric Device

NASA Astrophysics Data System (ADS)

Kajitani, T.; Ueno, T.; Miyazaki, Y.; Hayashi, K.; Fujiwara, T.; Ihara, R.; Nakamura, T.; Takakura, M.

2014-06-01

This research aims to develop a direct-contact manganese silicon p/ n multilayer-type thermoelectric power generation block. p-type MnSi1.74 and n-type Mn0.7Fe0.3Si1.68 ball-milled powders with diameter of about 10 μm or less were mixed with polyvinyl butyl alcohol diluted with methylbenzene at pigment volume concentration of approximately 70%. The doctor-blade method produced 45- μm-thick p- and n-type pigment plates. The insulator, i.e., powdered glass, was mixed with cellulose to form insulator slurry. Lamination of manganese silicide pigment layers and screen-printed insulator layers was carried out to fabricate multilayer direct-contact thermoelectric devices. Hot pressing and spark plasma sintering were carried out at 450°C and 900°C, respectively. Four to 30 thermoelectric (TE) p/ n pairs were fabricated in a 10 mm × 10 mm × 10 mm sintered TE block. The maximum output was 11.7 mW/cm2 at a temperature difference between 20°C and 700°C, which was about 1/85 of the ideal power generation estimated from the thermoelectric data of the bulk MnSi1.74 and Mn0.7Fe0.3Si1.68 materials. A power generation test using an engine test bench was also carried out.

Floquet high Chern insulators in periodically driven chirally stacked multilayer graphene

NASA Astrophysics Data System (ADS)

Li, Si; Liu, Cheng-Cheng; Yao, Yugui

2018-03-01

Chirally stacked N-layer graphene is a semimetal with ±p N band-touching at two nonequivalent corners in its Brillioun zone. We predict that an off-resonant circularly polarized light (CPL) drives chirally stacked N-layer graphene into a Floquet Chern insulators (FCIs), aka quantum anomalous Hall insulators, with tunable high Chern number C F = ±N and large gaps. A topological phase transition between such a FCI and a valley Hall (VH) insulator with high valley Chern number C v = ±N induced by a voltage gate can be engineered by the parameters of the CPL and voltage gate. We propose a topological domain wall between the FCI and VH phases, along which perfectly valley-polarized N-channel edge states propagate unidirectionally without backscattering.

Emergent Chiral Spin State in the Mott Phase of a Bosonic Kane-Mele-Hubbard Model

NASA Astrophysics Data System (ADS)

Plekhanov, Kirill; Vasić, Ivana; Petrescu, Alexandru; Nirwan, Rajbir; Roux, Guillaume; Hofstetter, Walter; Le Hur, Karyn

2018-04-01

Recently, the frustrated X Y model for spins 1 /2 on the honeycomb lattice has attracted a lot of attention in relation with the possibility to realize a chiral spin liquid state. This model is relevant to the physics of some quantum magnets. Using the flexibility of ultracold atom setups, we propose an alternative way to realize this model through the Mott regime of the bosonic Kane-Mele-Hubbard model. The phase diagram of this model is derived using bosonic dynamical mean-field theory. Focusing on the Mott phase, we investigate its magnetic properties as a function of frustration. We do find an emergent chiral spin state in the intermediate frustration regime. Using exact diagonalization we study more closely the physics of the effective frustrated X Y model and the properties of the chiral spin state. This gapped phase displays a chiral order, breaking time-reversal and parity symmetry, but is not topologically ordered (the Chern number is zero).

Low trap states in in situ SiN{sub x}/AlN/GaN metal-insulator-semiconductor structures grown by metal-organic chemical vapor deposition

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

Lu, Xing; Ma, Jun; Jiang, Huaxing

2014-09-08

We report the use of SiN{sub x} grown in situ by metal-organic chemical vapor deposition as the gate dielectric for AlN/GaN metal-insulator-semiconductor (MIS) structures. Two kinds of trap states with different time constants were identified and characterized. In particular, the SiN{sub x}/AlN interface exhibits remarkably low trap state densities in the range of 10{sup 11}–10{sup 12 }cm{sup −2}eV{sup −1}. Transmission electron microscopy and X-ray photoelectron spectroscopy analyses revealed that the in situ SiN{sub x} layer can provide excellent passivation without causing chemical degradation to the AlN surface. These results imply the great potential of in situ SiN{sub x} as an effectivemore » gate dielectric for AlN/GaN MIS devices.« less

Explosion resistant insulator and method of making same

DOEpatents

Meyer, Jeffry R.; Billings, Jr., John S.; Spindle, Harvey E.; Hofmann, Charles F.

1983-01-01

An electrical insulator assembly and method of manufacturing same, having a generally cylindrical or conical body portion formed of a breakable cast solid insulation system and a reinforcing member having a corrugated configuration and formed of a web or mesh type reinforcing fabric. When the breakable body member has been broken, the corrugated configured reinforcing web member provides a path of escape for pressurized insulating fluid while limiting the movement of body member fragments in the direction of escape of the pressurized fluid.

Nonequilibrium Phase Precursors during a Photoexcited Insulator-to-Metal Transition in V2O3

NASA Astrophysics Data System (ADS)

Singer, Andrej; Ramirez, Juan Gabriel; Valmianski, Ilya; Cela, Devin; Hua, Nelson; Kukreja, Roopali; Wingert, James; Kovalchuk, Olesya; Glownia, James M.; Sikorski, Marcin; Chollet, Matthieu; Holt, Martin; Schuller, Ivan K.; Shpyrko, Oleg G.

2018-05-01

Here, we photoinduce and directly observe with x-ray scattering an ultrafast enhancement of the structural long-range order in the archetypal Mott system V2O3 . Despite the ultrafast increase in crystal symmetry, the change of unit cell volume occurs an order of magnitude slower and coincides with the insulator-to-metal transition. The decoupling between the two structural responses in the time domain highlights the existence of a transient photoinduced precursor phase, which is distinct from the two structural phases present in equilibrium. X-ray nanoscopy reveals that acoustic phonons trapped in nanoscale twin domains govern the dynamics of the ultrafast transition into the precursor phase, while nucleation and growth of metallic domains dictate the duration of the slower transition into the metallic phase. The enhancement of the long-range order before completion of the electronic transition demonstrates the critical role the nonequilibrium structural phases play during electronic phase transitions in correlated electrons systems.

Microsphere insulation systems

NASA Technical Reports Server (NTRS)

Allen, Mark S. (Inventor); Willen, Gary S. (Inventor); Mohling, Robert A. (Inventor)

2005-01-01

A new insulation system is provided that contains microspheres. This insulation system can be used to provide insulated panels and clamshells, and to insulate annular spaces around objects used to transfer, store, or transport cryogens and other temperature-sensitive materials. This insulation system provides better performance with reduced maintenance than current insulation systems.

Mott Polarimeter Upgrade at Jefferson Lab

NASA Astrophysics Data System (ADS)

McHugh, M.; Opper, A. K.; Grames, J.; Poelker, M.; Suleiman, R.; Horowitz, C.; Rhodes, S.; Roca Maza, X.; Sinclair, C.

2013-10-01

A Mott polarimeter with a design optimized for 5.5 MeV/c has been in routine use at the CEBAF accelerator for well over a decade, providing polarization measurements approaching 1% accuracy. Measurements with different target elements (Au, Ag, Cu) over decades of target thicknesses (100 - 10,000 angstroms), and beam energies between 2 and 8 MeV allow us to determine the effective analyzing power with a high degree of certainty. Recent and planned improvements in our polarimeter configuration, detectors and data acquisition system, coupled with a low 31 MHz repetition rate beam allow us to distinguish and suppress electrons that do not originate from the target foil. This work coupled with a significant effort to produce a detailed GEANT4 model of the polarimeter is part of an effort to determine systematic uncertainties at the level of the theoretically calculated analyzing power. We describe our activities and a series of planned measurements that will allow us to demonstrate and possibly improve the precision and accuracy of polarization measurements at JLab, as required for future parity violation experiments.

Facts on Grants, 1983. A Report on Grantmaking of the Charles Stewart Mott Foundation.

ERIC Educational Resources Information Center

Mott (C.S.) Foundation, Flint, MI.

Summaries of 349 grants made in 1983 by the Charles Stewart Mott Foundation are presented. The guide contains fact sheets on grants for $15,000 or above; all grants for amounts under $15,000 are listed with brief descriptions. Most of the fact sheets provide information on how grants meet the objectives of the foundation, what they might…

Computer supplies insulation recipe for Cookie Company Roof

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

Not Available

Roofing contractors no longer have to rely on complicated calculations and educated guesses to determine cost-efficient levels of roof insulation. A simple hand-held calculator and printer offers seven different programs for fast figuring insulation thickness based on job type, roof size, tax rates, and heating and cooling cost factors.

High-quality LaVO 3 films as solar energy conversion material

DOE PAGES

Zhang, Hai -Tian; Brahlek, Matthew; Ji, Xiaoyu; ...

2017-03-21

Mott insulating oxides and their heterostructures have recently been identified as potential photovoltaic materials with favorable absorption properties and an intrinsic built-in electric field that can efficiently separate excited electron hole pairs. At the same time, they are predicted to overcome the Shockley-Queisser limit due to strong electron electron interaction present. Despite these premises a high concentration of defects commonly observed in Mott insulating films acting as recombination centers can derogate the photovoltaic conversion efficiency. With use of the self-regulated growth kinetics in hybrid molecular beam epitaxy, this obstacle can be overcome. High-quality, stoichiometric LaVO 3 films were grown withmore » defect densities of in-gap states up to 2 orders of magnitude lower compared to the films in the literature, and a factor of 3 lower than LaVO 3 bulk single crystals. Photoconductivity measurements revealed a significant photoresponsivity increase as high as tenfold of stoichiometric LaVO 3 films compared to their nonstoichiometric counterparts. Furthermore, this work marks a critical step toward the realization of high-performance Mott insulator solar cells beyond conventional semiconductors.« less

Evidence for a quantum dipole liquid state in an organic quasi–two-dimensional material

NASA Astrophysics Data System (ADS)

Hassan, Nora; Cunningham, Streit; Mourigal, Martin; Zhilyaeva, Elena I.; Torunova, Svetlana A.; Lyubovskaya, Rimma N.; Schlueter, John A.; Drichko, Natalia

2018-06-01

Mott insulators are commonly pictured with electrons localized on lattice sites, with their low-energy degrees of freedom involving spins only. Here, we observe emergent charge degrees of freedom in a molecule-based Mott insulator κ-(BEDT-TTF)2Hg(SCN)2Br, resulting in a quantum dipole liquid state. Electrons localized on molecular dimer lattice sites form electric dipoles that do not order at low temperatures and fluctuate with frequency detected experimentally in our Raman spectroscopy experiments. The heat capacity and Raman scattering response are consistent with a scenario in which the composite spin and electric dipole degrees of freedom remain fluctuating down to the lowest measured temperatures.

5 MeV Mott polarimeter for rapid precise electron beam polarization measurements

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

Price, J.S.; Poelker, B.M.; Sinclair, C.K.

1997-11-01

Low energy (E{sub k} = 100 keV) Mott scattering polarimeters are ill-suited to support operations foreseen for the polarized electron injector at Jefferson Lab. One solution is to measure the polarization at 5 MeV where multiple and plural scattering are unimportant and precision beam monitoring is straightforward. The higher injector beam current offsets the lower cross-sections; measured rates scale to 1 kHz/{mu}A with a 1 {mu}m thick gold target foil.

Planar Nernst effect and Mott relation in (In,Fe)Sb ferromagnetic semiconductor

NASA Astrophysics Data System (ADS)

Bui, Cong Tinh; Garcia, Christina A. C.; Tu, Nguyen Thanh; Tanaka, Masaaki; Hai, Pham Nam

2018-05-01

Transverse magneto-thermoelectric effects were studied in an (In,Fe)Sb ferromagnetic semiconductor thin film under an in-plane magnetic field. We find that the thermal voltage is governed by the planar Nernst effect. We show that the magnetic field intensity dependence, magnetic field direction dependence, and temperature dependence of the transverse Seebeck coefficient can be explained by assuming a Mott relation between the in-plane magneto-transport and magneto-thermoelectric phenomena in (In,Fe)Sb.

Describing a Strongly Correlated Model System with Density Functional Theory.

PubMed

Kong, Jing; Proynov, Emil; Yu, Jianguo; Pachter, Ruth

2017-07-06

The linear chain of hydrogen atoms, a basic prototype for the transition from a metal to Mott insulator, is studied with a recent density functional theory model functional for nondynamic and strong correlation. The computed cohesive energy curve for the transition agrees well with accurate literature results. The variation of the electronic structure in this transition is characterized with a density functional descriptor that yields the atomic population of effectively localized electrons. These new methods are also applied to the study of the Peierls dimerization of the stretched even-spaced Mott insulator to a chain of H 2 molecules, a different insulator. The transitions among the two insulating states and the metallic state of the hydrogen chain system are depicted in a semiquantitative phase diagram. Overall, we demonstrate the capability of studying strongly correlated materials with a mean-field model at the fundamental level, in contrast to the general pessimistic view on such a feasibility.

Evidence for Jahn-Teller distortions at the antiferromagnetic transition in LaTiO3.

PubMed

Hemberger, J; Krug von Nidda, H-A; Fritsch, V; Deisenhofer, J; Lobina, S; Rudolf, T; Lunkenheimer, P; Lichtenberg, F; Loidl, A; Bruns, D; Büchner, B

2003-08-08

LaTiO3 is known as a Mott insulator which orders antiferromagnetically at T(N)=146 K. We report on results of thermal expansion and temperature dependent x-ray diffraction together with measurements of the heat capacity, electrical transport measurements, and optical spectroscopy in untwinned single crystals. At T(N) significant structural changes appear, which are volume conserving. Concomitant anomalies are also observed in the dc resistivity, in bulk modulus, and optical reflectivity spectra. We interpret these experimental observations as evidence of orbital order.

Silicon-on-insulator with hybrid orientations for heterogeneous integration of GaN on Si (100) substrate

NASA Astrophysics Data System (ADS)

Zhang, Runchun; Zhao, Beiji; Huang, Kai; You, Tiangui; Jia, Qi; Lin, Jiajie; Zhang, Shibin; Yan, Youquan; Yi, Ailun; Zhou, Min; Ou, Xin

2018-05-01

Heterogeneous integration of materials pave a new way for the development of the microsystem with miniaturization and complex functionalities. Two types of hybrid silicon on insulator (SOI) structures, i.e., Si (100)-on-Si (111) and Si (111)-on-Si (100), were prepared by the smart-cut technique, which is consist of ion-slicing and wafer bonding. The precise calculation of the lattice strain of the transferred films without the epitaxial matching relationship to the substrate was demonstrated based on X-ray diffraction (XRD) measurements. The XRD and Raman measurement results suggest that the transferred films possess single crystalline quality. With a chemical mechanical polishing (CMP) process, the surface roughness of the transferred thin films can be reduced from 5.57 nm to 0.30 nm. The 4-inch GaN thin film epitaxially grown on the as-prepared hybrid SOI of Si (111)-on-Si (100) by metalorganic chemical vapor deposition (MOCVD) is of improved quality with a full width at half maximum (FWHM) of 672.54 arcsec extracted from the XRD rocking curve and small surface roughness of 0.40 nm. The wafer-scale GaN on Si (111)-on-Si (100) can serve as a potential platform for the one chip integration of GaN-based high electron mobility transistors (HEMT) or photonics with the Si (100)-based complementary metal oxide semiconductor (CMOS).

The study of the mobile compressor unit heat losses recovery system waste heat exchanger thermal insulation types influence on the operational efficiency

NASA Astrophysics Data System (ADS)

Yusha, V. L.; Chernov, G. I.; Kalashnikov, A. M.

2017-08-01

The paper examines the mobile compressor unit (MCU) heat losses recovery system waste heat exchanger prototype external thermal insulation types influence on the operational efficiency. The study is conducted by means of the numerical method through the modellingof the heat exchange processes carried out in the waste heat exchanger in ANSUS. Thermaflex, mineral wool, penofol, water and air were applied as the heat exchanger external insulation. The study results showed the waste heat exchanger external thermal insulationexistence or absence to have a significant impact on the heat exchanger operational efficiency.

Conductivity Variation Observed by Polarization and Depolarization Current Measurements of High-Voltage Equipment Insulation System

NASA Astrophysics Data System (ADS)

Jamail, Nor Akmal Mohd; Piah, Mohamed Afendi Mohamed; Muhamad, Nor Asiah

2012-09-01

Nondestructive and time domain dielectric measurement techniques such as polarization and depolarization current (PDC) measurements have recently been widely used as a potential tool for determining high-voltage insulation conditions by analyzing the insulation conductivity. The variation in the conductivity of an insulator was found to depend on several parameters: the difference between the polarization and depolarization currents, geometric capacitance, and the relative permittivity of the insulation material. In this paper the conductivities of different types of oil-paper insulation material are presented. The insulation conductivities of several types of electrical apparatus were simulated using MATLAB. Conductivity insulation was found to be high at high polarizations and at the lowest depolarization current. It was also found to increase with increasing relative permittivity as well as with decreasing geometric capacitance of the insulating material.

Mg-doped VO2 nanoparticles: hydrothermal synthesis, enhanced visible transmittance and decreased metal-insulator transition temperature.

PubMed

Zhou, Jiadong; Gao, Yanfeng; Liu, Xinling; Chen, Zhang; Dai, Lei; Cao, Chuanxiang; Luo, Hongjie; Kanahira, Minoru; Sun, Chao; Yan, Liuming

2013-05-28

This paper reports the successful preparation of Mg-doped VO2 nanoparticles via hydrothermal synthesis. The metal-insulator transition temperature (T(c)) decreased by approximately 2 K per at% Mg. The Tc decreased to 54 °C with 7.0 at% dopant. The composite foils made from Mg-doped VO2 particles displayed excellent visible transmittance (up to 54.2%) and solar modulation ability (up to 10.6%). In addition, the absorption edge blue-shifted from 490 nm to 440 nm at a Mg content of 3.8 at%, representing a widened optical band gap from 2.0 eV for pure VO2 to 2.4 eV at 3.8 at% doping. As a result, the colour of the Mg-doped films was modified to increase their brightness and lighten the yellow colour over that of the undoped-VO2 film. A first principle calculation was conducted to understand how dopants affect the optical, Mott phase transition and structural properties of VO2.

Novel Electronic Behavior Driving NdNiO 3 Metal-Insulator Transition

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

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

2015-07-01

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

Pressure Dependence of Insulator-Insulator Contact Charging

NASA Technical Reports Server (NTRS)

Hogue, Michael D.

2005-01-01

The mechanism of insulator-insulator triboelectric (contact) charging is being studied by the Electrostatics and Surface Physics Laboratory at KSC. The hypothesis that surface ion exchange is the primary mechanism is being tested experimentally. A two-phase model based on a small partial pressure of singly charged ions in an ambient ideal gas in equilibrium with a submonolayer adsorbed film will provide predictions about charging as a function Of ion mass, pressure, temperature, and surface adsorption energy. Interactions between ions will be considered in terms of coulombic and screened potential energies. This work is yielding better understanding of the triboelectrification of insulators, which is an important problem in. space exploration technology. The work is also relevant to important industrial processes such as xerography and the application of paints and coatings. Determining a better understanding of the fundamental mechanism of insulator-insulator triboelectrification will hopefully lead to better means of eliminating or at least mitigating its hazards and enhancing its useful applications.

Design of a 1200-V ultra-thin partial SOI LDMOS with n-type buried layer

NASA Astrophysics Data System (ADS)

Qiao, Ming; Wang, Yuru; Li, Yanfei; Zhang, Bo; Li, Zhaoji

2014-11-01

A novel 1200-V ultra-thin partial silicon-on-insulator (PSOI) lateral double-diffusion metal oxide semiconductor (LDMOS) with n-type buried (n-buried) layer (NBL PSOI LDMOS) is proposed in this paper. The new PSOI LDMOS features an n-buried layer underneath the n-type drift (n-drift) region close to the source side, providing a large conduction region for majority carriers and a silicon window to improve self-heating effect (SHE). A combination of uniform and linear variable doping (ULVD) profile is utilized in the n-drift region, which alleviates the inherent tradeoff between specific on-resistance (Ron,sp) and breakdown voltage (BV). With the n-drift region length of 80 μm, the NBL PSOI LDMOS obtains a high BV of 1243 V which is improved by around 105 V in comparison to the conventional SOI LDMOS with linear variable doping (LVD) profile for the n-drift region (LVD SOI LDMOS). Besides, the 1200-V NBL PSOI LDMOS has a lower maximum temperature (Tmax) of 333 K at a power (P) of 1 mW/μm which is reduced by around 61 K. Meanwhile, Ron,sp and Tmax of the NBL PSOI LDMOS are lower than those of the conventional LVD SOI LDMOS for a wide range of BV.

Sizable band gap in organometallic topological insulator

NASA Astrophysics Data System (ADS)

Derakhshan, V.; Ketabi, S. A.

2017-01-01

Based on first principle calculation when Ceperley-Alder and Perdew-Burke-Ernzerh type exchange-correlation energy functional were adopted to LSDA and GGA calculation, electronic properties of organometallic honeycomb lattice as a two-dimensional topological insulator was calculated. In the presence of spin-orbit interaction bulk band gap of organometallic lattice with heavy metals such as Au, Hg, Pt and Tl atoms were investigated. Our results show that the organometallic topological insulator which is made of Mercury atom shows the wide bulk band gap of about ∼120 meV. Moreover, by fitting the conduction and valence bands to the band-structure which are produced by Density Functional Theory, spin-orbit interaction parameters were extracted. Based on calculated parameters, gapless edge states within bulk insulating gap are indeed found for finite width strip of two-dimensional organometallic topological insulators.

Insulated InP (100) semiconductor by nano nucleus generation in pure water

NASA Astrophysics Data System (ADS)

Ghorab, Farzaneh; Es'haghi, Zarrin

2018-01-01

Preparation of specified designs on optoelectronic devices such as Light-Emitting Diodes (LEDs) and Laser Diodes (LDs) by using insulated thin films is very important. InP as one of those semiconductors which is used as optoelectronic devices, have two different kinds of charge carriers as n-InP and p-InP in the microelectronic industry. The surface preparation of this kind of semiconductor can be accomplished with individually chemical, mechanical, chemo - mechanical and electrochemical methods. But electrochemical method can be suitably replaced instead of the other methods, like CMP (Chemical Mechanical Polishing), because of the simplicity. In this way, electrochemically formation of insulated thin films by nano nucleus generation on semiconductor (using constant current density of 0.07 mA /cm2) studied in this research. Insulated nano nucleus generation and their growth up to thin film formation on semiconductor single crystal (100), n-InP, inpure water (0.08 µs/cm,25°c) characterized by Atomic Force Microscopy (AFM), Scanning Electron Microscopy (SEM), Four-point probe and Styloprofilometer techniques. The SEM images show active and passive regions on the n-InP surface and not uniform area on p-InP surface by passing through the passive condition. So the passive regions were nonuniform, and only the active regions were uniform and clean. The various semiconducting behavior in electrochemical condition, studied and compared with structural specification of InP type group (III-V).

Improved linearity in AlGaN/GaN metal-insulator-semiconductor high electron mobility transistors with nonlinear polarization dielectric

NASA Astrophysics Data System (ADS)

Gao, Tao; Xu, Ruimin; Kong, Yuechan; Zhou, Jianjun; Kong, Cen; Dong, Xun; Chen, Tangsheng

2015-06-01

We demonstrate highly improved linearity in a nonlinear ferroelectric of Pb(Zr0.52Ti0.48)-gated AlGaN/GaN metal-insulator-semiconductor high electron mobility transistor (MIS-HEMT). Distinct double-hump feature in the transconductance-gate voltage (gm-Vg) curve is observed, yielding remarkable enhancement in gate voltage swing as compared to MIS-HEMT with conventional linear gate dielectric. By incorporating the ferroelectric polarization into a self-consistent calculation, it is disclosed that in addition to the common hump corresponding to the onset of electron accumulation, the second hump at high current level is originated from the nonlinear polar nature of ferroelectric, which enhances the gate capacitance by increasing equivalent dielectric constant nonlinearly. This work paves a way for design of high linearity GaN MIS-HEMT by exploiting the nonlinear properties of dielectric.

Magnon-induced superconductivity in a topological insulator coupled to ferromagnetic and antiferromagnetic insulators

NASA Astrophysics Data System (ADS)

Hugdal, Henning G.; Rex, Stefan; Nogueira, Flavio S.; Sudbø, Asle

2018-05-01

We study the effective interactions between Dirac fermions on the surface of a three-dimensional topological insulator due to the proximity coupling to the magnetic fluctuations in a ferromagnetic or antiferromagnetic insulator. Our results show that the magnetic fluctuations can mediate attractive interactions between Dirac fermions of both Amperean and BCS types. In the ferromagnetic case, we find pairing between fermions with parallel momenta, so-called Amperean pairing, whenever the effective Lagrangian for the magnetic fluctuations does not contain a quadratic term. The pairing interaction also increases with increasing Fermi momentum and is in agreement with previous studies in the limit of high chemical potential. If a quadratic term is present, the pairing is instead of BCS type above a certain chemical potential. In the antiferromagnetic case, BCS pairing occurs when the ferromagnetic coupling between magnons on the same sublattice exceeds the antiferromagnetic coupling between magnons on different sublattices. Outside this region in parameter space, we again find that Amperean pairing is realized.

Gaseous insulators for high voltage electrical equipment

DOEpatents

Christophorou, Loucas G.; James, David R.; Pace, Marshall O.; Pai, Robert Y.

1979-01-01

Gaseous insulators comprise compounds having high attachment cross sections for electrons having energies in the 0-1.3 electron volt range. Multi-component gaseous insulators comprise compounds and mixtures having overall high electron attachment cross sections in the 0-1.3 electron volt range and moderating gases having high cross sections for inelastic interactions with electrons of energies 1-4 electron volts. Suitable electron attachment components include hexafluorobutyne, perfluorobutene-2, perfluorocyclobutane, perfluorodimethylcyclobutane, perfluorocyclohexene, perfluoromethylcyclohexane, hexafluorobutadiene, perfluoroheptene-1 and hexafluoroazomethane. Suitable moderating gases include N.sub.2, CO, CO.sub.2 and H.sub.2. The gaseous insulating mixture can also contain SF.sub.6, perfluoropropane and perfluorobenzene.

Gaseous insulators for high voltage electrical equipment

DOEpatents

Christophorou, Loucas G.; James, David R.; Pace, Marshall O.; Pai, Robert Y.

1981-01-01

Gaseous insulators comprise compounds having high attachment cross sections for electrons having energies in the 0-1.3 electron volt range. Multi-component gaseous insulators comprise compounds and mixtures having overall high electron attachment cross sections in the 0-1.3 electron volt range and moderating gases having high cross sections for inelastic interactions with electrons of energies 1-4 electron volts. Suitable electron attachment components include hexafluorobutyne, perfluorobutene-2, perfluorocyclobutane, perfluorodimethylcyclobutane, perfluorocyclohexene, perfluoromethylcyclohexane, hexafluorobutadiene, perfluoroheptene-1 and hexafluoroazomethane. Suitable moderating gases include N.sub.2, CO, CO.sub.2 and H.sub.2. The gaseous insulating mixture can also contain SF.sub.6, perfluoropropane and perfluorobenzene.

A LINE POLE 20, DETAIL OF ORIGINAL GLASS PINTYPE INSULATORS ...

Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

A LINE POLE 20, DETAIL OF ORIGINAL GLASS PIN-TYPE INSULATORS AND INTACT COMMUNICATION LINE CROSS ARM WITH TWO GLASS INSULATORS. VIEW TO NORTHWEST. - Mystic Lake Hydroelectric Facility, Electric Transmission A Line, Along West Rosebud Creek, Fishtail, Stillwater County, MT

A LINE POLE 75, DETAIL OF ORIGINAL GLASS PINTYPE INSULATORS ...

Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

A LINE POLE 75, DETAIL OF ORIGINAL GLASS PIN-TYPE INSULATORS AND INTACT COMMUNICATION LINE CROSS ARM WITH ONE GLASS INSULATOR. VIEW TO SOUTHWEST. - Mystic Lake Hydroelectric Facility, Electric Transmission A Line, Along West Rosebud Creek, Fishtail, Stillwater County, MT

Ultrafast transient photocarrier dynamics of the bulk-insulating topological insulator B i1.5S b0.5T e1.7S e1.3

NASA Astrophysics Data System (ADS)

Choi, Young Gwan; Zhung, Chan June; Park, Sun-Hee; Park, Joonbum; Kim, Jun Sung; Kim, Seongheun; Park, Jaehun; Lee, J. S.

2018-02-01

Using optical-pump terahertz-probe spectroscopy, we investigated an ultrafast photocarrier relaxation behavior in a B i1.5S b0.5T e1.7S e1.3 (BSTS) single crystal, which is one of the most bulk-insulating topological insulators. Compared to n -type bulk-metallic B i2S e3 , we found that BSTS endows distinct behaviors in its photocarrier dynamics; the relaxation time turns out to be an order of magnitude longer, and the transient conductance spectrum exhibits a nonlinear increase as a function of the pumping power. Also, we observed an abrupt reduction of the photocarrier scattering rate in several picoseconds after the initial photoexcitation. We discuss these intriguing experimental observations based on a bulk-to-surface carrier injection assisted by the built-in electric field near the surface and electron-phonon scattering.

Wide-band operation of quasi-optical distributed superconductor/insulator/superconductor mixers with epitaxial NbN/AlN/NbN junctions

NASA Astrophysics Data System (ADS)

Kohjiro, S.; Shitov, S. V.; Wang, Z.; Uzawa, Y.; Miki, S.; Kawakami, A.; Shoji, A.

2004-05-01

For the optimum design of integrated receivers operating above the gap frequency of Nb, we have designed, fabricated and tested NbN-based quasi-optical superconductor/insulator/superconductor (SIS) mixers. The mixer chip incorporates a resonant half-wavelength epitaxial NbN/AlN/NbN junction, a twin-slot antenna and their coupling circuits. We adopted two kinds of coupling circuit between the antenna and the SIS junction: one is an in-phase feed with a length of 95 µm and the other is an anti-phase feed of 30 µm length. It was found that the anti-phase mixer reveals a 3 dB bandwidth of 43% of the centre frequency; the uncorrected double-sideband receiver noise temperature TRX = 691 K at 0.91 THz and TRX = 844 K at 0.80 THz, while 17% and TRX = 1250 K at 0.79 THz for the in-phase version. Possible reasons for this difference are discussed, which could be transmission loss and its robustness with respect to the variation of junction parameters. These experimental results suggest the NbN-based distributed mixer with the anti-phase feed is a better candidate for wide-band integrated receivers operating above 0.7 THz.

Topological magnetic phase in LaMnO3 (111) bilayer

NASA Astrophysics Data System (ADS)

Weng, Yakui; Huang, Xin; Yao, Yugui; Dong, Shuai

2015-11-01

Candidates for correlated topological insulators, originated from the spin-orbit coupling as well as the Hubbard-type correlation, are expected in the (111) bilayer of perovskite-structural transition-metal oxides. Based on the first-principles calculation and tight-binding model, the electronic structure of a LaMnO3 (111) bilayer sandwiched in LaScO3 barriers has been investigated. For the ideal undistorted perovskite structure, the Fermi energy of LaMnO3 (111) bilayer just stays at the Dirac point, rendering a semimetal (graphenelike) which is also a half metal [different from graphene or the previously studied LaNiO3 (111) bilayer]. The Dirac cone can be opened by the spin-orbit coupling, giving rise to nontrivial topological bands corresponding to the (quantized) anomalous Hall effect. For the realistic orthorhombic distorted lattice, the Dirac point moves with increasing Hubbard repulsion (or equivalent Jahn-Teller distortion). Finally, a Mott gap opens, establishing a phase boundary between the Mott insulator and topological magnetic insulator. Our calculation finds that the gap opened by spin-orbit coupling is much smaller in the orthorhombic distorted lattice (˜1.7 meV) than the undistorted one (˜11 meV). Therefore, to suppress the lattice distortion can be helpful to enhance the robustness of the topological phase in perovskite (111) bilayers.

Effective Hamiltonians for correlated narrow energy band systems and magnetic insulators: Role of spin-orbit interactions in metal-insulator transitions and magnetic phase transitions

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

Chakraborty, Subrata; Vijay, Amrendra, E-mail: avijay@iitm.ac.in

Using a second-quantized many-electron Hamiltonian, we obtain (a) an effective Hamiltonian suitable for materials whose electronic properties are governed by a set of strongly correlated bands in a narrow energy range and (b) an effective spin-only Hamiltonian for magnetic materials. The present Hamiltonians faithfully include phonon and spin-related interactions as well as the external fields to study the electromagnetic response properties of complex materials and they, in appropriate limits, reduce to the model Hamiltonians due to Hubbard and Heisenberg. With the Hamiltonian for narrow-band strongly correlated materials, we show that the spin-orbit interaction provides a mechanism for metal-insulator transition, whichmore » is distinct from the Mott-Hubbard (driven by the electron correlation) and the Anderson mechanism (driven by the disorder). Next, with the spin-only Hamiltonian, we demonstrate the spin-orbit interaction to be a reason for the existence of antiferromagnetic phase in materials which are characterized by a positive isotropic spin-exchange energy. This is distinct from the Néel-VanVleck-Anderson paradigm which posits a negative spin-exchange for the existence of antiferromagnetism. We also find that the Néel temperature increases as the absolute value of the spin-orbit coupling increases.« less

Fabrication of high-quality superconductor-insulator-superconductor junctions on thin SiN membranes

NASA Technical Reports Server (NTRS)

Garcia, Edouard; Jacobson, Brian R.; Hu, Qing

1993-01-01

We have successfully fabricated high-quality and high-current density superconductor-insulator-superconductor (SIS) junctions on freestanding thin silicon nitride (SIN) membranes. These devices can be used in a novel millimeter-wave and THz receiver system which is made using micromachining. The SIS junctions with planar antennas were fabricated first on a silicon wafer covered with a SiN membrane, the Si wafer underneath was then etched away using an anisotropic KOH etchant. The current-voltage characteristics of the SIS junctions remained unchanged after the whole process, and the junctions and the membrane survived thermal cycling.

Magnetic orders of LaTiO3 under epitaxial strain: A first-principles study

NASA Astrophysics Data System (ADS)

Weng, Yakui; Huang, Xin; Tang, Yankun; Dong, Shuai

2014-05-01

Perovskite LaTiO3 bulk is a typical Mott-insulator with G-type antiferromagnetic order. In this work, the biaxial strain effects on the ground magnetic order of LaTiO3 films grown on various substrates have been studied. For the compressive strain, LaTiO3 films grown on LaAlO3, LaGaO3, and SrTiO3 substrates undergo a phase transition from the original G-type antiferromagnet to A-type antiferromagnet. The underlying physical mechanisms are the lattice distortions tunned by strain. While for the tensile strain, the BaTiO3 and LaScO3 substrates have been tested, which show a tendency to transit the LaTiO3 to the C-type antiferromagnet. Furthermore, our calculations find that the magnetic transitions under epitaxial strain do not change the insulating fact of LaTiO3.

Thermoelectric properties of topological insulator BaSn2

NASA Astrophysics Data System (ADS)

Guo, San-Dong; Qiu, Liang

2017-01-01

Recently, \\text{BaS}{{\\text{n}}2} has been predicted to be a strong topological insulator by the first-principle calculations. It is well known that topological insulators have a close connection to thermoelectric materials, such as the \\text{B}{{\\text{i}}2}\\text{T}{{\\text{e}}3} family. In this work, we investigate thermoelectric properties of \\text{BaS}{{\\text{n}}2} by the first-principles calculations combined with the Boltzmann transport theory. The electronic part is carried out by a modified Becke and Johnson (mBJ) exchange potential, including spin-orbit coupling (SOC), while the phonon part is performed using a generalized gradient approximation (GGA). It was found that the electronic transport coefficients between the in-plane and cross-plane directions showed strong anisotropy, while lattice-lattice thermal conductivities demonstrated almost complete isotropy. Calculated results revealed a very low lattice thermal conductivity for \\text{BaS}{{\\text{n}}2} , and the corresponding average lattice thermal conductivity at room temperature is 1.69 \\text{W}~{{\\text{m}}-1}~{{\\text{K}}-1} , which is comparable or lower than those of lead chalcogenides and bismuth-tellurium systems as classic thermoelectric materials. Due to the complicated scattering mechanism, calculating the scattering time τ is challenging. By using an empirical τ ={{10}-14} s, the n-type figure of merit ZT is greater than 0.40 in wide temperature ranges. Experimentally, it is possible to attain better thermoelectric performance by strain or tuning size parameters. This work indicates that \\text{BaS}{{\\text{n}}2} may be a potential thermoelectric material, which can stimulate further theoretical and experimental work.

Mott Transition in GdMnO3: an Ab Initio Study

NASA Astrophysics Data System (ADS)

Ferreira, W. S.; Moreira, E.; Frazão, N. F.

2018-04-01

Orthorhombic GdMnO3 is studied using density functional theory considering the pseudo-potential plane-wave method within local-spin-density approximation, LSDA. The electronic band structure and density of states, for several hydrostatic pressures, are studied. The Mott transition was observed at 60 GPa. Calculated lattice parameters are close to the experimental measurements, and some indirect band gaps (S→Γ) were obtained within the LSDA level of calculation, between the occupied O-2 p and unoccupied Gd-4 f states. The variation of the gap reduces with increasing pressure, being well fitted to a quadratic function.

Two-Magnon Raman Scattering and Pseudospin-Lattice Interactions in Sr_{2}IrO_{4} and Sr_{3}Ir_{2}O_{7}.

PubMed

Gretarsson, H; Sung, N H; Höppner, M; Kim, B J; Keimer, B; Le Tacon, M

2016-04-01

We have used Raman scattering to investigate the magnetic excitations and lattice dynamics in the prototypical spin-orbit Mott insulators Sr_{2}IrO_{4} and Sr_{3}Ir_{2}O_{7}. Both compounds exhibit pronounced two-magnon Raman scattering features with different energies, line shapes, and temperature dependencies, which in part reflect the different influence of long-range frustrating exchange interactions. Additionally, we find strong Fano asymmetries in the line shapes of low-energy phonon modes in both compounds, which disappear upon cooling below the antiferromagnetic ordering temperatures. These unusual phonon anomalies indicate that the spin-orbit coupling in Mott-insulating iridates is not sufficiently strong to quench the orbital dynamics in the paramagnetic state.

Micalastic high-voltage insulation: Design features and experience

NASA Astrophysics Data System (ADS)

Wichmann, A.

1981-12-01

High-quality mica, carefully selected epoxy resins and a well-matched vacuum/pressure impregnation process determine the characteristics of the MICALASTIC insulation for large turbine-generators. Logical development and process manufacturing quality control have led to an insulation system of high quality and operating reliability. The first winding of a turbine-generator being impregnated and cured under vacuum with solvent-free synthetic resin in 1958 was designed for 10.5 kV rated voltage. Ever since, Siemens AG and Kraftwerk Union AG have used this type of insulation for all direct-cooled windings and also for an increasing number of indirect-cooled windings. At present, 240 turbine-generators with a total of more than 115,000 MVA output have been built. Since 1960, this insulation system has been registered for Siemens AG under the trade name MICALASTIC. The stator windings of the largest, single-shaft generators to date, rated 1560 MVA, 27 kV, has been built with MICALASTIC insulation.

The chromosomal association/dissociation of the chromatin insulator protein Cp190 of Drosophila melanogaster is mediated by the BTB/POZ domain and two acidic regions.

PubMed

Oliver, Daniel; Sheehan, Brian; South, Heather; Akbari, Omar; Pai, Chi-Yun

2010-12-31

Chromatin insulators or boundary elements are a class of functional elements in the eukaryotic genome. They regulate gene transcription by interfering with promoter-enhancer communication. The Cp190 protein of Drosophila melanogaster is essential to the function of at least three-types of chromatin insulator complexes organized by Su(Hw), CTCF and BEAF32. We mapped functional regions of Cp190 in vivo and identified three domains that are essential for the insulator function and for the viability of flies: the BTB/POZ domain, an aspartic acid-rich (D-rich) region and a C-terminal glutamic acid-rich (E-rich) region. Other domains including the centrosomal targeting domain and the zinc fingers are dispensable. The N-terminal CP190BTB-D fragment containing the BTB/POZ domain and the D-rich region is sufficient to mediate association with all three types of insulator complexes. The fragment however is not sufficient for insulator activity or viability. The Cp190 and CP190BTB-D are regulated differently in cells treated with heat-shock. The Cp190 dissociated from chromosomes during heat-shock, indicating that dissociation of Cp190 with chromosomes can be regulated. In contrast, the CP190BTB-D fragment didn't dissociate from chromosomes in the same heat-shocked condition, suggesting that the deleted C-terminal regions have a role in regulating the dissociation of Cp190 with chromosomes. The N-terminal fragment of Cp190 containing the BTB/POZ domain and the D-rich region mediates association of Cp190 with all three types of insulator complexes and that the E-rich region of Cp190 is required for dissociation of Cp190 from chromosomes during heat-shock. The heat-shock-induced dissociation is strong evidence indicating that dissociation of the essential insulator protein Cp190 from chromosomes is regulated. Our results provide a mechanism through which activities of an insulator can be modulated by internal and external cues.

Insulators obtained by electron cyclotron resonance plasmas on Si or GaAs

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

Diniz, J.A.; Doi, I.; Swart, J.W

2003-03-15

Silicon oxynitride (SiO{sub x}N{sub y}) and nitride (SiN{sub x}) insulators have been deposited or grown (with or without silane in the gas mixture, respectively) by electron cyclotron resonance (ECR) plasmas on Si and/or GaAs substrates at room temperature (20 deg. C) and low pressures (up to 10 mTorr). Chemical bonding characteristics of the SiO{sub x}N{sub y} and SiN{sub x} films were evaluated using Fourier transform infrared spectrometry (FTIR). The profile measurements determined the film thickness, the deposition (or oxidation) rate and the etch rates in buffered HF (BHF). The refractive indexes and the thicknesses were determined by ellipsometry. The effectivemore » interface charge densities were determined by capacitance-voltage (C-V) measurements. With these processes and analyses, different films were obtained and optimized. Suitable gate insulators for metal-insulator-semiconductor (MIS) devices with low interface charge densities were developed: (a) SiN{sub x} films deposited by ECR-chemical vapor deposition (ECR-PECVD) on GaAs substrates; (b) SiO{sub x}N{sub y} insulators obtained by low-energy molecular nitrogen ion ({sup 28}N{sub 2}{sup +}) implantation (energy of 5 keV and dose of 1x10{sup 15}/cm{sup 2}) in Si substrates prior to high-density O{sub 2} ECR plasma oxidation; and (c) SiO{sub x}N{sub y} insulators grown (without silane in the gas mixture) by O{sub 2}/N{sub 2}/Ar ECR plasma 'oxynitridation'. Furthermore, some SiN{sub x} films also present very good masking characteristics for local oxidation of silicon process.« less

Field-tuned superconductor-insulator transitions and Hall resistance in thin polycrystalline MoN films

NASA Astrophysics Data System (ADS)

Makise, Kazumasa; Ichikawa, Fusao; Asano, Takayuki; Shinozaki, Bunju

2018-02-01

We report on the superconductor-insulator transitions (SITs) of disordered molybdenum nitride (MoN) thin films on (1 0 0) MgO substrates as a function of the film thickness and magnetic fields. The T c of the superconducting MoN films, which exhibit a sharp superconducting transition, monotonically decreases as the normal state R sq increases with a decreasing film thickness. For several films with different thicknesses, we estimate the critical field H c and the product zν  ≃  0.6 of the dynamical exponent z and the correlation length exponent ν using a finite scaling analysis. The value of this product can be explained by the (2  +  1) XY model. We found that the Hall resistance ΔR xy (H) is maximized when the magnetic field satisfies H HP(T) \\propto |1  -  T/T C0| in the superconducting state and also in the normal states owning to the superconducting fluctuation corresponding to the ghost critical magnetic field. We measured the Hall conductivity δσ xy (H)  =  σ xy (H)  -  σ xyn and fit the Gaussian approximation theory for δσ xy (H) to the experimental data. Agreement between the data and the theory beyond H c suggests the survival of the Cooper pair in the insulating region of the SIT.

Field-tuned superconductor-insulator transitions and Hall resistance in thin polycrystalline MoN films.

PubMed

Makise, Kazumasa; Ichikawa, Fusao; Asano, Takayuki; Shinozaki, Bunju

2018-02-14

We report on the superconductor-insulator transitions (SITs) of disordered molybdenum nitride (MoN) thin films on (1 0 0) MgO substrates as a function of the film thickness and magnetic fields. The T c of the superconducting MoN films, which exhibit a sharp superconducting transition, monotonically decreases as the normal state R sq increases with a decreasing film thickness. For several films with different thicknesses, we estimate the critical field H c and the product zν  ≃  0.6 of the dynamical exponent z and the correlation length exponent ν using a finite scaling analysis. The value of this product can be explained by the (2  +  1) XY model. We found that the Hall resistance ΔR xy (H) is maximized when the magnetic field satisfies H HP (T) [Formula: see text] |1  -  T/T C0 | in the superconducting state and also in the normal states owning to the superconducting fluctuation corresponding to the ghost critical magnetic field. We measured the Hall conductivity δσ xy (H)  =  σ xy (H)  -  [Formula: see text] and fit the Gaussian approximation theory for δσ xy (H) to the experimental data. Agreement between the data and the theory beyond H c suggests the survival of the Cooper pair in the insulating region of the SIT.

UV light induced insulator-metal transition in ultra-thin ZnO/TiOx stacked layer grown by atomic layer deposition

NASA Astrophysics Data System (ADS)

Saha, D.; Misra, P.; Joshi, M. P.; Kukreja, L. M.

2016-08-01

In the present study, atomic layer deposition has been used to grow a series of Ti incorporated ZnO thin films by vertically stacking different numbers (n = 1-7) of ZnO/TiOx layers on (0001) sapphire substrates. The effects of defect states mediated chemisorption of O2 and/OH groups on the electrical properties of these films have been investigated by illuminating the samples under UV light inside a high vacuum optical cryostat. The ultra-thin film having one stacked layer (n = 1) did not show any change in its electrical resistance upon UV light exposure. On the contrary, marginal drop in the electrical resistivity was measured for the samples with n ≥ 3. Most surprisingly, the sample with n = 2 (thickness ˜ 12 nm) showed an insulator to metal transition upon UV light exposure. The temperature dependent electrical resistivity measurement on the as grown film (n = 2) showed insulating behaviour, i.e., diverging resistivity on extrapolation to T→ 0 K. However, upon UV light exposure, it transformed to a metallic state, i.e., finite resistivity at T → 0 K. Such an insulator-metal transition plausibly arises due to the de-trapping of conduction electrons from the surface defect sites which resulted in an upward shift of the Fermi level above the mobility edge. The low-temperature electron transport properties on the insulating film (n = 2) were investigated by a combined study of zero field electrical resistivity ρ(T) and magnetoresistance (MR) measurements. The observed negative MR was found to be in good agreement with the magnetic field induced suppression of quantum interference between forward-going paths of tunnelling electrons. Both ρ(T) and MR measurements provided strong evidence for the Efros-Shklovskii type variable range hopping conduction in the low-temperature (≤40 K) regime. Such studies on electron transport in ultra-thin n-type doped ZnO films are crucial to achieve optimum functionality with long term reliability of ZnO based transparent

Improved linearity in AlGaN/GaN metal-insulator-semiconductor high electron mobility transistors with nonlinear polarization dielectric

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

Gao, Tao; Science and Technology on Monolithic Integrated Circuits and Modules Laboratory, Nanjing Electronic Devices Institute, Nanjing 210016; Xu, Ruimin

2015-06-15

We demonstrate highly improved linearity in a nonlinear ferroelectric of Pb(Zr{sub 0.52}Ti{sub 0.48})-gated AlGaN/GaN metal-insulator-semiconductor high electron mobility transistor (MIS-HEMT). Distinct double-hump feature in the transconductance-gate voltage (g{sub m}-V{sub g}) curve is observed, yielding remarkable enhancement in gate voltage swing as compared to MIS-HEMT with conventional linear gate dielectric. By incorporating the ferroelectric polarization into a self-consistent calculation, it is disclosed that in addition to the common hump corresponding to the onset of electron accumulation, the second hump at high current level is originated from the nonlinear polar nature of ferroelectric, which enhances the gate capacitance by increasing equivalent dielectricmore » constant nonlinearly. This work paves a way for design of high linearity GaN MIS-HEMT by exploiting the nonlinear properties of dielectric.« less

Ion beam modification of topological insulator bismuth selenide

DOE PAGES

Sharma, Peter Anand; Sharma, A. L. Lima; Hekmaty, Michelle A.; ...

2014-12-17

In this study, we demonstrate chemical doping of a topological insulator Bi 2Se 3 using ion implantation. Ion beam-induced structural damage was characterized using grazing incidence X-ray diffraction and transmission electron microscopy. Ion damage was reversed using a simple thermal annealing step. Carrier-type conversion was achieved using ion implantation followed by an activation anneal in Bi 2Se 3 thin films. These two sets of experiments establish the feasibility of ion implantation for chemical modification of Bi 2Se 3, a prototypical topological insulator. Ion implantation can, in principle, be used for any topological insulator. The direct implantation of dopants should allowmore » better control over carrier concentrations for the purposes of achieving low bulk conductivity. Ion implantation also enables the fabrication of inhomogeneously doped structures, which in turn should make possible new types of device designs.« less

Material-controlled dynamic vacuum insulation

DOEpatents

Benson, D.K.; Potter, T.F.

1996-10-08

A compact vacuum insulation panel is described comprising a chamber enclosed by two sheets of metal, glass-like spaces disposed in the chamber between the sidewalls, and a high-grade vacuum in the chamber includes apparatus and methods for enabling and disabling, or turning ``on`` and ``off`` the thermal insulating capability of the panel. One type of enabling and disabling apparatus and method includes a metal hydride for releasing hydrogen gas into the chamber in response to heat, and a hydrogen grate between the metal hydride and the chamber for selectively preventing and allowing return of the hydrogen gas to the metal hydride. Another type of enabling and disabling apparatus and method includes a variable emissivity coating on the sheets of metal in which the emissivity is controllably variable by heat or electricity. Still another type of enabling and disabling apparatus and method includes metal-to-metal contact devices that can be actuated to establish or break metal-to-metal heat paths or thermal short circuits between the metal sidewalls. 25 figs.

Variably insulating portable heater/cooler

DOEpatents

Potter, Thomas F.

1998-01-01

A compact vacuum insulation panel comprising a chamber enclosed by two sheets of metal, glass-like spaces disposed in the chamber between the sidewalls, and a high-grade vacuum in the chamber includes apparatus and methods for enabling and disabling, or turning "on" and "off" the thermal insulating capability of the panel. One type of enabling and disabling apparatus and method includes a metal hydride for releasing hydrogen gas into the chamber in response to heat, and a hydrogen grate between the metal hydride and the chamber for selectively preventing and allowing return of the hydrogen gas to the metal hydride. Another type of enabling and disabling apparatus and method includes a variable emissivity coating on the sheets of metal in which the emissivity is controllably variable by heat or electricity. Still another type of enabling and disabling apparatus and method includes metal-to-metal contact devices that can be actuated to establish or break metal-to-metal heat paths or thermal short circuits between the metal sidewalls.

Material-controlled dynamic vacuum insulation

DOEpatents

Benson, David K.; Potter, Thomas F.

1996-10-08

A compact vacuum insulation panel comprising a chamber enclosed by two sheets of metal, glass-like spaces disposed in the chamber between the sidewalls, and a high-grade vacuum in the chamber includes apparatus and methods for enabling and disabling, or turning "on" and "off" the thermal insulating capability of the panel. One type of enabling and disabling apparatus and method includes a metal hydride for releasing hydrogen gas into the chamber in response to heat, and a hydrogen grate between the metal hydride and the chamber for selectively preventing and allowing return of the hydrogen gas to the metal hydride. Another type of enabling and disabling apparatus and method includes a variable emissivity coating on the sheets of metal in which the emissivity is controllably variable by heat or electricity. Still another type of enabling and disabling apparatus and method includes metal-to-metal contact devices that can be actuated to establish or break metal-to-metal heat paths or thermal short circuits between the metal sidewalls.

Radiation-controlled dynamic vacuum insulation

DOEpatents

Benson, David K.; Potter, Thomas F.

1995-01-01

A compact vacuum insulation panel comprising a chamber enclosed by two sheets of metal, glass-like spaces disposed in the chamber between the sidewalls, and a high-grade vacuum in the chamber that includes apparatus and methods for enabling and disabling, or turning "on" and "off" the thermal insulating capability of the panel. One type of enabling and disabling apparatus and method includes a metal hydride for releasing hydrogen gas into the chamber in response to heat, and a hydrogen grate between the metal hydride and the chamber for selectively preventing and allowing return of the hydrogen gas to the metal hydride. Another type of enabling and disabling apparatus and method includes a variable emissivity coating on the sheets of metal in which the emissivity is controllably variable by heat or electricity. Still another type of enabling and disabling apparatus and method includes metal-to-metal contact devices that can be actuated to establish or break metal-to-metal heat paths or thermal short circuits between the metal sidewalls.

Radiation-controlled dynamic vacuum insulation

DOEpatents

Benson, D.K.; Potter, T.F.

1995-07-18

A compact vacuum insulation panel is described comprising a chamber enclosed by two sheets of metal, glass-like spaces disposed in the chamber between the sidewalls, and a high-grade vacuum in the chamber that includes apparatus and methods for enabling and disabling, or turning ``on`` and ``off`` the thermal insulating capability of the panel. One type of enabling and disabling apparatus and method includes a metal hydride for releasing hydrogen gas into the chamber in response to heat, and a hydrogen grate between the metal hydride and the chamber for selectively preventing and allowing return of the hydrogen gas to the metal hydride. Another type of enabling and disabling apparatus and method includes a variable emissivity coating on the sheets of metal in which the emissivity is controllably variable by heat or electricity. Still another type of enabling and disabling apparatus and method includes metal-to-metal contact devices that can be actuated to establish or break metal-to-metal heat paths or thermal short circuits between the metal sidewalls. 25 figs.

Variably insulating portable heater/cooler

DOEpatents

Potter, T.F.

1998-09-29

A compact vacuum insulation panel is described comprising a chamber enclosed by two sheets of metal, glass-like spaces disposed in the chamber between the sidewalls, and a high-grade vacuum in the chamber includes apparatus and methods for enabling and disabling, or turning ``on`` and ``off`` the thermal insulating capability of the panel. One type of enabling and disabling apparatus and method includes a metal hydride for releasing hydrogen gas into the chamber in response to heat, and a hydrogen grate between the metal hydride and the chamber for selectively preventing and allowing return of the hydrogen gas to the metal hydride. Another type of enabling and disabling apparatus and method includes a variable emissivity coating on the sheets of metal in which the emissivity is controllably variable by heat or electricity. Still another type of enabling and disabling apparatus and method includes metal-to-metal contact devices that can be actuated to establish or break metal-to-metal heat paths or thermal short circuits between the metal sidewalls. 25 figs.

Composite Behavior of Insulated Concrete Sandwich Wall Panels Subjected to Wind Pressure and Suction.

PubMed

Choi, Insub; Kim, JunHee; Kim, Ho-Ryong

2015-03-19

A full-scale experimental test was conducted to analyze the composite behavior of insulated concrete sandwich wall panels (ICSWPs) subjected to wind pressure and suction. The experimental program was composed of three groups of ICSWP specimens, each with a different type of insulation and number of glass-fiber-reinforced polymer (GFRP) shear grids. The degree of composite action of each specimen was analyzed according to the load direction, type of the insulation, and number of GFRP shear grids by comparing the theoretical and experimental values. The failure modes of the ICSWPs were compared to investigate the effect of bonds according to the load direction and type of insulation. Bonds based on insulation absorptiveness were effective to result in the composite behavior of ICSWP under positive loading tests only, while bonds based on insulation surface roughness were effective under both positive and negative loading tests. Therefore, the composite behavior based on surface roughness can be applied to the calculation of the design strength of ICSWPs with continuous GFRP shear connectors.

Composite Behavior of Insulated Concrete Sandwich Wall Panels Subjected to Wind Pressure and Suction

PubMed Central

Choi, Insub; Kim, JunHee; Kim, Ho-Ryong

2015-01-01

A full-scale experimental test was conducted to analyze the composite behavior of insulated concrete sandwich wall panels (ICSWPs) subjected to wind pressure and suction. The experimental program was composed of three groups of ICSWP specimens, each with a different type of insulation and number of glass-fiber-reinforced polymer (GFRP) shear grids. The degree of composite action of each specimen was analyzed according to the load direction, type of the insulation, and number of GFRP shear grids by comparing the theoretical and experimental values. The failure modes of the ICSWPs were compared to investigate the effect of bonds according to the load direction and type of insulation. Bonds based on insulation absorptiveness were effective to result in the composite behavior of ICSWP under positive loading tests only, while bonds based on insulation surface roughness were effective under both positive and negative loading tests. Therefore, the composite behavior based on surface roughness can be applied to the calculation of the design strength of ICSWPs with continuous GFRP shear connectors. PMID:28788001

Analysis of Deep and Shallow Traps in Semi-Insulating CdZnTe

DOE PAGES

Kim, Kihyun; Yoon, Yongsu; James, Ralph B.

2018-03-13

Trap levels which are deep or shallow play an important role in the electrical and the optical properties of a semiconductor; thus, a trap level analysis is very important in most semiconductor devices. Deep-level defects in CdZnTe are essential in Fermi level pinning at the middle of the bandgap and are responsible for incomplete charge collection and polarization effects. However, a deep level analysis in semi-insulating CdZnTe (CZT) is very difficult. Theoretical capacitance calculation for a metal/insulator/CZT (MIS) device with deep-level defects exhibits inflection points when the donor/acceptor level crosses the Fermi level in the surface-charge layer (SCL). Three CZTmore » samples with different resistivities, 2 × 10 4 (n-type), 2 × 10 6 (p-type), and 2 × 10 10 (p-type) Ω·cm, were used in fabricating the MIS devices. These devices showed several peaks in their capacitance measurements due to upward/downward band bending that depend on the surface potential. In conclusion, theoretical and experimental capacitance measurements were in agreement, except in the fully compensated case.« less

Analysis of Deep and Shallow Traps in Semi-Insulating CdZnTe

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

Kim, Kihyun; Yoon, Yongsu; James, Ralph B.

Trap levels which are deep or shallow play an important role in the electrical and the optical properties of a semiconductor; thus, a trap level analysis is very important in most semiconductor devices. Deep-level defects in CdZnTe are essential in Fermi level pinning at the middle of the bandgap and are responsible for incomplete charge collection and polarization effects. However, a deep level analysis in semi-insulating CdZnTe (CZT) is very difficult. Theoretical capacitance calculation for a metal/insulator/CZT (MIS) device with deep-level defects exhibits inflection points when the donor/acceptor level crosses the Fermi level in the surface-charge layer (SCL). Three CZTmore » samples with different resistivities, 2 × 10 4 (n-type), 2 × 10 6 (p-type), and 2 × 10 10 (p-type) Ω·cm, were used in fabricating the MIS devices. These devices showed several peaks in their capacitance measurements due to upward/downward band bending that depend on the surface potential. In conclusion, theoretical and experimental capacitance measurements were in agreement, except in the fully compensated case.« less

Multilayer Impregnated Fibrous Thermal Insulation Tiles

NASA Technical Reports Server (NTRS)

Tran, Huy K.; Rasky, Daniel J.; Szalai, Christine e.; Hsu, Ming-ta; Carroll, Joseph A.

2007-01-01

The term "secondary polymer layered impregnated tile" ("SPLIT") denotes a type of ablative composite-material thermal- insulation tiles having engineered, spatially non-uniform compositions. The term "secondary" refers to the fact that each tile contains at least two polymer layers wherein endothermic reactions absorb considerable amounts of heat, thereby helping to prevent overheating of an underlying structure. These tiles were invented to afford lighter-weight alternatives to the reusable thermal-insulation materials heretofore variously used or considered for use in protecting the space shuttles and other spacecraft from intense atmospheric-entry heating.

Change of carrier density at the pseudogap critical point of a cuprate superconductor.

PubMed

Badoux, S; Tabis, W; Laliberté, F; Grissonnanche, G; Vignolle, B; Vignolles, D; Béard, J; Bonn, D A; Hardy, W N; Liang, R; Doiron-Leyraud, N; Taillefer, Louis; Proust, Cyril

2016-03-10

The pseudogap is a partial gap in the electronic density of states that opens in the normal (non-superconducting) state of cuprate superconductors and whose origin is a long-standing puzzle. Its connection to the Mott insulator phase at low doping (hole concentration, p) remains ambiguous and its relation to the charge order that reconstructs the Fermi surface at intermediate doping is still unclear. Here we use measurements of the Hall coefficient in magnetic fields up to 88 tesla to show that Fermi-surface reconstruction by charge order in the cuprate YBa2Cu3Oy ends sharply at a critical doping p = 0.16 that is distinctly lower than the pseudogap critical point p* = 0.19 (ref. 11). This shows that the pseudogap and charge order are separate phenomena. We find that the change in carrier density n from n = 1 + p in the conventional metal at high doping (ref. 12) to n = p at low doping (ref. 13) starts at the pseudogap critical point. This shows that the pseudogap and the antiferromagnetic Mott insulator are linked.

Development of High Performance Composite Foam Insulation with Vacuum Insulation Cores

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

Biswas, Kaushik; Desjarlais, Andre Omer; SmithPhD, Douglas

Development of a high performance thermal insulation (thermal resistance or R-value per inch of R-12 hr-ft2- F/Btu-in or greater), with twice the thermal resistance of state-of-the-art commercial insulation materials ( R6/inch for foam insulation), promises a transformational impact in the area of building insulation. In 2010, in the US, the building envelope-related primary energy consumption was 15.6 quads, of which 5.75 quads were due to opaque wall and roof sections; the total US consumption (building, industrial and transportation) was 98 quads. In other words, the wall and roof contribution was almost 6% of the entire US primary energy consumption. Buildingmore » energy modeling analyses have shown that adding insulation to increase the R-value of the external walls of residential buildings by R10-20 (hr-ft2- F/Btu) can yield savings of 38-50% in wall-generated heating and cooling loads. Adding R20 will require substantial thicknesses of current commercial insulation materials, often requiring significant (and sometimes cost-prohibitive) alterations to existing buildings. This article describes the development of a next-generation composite insulation with a target thermal resistance of R25 for a 2 inch thick board (R12/inch or higher). The composite insulation will contain vacuum insulation cores, which are nominally R35-40/inch, encapsulated in polyisocyanurate foam. A recently-developed variant of vacuum insulation, called modified atmosphere insulation (MAI), was used in this research. Some background information on the thermal performance and distinguishing features of MAI has been provided. Technical details of the composite insulation development and manufacturing as well as laboratory evaluation of prototype insulation boards are presented.« less

Evaluation of propellent tank insulation concepts for low-thrust chemical propulsion systems: Executive summary

NASA Technical Reports Server (NTRS)

Kramer, T.; Brogren, E.; Siegel, B.

1984-01-01

Cryogenic propellant tank insulations or liquid oxygen/liquid hydrogen low-thrust 2224N (500 lbf) propulsion systems (LTPS) were assessed. The insulation studied consisted of combinations of N2-purged foam and multilayer insulation (MLI) as well as He-purged MLI-only. Heat leak and payload performance predictions were made for three shuttle-launched LTPS designed for shuttle bay packaged payload densities of 56 kg cu/m (3.5 lbm/cu ft), 40 kg/cu m (2.5 lbm/cu ft) and 24 kg/cu m (1.5 lbm/cu ft). Foam/MLI insulations were found to increase LTPS payload delivery capability when compared with He-purged MLI-only. An additional benefit of foam/MLI was reduced operational complexity because orbiter cargo bay N2 purge gas could be used for MLI purging. Maximum payload mass benefit occurred when an enhanced convection, rather than natural convection, heat transfer was specified for the insulation purge enclosure. The enhanced convection environment allowed minimum insulation thickness to be used for the foam/MLI interface temperature selected to correspond to the moisture dew point in the N2 purge gas. Experimental verification of foam/MLI benefits was recommended. A conservative program cost estimate for testing a MLI-foam insulated tank was 2.1 million dollars. This cost could be reduced significantly without increasing program risk.

A Chromatin Insulator-Like Element in the Herpes Simplex Virus Type 1 Latency-Associated Transcript Region Binds CCCTC-Binding Factor and Displays Enhancer-Blocking and Silencing Activities

PubMed Central

Amelio, Antonio L.; McAnany, Peterjon K.; Bloom, David C.

2006-01-01

A previous study demonstrated that the latency-associated transcript (LAT) promoter and the LAT enhancer/reactivation critical region (rcr) are enriched in acetyl histone H3 (K9, K14) during herpes simplex virus type 1 (HSV-1) latency, whereas all lytic genes analyzed (ICP0, UL54, ICP4, and DNA polymerase) are not (N. J. Kubat, R. K. Tran, P. McAnany, and D. C. Bloom, J. Virol. 78:1139-1149, 2004). This suggests that the HSV-1 latent genome is organized into histone H3 (K9, K14) hyperacetylated and hypoacetylated regions corresponding to transcriptionally permissive and transcriptionally repressed chromatin domains, respectively. Such an organization implies that chromatin insulators, similar to those of cellular chromosomes, may separate distinct transcriptional domains of the HSV-1 latent genome. In the present study, we sought to identify cis elements that could partition the HSV-1 genome into distinct chromatin domains. Sequence analysis coupled with chromatin immunoprecipitation and luciferase reporter assays revealed that (i) the long and short repeats and the unique-short region of the HSV-1 genome contain clustered CTCF (CCCTC-binding factor) motifs, (ii) CTCF motif clusters similar to those in HSV-1 are conserved in other alphaherpesviruses, (iii) CTCF binds to these motifs on latent HSV-1 genomes in vivo, and (iv) a 1.5-kb region containing the CTCF motif cluster in the LAT region possesses insulator activities, specifically, enhancer blocking and silencing. The finding that CTCF, a cellular protein associated with chromatin insulators, binds to motifs on the latent genome and insulates the LAT enhancer suggests that CTCF may facilitate the formation of distinct chromatin boundaries during herpesvirus latency. PMID:16474142

Role of the dielectric for the charging dynamics of the dielectric/barrier interface in AlGaN/GaN based metal-insulator-semiconductor structures under forward gate bias stress

NASA Astrophysics Data System (ADS)

Lagger, P.; Steinschifter, P.; Reiner, M.; Stadtmüller, M.; Denifl, G.; Naumann, A.; Müller, J.; Wilde, L.; Sundqvist, J.; Pogany, D.; Ostermaier, C.

2014-07-01

The high density of defect states at the dielectric/III-N interface in GaN based metal-insulator-semiconductor structures causes tremendous threshold voltage drifts, ΔVth, under forward gate bias conditions. A comprehensive study on different dielectric materials, as well as varying dielectric thickness tD and barrier thickness tB, is performed using capacitance-voltage analysis. It is revealed that the density of trapped electrons, ΔNit, scales with the dielectric capacitance under spill-over conditions, i.e., the accumulation of a second electron channel at the dielectric/AlGaN barrier interface. Hence, the density of trapped electrons is defined by the charging of the dielectric capacitance. The scaling behavior of ΔNit is explained universally by the density of accumulated electrons at the dielectric/III-N interface under spill-over conditions. We conclude that the overall density of interface defects is higher than what can be electrically measured, due to limits set by dielectric breakdown. These findings have a significant impact on the correct interpretation of threshold voltage drift data and are of relevance for the development of normally off and normally on III-N/GaN high electron mobility transistors with gate insulation.

Cryopumping in Cryogenic Insulations for a Reusable Launch Vehicle

NASA Technical Reports Server (NTRS)

Johnson, Theodore F.; Weiser, Erik S.; Grimsley, Brian W.; Jensen, Brian J.

2003-01-01

Testing at cryogenic temperatures was performed to verify the material characteristics and manufacturing processes of reusable propellant tank cryogenic insulations for a Reusable Launch Vehicle (RLV). The unique test apparatus and test methods developed for the investigation of cryopumping in cryogenic insulations are described. Panel level test specimens with various types of cryogenic insulations were subjected to a specific thermal profile where the temperature varied from -262 C to 21 C. Cryopumping occurred if the interior temperature of the specimen exhibited abnormal temperature fluctuations, such as a sudden decrease in temperature during the heating phase.

Insulated Foamy Viral Vectors

PubMed Central

Browning, Diana L.; Collins, Casey P.; Hocum, Jonah D.; Leap, David J.; Rae, Dustin T.; Trobridge, Grant D.

2016-01-01

Retroviral vector-mediated gene therapy is promising, but genotoxicity has limited its use in the clinic. Genotoxicity is highly dependent on the retroviral vector used, and foamy viral (FV) vectors appear relatively safe. However, internal promoters may still potentially activate nearby genes. We developed insulated FV vectors, using four previously described insulators: a version of the well-studied chicken hypersensitivity site 4 insulator (650cHS4), two synthetic CCCTC-binding factor (CTCF)-based insulators, and an insulator based on the CCAAT box-binding transcription factor/nuclear factor I (7xCTF/NF1). We directly compared these insulators for enhancer-blocking activity, effect on FV vector titer, and fidelity of transfer to both proviral long terminal repeats. The synthetic CTCF-based insulators had the strongest insulating activity, but reduced titers significantly. The 7xCTF/NF1 insulator did not reduce titers but had weak insulating activity. The 650cHS4-insulated FV vector was identified as the overall most promising vector. Uninsulated and 650cHS4-insulated FV vectors were both significantly less genotoxic than gammaretroviral vectors. Integration sites were evaluated in cord blood CD34+ cells and the 650cHS4-insulated FV vector had fewer hotspots compared with an uninsulated FV vector. These data suggest that insulated FV vectors are promising for hematopoietic stem cell gene therapy. PMID:26715244

FInvestigation of enhancement mode HfO2 insulated N-polarity GaN/InN/GaN/In0.9Al0.1N heterostructure MISHEMT for high-frequency applications

NASA Astrophysics Data System (ADS)

Mohanbabu, A.; Mohankumar, N.; Godwin Raj, D.; Sarkar, Partha

2017-08-01

In this paper, we examined normally-OFF N-polar InN-channel Metal insulated semiconductor high-electron mobility transistors (MISHEMTs) device with a relaxed In0.9Al0.1N buffer layer. In addition, the enhancement-mode operation of the N-polar structure was investigated. The effect of scaling in N-polar MISHEMT, such as the dielectric and the channel thickness, alter the electrical behavior of the device. We have achieved a maximum drain current of 1.17 A/mm, threshold voltage (VT) =0.728 V, transconductance (gm) of 2.9 S mm-1, high ION/IOFF current ratio of 3.23×103, lowest ON-state resistance (RON) of 0.41 Ω mm and an intrinsic delay time (τ) of 1.456 Fs along with high-frequency performance with ft/ fmaxof 90 GHz/109 GHz and 180 GHz/260 GHz for TCH =0.5 nm at Vds =0.5 V and 1.0 V. The numerically simulated results of highly confined GaN/InN/GaN/In0.9Al0.1N heterostructure MISHEMT exhibits outstanding potential as one of the possibility to replace presently used N-polar MISHEMTs for delivering high power density and frequency at RF/power amplifier applications.

Research and application of high performance GPES rigid foam composite plastic insulation boards

NASA Astrophysics Data System (ADS)

sun, Hongming; xu, Hongsheng; Han, Feifei

2017-09-01

A new type of heat insulation board named GPES was prepared by several polymers and modified nano-graphite particles, injecting high-pressure supercritical CO2. Compared with the traditional thermal insulation material, GPES insulation board has higher roundness bubble and thinner bubble wall. Repeatability and reproducibility tests show that melting knot, dimensional stability, strength and other physical properties are significantly better than traditional organic heat insulation materials. Especially the lower and more stable thermal conductivity of GPES can significantly reduce thermal insulation layer thickness. Obviously GPES is the best choice of insulation materials with the implement of 75% and higher energy efficiency standard.

FIBER AND INTEGRATED OPTICS: New type of heterogeneous nanophotonic silicon-on-insulator optical waveguides

NASA Astrophysics Data System (ADS)

Tsarev, Andrei V.

2007-08-01

A new type of optical waveguides in silicon-on-insulator nanostructures is proposed and studied. Their optical properties are simulated by the beam propagation method and discussed. A new design in the form of heterogeneous waveguide structures is based on the production of additionally heavily doped p+-regions on the sides of a multimode stripe waveguide (the silicon core cross section is ~200 nm × 16 μm). Such doping provides the 'single-mode' behaviour of the heterogeneous waveguide due to the decrease in the optical losses for the fundamental mode and increase in losses for higher-order modes. Single-mode heterogeneous waveguides can be used as base waveguides in photonic and integrated optical elements.

Cryogenic Insulation Systems

NASA Technical Reports Server (NTRS)

Augustynowicz, S. D.; Fesmire, J. E.; Wikstrom, J. P.

1999-01-01

The results of a comparative study of cryogenic insulation systems performed are presented. The key aspects of thermal insulation relative to cryogenic system design, testing, manufacturing, and maintenance are discussed. An overview of insulation development from an energy conservation perspective is given. Conventional insulation materials for cryogenic applications provide three levels of thermal conductivity. Actual thermal performance of standard multilayer insulation (MLI) is several times less than laboratory performance and often 10 times worse than ideal performance. The cost-effectiveness of the insulation system depends on thermal performance; flexibility and durability; ease of use in handling, installation, and maintenance; and overall cost including operations, maintenance, and life cycle. Results of comprehensive testing of both conventional and novel materials such as aerogel composites using cryostat boil-off methods are given. The development of efficient, robust cryogenic insulation systems that operate at a soft vacuum level is the primary focus of this paper.

Dirac-electron-mediated magnetic proximity effect in topological insulator/magnetic insulator heterostructures

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

Li, Mingda; Song, Qichen; Zhao, Weiwei

The possible realization of dissipationless chiral edge current in a topological insulator/magnetic insulator heterostructure is based on the condition that the magnetic proximity exchange coupling at the interface is dominated by the Dirac surface states of the topological insulator. We report a polarized neutron reflectometry observation of Dirac-electron-mediated magnetic proximity effect in a bulk-insulating topological insulator (Bi 0.2Sb 0.8) 2Te 3/magnetic insulator EuS heterostructure. We are able to maximize the proximity-induced magnetism by applying an electrical back gate to tune the Fermi level of topological insulator to be close to the Dirac point. A phenomenological model based on diamagnetic screeningmore » is developed to explain the suppressed proximity-induced magnetism at high carrier density. Our work paves the way to utilize the magnetic proximity effect at the topological insulator/magnetic insulator heterointerface for low-power spintronic applications.« less

Dirac-electron-mediated magnetic proximity effect in topological insulator/magnetic insulator heterostructures

DOE PAGES

Li, Mingda; Song, Qichen; Zhao, Weiwei; ...

2017-11-01

The possible realization of dissipationless chiral edge current in a topological insulator/magnetic insulator heterostructure is based on the condition that the magnetic proximity exchange coupling at the interface is dominated by the Dirac surface states of the topological insulator. We report a polarized neutron reflectometry observation of Dirac-electron-mediated magnetic proximity effect in a bulk-insulating topological insulator (Bi 0.2Sb 0.8) 2Te 3/magnetic insulator EuS heterostructure. We are able to maximize the proximity-induced magnetism by applying an electrical back gate to tune the Fermi level of topological insulator to be close to the Dirac point. A phenomenological model based on diamagnetic screeningmore » is developed to explain the suppressed proximity-induced magnetism at high carrier density. Our work paves the way to utilize the magnetic proximity effect at the topological insulator/magnetic insulator heterointerface for low-power spintronic applications.« less

Plate-type metamaterials for extremely broadband low-frequency sound insulation

NASA Astrophysics Data System (ADS)

Wang, Xiaopeng; Guo, Xinwei; Chen, Tianning; Yao, Ge

2018-01-01

A novel plate-type acoustic metamaterial with a high sound transmission loss (STL) in the low-frequency range ( ≤1000 Hz) is designed, theoretically proven and then experimentally verified. The thin plates with large modulus used in this paper mean that we do not need to apply tension to the plates, which is more applicable to practical engineering, the achievement of noise reduction is better and the installation of plates is more user-friendly than that of the membranes. The effects of different structural parameters of the plates on the sound-proofed performance at low-frequencies were also investigated by experiment and finite element method (FEM). The results showed that the STL can be modulated effectively and predictably using vibration theory by changing the structural parameters, such as the radius and thickness of the plate. Furthermore, using unit cells of different geometric sizes which are responsible for different frequency regions, the stacked panels with thickness ≤16 mm and weight ≤5 kg/m2 showed high STL below 2000 Hz. The acoustic metamaterial proposed in this study could provide a potential application in the low-frequency noise insulation.

Admittance of MIS-Structures Based on HgCdTe with a Double-Layer CdTe/Al2O3 Insulator

NASA Astrophysics Data System (ADS)

Dzyadukh, S. M.; Voitsekhovskii, A. V.; Nesmelov, S. N.; Sidorov, G. Yu.; Varavin, V. S.; Vasil'ev, V. V.; Dvoretsky, S. A.; Mikhailov, N. N.; Yakushev, M. V.

2018-03-01

Admittance of MIS structures based on n( p)- Hg1-xCdxTe (at x from 0.22 to 0.40) with SiO2/Si3N4, Al2O3, and CdTe/Al2O3 insulators is studied experimentally at 77 K. Growth of an intermediate CdTe layer during epitaxy results in the almost complete disappearance of the hysteresis of electrophysical characteristics of MIS structures based on graded-gap n-HgCdTe for a small range of the voltage variation. For a wide range of the voltage variation, the hysteresis of the capacitance-voltage characteristics appears for MIS structures based on n-HgCdTe with the CdTe/Al2O3 insulator. However, the hysteresis mechanism differs from that in case of a single-layer Al2O3 insulator. For MIS structures based on p-HgCdTe, introduction of an additional CdTe layer does not lead to a significant decrease of the hysteresis phenomena, which may be due to the degradation of the interface properties when mercury leaves the film as a result of low-temperature annealing changing the conductivity type of the semiconductor.

Development of 72kV High Pressure Air-insulated GIS with Vacuum Circuit Breaker

NASA Astrophysics Data System (ADS)

Rokunohe, Toshiaki; Yagihashi, Yoshitaka; Endo, Fumihiro; Aoyagi, Kenji; Saitoh, Hitoshi; Oomori, Takashi

SF6 gas has excellent dielectric strength and interruption performance. For these reasons, it has been widely used for gas insulated switchgear (GIS). However, use of SF6 gas has become regulated under agreements set at the 1997 COP3. So investigation and development for GIS with a lower amount of SF6 gas are being carried out worldwide. Presently, SF6 gas-free GIS has been commercialized for the 24kV class. Air or N2 gas is used as insulation gas for this GIS. On the other hand, SF6 gas-free GIS has not been commercialized for 72kV class GIS. Dielectric strengths of air and N2 gas are approximately 1/3 that of SF6 gas. So to enhance insulation performance of air and N2, we have investigated a hybrid gas insulation system which has the combined features of providing an insulation coating and suitable insulation gas. We have developed the world's first 72kV SF6 gas-free GIS. This paper deals with key technologies for SF6 gas-free GIS such as the hybrid insulation structure, bellows for the high pressure vacuum circuit breaker, a newly designed disconnector and spacer and prevention of particle levitation. Test results of 72kV high pressure air-insulated GIS with the vacuum circuit breaker are described.

Dimensionality Control of d-orbital Occupation in Oxide Superlattices

PubMed Central

Jeong, Da Woon; Choi, Woo Seok; Okamoto, Satoshi; Kim, Jae–Young; Kim, Kyung Wan; Moon, Soon Jae; Cho, Deok–Yong; Lee, Ho Nyung; Noh, Tae Won

2014-01-01

Manipulating the orbital state in a strongly correlated electron system is of fundamental and technological importance for exploring and developing novel electronic phases. Here, we report an unambiguous demonstration of orbital occupancy control between t2g and eg multiplets in quasi-two-dimensional transition metal oxide superlattices (SLs) composed of a Mott insulator LaCoO3 and a band insulator LaAlO3. As the LaCoO3 sublayer thickness approaches its fundamental limit (i.e. one unit-cell-thick), the electronic state of the SLs changed from a Mott insulator, in which both t2g and eg orbitals are partially filled, to a band insulator by completely filling (emptying) the t2g (eg) orbitals. We found the reduction of dimensionality has a profound effect on the electronic structure evolution, which is, whereas, insensitive to the epitaxial strain. The remarkable orbital controllability shown here offers a promising pathway for novel applications such as catalysis and photovoltaics, where the energy of d level is an essential parameter. PMID:25134975

Environmental Influence of Gravity and Pressure on Arc Tracking of Insulated Wires Investigated