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Sample records for 1d mott insulators

  1. Fragile Mott insulators.

    PubMed

    Yao, Hong; Kivelson, Steven A

    2010-10-15

    We prove that there exists a class of crystalline insulators, which we call "fragile Mott insulators," which are not adiabatically connected to any sort of band insulator provided time-reversal and certain point-group symmetries are respected, but which are otherwise unspectacular in that they exhibit no topological order nor any form of fractionalized quasiparticles. Different fragile Mott insulators are characterized by different nontrivial one-dimensional representations of the crystal point group. We illustrate this new type of insulators with two examples: the d Mott insulator discovered in the checkerboard Hubbard model at half-filling and the Affleck-Kennedy-Lieb-Tasaki insulator on the square lattice.

  2. Weyl Mott Insulator.

    PubMed

    Morimoto, Takahiro; Nagaosa, Naoto

    2016-01-01

    Relativistic Weyl fermion (WF) often appears in the band structure of three dimensional magnetic materials and acts as a source or sink of the Berry curvature, i.e., the (anti-)monopole. It has been believed that the WFs are stable due to their topological indices except when two Weyl fermions of opposite chiralities annihilate pairwise. Here, we theoretically show for a model including the electron-electron interaction that the Mott gap opens for each WF without violating the topological stability, leading to a topological Mott insulator dubbed Weyl Mott insulator (WMI). This WMI is characterized by several novel features such as (i) energy gaps in the angle-resolved photo-emission spectroscopy (ARPES) and the optical conductivity, (ii) the nonvanishing Hall conductance, and (iii) the Fermi arc on the surface with the penetration depth diverging as approaching to the momentum at which the Weyl point is projected. Experimental detection of the WMI by distinguishing from conventional Mott insulators is discussed with possible relevance to pyrochlore iridates. PMID:26822023

  3. Weyl Mott Insulator

    PubMed Central

    Morimoto, Takahiro; Nagaosa, Naoto

    2016-01-01

    Relativistic Weyl fermion (WF) often appears in the band structure of three dimensional magnetic materials and acts as a source or sink of the Berry curvature, i.e., the (anti-)monopole. It has been believed that the WFs are stable due to their topological indices except when two Weyl fermions of opposite chiralities annihilate pairwise. Here, we theoretically show for a model including the electron-electron interaction that the Mott gap opens for each WF without violating the topological stability, leading to a topological Mott insulator dubbed Weyl Mott insulator (WMI). This WMI is characterized by several novel features such as (i) energy gaps in the angle-resolved photo-emission spectroscopy (ARPES) and the optical conductivity, (ii) the nonvanishing Hall conductance, and (iii) the Fermi arc on the surface with the penetration depth diverging as approaching to the momentum at which the Weyl point is projected. Experimental detection of the WMI by distinguishing from conventional Mott insulators is discussed with possible relevance to pyrochlore iridates. PMID:26822023

  4. Constraints on topological order in mott insulators.

    PubMed

    Zaletel, Michael P; Vishwanath, Ashvin

    2015-02-20

    We point out certain symmetry induced constraints on topological order in Mott insulators (quantum magnets with an odd number of spin 1/2 moments per unit cell). We show, for example, that the double-semion topological order is incompatible with time reversal and translation symmetry in Mott insulators. This sharpens the Hastings-Oshikawa-Lieb-Schultz-Mattis theorem for 2D quantum magnets, which guarantees that a fully symmetric gapped Mott insulator must be topologically ordered, but is silent about which topological order is permitted. Our result applies to the kagome lattice quantum antiferromagnet, where recent numerical calculations of the entanglement entropy indicate a ground state compatible with either toric code or double-semion topological order. Our result rules out the latter possibility.

  5. Constraints on topological order in mott insulators.

    PubMed

    Zaletel, Michael P; Vishwanath, Ashvin

    2015-02-20

    We point out certain symmetry induced constraints on topological order in Mott insulators (quantum magnets with an odd number of spin 1/2 moments per unit cell). We show, for example, that the double-semion topological order is incompatible with time reversal and translation symmetry in Mott insulators. This sharpens the Hastings-Oshikawa-Lieb-Schultz-Mattis theorem for 2D quantum magnets, which guarantees that a fully symmetric gapped Mott insulator must be topologically ordered, but is silent about which topological order is permitted. Our result applies to the kagome lattice quantum antiferromagnet, where recent numerical calculations of the entanglement entropy indicate a ground state compatible with either toric code or double-semion topological order. Our result rules out the latter possibility. PMID:25763971

  6. Electronic reconstruction of doped Mott insulator heterojunctions

    NASA Astrophysics Data System (ADS)

    Charlebois, M.; Hassan, S. R.; Karan, R.; Dion, M.; Senechal, D.; Tremblay, A.-M. S.

    2012-02-01

    Correlated electron heterostructures became a possible alternative when thin-film deposition techniques achieved structures with a sharp interface transition [1]. Soon thereafter, Okamoto & Millis introduced the concept of ``electronic reconstruction'' [2]. We study here the electronic reconstruction of doped Mott insulator heterostructures based on a Cluster Dynamical Mean Field Theory (CDMFT) calculations of the Hubbard model in the limit where electrostatic energy dominates over the kinetic energy associated with transport across layers. The grand potential of individual layers is first computed within CDMFT and then the electrostatic potential energy is taken into account in the Hartree approximation. The charge reconstruction in an ensemble of stacked planes of different nature can lead to a distribution of electron charge and to transport properties that are unique to doped-Mott insulators.[4pt] [1] J. Mannhart, D. G. Schlom, Science 327, 1607 (2010).[0pt] [2] S. Okamoto and A. J. Millis, Nature 428, 630 (2004).

  7. Charge relaxation and recombination in photo-excited Mott insulators

    NASA Astrophysics Data System (ADS)

    Prelovšek, P.; Lenarčič, Z.

    2016-04-01

    Recent femtosecond pump-probe experiments on Mott insulators reveal charge recombination, which is in picosecond range, i.e., much faster than in clean bandgap semiconductors although excitation gaps in Mott insulators are even larger. The charge response in photo-excited insulators can be generally divided in femtosecond transient relaxation of charge excitations, which are holons and doublons, and a second slower, but still very fast, holon-doublon (HD) recombination. We present a theory of the recombination rate of the excited HD pairs, based on the two-dimensional (2D) model relevant for cuprates, which shows that such fast processes can be explained even quantitatively with the multi-magnon emission. We show that the condition for the exponential decay as observed in the experiment is the existence of the exciton, i.e., the bound HD pair. Its recombination rate is exponentially dependent on the charge gap and on the magnon energy, while the ultrafast process can be traced back to strong charge-spin coupling. We comment also fast recombination times in the one-dimensional (1D) Mott insulators, as e.g., organic salts. The recombination rate in the latter cases can be explained with the stronger coupling with phonon excitations.

  8. DYNAMICAL RESPONSE OF QUASI ID MOTT INSULATORS.

    SciTech Connect

    ESSLER,F.H.L.TSVELIK,A.M.

    2004-01-14

    At low energies certain one dimensional Mott insulators can be described in terms of an exactly solvable quantum field theory, the U(1) Thirring model. Using exact results derived from integrability we determine dynamical properties like the frequency dependent optical conductivity and the single-particle Green's function. We discuss the effects of a small temperature and the effects on interchain tunneling in a model of infinitely many weakly coupled chains.

  9. Dual vortex theory of doped Mott insulators

    SciTech Connect

    Balents, Leon; Sachdev, Subir

    2007-11-15

    We present a general framework for describing the quantum phases obtained by doping paramagnetic Mott insulators on the square lattice. The undoped insulators are efficiently characterized by the projective transformations of various fields under the square lattice space group (the PSG). We show that the PSG also imposes powerful constraints on the doped system, and on the effective action for the vortex and Bogoliubov quasiparticle excitations of superconducting states. This action can also be extended across transitions to supersolid or insulating states at non-zero doping. For the case of a valence bond solid (VBS) insulator, we show that the doped system has the same PSG as that of elementary bosons with density equal to the density of electron Cooper pairs. We also discuss aspects of the action for a d-wave superconductor obtained by doping a 'staggered-flux' spin liquid state.

  10. Ferroelectric control of a Mott insulator.

    PubMed

    Yamada, Hiroyuki; Marinova, Maya; Altuntas, Philippe; Crassous, Arnaud; Bégon-Lours, Laura; Fusil, Stéphane; Jacquet, Eric; Garcia, Vincent; Bouzehouane, Karim; Gloter, Alexandre; Villegas, Javier E; Barthélémy, Agnès; Bibes, Manuel

    2013-10-03

    The electric field control of functional properties is an important goal in oxide-based electronics. To endow devices with memory, ferroelectric gating is interesting, but usually weak compared to volatile electrolyte gating. Here, we report a very large ferroelectric field-effect in perovskite heterostructures combining the Mott insulator CaMnO3 and the ferroelectric BiFeO3 in its "supertetragonal" phase. Upon polarization reversal of the BiFeO3 gate, the CaMnO3 channel resistance shows a fourfold variation around room temperature, and a tenfold change at ~200 K. This is accompanied by a carrier density modulation exceeding one order of magnitude. We have analyzed the results for various CaMnO3 thicknesses and explain them by the electrostatic doping of the CaMnO3 layer and the presence of a fixed dipole at the CaMnO3/BiFeO3 interface. Our results suggest the relevance of ferroelectric gates to control orbital- or spin-ordered phases, ubiquitous in Mott systems, and pave the way toward efficient Mott-tronics devices.

  11. Ferroelectric control of a Mott insulator

    PubMed Central

    Yamada, Hiroyuki; Marinova, Maya; Altuntas, Philippe; Crassous, Arnaud; Bégon-Lours, Laura; Fusil, Stéphane; Jacquet, Eric; Garcia, Vincent; Bouzehouane, Karim; Gloter, Alexandre; Villegas, Javier E.; Barthélémy, Agnès; Bibes, Manuel

    2013-01-01

    The electric field control of functional properties is an important goal in oxide-based electronics. To endow devices with memory, ferroelectric gating is interesting, but usually weak compared to volatile electrolyte gating. Here, we report a very large ferroelectric field-effect in perovskite heterostructures combining the Mott insulator CaMnO3 and the ferroelectric BiFeO3 in its “supertetragonal” phase. Upon polarization reversal of the BiFeO3 gate, the CaMnO3 channel resistance shows a fourfold variation around room temperature, and a tenfold change at ~200 K. This is accompanied by a carrier density modulation exceeding one order of magnitude. We have analyzed the results for various CaMnO3 thicknesses and explain them by the electrostatic doping of the CaMnO3 layer and the presence of a fixed dipole at the CaMnO3/BiFeO3 interface. Our results suggest the relevance of ferroelectric gates to control orbital- or spin-ordered phases, ubiquitous in Mott systems, and pave the way toward efficient Mott-tronics devices. PMID:24089020

  12. Proximity effects in a topological-insulator/Mott-insulator heterostructure

    NASA Astrophysics Data System (ADS)

    Ueda, Suguru; Kawakami, Norio; Sigrist, Manfred

    2013-04-01

    We investigate proximity effects in a correlated heterostructure of a two-dimensional Mott insulator (MI) and a topological insulator (TI) by employing inhomogeneous dynamical mean-field theory. We show that the edge state of the TI induces strongly renormalized midgap states inside the MI region, which still have a remnant of the helical energy spectrum. The penetration of low-energy electrons, which is controlled by the interface tunneling V, largely enhances the electron mass inside the MI and also splits a single Dirac cone at edge sites into the spatially separated two Dirac cones in the strong V region.

  13. Quench from Mott Insulator to Superfluid

    SciTech Connect

    Zurek, Wojciech H.; Dziarmaga, Jacek; Tylutki, Marek

    2012-06-01

    We study a linear ramp of the nearest-neighbor tunneling rate in the Bose-Hubbard model driving the system from the Mott insulator state into the superfluid phase. We employ the truncated Wigner approximation to simulate linear quenches of a uniform system in 1...3 dimensions, and in a harmonic trap in 3 dimensions. In all these setups the excitation energy decays like one over third root of the quench time. The -1/3 scaling is explained by an impulse-adiabatic approximation - a variant of the Kibble-Zurek mechanism - describing a crossover from non-adiabatic to adiabatic evolution when the system begins to keep pace with the increasing tunneling rate.

  14. Suppression of rectification at metal-Mott insulator interfaces

    NASA Astrophysics Data System (ADS)

    Yonemitsu, Kenji; Maeshima, Nobuya; Hasegawa, Tatsuo

    2007-12-01

    Charge transport through metal-Mott insulator interfaces is studied and compared with that through metal-band-insulator interfaces. For band insulators, rectification has been known to occur owing to a Schottky barrier, which is produced by the work-function difference. For Mott insulators, however, qualitatively different current-voltage characteristics are obtained. Theoretically, we use the one-dimensional Hubbard model for a Mott insulator and attach to it the tight-binding model for metallic electrodes. A Schottky barrier is introduced by a solution to the Poisson equation with a simplified density-potential relation. The current density is calculated by solving the time-dependent Schrödinger equation. We mainly use the time-dependent Hartree-Fock approximation and also use exact many-electron wave functions on small systems for comparison. Rectification is found to be strongly suppressed even for large work-function differences. We show its close relationship with the fact that field-effect injections into one-dimensional Mott insulators are ambipolar. Experimentally, we fabricated asymmetric contacts on top of single crystals of quasi-one-dimensional organic Mott and band insulators. Rectification is strongly suppressed at an interface between metallic magnesium and Mott-insulating (BEDT-TTF)(F2TCNQ) [ BEDT-TTF=bis(ethylenedithio)tetrathiafulvalene ; F2TCNQ=2,5-difluorotetracyanoquinodimethane ].

  15. Precision measurements on a tunable Mott insulator of ultracold atoms.

    PubMed

    Mark, M J; Haller, E; Lauber, K; Danzl, J G; Daley, A J; Nägerl, H-C

    2011-10-21

    We perform precision measurements on a Mott-insulator quantum state of ultracold atoms with tunable interactions. We probe the dependence of the superfluid-to-Mott-insulator transition on the interaction strength and explore the limits of the standard Bose-Hubbard model description. By tuning the on-site interaction energies to values comparable to the interband separation, we are able to quantitatively measure number-dependent shifts in the excitation spectrum caused by effective multibody interactions. PMID:22107531

  16. Theoretical prediction of fragile Mott insulators on plaquette Hubbard lattices

    NASA Astrophysics Data System (ADS)

    Wu, Han-Qing; He, Rong-Qiang; Meng, Zi Yang; Lu, Zhong-Yi

    2015-03-01

    Employing extensive cellular dynamical mean-field theory calculations with an exact diagonalization impurity solver, we investigate the ground-state phase diagrams and nonmagnetic metal-insulator transitions of the half-filled Hubbard model on two plaquette (the 1/5 depleted and checkerboard) square lattices. We identify three different insulators in the phase diagrams: dimer insulator, antiferromagnetic insulator, and plaquette insulator. We also demonstrate that the plaquette insulator is a novel fragile Mott insulator (FMI) which features a nontrivial one-dimensional irreducible representation of the C4 v crystalline point group and cannot be adiabatically connected to any band insulator with time-reversal symmetry. Furthermore, we study the nonmagnetic quantum phase transitions from the metal to the FMI and find that this Mott metal-insulator transition is characterized by the splitting of the noninteracting bands due to interaction effects.

  17. Site-resolved imaging of a fermionic Mott insulator

    NASA Astrophysics Data System (ADS)

    Chiu, Christie; Greif, Daniel; Parsons, Maxwell F.; Mazurenko, Anton; Blatt, Sebastian; Huber, Florian; Ji, Geoffrey; Greiner, Markus

    2016-05-01

    Quantum gas microscopy of ultracold fermionic atoms in an optical lattice opens new perspectives for addressing long-standing open questions on strongly correlated low-temperature phases in the Hubbard model. Here we report on site-resolved imaging of two-component fermionic Mott insulators, metals, and band insulators with Lithium-6. For strong repulsive interactions we observe Mott insulators with more than 400 atoms and for intermediate interactions we observe a coexistence of phases. From comparison to theory, we find trap-averaged entropies per particle of 1 . 0kB in the Mott insulator and local entropies in the band insulator as low as 0 . 5kB . Our measurements serve as a benchmark for the performance of our experiment and are a starting point for accessing the low-temperature regime of magnetic ordering. Current address: Max-Planck-Institut für Quantenoptik, 85748 Garching, Germany.

  18. Site-resolved imaging of a fermionic Mott insulator.

    PubMed

    Greif, Daniel; Parsons, Maxwell F; Mazurenko, Anton; Chiu, Christie S; Blatt, Sebastian; Huber, Florian; Ji, Geoffrey; Greiner, Markus

    2016-02-26

    The complexity of quantum many-body systems originates from the interplay of strong interactions, quantum statistics, and the large number of quantum-mechanical degrees of freedom. Probing these systems on a microscopic level with single-site resolution offers important insights. Here we report site-resolved imaging of two-component fermionic Mott insulators, metals, and band insulators, using ultracold atoms in a square lattice. For strong repulsive interactions, we observed two-dimensional Mott insulators containing over 400 atoms. For intermediate interactions, we observed a coexistence of phases. From comparison to theory, we find trap-averaged entropies per particle of 1.0 times the Boltzmann constant (k(B)). In the band insulator, we find local entropies as low as 0.5 k(B). Access to local observables will aid the understanding of fermionic many-body systems in regimes inaccessible by modern theoretical methods.

  19. 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.

  20. Orbital magnetism induced by heat currents in Mott insulators.

    PubMed

    Lin, Shi-Zeng; Batista, Cristian D

    2013-10-18

    We derive the effective heat current density operator for the strong-coupling regime of Mott insulators. Similarly to the case of the electric current density, the leading contribution to this effective operator is proportional to the local scalar spin chirality χ(jkl)=S(l)·(S(j)×S(k)). This common form of the effective heat and electric current density operators leads to a novel cross response in Mott insulators. A heat current induces a distribution of orbital magnetic moments in systems containing loops of an odd number of hopping terms. The relative orientation of the orbital moments depends on the particular lattice of magnetic ions. This subtle effect arises from the symmetries that the heat and electric currents have in common. PMID:24182288

  1. Theory of high Tc ferrimagnetism in a multiorbital Mott insulator.

    PubMed

    Meetei, O Nganba; Erten, Onur; Randeria, Mohit; Trivedi, Nandini; Woodward, Patrick

    2013-02-22

    We propose a model for the multiorbital material Sr(2)CrOsO(6), an insulator with remarkable magnetic properties and the highest T(c) ~/= 725 K among all perovskites with a net moment. We derive a new criterion for the Mott transition (U(1)U(2))(1/2)>2.5W by using slave-rotor mean field theory, where W is the bandwidth and U(1(2)) are the effective Coulomb interactions on Cr(Os) including Hund's coupling. We show that Sr(2)CrOsO(6) is a Mott insulator, where the large Cr U(1) compensates for the small Os U(2). The spin sector is described by a frustrated antiferromagnetic Heisenberg model that naturally explains the net moment arising from canting and also the observed nonmonotonic magnetization M(T). We predict characteristic magnetic structure factor peaks that can be probed by neutron experiments.

  2. Compressibility of a fermionic mott insulator of ultracold atoms.

    PubMed

    Duarte, Pedro M; Hart, Russell A; Yang, Tsung-Lin; Liu, Xinxing; Paiva, Thereza; Khatami, Ehsan; Scalettar, Richard T; Trivedi, Nandini; Hulet, Randall G

    2015-02-20

    We characterize the Mott insulating regime of a repulsively interacting Fermi gas of ultracold atoms in a three-dimensional optical lattice. We use in situ imaging to extract the central density of the gas and to determine its local compressibility. For intermediate to strong interactions, we observe the emergence of a plateau in the density as a function of atom number, and a reduction of the compressibility at a density of one atom per site, indicating the formation of a Mott insulator. Comparisons to state-of-the-art numerical simulations of the Hubbard model over a wide range of interactions reveal that the temperature of the gas is of the order of, or below, the tunneling energy scale. Our results hold great promise for the exploration of many-body phenomena with ultracold atoms, where the local compressibility can be a useful tool to detect signatures of different phases or phase boundaries at specific values of the filling. PMID:25763942

  3. How fast can a Peierls-Mott insulator be melted?

    PubMed

    Sohrt, C; Stange, A; Bauer, M; Rossnagel, K

    2014-01-01

    Time- and angle-resolved extreme ultraviolet photoemission spectroscopy is used to directly determine the momentum-dependent electronic structure dynamics in the layered Peierls-Mott insulators 1T-TaS(2) and 1T-TaSe(2) on the sub-300 fs time scale. Extracted spectroscopic order parameters display a global two-time-scale dynamics indicating a quasi-instantaneous loss of the electronic orders and a subsequent coherent suppression of the lattice distortion on a time scale related to the frequency of the charge-density-wave amplitude mode. After one half-cycle of coherent amplitude-mode vibration, a crossover state between insulator and metal with partially filled-in and partially closed Mott and Peierls gaps is reached. The results are discussed within the wider context of electronic order quenching in complex materials. PMID:25415852

  4. Optical properties of a vibrationally modulated solid state Mott insulator.

    PubMed

    Kaiser, S; Clark, S R; Nicoletti, D; Cotugno, G; Tobey, R I; Dean, N; Lupi, S; Okamoto, H; Hasegawa, T; Jaksch, D; Cavalleri, A

    2014-01-01

    Optical pulses at THz and mid-infrared frequencies tuned to specific vibrational resonances modulate the lattice along chosen normal mode coordinates. In this way, solids can be switched between competing electronic phases and new states are created. Here, we use vibrational modulation to make electronic interactions (Hubbard-U) in Mott-insulator time dependent. Mid-infrared optical pulses excite localized molecular vibrations in ET-F2TCNQ, a prototypical one-dimensional Mott-insulator. A broadband ultrafast probe interrogates the resulting optical spectrum between THz and visible frequencies. A red-shifted charge-transfer resonance is observed, consistent with a time-averaged reduction of the electronic correlation strength U. Secondly, a sideband manifold inside of the Mott-gap appears, resulting from a periodically modulated U. The response is compared to computations based on a quantum-modulated dynamic Hubbard model. Heuristic fitting suggests asymmetric holon-doublon coupling to the molecules and that electron double-occupancies strongly squeeze the vibrational mode.

  5. The Mott-Hubbard Insulator: localization and topological quantum order

    NASA Astrophysics Data System (ADS)

    Martin, Richard M.

    2010-03-01

    An insulating state of condensed matter is characterized by localization of the center of mass of the electrons. This criterion can be addressed in terms of the ground state on a torus with boundary conditions ψK(x1+L,x2, ) = exp( i K L) ψK(x1,x2, ). As shown by Kohn[1], in an insulator the energy is insensitive to K as L ->∞, whereas in an ideal metal it increases as K^2. In addition, Souza, et al. derived expressions for the localization length in terms of the wavefunction as a function of K. The present work generalizes the arguments to provide a fundamental distinction between ``band'' and ``Mott-Hubbard'' insulators. The criteria involve only counting of electrons and experimentally measurable quantities independent of models, and they lead to the requirement that a Mott-Hubbard insulator with no broken local symmetry must have topological quantum order.[4pt] [1] W. Kohn, Phys. Rev. 133, A171 (1964)[0pt] [2] I. Souza, et al., Phys. Rev. B 62, 1666 (2000).

  6. Coherent light scattering from a two-dimensional Mott insulator.

    PubMed

    Weitenberg, Christof; Schauss, Peter; Fukuhara, Takeshi; Cheneau, Marc; Endres, Manuel; Bloch, Immanuel; Kuhr, Stefan

    2011-05-27

    We experimentally demonstrate coherent light scattering from an atomic Mott insulator in a two-dimensional lattice. The far-field diffraction pattern of small clouds of a few hundred atoms was imaged while simultaneously laser cooling the atoms with the probe beams. We describe the position of the diffraction peaks and the scaling of the peak parameters by a simple analytic model. In contrast to Bragg scattering, scattering from a single plane yields diffraction peaks for any incidence angle. We demonstrate the feasibility of detecting spin correlations via light scattering by artificially creating a one-dimensional antiferromagnetic order as a density wave and observing the appearance of additional diffraction peaks.

  7. Orbital Ordering and Frustration of p-Band Mott Insulators

    SciTech Connect

    Wu Congjun

    2008-05-23

    We investigate the general structure of orbital exchange physics in Mott-insulating states of p-orbital systems in optical lattices. Orbital orders occur in both the triangular and kagome lattices. In contrast, orbital exchange in the honeycomb lattice is frustrated as described by a novel quantum 120 deg. model. Its classical ground states are mapped into configurations of the fully packed loop model with an extra U(1) rotation degree of freedom. Quantum orbital fluctuations select a six-site plaquette ground state ordering pattern in the semiclassical limit from the 'order from disorder' mechanism. This effect arises from the appearance of a zero energy flat band of orbital excitations.

  8. Charge dynamics of the antiferromagnetically ordered Mott insulator

    NASA Astrophysics Data System (ADS)

    Han, Xing-Jie; Liu, Yu; Liu, Zhi-Yuan; Li, Xin; Chen, Jing; Liao, Hai-Jun; Xie, Zhi-Yuan; Normand, B.; Xiang, Tao

    2016-10-01

    We introduce a slave-fermion formulation in which to study the charge dynamics of the half-filled Hubbard model on the square lattice. In this description, the charge degrees of freedom are represented by fermionic holons and doublons and the Mott-insulating characteristics of the ground state are the consequence of holon–doublon bound-state formation. The bosonic spin degrees of freedom are described by the antiferromagnetic Heisenberg model, yielding long-ranged (Néel) magnetic order at zero temperature. Within this framework and in the self-consistent Born approximation, we perform systematic calculations of the average double occupancy, the electronic density of states, the spectral function and the optical conductivity. Qualitatively, our method reproduces the lower and upper Hubbard bands, the spectral-weight transfer into a coherent quasiparticle band at their lower edges and the renormalisation of the Mott gap, which is associated with holon–doublon binding, due to the interactions of both quasiparticle species with the magnons. The zeros of the Green function at the chemical potential give the Luttinger volume, the poles of the self-energy reflect the underlying quasiparticle dispersion with a spin-renormalised hopping parameter and the optical gap is directly related to the Mott gap. Quantitatively, the square-lattice Hubbard model is one of the best-characterised problems in correlated condensed matter and many numerical calculations, all with different strengths and weaknesses, exist with which to benchmark our approach. From the semi-quantitative accuracy of our results for all but the weakest interaction strengths, we conclude that a self-consistent treatment of the spin-fluctuation effects on the charge degrees of freedom captures all the essential physics of the antiferromagnetic Mott–Hubbard insulator. We remark in addition that an analytical approximation with these properties serves a vital function in developing a full understanding of

  9. Critical conductance of a one-dimensional doped Mott insulator

    NASA Astrophysics Data System (ADS)

    Garst, M.; Novikov, D. S.; Stern, Ady; Glazman, L. I.

    2008-01-01

    We consider the two-terminal conductance of a one-dimensional Mott insulator undergoing the commensurate-incommensurate quantum phase transition to a conducting state. We treat the leads as Luttinger liquids. At a specific value of compressibility of the leads, corresponding to the Luther-Emery point, the conductance can be described in terms of the free propagation of noninteracting fermions with charge e/2 . At that point, the temperature dependence of the conductance across the quantum phase transition is described by a Fermi function. The deviation from the Luther-Emery point in the leads changes the temperature dependence qualitatively. In the metallic state, the low-temperature conductance is determined by the properties of the leads, and is described by the conventional Luttinger-liquid theory. In the insulating state, conductance occurs via activation of e/2 charges, and is independent of the Luttinger-liquid compressibility.

  10. Novel Pauli-paramagnetic quantum phase in a Mott insulator.

    PubMed

    Watanabe, D; Yamashita, M; Tonegawa, S; Oshima, Y; Yamamoto, H M; Kato, R; Sheikin, I; Behnia, K; Terashima, T; Uji, S; Shibauchi, T; Matsuda, Y

    2012-01-01

    In Mott insulators, the strong electron-electron Coulomb repulsion localizes electrons. In dimensions greater than one, their spins are usually ordered antiferromagnetically at low temperatures. Geometrical frustrations can destroy this long-range order, leading to exotic quantum spin liquid states. However, their magnetic ground states have been a long-standing mystery. Here we show that a quantum spin liquid state in the organic Mott insulator EtMe(3)Sb[Pd(dmit)(2)](2) (where Et is C(2)H(5)-, Me is CH(3)-, and dmit is 1,3-dithiole-2-thione-4,5-dithiolate) with two-dimensional triangular lattice has Pauli-paramagnetic-like low-energy excitations, which are a hallmark of itinerant fermions. Our torque magnetometry down to low temperatures (30 mK) up to high fields (32 T) reveals distinct residual paramagnetic susceptibility comparable to that in a half-filled two-dimensional metal, demonstrating the magnetically gapless nature of the ground state. Moreover, our results are robust against deuteration, pointing toward the emergence of an extended 'quantum critical phase', in which low-energy spin excitations behave as in paramagnetic metals with Fermi surface, despite the frozen charge degree of freedom.

  11. Möbius molecules and fragile Mott insulators

    NASA Astrophysics Data System (ADS)

    Muechler, Lukas; Maciejko, Joseph; Neupert, Titus; Car, Roberto

    2014-12-01

    Motivated by the concept of Möbius aromatics in organic chemistry, we extend the recently introduced concept of fragile Mott insulators (FMI) to ring-shaped molecules with repulsive Hubbard interactions threaded by a half-quantum of magnetic flux (h c /2 e ) . In this context, an FMI is the insulating ground state of a finite-size molecule that cannot be adiabatically connected to a single Slater determinant, i.e., to a band insulator, provided that time-reversal and lattice translation symmetries are preserved. Based on exact numerical diagonalization for finite Hubbard interaction strength U and existing Bethe-ansatz studies of the one-dimensional Hubbard model in the large-U limit, we establish a duality between Hubbard molecules with 4 n and 4 n +2 sites, with n integer. A molecule with 4 n sites is an FMI in the absence of flux but becomes a band insulator in the presence of a half-quantum of flux, while a molecule with 4 n +2 sites is a band insulator in the absence of flux but becomes an FMI in the presence of a half-quantum of flux. Including next-nearest-neighbor hoppings gives rise to new FMI states that belong to multidimensional irreducible representations of the molecular point group, giving rise to a rich phase diagram.

  12. Möbius molecules and fragile Mott insulators

    NASA Astrophysics Data System (ADS)

    Muechler, Lukas; Maciejko, Joseph; Neupert, Titus; Car, Roberto

    2015-03-01

    Motivated by the concept of Möbius aromatics in organic chemistry, we extend the recently introduced concept of fragile Mott insulators (FMI) to ring-shaped molecules with repulsive Hubbard interactions threaded by a half-quantum of magnetic flux (hc / 2 e). In this context, a FMI is the insulating ground state of a finite-size molecule that cannot be adiabatically connected to a single Slater determinant, i.e., to a band insulator, provided that time-reversal and lattice translation symmetries are preserved. Based on exact numerical diagonalization for finite Hubbard interaction strength U and existing Bethe-ansatz studies of the one-dimensional Hubbard model in the large- U limit, we establish a duality between Hubbard molecules with 4 n and 4 n + 2 sites, with n integer. A molecule with 4 n sites is an FMI in the absence of flux but becomes a band insulator in the presence of a half-quantum of flux, while a molecule with 4 n + 2 sites is a band insulator in the absence of flux but becomes an FMI in the presence of a half-quantum of flux. Including next-nearest-neighbor-hoppings gives rise to new FMI states that belong to multidimensional irreducible representations of the molecular point group, giving rise to a rich phase diagram. Reference: arXiv:1409.6732

  13. Resonant inelastic x-ray scattering in a Mott insulator

    NASA Astrophysics Data System (ADS)

    Pakhira, Nandan; Freericks, J. K.; Shvaika, A. M.

    2012-09-01

    We calculate the resonant inelastic x-ray scattering (RIXS) response in a Mott insulator, which is described by the Falicov-Kimball model. The model can be solved exactly within the single site dynamical mean-field theory (DMFT) approximation and the RIXS response can also be calculated accurately up to a local background correction. We find that on resonance the RIXS response is greatly enhanced. The response systematically evolves from a single-peak structure, arising due to relaxation processes within the lower Hubbard band, to a two-peak structure, arising due to relaxation processes within the upper Hubbard band and across the Mott gap into the lower Hubbard band. This occurs as we vary the incident photon frequency to allow excitations from the lower Hubbard band to the upper Hubbard band. The charge transfer excitations are found to disperse monotonically as we go from the center of the Brillouin zone towards the zone corner. These correlation-induced features have been observed by Hasan [Science0036-807510.1126/science.288.5472.1811 288, 1811 (2000)] and many other experimentalists in RIXS measurements over various transition-metal oxide compounds. They are found to be robust and survive even for large Auger lifetime broadening effects that can mask the many-body effects by smearing out spectral features. As a comparison, we also calculate the dynamic structure factor for this model, which is proportional to the nonresonant part of the response, and does not show these specific signatures.

  14. Cluster Mott insulators and two Curie-Weiss regimes on an anisotropic kagome lattice

    NASA Astrophysics Data System (ADS)

    Chen, Gang; Kee, Hae-Young; Kim, Yong Baek

    2016-06-01

    Motivated by recent experiments on the quantum-spin-liquid candidate material LiZn2Mo3O8 , we study a single-band extended Hubbard model on an anisotropic kagome lattice with the 1/6 electron filling. Due to the partial filling of the lattice, the intersite repulsive interaction is necessary to generate Mott insulators, where electrons are localized in clusters rather than at lattice sites. It is shown that these cluster Mott insulators are generally U(1) quantum spin liquids with spinon Fermi surfaces. The nature of charge excitations in cluster Mott insulators can be quite different from conventional Mott insulator and we show that there exists a cluster Mott insulator where charge fluctuations around the hexagonal cluster induce a plaquette charge order (PCO). The spinon excitation spectrum in this spin-liquid cluster Mott insulator is reconstructed due to the PCO so that only 1/3 of the total spinon excitations are magnetically active. Based on these results, we propose that the two Curie-Weiss regimes of the spin susceptibility in LiZn2Mo3O8 may be explained by finite-temperature properties of the cluster Mott insulator with the PCO as well as fractionalized spinon excitations. Existing and possible future experiments on LiZn2Mo3O8 , and other Mo-based cluster magnets are discussed in light of these theoretical predictions.

  15. First-order superfluid to Mott-insulator phase transitions in spinor condensates

    NASA Astrophysics Data System (ADS)

    Chen, Zihe; Jiang, Jie; Zhao, Lichao; Wang, Shengtao; Tang, Tao; Duan, Luming; Liu, Yingmei

    2016-05-01

    We observe evidence of first-order superfluid to Mott-insulator quantum phase transitions in a lattice-confined antiferromagnetic spinor Bose-Einstein condensate. The observed signatures include hysteresis effect, significant heatings across the phase transitions, and evolutions of spin populations due to the formation of spin singlets in the Mott-insulator phase. The nature of the phase transitions is found to strongly depend on the ratio of the quadratic Zeeman energy to the spin-dependent interaction. Our observations are qualitatively understood by the mean field theory, and in addition suggest tuning the quadratic Zeeman energy is a new approach to realize superfluid to Mott-insulator phase transitions.

  16. First-order superfluid-to-Mott-insulator phase transitions in spinor condensates

    NASA Astrophysics Data System (ADS)

    Jiang, J.; Zhao, L.; Wang, S.-T.; Chen, Z.; Tang, T.; Duan, L.-M.; Liu, Y.

    2016-06-01

    We observe evidence of first-order superfluid-to-Mott-insulator quantum phase transitions in a lattice-confined antiferromagnetic spinor Bose-Einstein condensate. The observed signatures include the hysteresis effect, significant heatings across the phase transitions, and changes in spin populations due to the formation of spin singlets in the Mott-insulator phase. The nature of the phase transitions is found to strongly depend on the ratio of the quadratic Zeeman energy to the spin-dependent interaction. Our observations are qualitatively understood by the mean field theory and suggest tuning the quadratic Zeeman energy is a new approach to realize superfluid-to-Mott-insulator phase transitions.

  17. Electrical permittivity driven metal-insulator transition in heterostructures of nonpolar Mott and band insulators

    NASA Astrophysics Data System (ADS)

    Omori, Yukiko; Rüegg, Andreas; Sigrist, Manfred

    2014-10-01

    Metallic interfaces between insulating perovskites are often observed in heterostructures combining polar and nonpolar materials. In these systems, the polar discontinuity across the interface may drive an electronic reconstruction inducing free carriers at the interface. Here, we theoretically show that a metallic interface between a Mott and a band insulator can also form in the absence of a polar discontinuity. The condition for the appearance of such a metallic state is consistent with the classical Mott criterion: the metallic state is stable if the screening length falls below the effective Bohr radius of a particle-hole pair. In this case, the metallic state bears a remarkable similarity to the one found in polar/nonpolar heterostructures. On the other hand, if the screening length approaches the size of the effective Bohr radius, particles and holes are bound to each other resulting in an overall insulating phase. We analyze this metal-insulator transition, which is tunable by the dielectric constant, in the framework of the slave-boson mean-field theory for a lattice model with both on-site and long-range Coulomb interactions. We discuss ground-state properties and transport coefficients, which we derive in the relaxation-time approximation. Interestingly, we find that the metal-insulator transition is accompanied by a strong enhancement of the Seebeck coefficient in the band-insulator region in the vicinity of the interface. The implications of our theoretical findings for various experimental systems such as nonpolar (110) interfaces are also discussed.

  18. Identification of Mott insulators and Anderson insulators in self-assembled gold nanoparticles thin films.

    PubMed

    Jiang, Cheng-Wei; Ni, I-Chih; Tzeng, Shien-Der; Wu, Cen-Shawn; Kuo, Watson

    2014-06-01

    How the interparticle tunnelling affects the charge conduction of self-assembled gold nanoparticles is studied by three means: tuning the tunnel barrier width by different molecule modification and by substrate bending, and tuning the barrier height by high-dose electron beam exposure. All approaches indicate that the metal-Mott insulator transition is governed predominantly by the interparticle coupling strength, which can be quantified by the room temperature sheet resistance. The Hubbard gap, following the prediction of quantum fluctuation theory, reduces to zero rapidly as the sheet resistance decreases to the quantum resistance. At very low temperature, the fate of devices near the Mott transition depends on the strength of disorder. The charge conduction is from nearest-neighbour hopping to co-tunnelling between nanoparticles in Mott insulators whereas it is from variable-range hopping through charge puddles in Anderson insulators. When the two-dimensional nanoparticle network is under a unidirectional strain, the interparticle coupling becomes anisotropic so the average sheet resistance is required to describe the charge conduction.

  19. Chiral Bosonic Mott Insulator on the Frustrated Triangular Lattice

    NASA Astrophysics Data System (ADS)

    Parameswaran, Siddharth; Zaletel, Michael; Rüegg, Andreas; Altman, Ehud

    2014-03-01

    We study the superfluid and insulating phases of interacting bosons on the triangular lattice with an inverted dispersion, corresponding to frustrated hopping between sites. The resulting single-particle dispersion has multiple minima at nonzero wavevectors in momentum space, in contrast to the unique zero-wavevector minimum of the unfrustrated problem. As a consequence, the superfluid phase is unstable against developing additional chiral order that breaks time reversal (T) and parity (P) symmetries by forming a condensate at nonzero wavevector. We demonstrate that the loss of superfluidity can lead to an even more exotic phase, the chiral Mott insulator, with nontrivial current order that breaks T, P. These results are obtained via variational estimates, as well as a combination of bosonization and DMRG of triangular ladders, which taken together permit a fairly complete characterization of the phase diagram. We discuss the relevance of these phases to optical lattice experiments, as well as signatures of chiral symmetry breaking in time-of-flight images. We acknowledge support from NSF Grants 1066293 (SP, EA) and DGE-1106400 (MPZ), the Simons Foundation (SP), the Swiss National Science Foundation (AR), the ISF, BSF, ERC Synergy UQUAM program and the Miller Institute at UC Berkeley (EA).

  20. Chiral bosonic Mott insulator on the frustrated triangular lattice

    NASA Astrophysics Data System (ADS)

    Zaletel, Michael P.; Parameswaran, S. A.; Rüegg, Andreas; Altman, Ehud

    2014-04-01

    We study the superfluid and insulating phases of interacting bosons on the triangular lattice with an inverted dispersion, corresponding to frustrated hopping between sites. The resulting single-particle dispersion has multiple minima at nonzero wave vectors in momentum space, in contrast to the unique zero-wave-vector minimum of the unfrustrated problem. As a consequence, the superfluid phase is unstable against developing additional chiral order that breaks time-reversal (T) and parity (P) symmetries by forming a condensate at nonzero wave vector. We demonstrate that the loss of superfluidity can lead to an even more exotic phase, the chiral Mott insulator, with nontrivial current order that breaks T ,P. These results are obtained via variational estimates, as well as a combination of bosonization and density-matrix renormalization group of triangular ladders, which, taken together, permit a fairly complete characterization of the phase diagram. We discuss the relevance of these phases to optical lattice experiments, as well as signatures of chiral symmetry breaking in time-of-flight images.

  1. Anderson localization and Mott insulator phase in the time domain.

    PubMed

    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

  2. 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

  3. Designing Quantum Spin-Orbital Liquids in Artificial Mott Insulators.

    PubMed

    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. 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.

  4. Designing Quantum Spin-Orbital Liquids in Artificial Mott Insulators.

    PubMed

    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

  5. Towards a photonic Mott insulator in superconducting circuits

    NASA Astrophysics Data System (ADS)

    Ma, Ruichao; Owen, John C.; Schuster, David; Simon, Jonathan

    2016-05-01

    Recent developments in circuit QED provide superconducting circuits as a unique platform for exploring quantum many-body phenomena with light. The absence of particle number conservation, however, makes creating and understanding of many-body photonic states challenging. Here we make a one-dimensional lattice of coupled superconducting qubits with an additional pumping site and a lossy site incorporated at the end of the chain, which serves as an effective chemical potential for photons. When driven on the pumping site, the photons can spontaneously thermalize into the ground state of the lattice while the excess energy is dissipated via the lossy site. In the presence of strong photon-photon interaction via the qubit non-linearity, we expect the creation of a Mott insulator state of light, which we probe with temporal- and spatially-resolved measurements. These experiments will give insights to the microscopic investigation of non-equilibrium thermodynamics in strongly-interacting quantum system, including the interplay between external driving and dissipation.

  6. 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

  7. Designing Quantum Spin-Orbital Liquids in Artificial Mott Insulators

    NASA Astrophysics Data System (ADS)

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

    2016-08-01

    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.

  8. 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

  9. Mott insulators and the doping-induced Mott transition within DMFT: exact results for the one-band Hubbard model

    NASA Astrophysics Data System (ADS)

    Logan, David E.; Galpin, Martin R.

    2016-01-01

    The paramagnetic phase of the one-band Hubbard model is studied at zero-temperature, within the framework of dynamical mean-field theory, and for general particle-hole asymmetry where a doping-induced Mott transition occurs. Our primary focus is the Mott insulator (MI) phase, and our main aim to establish what can be shown exactly about it. To handle the locally doubly-degenerate MI requires two distinct self-energies, which reflect the broken symmetry nature of the phase and together determine the standard single self-energy. Exact results are obtained for the local charge, local magnetic moment and associated spin susceptibilities, the interaction-renormalised levels, and the low-energy behaviour of the self-energy in the MI phase. The metallic phase is also considered briefly, and shown to acquire an emergent particle-hole symmetry as the Mott transition is approached. Throughout the metal, Luttinger’s theorem is reflected in the vanishing of the Luttinger integral; for the generic MI by contrast this is shown to be non-vanishing, but again to have a universal magnitude. Numerical results are also obtained using NRG, for the metal/MI phase boundary, the scaling behaviour of the charge as the Mott transition is aproached from the metal, and associated universal scaling of single-particle dynamics as the low-energy Kondo scale vanishes.

  10. Characterizing Featureless Mott Insulating State by Quasiparticle Interferences - A DMFT Prospect

    NASA Astrophysics Data System (ADS)

    Mukherjee, Shantanu; Lee, Wei-Cheng

    In this talk we discuss the quasiparticle interferences (QPIs) of a Mott insulator using a T-matrix formalism implemented with the dynamical mean-field theory (T-DMFT). In the Mott insulating state, the DMFT predicts a singularity in the real part of electron self energy s (w) at low frequencies, which completely washes out the QPI at small bias voltage. However, the QPI patterns produced by the non-interacting Fermi surfaces can appear at a critical bias voltage in Mott insulating state. The existence of this non-zero critical bias voltage is a direct consequence of the singular behavior of Re[s (w)] /sim n/w with n behaving as the 'order parameter' of Mott insulating state. We propose that this reentry of non-interacting QPI patterns could serve as an experimental signature of Mott insulating state, and the 'order parameter' can be experimentally measured W.C.L acknowledges financial support from start up fund from Binghamton University.

  11. Electron-hole doping asymmetry of Fermi surface reconstructed in a simple Mott insulator.

    PubMed

    Kawasugi, Yoshitaka; Seki, Kazuhiro; Edagawa, Yusuke; Sato, Yoshiaki; Pu, Jiang; Takenobu, Taishi; Yunoki, Seiji; Yamamoto, Hiroshi M; Kato, Reizo

    2016-01-01

    It is widely recognized that the effect of doping into a Mott insulator is complicated and unpredictable, as can be seen by examining the Hall coefficient in high Tc cuprates. The doping effect, including the electron-hole doping asymmetry, may be more straightforward in doped organic Mott insulators owing to their simple electronic structures. Here we investigate the doping asymmetry of an organic Mott insulator by carrying out electric-double-layer transistor measurements and using cluster perturbation theory. The calculations predict that strongly anisotropic suppression of the spectral weight results in the Fermi arc state under hole doping, while a relatively uniform spectral weight results in the emergence of a non-interacting-like Fermi surface (FS) in the electron-doped state. In accordance with the calculations, the experimentally observed Hall coefficients and resistivity anisotropy correspond to the pocket formed by the Fermi arcs under hole doping and to the non-interacting FS under electron doping. PMID:27492864

  12. Electron-hole doping asymmetry of Fermi surface reconstructed in a simple Mott insulator.

    PubMed

    Kawasugi, Yoshitaka; Seki, Kazuhiro; Edagawa, Yusuke; Sato, Yoshiaki; Pu, Jiang; Takenobu, Taishi; Yunoki, Seiji; Yamamoto, Hiroshi M; Kato, Reizo

    2016-01-01

    It is widely recognized that the effect of doping into a Mott insulator is complicated and unpredictable, as can be seen by examining the Hall coefficient in high Tc cuprates. The doping effect, including the electron-hole doping asymmetry, may be more straightforward in doped organic Mott insulators owing to their simple electronic structures. Here we investigate the doping asymmetry of an organic Mott insulator by carrying out electric-double-layer transistor measurements and using cluster perturbation theory. The calculations predict that strongly anisotropic suppression of the spectral weight results in the Fermi arc state under hole doping, while a relatively uniform spectral weight results in the emergence of a non-interacting-like Fermi surface (FS) in the electron-doped state. In accordance with the calculations, the experimentally observed Hall coefficients and resistivity anisotropy correspond to the pocket formed by the Fermi arcs under hole doping and to the non-interacting FS under electron doping.

  13. Electron-hole doping asymmetry of Fermi surface reconstructed in a simple Mott insulator

    NASA Astrophysics Data System (ADS)

    Kawasugi, Yoshitaka; Seki, Kazuhiro; Edagawa, Yusuke; Sato, Yoshiaki; Pu, Jiang; Takenobu, Taishi; Yunoki, Seiji; Yamamoto, Hiroshi M.; Kato, Reizo

    2016-08-01

    It is widely recognized that the effect of doping into a Mott insulator is complicated and unpredictable, as can be seen by examining the Hall coefficient in high Tc cuprates. The doping effect, including the electron-hole doping asymmetry, may be more straightforward in doped organic Mott insulators owing to their simple electronic structures. Here we investigate the doping asymmetry of an organic Mott insulator by carrying out electric-double-layer transistor measurements and using cluster perturbation theory. The calculations predict that strongly anisotropic suppression of the spectral weight results in the Fermi arc state under hole doping, while a relatively uniform spectral weight results in the emergence of a non-interacting-like Fermi surface (FS) in the electron-doped state. In accordance with the calculations, the experimentally observed Hall coefficients and resistivity anisotropy correspond to the pocket formed by the Fermi arcs under hole doping and to the non-interacting FS under electron doping.

  14. Geometry-induced phase transition from a bosonic superfluid to a Mott insulator

    NASA Astrophysics Data System (ADS)

    Barter, Thomas; Thomas, Claire; Leung, Tsz Him; Okano, Masayuki; Stamper-Kurn, Dan

    2016-05-01

    We describe a preliminary characterization of the superfluid and Mott insulating phases of ultracold Rb 87 bosonic atoms in a two-dimensional optical superlattice with tunable lattice geometry. By smoothly changing the lattice structure from the triangular to kagome geometries while maintaining near-constant tunneling and interaction energies, we observe a geometry-induced phase transition from the superfluid to the Mott-insulating state. We characterize the superfluid by measurements of the coherent population fraction in time of flight, and find that the superfluid is less robust in the kagome geometry than in the triangular lattice, owing to the lower its lower coordination number.

  15. Thermodynamics versus Local Density Fluctuations in the Metal-Mott-Insulator Crossover

    NASA Astrophysics Data System (ADS)

    Drewes, J. H.; Cocchi, E.; Miller, L. A.; Chan, C. F.; Pertot, D.; Brennecke, F.; Köhl, M.

    2016-09-01

    The crossover between a metal and a Mott insulator leads to a localization of fermions from delocalized Bloch states to localized states. We experimentally study this crossover using fermionic atoms in an optical lattice by measuring thermodynamic and local (on-site) density correlations. In the metallic phase at incommensurable filling we observe the violation of the local fluctuation-dissipation theorem indicating that the thermodynamics of the system cannot be characterized by local observables alone. In contrast, in the Mott insulator we observe the convergence of local and thermodynamic fluctuations indicating the absence of long-range density-density correlations.

  16. Strongly correlated superconductivity and pseudogap phase near a multiband Mott insulator.

    PubMed

    Capone, Massimo; Fabrizio, Michele; Castellani, Claudio; Tosatti, Erio

    2004-07-23

    Near a Mott transition, strong electron correlations may enhance Cooper pairing. This is demonstrated in the dynamical mean field theory solution of a twofold-orbital degenerate Hubbard model with an inverted on-site Hund rule exchange, favoring local spin-singlet configurations. Close to the Mott insulator (which here is a local version of a valence bond insulator) a pseudogap non-Fermi-liquid metal, a superconductor, and a normal metal appear, in striking similarity with the physics of cuprates. The strongly correlated s-wave superconducting state has a larger Drude weight than the corresponding normal state. The role of the impurity Kondo problem is underscored.

  17. Quantum critical Mott transitions in a bilayer Kondo insulator-metal model system

    NASA Astrophysics Data System (ADS)

    Sen, Sudeshna; Vidhyadhiraja, N. S.

    2016-04-01

    A bilayer system comprising a Kondo insulator coupled to a simple metal (KI-M) is considered. Employing the framework of dynamical mean-field theory, the model system is shown to exhibit a surface of quantum critical points (QCPs) that separates a Kondo screened, Fermi liquid phase from a local moment, Mott insulating phase. The quantum critical nature of these Mott transitions is characterized by the vanishing of (a) the coherence scale on the Fermi liquid side, and (b) the Mott gap on the MI side. In contrast to the usual "large-to-small" Fermi surface (FS) QCPs in heavy-fermion systems, the bilayer KI-M system exhibits a complete FS destruction.

  18. Coulomb Liquid Phases of Bosonic Cluster Mott Insulators on a Pyrochlore Lattice.

    PubMed

    Lv, Jian-Ping; Chen, Gang; Deng, Youjin; Meng, Zi Yang

    2015-07-17

    Employing large-scale quantum Monte Carlo simulations, we reveal the full phase diagram of the extended Hubbard model of hard-core bosons on the pyrochlore lattice with partial fillings. When the intersite repulsion is dominant, the system is in a cluster Mott insulator phase with an integer number of bosons localized inside the tetrahedral units of the pyrochlore lattice. We show that the full phase diagram contains three cluster Mott insulator phases with 1/4, 1/2, and 3/4 boson fillings, respectively. We further demonstrate that all three cluster Mott insulators are Coulomb liquid phases and its low-energy property is described by the emergent compact U(1) quantum electrodynamics. In addition to measuring the specific heat and entropy of the cluster Mott insulators, we investigate the correlation function of the emergent electric field and verify it is consistent with the compact U(1) quantum electrodynamics description. Our result sheds light on the magnetic properties of various pyrochlore systems, as well as the charge physics of the cluster magnets.

  19. Coulomb Liquid Phases of Bosonic Cluster Mott Insulators on a Pyrochlore Lattice.

    PubMed

    Lv, Jian-Ping; Chen, Gang; Deng, Youjin; Meng, Zi Yang

    2015-07-17

    Employing large-scale quantum Monte Carlo simulations, we reveal the full phase diagram of the extended Hubbard model of hard-core bosons on the pyrochlore lattice with partial fillings. When the intersite repulsion is dominant, the system is in a cluster Mott insulator phase with an integer number of bosons localized inside the tetrahedral units of the pyrochlore lattice. We show that the full phase diagram contains three cluster Mott insulator phases with 1/4, 1/2, and 3/4 boson fillings, respectively. We further demonstrate that all three cluster Mott insulators are Coulomb liquid phases and its low-energy property is described by the emergent compact U(1) quantum electrodynamics. In addition to measuring the specific heat and entropy of the cluster Mott insulators, we investigate the correlation function of the emergent electric field and verify it is consistent with the compact U(1) quantum electrodynamics description. Our result sheds light on the magnetic properties of various pyrochlore systems, as well as the charge physics of the cluster magnets. PMID:26230823

  20. 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. PMID:23215206

  1. New class of planar ferroelectric Mott insulators via first-principles design

    SciTech Connect

    Kim, Chanul; Park, Hyowon; Marianetti, Chris A.

    2015-12-11

    which is not common in known materials. Here we use first-principles calculations to design layered double perovskite oxides AABBO6 which achieve the aforementioned properties in the context of Mott insulators. In our design rules, the gap is dictated by B/B electronegativity difference in a Mott state, while the polarization is obtained via nominal d0 filling on the B-site, A-type cations bearing lone-pair electrons, and A = A size mismatch. Successful execution is demonstrated in BaBiCuVO6, BaBiNiVO6, BaLaCuVO6, and PbLaCuVO6.

  2. THz-Frequency Modulation of the Hubbard U in an Organic Mott Insulator.

    PubMed

    Singla, R; Cotugno, G; Kaiser, S; Först, M; Mitrano, M; Liu, H Y; Cartella, A; Manzoni, C; Okamoto, H; Hasegawa, T; Clark, S R; Jaksch, D; Cavalleri, A

    2015-10-30

    We use midinfrared pulses with stable carrier-envelope phase offset to drive molecular vibrations in the charge transfer salt ET-F_{2}TCNQ, a prototypical one-dimensional Mott insulator. We find that the Mott gap, which is probed resonantly with 10 fs laser pulses, oscillates with the pump field. This observation reveals that molecular excitations can coherently perturb the electronic on-site interactions (Hubbard U) by changing the local orbital wave function. The gap oscillates at twice the frequency of the vibrational mode, indicating that the molecular distortions couple quadratically to the local charge density.

  3. Correlation-driven charge order at the interface between a Mott and a band insulator.

    PubMed

    Pentcheva, Rossitza; Pickett, Warren E

    2007-07-01

    To study digital Mott insulator LaTiO3 and band insulator SrTiO3 interfaces, we apply correlated band theory within the local density approximation including a Hubbard U to (n, m) multilayers, 1Mott insulating behavior of undistorted LaTiO3, the charge imbalance at the interface is found in all cases to be accommodated by disproportionation (Ti4++Ti3+), charge ordering, and Ti3+ dxy-orbital ordering, with antiferromagnetic exchange coupling between the spins in the interface layer. Lattice relaxations lead to conducting behavior by shifting (slightly but importantly) the lower Hubbard band, but the charge and orbital order is robust against relaxation. PMID:17678179

  4. A simple metal-insulator criterion for the doped Mott-Hubbard materials

    NASA Astrophysics Data System (ADS)

    Gavrichkov, Vladimir A.

    2015-04-01

    A simple metal-insulator criterion for doped Mott-Hubbard materials has been derived. Its readings are closely related to the orbital and spin nature of the ground states of the unit cell. The available criterion readings (metal or insulator) in the paramagnetic phase reveal the possibility of the insulator state of doped materials with the forbidden first removal electron states. According to its physical meaning, the result is similar to the Wilson's criterion in itinerant electron systems. The application of the criterion to high-Tc cuprates is discussed.

  5. Tunnelling into the twisted Mott insulator Sr2IrO4 with atomic resolution

    NASA Astrophysics Data System (ADS)

    Ansary, Armin; Nichols, John; Bray-Ali, Noah; Cao, Gang; Ng, Kwok-Wai

    2014-03-01

    We studied the single-layered iridate Sr2IrO4 with a scanning tunneling microscope. The finite low temperature conductance enables the electronic structure of this antiferromagnetic Mott insulator to be measured by tunneling spectroscopy. We imaged the topography of freshly cleaved surfaces and measured differential tunneling conductance at cryogenic temperatures. We found the Mott gap in the tunneling density of states to be 2 Δ = 615 meV. Within the Mott gap, additional shoulders are observed which are interpreted as inelastic loss features due to magnons. This research was supported by NSF grants DMR- 0800367, DMR-0856234 and EPS-0814194. Noah Bray- Ali acknowledges support from the National Research Council Postdoctoral Research Associateship Program.

  6. 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

    2016-01-01

    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

  7. 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

  8. 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.

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

    DOE PAGES

    B. A. Frandsen; Liu, L.; Cheung, S. C.; Guguchia, Z.; Khasanov, R.; Morenzoni, E.; Munsie, T. J.S.; Hallas, A. M.; Wilson, M. N.; Cai, Y.; et al

    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 phasemore » 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

  10. Device Performance of the Mott Insulator LaVO3 as a Photovoltaic Material

    NASA Astrophysics Data System (ADS)

    Wang, Lingfei; Li, Yongfeng; Bera, Ashok; Ma, Chun; Jin, Feng; Yuan, Kaidi; Yin, Wanjian; David, Adrian; Chen, Wei; Wu, Wenbin; Prellier, Wilfrid; Wei, Suhuai; Wu, Tom

    2015-06-01

    Searching for solar-absorbing materials containing earth-abundant elements with chemical stability is of critical importance for advancing photovoltaic technologies. Mott insulators have been theoretically proposed as potential photovoltaic materials. In this paper, we evaluate their performance in solar cells by exploring the photovoltaic properties of Mott insulator LaVO3 (LVO). LVO films show an indirect band gap of 1.08 eV as well as strong light absorption over a wide wavelength range in the solar spectrum. First-principles calculations on the band structure of LVO further reveal that the d -d transitions within the upper and lower Mott-Hubbard bands and p -d transitions between the O 2 p and V 3 d band contribute to the absorption in visible and ultraviolet ranges, respectively. Transport measurements indicate strong carrier trapping and the formation of polarons in LVO. To utilize the strong light absorption of LVO and to overcome its poor carrier transport, we incorporate it as a light absorber in solar cells in conjunction with carrier transporters and evaluate its device performance. Our complementary experimental and theoretical results on such prototypical solar cells made of Mott-Hubbard transition-metal oxides pave the road for developing light-absorbing materials and photovoltaic devices based on strongly correlated electrons.

  11. 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.

  12. 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.

  13. Novel P-T Phase Diagram of the Multiorbital Mott Insulator Sr2VO4.

    PubMed

    Karmakar, S; Malavi, Pallavi S

    2015-04-24

    The electrical and optical properties of the Mott insulator Sr2VO4 are investigated under high pressure on a phase pure polycrystalline sample. The system undergoes a pressure-driven insulator to metal transition (IMT) with a crossover between 20 and 24 GPa. The effect of pressure on the thermally driven electronic changes resulting from spin-orbital ordering transitions is studied. A multiorbital analysis of the low frequency optical conductivity spectra suggests a bandwidth-controlled and orbital selective nature of the Mott IMT transition. Dramatic enhancement of the low energy spectral weight in the high pressure correlated metallic phase is explained in terms of the formation of a quasiparticle peak in the spectral function of the narrow and degenerate d(yz,zx) orbitals. Our results overall establish a novel electronic phase diagram of tetragonal Sr2VO4.

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

    DOE PAGES

    Hogan, Tom; Yamani, Z.; Walkup, D.; Chen, Xiang; Dally, Rebecca; Ward, Thomas Zac; Dean, M. P. M.; Hill, John P.; Islam, Z.; Madhavan, Vidya; et al

    2015-06-25

    Herein, the electronic phase diagram of the weak spin-orbit Mott insulator (Sr1-xLax)3Ir2O7 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 distortion develops and suggests a competingmore » instability with the parent spin-orbit Mott state.« less

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

    SciTech Connect

    Hogan, Tom; Yamani, Z.; Walkup, D.; Chen, Xiang; Dally, Rebecca; Ward, Thomas Zac; Dean, M. P. M.; Hill, John P.; Islam, Z.; Madhavan, Vidya; Wilson, Stephen D.

    2015-06-25

    Herein, the electronic phase diagram of the weak spin-orbit Mott insulator (Sr1-xLax)3Ir2O7 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 distortion develops and suggests a competing instability with the parent spin-orbit Mott state.

  16. Preparation and spectroscopy of a metastable Mott-insulator state with attractive interactions.

    PubMed

    Mark, M J; Haller, E; Lauber, K; Danzl, J G; Janisch, A; Büchler, H P; Daley, A J; Nägerl, H-C

    2012-05-25

    We prepare and study a metastable attractive Mott-insulator state formed with bosonic atoms in a three-dimensional optical lattice. Starting from a Mott insulator with Cs atoms at weak repulsive interactions, we use a magnetic Feshbach resonance to tune the interactions to large attractive values and produce a metastable state pinned by attractive interactions with a lifetime on the order of 10 s. We probe the (de)excitation spectrum via lattice modulation spectroscopy, measuring the interaction dependence of two- and three-body bound-state energies. As a result of increased on-site three-body loss we observe resonance broadening and suppression of tunneling processes that produce three-body occupation. PMID:23003276

  17. First-Order Melting of a Weak Spin-Orbit Mott Insulator into a Correlated Metal.

    PubMed

    Hogan, Tom; Yamani, Z; Walkup, D; Chen, Xiang; Dally, Rebecca; Ward, Thomas Z; Dean, M P M; Hill, John; Islam, Z; Madhavan, Vidya; Wilson, Stephen D

    2015-06-26

    The electronic phase diagram of the weak spin-orbit Mott insulator (Sr(1-x)La(x))(3)Ir(2)O(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. As the metallic state is stabilized, a weak structural distortion develops and suggests a competing instability with the parent spin-orbit Mott state.

  18. Transition from a Two-Dimensional Superfluid to a One-Dimensional Mott Insulator

    SciTech Connect

    Bergkvist, Sara; Rosengren, Anders; Saers, Robert; Lundh, Emil; Rehn, Magnus; Kastberg, Anders

    2007-09-14

    A two-dimensional system of atoms in an anisotropic optical lattice is studied theoretically. If the system is finite in one direction, it is shown to exhibit a transition between a two-dimensional superfluid and a one-dimensional Mott insulating chain of superfluid tubes. Monte Carlo simulations are consistent with the expectation that the phase transition is of Kosterlitz-Thouless type. The effect of the transition on experimental time-of-flight images is discussed.

  19. Non-local order in Mott insulators, duality and Wilson loops

    SciTech Connect

    Rath, Steffen Patrick; Simeth, Wolfgang; Endres, Manuel; Zwerger, Wilhelm

    2013-07-15

    It is shown that the Mott insulating and superfluid phases of bosons in an optical lattice may be distinguished by a non-local ‘parity order parameter’ which is directly accessible via single site resolution imaging. In one dimension, the lattice Bose model is dual to a classical interface roughening problem. We use known exact results from the latter to prove that the parity order parameter exhibits long range order in the Mott insulating phase, consistent with recent experiments by Endres et al. [M. Endres, M. Cheneau, T. Fukuhara, C. Weitenberg, P. Schauß, C. Gross, L. Mazza, M.C. Bañuls, L. Pollet, I. Bloch, et al., Science 334 (2011) 200]. In two spatial dimensions, the parity order parameter can be expressed in terms of an equal time Wilson loop of a non-trivial U(1) gauge theory in 2+1 dimensions which exhibits a transition between a Coulomb and a confining phase. The negative logarithm of the parity order parameter obeys a perimeter law in the Mott insulator and is enhanced by a logarithmic factor in the superfluid. -- Highlights: •Number statistics of cold atoms in optical lattices show non-local correlations. •These correlations are measurable via single site resolution imaging. •Incompressible phases exhibit an area law in particle number fluctuations. •This leads to long-range parity order of Mott-insulators in one dimension. •Parity order in 2d is connected with a Wilson-loop in a lattice gauge theory.

  20. Unquenched eg1 orbital moment in the Mott-insulating antiferromagnet KOsO4

    NASA Astrophysics Data System (ADS)

    Song, Young-Joon; Ahn, Kyo-Hoon; Lee, Kwan-Woo; Pickett, Warren E.

    2014-12-01

    Applying the correlated electronic structure method based on density functional theory plus the Hubbard U interaction, we have investigated the tetragonal scheelite structure Mott insulator KOsO4, whose eg1 configuration should be affected only slightly by spin-orbit coupling (SOC). The method reproduces the observed antiferromagnetic Mott-insulating state, populating the Os dz2 majority orbital. The quarter-filled eg manifold is characterized by a symmetry breaking due to the tetragonal structure, and the Os ion shows a crystal field splitting Δcf=1.7 eV from the t2 g complex, which is relatively small considering the high formal oxidation state Os 7 +. The small magnetocrystalline anisotropy before including correlation (i.e., in the metallic state) is increased by more than an order of magnitude in the Mott-insulating state, a result of a strong interplay between large SOC and a strong correlation. In contrast to conventional wisdom that the eg complex will not support orbital magnetism, we find that for the easy axis [100] direction the substantial Os orbital moment ML≈-0.2 μB compensates half of the Os spin moment MS=0.4 μB . The origin of the orbital moment is analyzed and understood in terms of additional spin-orbital lowering of symmetry, and beyond that due to structural distortion, for magnetization along [100]. Further interpretation is assisted by analysis of the spin density and the Wannier function with SOC included.

  1. The amplitude mode at the superfluid-mott insulator transition

    NASA Astrophysics Data System (ADS)

    Pekker, David

    2012-02-01

    We study a two dimensional gas of repulsively interacting bosons in the presence of both an optical lattice and a trap using optical lattice modulation spectroscopy. The strongly interacting superfluid supports two types of low energy modes associated with the symmetry breaking at the phase transition: gapless phase (Goldstone) modes and gapped amplitude (Anderson-Higgs) modes. Both experimentally and in theoretical simulations lattice modulation spectroscopy shows an onset of absorption at a frequency associated with the amplitude mode gap, followed by a broad absorption peak at higher frequencies. From the simulations, we learn that energy is being absorbed by various amplitude modes, which inside a trap resemble the modes of a (gapped) drum. Our main results are: (1) despite coupling to the phase modes, modulation spectroscopy shows a sharp absorption onset at the frequency associated with the amplitude mode gap; (2) as we approach the Mott transition the gap softens and finally disappears at the transition point; (3) in the weak coupling regime, deep in the superfluid phase, the amplitude mode disappears.

  2. Mott-insulator phases of spin-3/2 fermions in the presence of quadratic Zeeman coupling.

    PubMed

    Rodríguez, K; Argüelles, A; Colomé-Tatché, M; Vekua, T; Santos, L

    2010-07-30

    We study the influence of the quadratic Zeeman effect on the Mott-insulator phases of hard-core 1D spin-3/2 fermions. We show that, contrary to spinor bosons, the quadratic Zeeman coupling preserves an SU(2)⊗SU(2) symmetry, leading for large-enough quadratic Zeeman coupling to an isotropic pseudo-spin-1/2 Heisenberg antiferromagnet. Decreasing the quadratic Zeeman coupling, this phase undergoes, depending on the scattering lengths, either a Kosterlitz-Thouless transition into a gapped dimerized phase or a commensurate-incommensurate transition into a gapless spin liquid. This rich phase diagram can be observed experimentally in four-component fermions in optical lattices under similar entropy constraints to those needed for Néel order in spin-1/2 gases.

  3. Mott-insulator phases of spin-3/2 fermions in the presence of quadratic Zeeman coupling

    SciTech Connect

    Rodriguez, K.; Argueelles, A.; Colome-Tatche, M.; Vekua, T.; Santos, L.

    2010-07-30

    We study the influence of the quadratic Zeeman effect on the Mott-insulator phases of hard-core 1D spin-3/2 fermions. We show that, contrary to spinor bosons, the quadratic Zeeman coupling preserves an SU(2) x SU(2) symmetry, leading for large-enough quadratic Zeeman coupling to an isotropic pseudo-spin-1/2 Heisenberg antiferromagnet. Decreasing the quadratic Zeeman coupling, this phase undergoes, depending on the scattering lengths, either a Kosterlitz-Thouless transition into a gapped dimerized phase or a commensurate-incommensurate transition into a gapless spin liquid. This rich phase diagram can be observed experimentally in four-component fermions in optical lattices under similar entropy constraints to those needed for Neel order in spin-1/2 gases.

  4. Observation of 2D Fermionic Mott Insulators of 40K with Single-Site Resolution

    NASA Astrophysics Data System (ADS)

    Cheuk, Lawrence W.; Nichols, Matthew A.; Lawrence, Katherine R.; Okan, Melih; Zhang, Hao; Zwierlein, Martin W.

    2016-06-01

    We report on the site-resolved observation of characteristic states of the two-dimensional repulsive Fermi-Hubbard model, using ultracold 40K atoms in an optical lattice. By varying the tunneling, interaction strength, and external confinement, we realize metallic, Mott-insulating, and band-insulating states. We directly measure the local moment, which quantifies the degree of on-site magnetization, as a function of temperature and chemical potential. Entropies per particle as low as 0.99 (6 )kB indicate that nearest-neighbor antiferromagnetic correlations should be detectable using spin-sensitive imaging.

  5. Dimensional crossover and cold-atom realization of topological Mott insulators.

    PubMed

    Scheurer, Mathias S; Rachel, Stephan; Orth, Peter P

    2015-02-11

    Interacting cold-atomic gases in optical lattices offer an experimental approach to outstanding problems of many body physics. One important example is the interplay of interaction and topology which promises to generate a variety of exotic phases such as the fractionalized Chern insulator or the topological Mott insulator. Both theoretically understanding these states of matter and finding suitable systems that host them have proven to be challenging problems. Here we propose a cold-atom setup where Hubbard on-site interactions give rise to spin liquid-like phases: weak and strong topological Mott insulators. They represent the celebrated paradigm of an interacting and topological quantum state with fractionalized spinon excitations that inherit the topology of the non-interacting system. Our proposal shall help to pave the way for a controlled experimental investigation of this exotic state of matter in optical lattices. Furthermore, it allows for the investigation of a dimensional crossover from a two-dimensional quantum spin Hall insulating phase to a three-dimensional strong topological insulator by tuning the hopping between the layers.

  6. Dimensional crossover and cold-atom realization of topological Mott insulators

    PubMed Central

    Scheurer, Mathias S.; Rachel, Stephan; Orth, Peter P.

    2015-01-01

    Interacting cold-atomic gases in optical lattices offer an experimental approach to outstanding problems of many body physics. One important example is the interplay of interaction and topology which promises to generate a variety of exotic phases such as the fractionalized Chern insulator or the topological Mott insulator. Both theoretically understanding these states of matter and finding suitable systems that host them have proven to be challenging problems. Here we propose a cold-atom setup where Hubbard on-site interactions give rise to spin liquid-like phases: weak and strong topological Mott insulators. They represent the celebrated paradigm of an interacting and topological quantum state with fractionalized spinon excitations that inherit the topology of the non-interacting system. Our proposal shall help to pave the way for a controlled experimental investigation of this exotic state of matter in optical lattices. Furthermore, it allows for the investigation of a dimensional crossover from a two-dimensional quantum spin Hall insulating phase to a three-dimensional strong topological insulator by tuning the hopping between the layers. PMID:25669431

  7. Pressure-Induced Confined Metal from the Mott Insulator Sr_{3}Ir_{2}O_{7}.

    PubMed

    Ding, Yang; Yang, Liuxiang; Chen, Cheng-Chien; Kim, Heung-Sik; Han, Myung Joon; Luo, Wei; Feng, Zhenxing; Upton, Mary; Casa, Diego; Kim, Jungho; Gog, Thomas; Zeng, Zhidan; Cao, Gang; Mao, Ho-Kwang; van Veenendaal, Michel

    2016-05-27

    The spin-orbit Mott insulator Sr_{3}Ir_{2}O_{7} provides a fascinating playground to explore insulator-metal transition driven by intertwined charge, spin, and lattice degrees of freedom. Here, we report high-pressure electric resistance and resonant inelastic x-ray scattering measurements on single-crystal Sr_{3}Ir_{2}O_{7} up to 63-65 GPa at 300 K. The material becomes a confined metal at 59.5 GPa, showing metallicity in the ab plane but an insulating behavior along the c axis. Such an unusual phenomenon resembles the strange metal phase in cuprate superconductors. Since there is no sign of the collapse of spin-orbit or Coulomb interactions in x-ray measurements, this novel insulator-metal transition is potentially driven by a first-order structural change at nearby pressures. Our discovery points to a new approach for synthesizing functional materials. PMID:27284666

  8. Pressure-Induced Confined Metal from the Mott Insulator Sr3 Ir2 O7

    NASA Astrophysics Data System (ADS)

    Ding, Yang; Yang, Liuxiang; Chen, Cheng-Chien; Kim, Heung-Sik; Han, Myung Joon; Luo, Wei; Feng, Zhenxing; Upton, Mary; Casa, Diego; Kim, Jungho; Gog, Thomas; Zeng, Zhidan; Cao, Gang; Mao, Ho-kwang; van Veenendaal, Michel

    2016-05-01

    The spin-orbit Mott insulator Sr3Ir2O7 provides a fascinating playground to explore insulator-metal transition driven by intertwined charge, spin, and lattice degrees of freedom. Here, we report high-pressure electric resistance and resonant inelastic x-ray scattering measurements on single-crystal Sr3Ir2O7 up to 63-65 GPa at 300 K. The material becomes a confined metal at 59.5 GPa, showing metallicity in the a b plane but an insulating behavior along the c axis. Such an unusual phenomenon resembles the strange metal phase in cuprate superconductors. Since there is no sign of the collapse of spin-orbit or Coulomb interactions in x-ray measurements, this novel insulator-metal transition is potentially driven by a first-order structural change at nearby pressures. Our discovery points to a new approach for synthesizing functional materials.

  9. Mean-field theory for the Mott-insulator-paired-superfluid phase transition in the two-species Bose-Hubbard model

    SciTech Connect

    Iskin, M.

    2010-11-15

    The standard mean-field theory for the Mott-insulator-superfluid phase transition is not sufficient to describe the Mott-insulator-paired-superfluid phase transition. Therefore, by restricting the two-species Bose-Hubbard Hamiltonian to the subspace of paired particles, and using perturbation theory, here we derive an analytic mean-field expression for the Mott-insulator-paired-superfluid transition boundary.

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

    NASA Astrophysics Data System (ADS)

    Ronning, F.

    2002-03-01

    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 the compound Ca2-xNaxCuO2Cl2. 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 La2-xSrxCuO4 where the chemical potential remains fixed and states are created inside the gap. Furthermore, the low energy excitations (ie the Fermi surface) in metallic Ca1.9Na0.1CuO2Cl2 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 provide a new avenue for understanding the evolution of the Mott insulator to

  11. Large Fermi Surface of Heavy Electrons at the Border of Mott Insulating State in NiS2

    DOE PAGES

    Friedemann, S.; Chang, H.; Gamża, M. B.; Reiss, P.; Chen, X.; Alireza, P.; Coniglio, W. A.; Graf, D.; Tozer, S.; Grosche, F. M.

    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 NiS2. 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

  12. Large Fermi Surface of Heavy Electrons at the Border of Mott Insulating State in NiS2

    PubMed Central

    Friedemann, S.; Chang, H.; Gamża, M. B.; Reiss, P.; Chen, X.; Alireza, P.; Coniglio, W. A.; Graf, D.; Tozer, S.; Grosche, F. M.

    2016-01-01

    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 of 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 NiS2. 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. PMID:27174799

  13. Large Fermi Surface of Heavy Electrons at the Border of Mott Insulating State in NiS2

    NASA Astrophysics Data System (ADS)

    Friedemann, S.; Chang, H.; Gamża, M. B.; Reiss, P.; Chen, X.; Alireza, P.; Coniglio, W. A.; Graf, D.; Tozer, S.; Grosche, F. M.

    2016-05-01

    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 of 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 NiS2. 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.

  14. Avalanche breakdown in GaTa4Se(8-x)Te(x) narrow-gap Mott insulators.

    PubMed

    Guiot, V; Cario, L; Janod, E; Corraze, B; Phuoc, V Ta; Rozenberg, M; Stoliar, P; Cren, T; Roditchev, D

    2013-01-01

    Mott transitions induced by strong electric fields are receiving growing interest. Recent theoretical proposals have focused on the Zener dielectric breakdown in Mott insulators. However, experimental studies are still too scarce to conclude about the mechanism. Here we report a study of the dielectric breakdown in the narrow-gap Mott insulators GaTa4Se(8-x)Te(x). We find that the I-V characteristics and the magnitude of the threshold electric field (Eth) do not correspond to a Zener breakdown, but rather to an avalanche breakdown. Eth increases as a power law of the Mott-Hubbard gap (Eg), in surprising agreement with the universal law Eth is proportional to Eg(2.5) reported for avalanche breakdown in semiconductors. However, the delay time for the avalanche that we observe in Mott insulators is over three orders of magnitude greater than in conventional semiconductors. Our results suggest that the electric field induces local insulator-to-metal Mott transitions that create conductive domains that grow to form filamentary paths across the sample.

  15. Realizing topological Mott insulators from the RKKY interaction

    NASA Astrophysics Data System (ADS)

    Liu, Tianhan; Douçot, Benoît; Le Hur, Karyn

    2016-05-01

    We engineer topological insulating phases in a fermion-fermion mixture on the honeycomb lattice, without resorting to artificial gauge fields or spin-orbit couplings and considering only local interactions. Essentially, upon integrating out the fast component (characterized by a larger hopping amplitude) in a finite region of dopings, we obtain an effective interaction between the slow fermions at half-filling, which acquires a Haldane mass with opposite parity in the two valleys of the Dirac cones, thus triggering a quantum anomalous Hall effect. We carefully analyze the competition between the induced Semenoff-type mass (producing charge density wave orders in real space) versus the Haldane mass (quantum anomalous Hall phase), as a function of the chemical potential of the fast fermions. If the second species involves spin-1/2 particles, this interaction may induce a quantum spin Hall phase. Such fermion-fermion mixtures can be realized in optical lattices or in graphene heterostructures.

  16. Migration of Bosonic Particles across a Mott Insulator to a Superfluid Phase Interface

    NASA Astrophysics Data System (ADS)

    Hartmann, Michael J.; Plenio, Martin B.

    2008-02-01

    We consider a boundary between a Mott insulator and a superfluid region of a Bose-Hubbard model at unit filling. Initially both regions are decoupled and cooled to their respective ground states. We show that, after switching on a small tunneling rate between both regions, all particles of the Mott region migrate to the superfluid area. This migration takes place whenever the difference between the chemical potentials of both regions is less than the maximal energy of any eigenmode of the superfluid. We verify our results numerically with density matrix renormalization group simulations and explain them analytically with a master equation approximation, finding good agreement between both approaches. Finally we carry out a feasibility study for the observation of the effect in coupled arrays of microcavities and optical lattices.

  17. 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.

  18. Ultrafast and reversible control of the exchange interaction in Mott insulators

    PubMed Central

    Mentink, J. H.; Balzer, K.; Eckstein, M.

    2015-01-01

    The strongest interaction between microscopic spins in magnetic materials is the exchange interaction Jex. Therefore, ultrafast control of Jex holds the promise to control spins on ultimately fast timescales. We demonstrate that time-periodic modulation of the electronic structure by electric fields can be used to reversibly control Jex on ultrafast timescales in extended antiferromagnetic Mott insulators. In the regime of weak driving strength, we find that Jex can be enhanced and reduced for frequencies below and above the Mott gap, respectively. Moreover, for strong driving strength, even the sign of Jex can be reversed and we show that this causes time reversal of the associated quantum spin dynamics. These results suggest wide applications, not only to control magnetism in condensed matter systems, for example, via the excitation of spin resonances, but also to assess fundamental questions concerning the reversibility of the quantum many-body dynamics in cold atom systems. PMID:25819547

  19. 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.

  20. Phase coexistence and Mott metal-insulator transition in the doped Hubbard-Holstein model

    NASA Astrophysics Data System (ADS)

    Moradi Kurdestany, Jamshid; Satpathy, Sashi

    2015-03-01

    Motivated by recent progress in the understanding of the Mott insulators away from half filling [?], often observed in the oxide materials, we study the role of the electron-lattice interaction vis-à-vis the electron correlations by studying the one-band Hubbard-Holstein model using the Gutzwiller variational method. Our theory predicts phase separation for sufficiently strong electron-lattice interaction, which however is frustrated in the solid due to the long-range Coulomb interaction of the dopant atoms, resulting in puddles of metallic phases embedded in the insulating matrix. Metallic state occurs when the volume fraction of the metallic phase exceeds the percolation threshold, as the dopant concentration is increased. Connection is made with the experimentally observed metal-insulator transition in the complex oxides.

  1. Electronic structure study of strongly correlated Mott-insulators

    NASA Astrophysics Data System (ADS)

    Yin, Quan

    Strongly correlated electronic systems have presented the most challenging problems to condensed matter theorists for many years and this continues to be the case. They are complicated materials with active d or f orbitals, whose valence electrons are in the intermediate region between itinerant (band-like) and highly localized (atomic-like) limits, which demand genuine many-body treatment. Although dealing with strongly correlated systems is a notorious problem, they have drawn broad interests of both theoretical and experimental condensed matter physicists, with intensive studies carried out in the past and present. This is due to the most exotic properties associated with strongly correlated materials, such as high-temperature superconductivity, metal-insulator transition, volume collapse, Kondo effect, colossal magnetoresistance, and many others. Although density functional theory (DFT) within local density approximation (LDA) is very successful in describing a wide range of materials, it encounters difficulty in predicting strongly correlated systems. Traditionally, they have been studied by model Hamiltonians with empirical parameters. The development of dynamical mean field theory (DMFT) and its marriage to DFT have brought new hope for first-principle study of strongly correlated systems. In this work, electronic structures of select strongly correlated systems are studied using LDA+DMFT. As theoretical backgrounds, reviews of DFT and DMFT are given in the first few chapters, where we also introduce the philosophy and workflow of LDA+DMFT. In the following chapters, applications to transition metal oxides, undoped high-temperature superconductors and actinide oxides are presented, where electronic structures of these materials and other properties derived from electronic structures are calculated and compared with experiments where available. Generally good agreements have been found between theory and experiments.

  2. Hallmarks of the Mott-metal crossover in the hole-doped pseudospin-1/2 Mott insulator Sr2IrO4.

    PubMed

    Cao, Yue; Wang, Qiang; Waugh, Justin A; Reber, Theodore J; Li, Haoxiang; Zhou, Xiaoqing; Parham, Stephen; Park, S-R; Plumb, Nicholas C; Rotenberg, Eli; Bostwick, Aaron; Denlinger, Jonathan D; Qi, Tongfei; Hermele, Michael A; Cao, Gang; Dessau, Daniel S

    2016-04-22

    The physics of doped Mott insulators remains controversial after decades of active research, hindered by the interplay among competing orders and fluctuations. It is thus highly desired to distinguish the intrinsic characters of the Mott-metal crossover from those of other origins. Here we investigate the evolution of electronic structure and dynamics of the hole-doped pseudospin-1/2 Mott insulator Sr2IrO4. The effective hole doping is achieved by replacing Ir with Rh atoms, with the chemical potential immediately jumping to or near the top of the lower Hubbard band. The doped iridates exhibit multiple iconic low-energy features previously observed in doped cuprates-pseudogaps, Fermi arcs and marginal-Fermi-liquid-like electronic scattering rates. We suggest these signatures are most likely an integral part of the material's proximity to the Mott state, rather than from many of the most claimed mechanisms, including preformed electron pairing, quantum criticality or density-wave formation.

  3. Hallmarks of the Mott-metal crossover in the hole-doped pseudospin-1/2 Mott insulator Sr2IrO4

    NASA Astrophysics Data System (ADS)

    Cao, Yue; Wang, Qiang; Waugh, Justin A.; Reber, Theodore J.; Li, Haoxiang; Zhou, Xiaoqing; Parham, Stephen; Park, S.-R.; Plumb, Nicholas C.; Rotenberg, Eli; Bostwick, Aaron; Denlinger, Jonathan D.; Qi, Tongfei; Hermele, Michael A.; Cao, Gang; Dessau, Daniel S.

    2016-04-01

    The physics of doped Mott insulators remains controversial after decades of active research, hindered by the interplay among competing orders and fluctuations. It is thus highly desired to distinguish the intrinsic characters of the Mott-metal crossover from those of other origins. Here we investigate the evolution of electronic structure and dynamics of the hole-doped pseudospin-1/2 Mott insulator Sr2IrO4. The effective hole doping is achieved by replacing Ir with Rh atoms, with the chemical potential immediately jumping to or near the top of the lower Hubbard band. The doped iridates exhibit multiple iconic low-energy features previously observed in doped cuprates--pseudogaps, Fermi arcs and marginal-Fermi-liquid-like electronic scattering rates. We suggest these signatures are most likely an integral part of the material's proximity to the Mott state, rather than from many of the most claimed mechanisms, including preformed electron pairing, quantum criticality or density-wave formation.

  4. Hallmarks of the Mott-metal crossover in the hole-doped pseudospin-1/2 Mott insulator Sr2IrO4.

    PubMed

    Cao, Yue; Wang, Qiang; Waugh, Justin A; Reber, Theodore J; Li, Haoxiang; Zhou, Xiaoqing; Parham, Stephen; Park, S-R; Plumb, Nicholas C; Rotenberg, Eli; Bostwick, Aaron; Denlinger, Jonathan D; Qi, Tongfei; Hermele, Michael A; Cao, Gang; Dessau, Daniel S

    2016-01-01

    The physics of doped Mott insulators remains controversial after decades of active research, hindered by the interplay among competing orders and fluctuations. It is thus highly desired to distinguish the intrinsic characters of the Mott-metal crossover from those of other origins. Here we investigate the evolution of electronic structure and dynamics of the hole-doped pseudospin-1/2 Mott insulator Sr2IrO4. The effective hole doping is achieved by replacing Ir with Rh atoms, with the chemical potential immediately jumping to or near the top of the lower Hubbard band. The doped iridates exhibit multiple iconic low-energy features previously observed in doped cuprates-pseudogaps, Fermi arcs and marginal-Fermi-liquid-like electronic scattering rates. We suggest these signatures are most likely an integral part of the material's proximity to the Mott state, rather than from many of the most claimed mechanisms, including preformed electron pairing, quantum criticality or density-wave formation. PMID:27102065

  5. Hallmarks of the Mott-metal crossover in the hole-doped pseudospin-1/2 Mott insulator Sr2IrO4

    PubMed Central

    Cao, Yue; Wang, Qiang; Waugh, Justin A.; Reber, Theodore J.; Li, Haoxiang; Zhou, Xiaoqing; Parham, Stephen; Park, S.-R.; Plumb, Nicholas C.; Rotenberg, Eli; Bostwick, Aaron; Denlinger, Jonathan D.; Qi, Tongfei; Hermele, Michael A.; Cao, Gang; Dessau, Daniel S.

    2016-01-01

    The physics of doped Mott insulators remains controversial after decades of active research, hindered by the interplay among competing orders and fluctuations. It is thus highly desired to distinguish the intrinsic characters of the Mott-metal crossover from those of other origins. Here we investigate the evolution of electronic structure and dynamics of the hole-doped pseudospin-1/2 Mott insulator Sr2IrO4. The effective hole doping is achieved by replacing Ir with Rh atoms, with the chemical potential immediately jumping to or near the top of the lower Hubbard band. The doped iridates exhibit multiple iconic low-energy features previously observed in doped cuprates—pseudogaps, Fermi arcs and marginal-Fermi-liquid-like electronic scattering rates. We suggest these signatures are most likely an integral part of the material's proximity to the Mott state, rather than from many of the most claimed mechanisms, including preformed electron pairing, quantum criticality or density-wave formation. PMID:27102065

  6. Topological edge Mott insulating state in two dimensions at finite temperatures: Bulk and edge analysis

    NASA Astrophysics Data System (ADS)

    Yoshida, Tsuneya; Kawakami, Norio

    2016-08-01

    We study a bilayer Kane-Mele-Hubbard model with lattice distortion and interlayer spin exchange interaction under cylinder geometry. Our analysis based on real-space dynamical mean field theory with continuous-time quantum Monte Carlo demonstrates the emergence of a topological edge Mott insulating (TEMI) state which hosts gapless edge modes only in collective spin excitations. This is confirmed by the numerical calculations at finite temperatures for the spin-Hall conductivity and the single-particle excitation spectrum; the spin-Hall conductivity is almost quantized, σspinx y˜2 (e /2 π ) , predicting gapless edge modes carrying the spin current, while the helical edge modes in the single-particle spectrum are gapped out with respecting symmetry. It is clarified how the TEMI state evolves from the ordinary spin-Hall insulating state with increasing the Hubbard interaction at a given temperature and then undergoes a phase transition to a trivial Mott insulating state. With a bosonization approach at zero temperature, we further address which collective modes host gapless edge modes in the TEMI state.

  7. Haldane-Hubbard Mott Insulator: From Tetrahedral Spin Crystal to Chiral Spin Liquid

    NASA Astrophysics Data System (ADS)

    Hickey, Ciaran; Cincio, Lukasz; Papic, Zlatko; Paramekanti, Arun

    Motivated by recent experimental realizations of artificial gauge fields in ultracold atoms, we study the honeycomb lattice Haldane-Hubbard Mott insulator of spin- 1 / 2 fermions using exact diagonalization and density matrix renormalization group methods. We show that this model exhibits various chiral magnetic orders including a wide regime of triple-Q tetrahedral order. Incorporating third-neighbor hopping frustrates and ultimately melts this tetrahedral spin crystal. From analyzing low energy spectra, many-body Chern numbers, entanglement spectra, and modular matrices, we identify the molten state as a chiral spin liquid with gapped semion excitations.

  8. Appearance of "fragile" Fermi liquids in finite-width Mott insulators sandwiched between metallic leads.

    PubMed

    Zenia, H; Freericks, J K; Krishnamurthy, H R; Pruschke, Th

    2009-09-11

    Using inhomogeneous dynamical mean-field theory, we show that the normal-metal proximity effect could force any finite number of Mott-insulating "barrier" planes sandwiched between semi-infinite metallic leads to become "fragile" Fermi liquids. They are fully Fermi-liquid-like at T=0, leading to a restoration of lattice periodicity at zero frequency, with a well-defined Fermi surface, and perfect (ballistic) conductivity. However, the Fermi-liquid character can rapidly disappear at finite omega, V, T, disorder, or magnetism, all of which restore the expected quantum tunneling regime, leading to fascinating possibilities for nonlinear response in devices.

  9. Mott insulators of ultracold fermionic alkaline Earth atoms: underconstrained magnetism and chiral spin liquid.

    PubMed

    Hermele, Michael; Gurarie, Victor; Rey, Ana Maria

    2009-09-25

    We study Mott insulators of fermionic alkaline earth atoms, described by Heisenberg spin models with enhanced SU(N) symmetry. In dramatic contrast to SU(2) magnetism, more than two spins are required to form a singlet. On the square lattice, the classical ground state is highly degenerate and magnetic order is thus unlikely. In a large-N limit, we find a chiral spin liquid ground state with topological order and Abelian fractional statistics. We discuss its experimental detection. Chiral spin liquids with non-Abelian anyons may also be realizable with alkaline earth atoms.

  10. Theory of the optical conductivity of spin liquid states in one-dimensional Mott insulators.

    PubMed

    Katsura, Hosho; Sato, Masahiro; Furuta, Takashi; Nagaosa, Naoto

    2009-10-23

    The low-energy dynamical optical response of dimerized and undimerized spin liquid states in a one-dimensional charge transfer Mott insulator is theoretically studied. An exact analysis is given for the low-energy asymptotic behavior using conformal field theory for the undimerized state. In the dimerized state, the infrared absorption due to the bound state of two solitons, i.e., the breather mode, is predicted with an accurate estimate for its oscillator strength, offering a way to detect experimentally the excited singlet state. The effects of external magnetic fields are also discussed.

  11. Antiferromagnetic resonance in the Mott insulator fcc-Cs3C60.

    PubMed

    Suzuki, Yuta; Shibasaki, Seiji; Kubozono, Yoshihiro; Kambe, Takashi

    2013-09-11

    The magnetic ground state of the fcc phase of the Mott insulator Cs3C60 was studied using a low-temperature electron spin resonance technique, and antiferromagnetic resonance (AFMR) below 1.57 K was directly observed at ambient pressure. The AFMR modes for the fcc phase of Cs3C60 were investigated using a conventional two-sublattice model with uniaxial anisotropy, and the spin-flop field was determined to be 4.7 kOe at 1.57 K. The static magnetic exchange interactions and anisotropy field for fcc-Cs3C60 were also estimated.

  12. Phase boundary of the boson Mott insulator in a rotating optical lattice

    SciTech Connect

    Umucalilar, R. O.; Oktel, M. Oe.

    2007-11-15

    We consider the Bose-Hubbard model in a two-dimensional rotating optical lattice and investigate the consequences of the effective magnetic field created by rotation. Using a Gutzwiller-type variational wave function, we find an analytical expression for the Mott insulator (MI)-superfluid (SF) transition boundary in terms of the maximum eigenvalue of the Hofstadter butterfly. The dependence of phase boundary on the effective magnetic field is complex, reflecting the self-similar properties of the single particle energy spectrum. Finally, we argue that fractional quantum Hall phases exist close to the MI-SF transition boundaries, including MI states with particle densities greater than one.

  13. Thermometry and refrigeration in a two-component Mott insulator of ultracold atoms

    SciTech Connect

    Weld, David M.; Miyake, Hirokazu; Medley, Patrick; Pritchard, David E.; Ketterle, Wolfgang

    2010-11-15

    Interesting spin Hamiltonians can be realized with ultracold atoms in a two-component Mott insulator (2CMI) [Adv. Phys. 56, 243 (2007); Rev. Mod. Phys. 80, 885 (2008)]. It was recently demonstrated that the application of a magnetic field gradient to the 2CMI enables new techniques of thermometry [Phys. Rev. Lett. 103, 245301 (2009)] and adiabatic cooling [e-print arXiv:1006.4674]. Here we present a theoretical description which provides quantitative analysis of these two techniques. We show that adiabatic reduction of the field gradient is capable of cooling below the Curie or Neel temperature of certain spin-ordered phases.

  14. Ferromagnetism in the Mott insulator Ba2NaOsO6

    SciTech Connect

    Erickson, A.S.; Misra, S.; Miller, G.J.; Harrison, W.A.; Kim, J.M.; Fisher, I.R.; /Stanford U., Appl. Phys. Dept. /Stanford U., Geballe Lab.

    2010-01-15

    Results are presented of single crystal structural, thermodynamic, and reflectivity measurements of the double-perovskite Ba{sub 2}NaOsO{sub 6}. These characterize the material as a 5d1 ferromagnetic Mott insulator with an ordered moment of {approx} 0.2 {micro}B per formula unit and T{sub C} = 6.8(3) K. The magnetic entropy associated with this phase transition is close to Rln2, indicating that the quartet groundstate anticipated from consideration of the crystal structure is split, consistent with a scenario in which the ferromagnetism is associated with orbital ordering.

  15. Doped Mott insulators in (111) bilayers of perovskite transition-metal oxides with a strong spin-orbit coupling.

    PubMed

    Okamoto, Satoshi

    2013-02-01

    The electronic properties of Mott insulators realized in (111) bilayers of perovskite transition-metal oxides are studied. The low-energy effective Hamiltonians for such Mott insulators are derived in the presence of a strong spin-orbit coupling. These models are characterized by the antiferromagnetic Heisenberg interaction and the anisotropic interaction whose form depends on the d orbital occupancy. From exact diagonalization analyses on finite clusters, the ground state phase diagrams are derived, including a Kitaev spin liquid phase in a narrow parameter regime for t(2g) systems. Slave-boson mean-field analyses indicate the possibility of novel superconducting states induced by carrier doping into the Mott-insulating parent systems, suggesting the present model systems as unique playgrounds for studying correlation-induced novel phenomena. Possible experimental realizations are also discussed.

  16. Doped Mott Insulators in (111) Bilayers of Perovskite Transition-Metal Oxides with a Strong Spin-Orbit Coupling

    SciTech Connect

    Okamoto, Satoshi

    2013-01-01

    The electronic properties of Mott insulators realized in (111) bilayers of perovskite transition-metal oxides are studied. The low-energy effective Hamiltonians for such Mott insulators are derived in the presence of a strong spin-orbit coupling. These models are characterized by the antiferromagnetic Heisenberg interaction and the anisotropic interaction whose form depends on the $d$ orbital occupancy. From exact diagonalization analyses on finite clusters, the ground state phase diagrams are derived, including a Kitaev spin liquid phase in a narrow parameter regime for $t_{2g}$ systems. Slave-boson mean-field analyses indicate the possibility of novel superconducting states induced by carrier doping into the Mott-insulating parent systems, suggesting the present model systems as unique playgrounds for studying correlation-induced novel phenomena. Possible experimental realizations are also discussed.

  17. 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.

  18. 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. PMID:27451640

  19. Chiral magnetism and spin liquid Mott insulators induced by synthetic gauge fields

    NASA Astrophysics Data System (ADS)

    Paramekanti, Arun; Hickey, Ciaran; Cincio, Lukasz; Papic, Zlatko; Vellat-Sadashivan, Arun; Sohal, Ramanjit

    2016-05-01

    Recent experiments using Raman-assisted tunneling or lattice-shaking have realized synthetic gauge fields and optical lattice bands with nontrivial band topology. Here we examine the effect of particle interactions in such bands, focussing on two-component fermions with local Hubbard repulsion. We show that interactions can drive the integer quantum Hall insulator into Mott insulating states which possess noncoplanar chiral magnetic textures and even chiral spin liquids with many-body topological order. We establish our results using a combination of mean field theory, strong coupling expansions, numerical exact diagonalization and DMRG methods. We also discuss possible signatures of such non-coplanar orders in Bragg scattering and noise measurements.

  20. Haldane-Hubbard Mott Insulator: From Tetrahedral Spin Crystal to Chiral Spin Liquid.

    PubMed

    Hickey, Ciarán; Cincio, Lukasz; Papić, Zlatko; Paramekanti, Arun

    2016-04-01

    Motivated by cold atom experiments on Chern insulators, we study the honeycomb lattice Haldane-Hubbard Mott insulator of spin-1/2 fermions using exact diagonalization and density matrix renormalization group methods. We show that this model exhibits various chiral magnetic orders including a wide regime of triple-Q tetrahedral order. Incorporating third-neighbor hopping frustrates and ultimately melts this tetrahedral spin crystal. From analyzing the low energy spectrum, many-body Chern numbers, entanglement spectra, and modular matrices, we identify the molten state as a chiral spin liquid (CSL) with gapped semion excitations. We formulate and study the Chern-Simons-Higgs field theory of the exotic CSL-to-tetrahedral spin crystallization transition.

  1. Haldane-Hubbard Mott Insulator: From Tetrahedral Spin Crystal to Chiral Spin Liquid

    NASA Astrophysics Data System (ADS)

    Hickey, Ciarán; Cincio, Lukasz; Papić, Zlatko; Paramekanti, Arun

    2016-04-01

    Motivated by cold atom experiments on Chern insulators, we study the honeycomb lattice Haldane-Hubbard Mott insulator of spin-1 /2 fermions using exact diagonalization and density matrix renormalization group methods. We show that this model exhibits various chiral magnetic orders including a wide regime of triple-Q tetrahedral order. Incorporating third-neighbor hopping frustrates and ultimately melts this tetrahedral spin crystal. From analyzing the low energy spectrum, many-body Chern numbers, entanglement spectra, and modular matrices, we identify the molten state as a chiral spin liquid (CSL) with gapped semion excitations. We formulate and study the Chern-Simons-Higgs field theory of the exotic CSL-to-tetrahedral spin crystallization transition.

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

    PubMed

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

    2016-01-01

    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. PMID:27185665

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

    NASA Astrophysics Data System (ADS)

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

    2016-05-01

    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.

  4. Haldane-Hubbard Mott Insulator: From Tetrahedral Spin Crystal to Chiral Spin Liquid.

    PubMed

    Hickey, Ciarán; Cincio, Lukasz; Papić, Zlatko; Paramekanti, Arun

    2016-04-01

    Motivated by cold atom experiments on Chern insulators, we study the honeycomb lattice Haldane-Hubbard Mott insulator of spin-1/2 fermions using exact diagonalization and density matrix renormalization group methods. We show that this model exhibits various chiral magnetic orders including a wide regime of triple-Q tetrahedral order. Incorporating third-neighbor hopping frustrates and ultimately melts this tetrahedral spin crystal. From analyzing the low energy spectrum, many-body Chern numbers, entanglement spectra, and modular matrices, we identify the molten state as a chiral spin liquid (CSL) with gapped semion excitations. We formulate and study the Chern-Simons-Higgs field theory of the exotic CSL-to-tetrahedral spin crystallization transition. PMID:27082001

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

    PubMed Central

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

    2016-01-01

    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. PMID:27185665

  6. 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.

  7. Ultra-fast photo-carrier relaxation in Mott insulators with short-range spin correlations

    PubMed Central

    Eckstein, Martin; Werner, Philipp

    2016-01-01

    Ultra-fast spectroscopy can reveal the interplay of charges with low energy degrees of freedom, which underlies the rich physics of correlated materials. As a potential glue for superconductivity, spin fluctuations in Mott insulators are of particular interest. A theoretical description of the coupled spin and charge degrees of freedom is challenging, because magnetic order is often only short-lived and short-ranged. In this work we theoretically investigate how the spin-charge interactions influence the relaxation of a two-dimensional Mott-Hubbard insulator after photo-excitation. We use a nonequilibrium variant of the dynamical cluster approximation, which, in contrast to single-site dynamical mean-field theory, captures the effect of short-range correlations. The relaxation time is found to scale with the strength of the nearest-neighbor spin correlations, and can be 10–20 fs in the cuprates. Increasing the temperature or excitation density decreases the spin correlations and thus implies longer relaxation times. This may help to distinguish the effect of spin-fluctuations on the charge relaxation from the influence of other bosonic modes in the solid. PMID:26883536

  8. Quantum simulation of a topological Mott insulator with Rydberg atoms in a Lieb lattice

    NASA Astrophysics Data System (ADS)

    Dauphin, A.; Müller, M.; Martin-Delgado, M. A.

    2016-04-01

    We propose a realistic scheme to quantum simulate the so-far experimentally unobserved topological Mott insulator phase—an interaction-driven topological insulator—using cold atoms in an optical Lieb lattice. To this end, we study a system of spinless fermions in a Lieb lattice, exhibiting repulsive nearest- and next-to-nearest-neighbor interactions and derive the associated zero-temperature phase diagram within mean-field approximation. In particular, we analyze how the interactions can dynamically generate a charge density wave ordered, a nematic, and a topologically nontrivial quantum anomalous Hall phase. We characterize the topology of the different phases by the Chern number and discuss the possibility of phase coexistence. Based on the identified phases, we propose a realistic implementation of this model using cold Rydberg-dressed atoms in an optical lattice. The scheme, which allows one to access, in particular, the topological Mott insulator phase, robustly and independently of its exact position in parameter space, merely requires global, always-on off-resonant laser coupling to Rydberg states and is feasible with state-of-the-art experimental techniques that have already been demonstrated in the laboratory.

  9. Mott insulating states and quantum phase transitions of correlated SU(2 N ) Dirac fermions

    NASA Astrophysics Data System (ADS)

    Zhou, Zhichao; Wang, Da; Meng, Zi Yang; Wang, Yu; Wu, Congjun

    2016-06-01

    The interplay between charge and spin degrees of freedom in strongly correlated fermionic systems, in particular of Dirac fermions, is a long-standing problem in condensed matter physics. We investigate the competing orders in the half-filled SU (2 N ) Hubbard model on a honeycomb lattice, which can be accurately realized in optical lattices with ultracold large-spin alkaline-earth fermions. Employing large-scale projector determinant quantum Monte Carlo simulations, we have explored quantum phase transitions from the gapless Dirac semimetals to the gapped Mott insulating phases in the SU(4) and SU(6) cases. Both of these Mott insulating states are found to be columnar valence bond solid (cVBS) and to be absent of the antiferromagnetic Néel ordering and the loop current ordering. Inside the cVBS phases, the dimer ordering is enhanced by increasing fermion components and behaves nonmonotonically as the interaction strength increases. Although the transitions generally should be of first order due to a cubic invariance possessed by the cVBS order, the coupling to gapless Dirac fermions can soften the transitions to second order through a nonanalytic term in the free energy. Our simulations provide important guidance for the experimental explorations of novel states of matter with ultracold alkaline-earth fermions.

  10. 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

  11. Interference of atomic levels and superfluid-Mott insulator phase transitions in a two-component Bose-Einstein condensate.

    PubMed

    Krutitsky, K V; Graham, R

    2003-12-12

    The superfluid-Mott insulator phase transition in a Bose-Einstein condensate of neutral atoms with doubly degenerate internal ground states in an optical lattice is theoretically investigated. The optical lattice is created by two counterpropagating linearly polarized laser beams with the angle theta between the polarization vectors (lin-angle-lin configuration). The phase diagram of the system and the critical values of the parameters are worked out. It is shown that the sign of the detuning plays an important role and that there is a strong suppression of the Mott transition in the case of blue detuning. Varying the laser intensity and/or the angle theta one can manipulate the Mott insulator to superfluid quantum phase transition as well as prepare the condensate in physically distinguishable "ferromagnetic" and "antiferromagnetic" superfluid states.

  12. Featureless and nonfractionalized Mott insulators on the honeycomb lattice at 1/2 site filling

    PubMed Central

    Kimchi, Itamar; Parameswaran, S. A.; Turner, Ari M.; Wang, Fa; Vishwanath, Ashvin

    2013-01-01

    Within the Landau paradigm, phases of matter are distinguished by spontaneous symmetry breaking. Implicit here is the assumption that a completely symmetric state exists: a paramagnet. At zero temperature such quantum featureless insulators may be forbidden, triggering either conventional order or topological order with fractionalized excitations. Such is the case for interacting particles when the particle number per unit cell, f, is not an integer. However, can lattice symmetries forbid featureless insulators even at integer f? An especially relevant case is the honeycomb (graphene) lattice—where free spinless fermions at (the two sites per unit cell mean is half-filling per site) are always metallic. Here we present wave functions for bosons, and a related spin-singlet wave function for spinful electrons, on the honeycomb lattice and demonstrate via quantum to classical mappings that they do form featureless Mott insulators. The construction generalizes to symmorphic lattices at integer f in any dimension. Our results explicitly demonstrate that in this case, despite the absence of a noninteracting insulator at the same filling, lack of order at zero temperature does not imply fractionalization.

  13. Topological mott insulator in three-dimensional systems with quadratic band touching.

    PubMed

    Herbut, Igor F; Janssen, Lukas

    2014-09-01

    We argue that a three-dimensional electronic system with the Fermi level at the quadratic band touching point such as HgTe could be unstable with respect to the spontaneous formation of the (topological) Mott insulator at arbitrary weak long-range Coulomb interaction. The mechanism of the instability can be understood as the collision of Abrikosov's non-Fermi liquid fixed point with another, quantum critical, fixed point, which approaches it in the coupling space as the system's dimensionality d→dlow+, with the "lower critical dimension" 2Mott transition finally takes place at the critical temperature Tc∼T*exp[-zC/(dlow-d)1/2]. We estimate C=π/1.1, dynamical critical exponent z≈1.8, and the temperature scale kBT*≈(4m/melϵ^2)13.6  eV, with m as the band mass and ϵ as the dielectric constant.

  14. Quantum melting of magnetic order in an organic dimer Mott-insulating system

    NASA Astrophysics Data System (ADS)

    Naka, Makoto; Ishihara, Sumio

    2016-05-01

    Quantum entanglement effects between the electronic spin and charge degrees of freedom are examined in an organic molecular solid, termed a dimer Mott-insulating system, in which molecular dimers are arranged in a crystal as fundamental units. A low energy effective model includes an antisymmetric exchange interaction, as one of the dominant magnetic interactions. This interaction favors a 90 deg spin configuration, and competes with the Heisenberg-type exchange interaction. Stabilities of the magnetic ordered phases are examined by using the spin-wave theory, as well as the Schwinger-boson theory. It is found that the spin-charge interaction promotes an instability of the long-range magnetic ordered state around a parameter region where two spin-spiral phases are merged. Implication for the quantum spin liquid state observed in κ -(BEDT-TTF)2Cu2 (CN) 3 is discussed.

  15. Excitonic magnetism in Van Vleck-type d4 Mott insulators.

    PubMed

    Khaliullin, Giniyat

    2013-11-01

    In Mott insulators with the t(2g)4 electronic configuration such as of Re3+, Ru4+, Os4+, and Ir5+ ions, spin-orbit coupling dictates a Van Vleck-type nonmagnetic ground state with an angular momentum J=0, and the magnetic response is governed by gapped singlet-triplet excitations. We derive the exchange interactions between these excitons and study their collective behavior on different lattices. In perovskites, a conventional Bose condensation of excitons into a magnetic state is found, while an unexpected one-dimensional behavior supporting spin-liquid states emerges in honeycomb lattices, due to the bond directional nature of exciton interactions in the case of 90° d-p-d bonding geometry.

  16. Mott metal-insulator transition in a metallic liquid - Gutzwiller molecular dynamics simulations

    NASA Astrophysics Data System (ADS)

    Barros, Kipton; Chern, Gia-Wei; Batista, Cristian D.; Kress, Joel D.; Kotliar, Gabriel

    2015-03-01

    Molecular dynamics (MD) simulations are crucial to modern computational physics, chemistry, and materials science, especially when combined with potentials derived from density-functional theory. However, even in state of the art MD codes, the on-site Coulomb repulsion is only treated at the self-consistent Hartree-Fock level. This standard approximation may miss important effects due to electron correlations. The Gutzwiller variational method captures essential correlated-electron physics yet is much faster than, e.g., the dynamical-mean field theory approach. We present our efficient Gutzwiller-MD implementation. With it, we investigate the Mott metal-insulator transition in a metallic fluid and uncover several surprising static and dynamic properties of this system.

  17. Spin-orbit coupling and electronic charge effects in Mott insulators

    DOE PAGES

    Zhu, Shan; Li, You -Quan; Batista, Cristian D.

    2014-11-04

    We derive the effective charge- and current-density operators for the strong-coupling limit of a single-band Mott insulator in the presence of spin-orbit coupling and show that the spin-orbit contribution to the effective charge density leads to novel mechanisms for multiferroic behavior. In some sense, these mechanisms are the electronic counterpart of the ionic-based mechanisms, which have been proposed for explaining the electric polarization induced by spiral spin orderings. In addition, the new electronic mechanisms are illustrated by considering cycloidal and proper-screw magnetic orderings on sawtooth and kagome lattices. As for the isotropic case, geometric frustration is crucial for achieving thismore » purely electronic coupling between spin and charge degrees of freedom.« less

  18. Photoinduced phase transitions in narrow-gap Mott insulators: The case of VO2

    NASA Astrophysics Data System (ADS)

    He, Zhuoran; Millis, Andrew J.

    2016-03-01

    We study the nonequilibrium dynamics of photoexcited electrons in the narrow-gap Mott insulator VO2. The initial stages of relaxation are treated using a quantum Boltzmann equation methodology, which reveals a rapid (˜femtosecond time scale) relaxation to a pseudothermal state characterized by a few parameters that vary slowly in time. The long-time limit is then studied by a Hartree-Fock methodology, which reveals the possibility of nonequilibrium excitation to a new metastable M1 metal phase that is qualitatively consistent with a recent experiment. The general physical picture of photoexcitation driving a correlated electron system to a new state that is not accessible in equilibrium may be applicable in similar materials.

  19. Spin-orbit coupling and electronic charge effects in Mott insulators

    SciTech Connect

    Zhu, Shan; Li, You -Quan; Batista, Cristian D.

    2014-11-04

    We derive the effective charge- and current-density operators for the strong-coupling limit of a single-band Mott insulator in the presence of spin-orbit coupling and show that the spin-orbit contribution to the effective charge density leads to novel mechanisms for multiferroic behavior. In some sense, these mechanisms are the electronic counterpart of the ionic-based mechanisms, which have been proposed for explaining the electric polarization induced by spiral spin orderings. In addition, the new electronic mechanisms are illustrated by considering cycloidal and proper-screw magnetic orderings on sawtooth and kagome lattices. As for the isotropic case, geometric frustration is crucial for achieving this purely electronic coupling between spin and charge degrees of freedom.

  20. Chiral Spin Liquids in Triangular-Lattice SU (N ) Fermionic Mott Insulators with Artificial Gauge Fields

    NASA Astrophysics Data System (ADS)

    Nataf, Pierre; Lajkó, Miklós; Wietek, Alexander; Penc, Karlo; Mila, Frédéric; Läuchli, Andreas M.

    2016-10-01

    We show that, in the presence of a π /2 artificial gauge field per plaquette, Mott insulating phases of ultracold fermions with SU (N ) symmetry and one particle per site generically possess an extended chiral phase with intrinsic topological order characterized by an approximate ground space of N low-lying singlets for periodic boundary conditions, and by chiral edge states described by the SU(N ) 1 Wess-Zumino-Novikov-Witten conformal field theory for open boundary conditions. This has been achieved by extensive exact diagonalizations for N between 3 and 9, and by a parton construction based on a set of N Gutzwiller projected fermionic wave functions with flux π /N per triangular plaquette. Experimental implications are briefly discussed.

  1. JeffDescription of the Honeycomb Mott Insulatorα‑RuCl3

    NASA Astrophysics Data System (ADS)

    Koitzsch, A.; Habenicht, C.; Müller, E.; Knupfer, M.; Büchner, B.; Kandpal, H. C.; van den Brink, J.; Nowak, D.; Isaeva, A.; Doert, Th.

    2016-09-01

    Novel ground states might be realized in honeycomb lattices with strong spin-orbit coupling. Here we study the electronic structure of {\\alpha}-RuCl_3, in which the Ru ions are in a d5 configuration and form a honeycomb lattice, by angle-resolved photoemission, x-ray photoemission and electron energy loss spectroscopy supported by density functional theory and multiplet calculations. We find that {\\alpha}-RuCl_3 is a Mott insulator with significant spin-orbit coupling, whose low energy electronic structure is naturally mapped onto Jeff states. This makes {\\alpha}-RuCl_3 a promising candidate for the realization of Kitaev physics. Relevant electronic parameters such as the Hubbard energy U, the crystal field splitting 10Dq and the charge transfer energy are evaluated. Furthermore, we observe significant Cl photodesorption with time, which must be taken into account when interpreting photoemission and other surface sensitive experiments.

  2. Wigner-Mott insulator-to-insulator transition at pressure in charge-ordered Fe2OBO3

    NASA Astrophysics Data System (ADS)

    Diguet, G.; Hearne, G. R.; Sibanda, W. N.; Carleschi, E.; Musyimi, P.; Pischedda, V.; Attfield, J. P.

    2014-01-01

    Magnetic-electronic studies of mixed-valence Fe2OBO3 have shown that ionic charge order (CO) is disrupted at ˜16 GPa. The pertinent minority-spin carrier exhibits persistent intersite electron exchange Fe2+ ⇔ Fe3+ to well beyond this pressure. Temperature-dependent electrical transport measurements over an extended pressure range presented here demonstrate that the electronic structure remains gapped to well beyond 16 GPa. Extrapolation of data to higher pressure suggests that metallization will only prevail at P>50 GPa. Both the persistent gapped electronic state across the CO instability and signature of carrier confinement to Fe-Fe dimers in the Fe2+ ⇔ Fe3+ electron exchange are rationalized as crossover from a Wigner crystal (site centered) insulator to a dimer Mott (bond centered type) insulator—"Wigner-Mott transition" at ˜16 GPa. The dimer insulating state is a consequence of modulation of the relevant hopping parameter t in quasi-low-dimensional features in the structure (ribbons and chains). Complementary structural studies suggest that the a axis is appreciably more compressible than other crystallographic directions of the original monoclinic unit cell. Therefore, such a modulation in t may arise from Peierls type distortions along the a axis or else stems from intrinsic modulation in the c axis direction of the unit cell. This is aided by a monoclinic (P21/c) → orthorhombic (Pmcn) structural adjustment that is concurrent across the electronic transition. Pressure tuning of relative values of on-site U/t and intersite V/t Coulomb interaction parameters of the quasi-low-dimensional features evolve the system from site-centered to dimer-centered electron localization.

  3. Design of Chern and Mott insulators in buckled 3 d oxide honeycomb lattices

    NASA Astrophysics Data System (ADS)

    Doennig, David; Baidya, Santu; Pickett, Warren E.; Pentcheva, Rossitza

    2016-04-01

    Perovskite (La X O3 )2/(LaAlO3)4(111) superlattices with X spanning the entire 3 d transition-metal series combine the strongly correlated, multiorbital nature of electrons in transition-metal oxides with a honeycomb lattice as a key feature. Based on density functional theory calculations including strong interaction effects, we establish trends in the evolution of electronic states as a function of several control parameters: band filling, interaction strength, spin-orbit coupling (SOC), and lattice instabilities. Competition between local pseudocubic and global trigonal symmetry as well as the additional flexibility provided by the magnetic and spin degrees of freedom of 3 d ions lead to a broad array of distinctive broken-symmetry ground states not accessible for the (001)-growth direction, offering a platform to design two-dimensional electronic functionalities. Constraining the symmetry between the two triangular sublattices causes X =Mn , Co, and Ti to emerge as Chern insulators driven by SOC. For X =Mn we illustrate how interaction strength and lattice distortions can tune these systems between a Dirac semimetal, a Chern and a trivial Mott insulator.

  4. Ca2O3Fe2.6S2: an antiferromagnetic Mott insulator at proximity to bad metal

    NASA Astrophysics Data System (ADS)

    Zhang, Han; Wu, Xiaozhi; Li, Dandan; Jin, Shifeng; Chen, Xiao; Zhang, Tao; Lin, Zhiping; Shen, Shijie; Yuan, Duanduan; Chen, Xiaolong

    2016-04-01

    We report here the first layered iron oxychalcogenide Ca2O3Fe2.6S2 that contains both planar [Ca2FeO2]2+ and [Fe2OS2]2- layers with the shortest Fe-Fe bond length. This compound is a narrow band gap (~0.073 eV) Mott insulator. The observed antiferromagnetic (AFM) transition at 77 K is due to the ordered Fe vacancies, which can be suppressed by partial substitution of Se for S. We show that the vacancy-free phase Ca2O3Fe3S2 may become a metal with moderate electron correlation comparable to the parent compound LaOFeAs of corresponding superconductors. Our results imply that iron oxychalcogenide can be converted from an AFM Mott insulator into a bad metal like iron pnictides through Fe-Fe bond length shrinking.

  5. Superfluid-Mott insulator transition in spin-orbit coupled Bose-Hubbard Model

    NASA Astrophysics Data System (ADS)

    Iskin, Menderes; Bolukbasi, Ahmet T. B.

    2014-05-01

    We consider a square optical lattice in two dimensions and study the effects of both the strength and symmetry of spin-orbit coupling (SOC) and Zeeman field on the ground-state, i.e., Mott insulator (MI) and superfluid (SF), phases and phase diagram, i.e., MI-SF phase transition boundary, of the two-component Bose-Hubbard model. In particular, based on a variational Gutzwiller ansatz, our numerical calculations show that the spin-orbit coupled SF phase is a nonuniform (twisted) one with its phase (but not the magnitude) of the order parameter modulating from site to site. Fully analytical insights into the numerical results are also given. A. T. B is supported by TÜBİTAK 2218 Domestic Postdoctoral Fellowship Program, and M. I. is supported by the Marie Curie IRG Grant No. FP7-PEOPLE-IRG-2010-268239, TÜBİTAK Career Grant No. 3501-110T839, and TÜBA-GEBİP.

  6. Li2RhO3: A spin-glassy relativistic Mott insulator

    NASA Astrophysics Data System (ADS)

    Luo, Yongkang; Cao, Chao; Si, Bingqi; Li, Yuke; Bao, Jinke; Guo, Hanjie; Yang, Xiaojun; Shen, Chenyi; Feng, Chunmu; Dai, Jianhui; Cao, Guanghan; Xu, Zhu-an

    2013-04-01

    Motivated by the rich interplay among electronic correlation, spin-orbit coupling (SOC), crystal-field splitting, and geometric frustrations in the honeycomblike lattice, we systematically investigated the electronic and magnetic properties of Li2RhO3. The material is semiconducting with a narrow band gap of Δ˜78 meV, and its temperature dependence of resistivity conforms to a three-dimensional variable range hopping mechanism. No long-range magnetic ordering was found down to 0.5 K, due to the geometric frustrations. Instead, single atomic spin-glass behavior below the spin-freezing temperature (˜6 K) was observed and its spin dynamics obeys the universal critical slowing down scaling law. A first-principles calculation suggested it to be a relativistic Mott insulator mediated by both electronic correlation and SOC. With moderate strength of electronic correlation and SOC, our results shed light on the research of the Heisenberg-Kitaev model in realistic materials.

  7. 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

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

    SciTech Connect

    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. Standard 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.

  9. 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

  10. Rydberg-Atom Quantum Simulation and Chern Number Characterization of a Topological Mott Insulator

    NASA Astrophysics Data System (ADS)

    Dauphin, Alexandre; Mueller, Markus; Martin-Delgado, Miguel-Angel

    2013-03-01

    In this talk we consider a system of spinless fermions with nearest and next-to-nearest neighbor repulsive Hubbard interactions on a honeycomb lattice within the mean-field treatment, and propose and analyze a realistic scheme for analog quantum simulation of this model with cold atoms in a two-dimensional hexagonal optical lattice. Besides a semi-metallic and a charge-density-wave ordered phase, the system exhibits a quantum anomalous Hall phase, which is generated dynamically, i.e. purely as a result of the repulsive fermionic interactions and in the absence of any external gauge fields. We establish the topological nature of this dynamically created Mott insulating phase by the numerical calculation of a Chern number, and study the possibility of coexistence of this phase with the other phases characterized by local order parameters. Based on the knowledge of the mean-field phase diagram, we then discuss in detail how the interacting Hamiltonian can be engineered effective ly by state-of-the-art experimental techniques for laser-dressing of cold fermionic ground-state atoms with electronically excited Rydberg states that exhibit strong dipolar interactions.

  11. Spin-orbit coupling, strong correlation, and insulator-metal transitions: The Jeff=3/2 ferromagnetic Dirac-Mott insulator Ba2NaOsO6

    NASA Astrophysics Data System (ADS)

    Gangopadhyay, Shruba; Pickett, Warren E.

    2015-01-01

    The double perovskite Ba2NaOsO6 (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 realistic 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 -0.4 μB strongly compensates the +0.5 μB 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. Comparison is made with the isostructural, isovalent insulator Ba2LiOsO6 , which, however, orders antiferromagnetically.

  12. The 'Higgs' amplitude mode at the two-dimensional superfluid/Mott insulator transition.

    PubMed

    Endres, Manuel; Fukuhara, Takeshi; Pekker, David; Cheneau, Marc; Schauss, Peter; Gross, Christian; Demler, Eugene; Kuhr, Stefan; Bloch, Immanuel

    2012-07-25

    Spontaneous symmetry breaking plays a key role in our understanding of nature. In relativistic quantum field theory, a broken continuous symmetry leads to the emergence of two types of fundamental excitation: massless Nambu-Goldstone modes and a massive 'Higgs' amplitude mode. An excitation of Higgs type is of crucial importance in the standard model of elementary particle physics, and also appears as a fundamental collective mode in quantum many-body systems. Whether such a mode exists in low-dimensional systems as a resonance-like feature, or whether it becomes overdamped through coupling to Nambu-Goldstone modes, has been a subject of debate. Here we experimentally find and study a Higgs mode in a two-dimensional neutral superfluid close to a quantum phase transition to a Mott insulating phase. We unambiguously identify the mode by observing the expected reduction in frequency of the onset of spectral response when approaching the transition point. In this regime, our system is described by an effective relativistic field theory with a two-component quantum field, which constitutes a minimal model for spontaneous breaking of a continuous symmetry. Additionally, all microscopic parameters of our system are known from first principles and the resolution of our measurement allows us to detect excited states of the many-body system at the level of individual quasiparticles. This allows for an in-depth study of Higgs excitations that also addresses the consequences of the reduced dimensionality and confinement of the system. Our work constitutes a step towards exploring emergent relativistic models with ultracold atomic gases.

  13. Spin Correlations and the Mott-Hubbard Metal-Insulator Transition in Vanadium Trioxide: a Neutron Scattering Study.

    NASA Astrophysics Data System (ADS)

    Bao, Wei

    rm V_2O_3 is a canonical Mott system where strong correlations among electrons drive spectacular metal-insulator transitions and the metallic rm V_2O_3 has served as a prototype of the Brinkman-Rice strongly correlated Fermi liquid. Research in Mott-Hubbard systems has largely focused on charge dynamics. Spin dynamics is widely assumed as described by localized spin fluctuations on the grounds that the electrons in the metal are nearly localized near the Mott transition. Discovery of high T_{C} superconductivity in cuprates and the subsequent attribution of spin fluctuations in pairing electrons demand a better understanding of strongly correlated electron systems in general and spin dynamics of these systems in particular. Using magnetic neutron scattering, we discovered an incommensurate spin density wave in doping stabilized metallic V_{2-y}O _3 at low temperatures, which appears not to be directly related to the antiferromagnetic order in the insulating rm V_2O_3. This weak ordering phenomenon at low temperatures is accompanied by energetic spin fluctuations with large spectral weight throughout the paramagnetic metallic phase of rm V_2O_3, reflecting the itinerant nature of magnetism with an energy scale related to the Fermi energy, in contrast to the conventional k _{B}T ~ J of a localized -spin model, even on the verge of Mott transition. Spin fluctuations in the paramagnetic insulating (V _{1-x}Cr_{x })_2O_3 were discovered to relate to those of paramagnetic metallic rm V_2O_3 rather than to the antiferromagnetic order of the low temperature insulating phase. The short correlation length in the paramagnetic insulator was discovered to be controlled by a mechanism other than thermal spin fluctuations. This unusual property invalidates previous claims of explaining the phase diagram of rm V_2O_3 based on a one-band Hubbard model and indicates the important physical consequences of degenerate Hubbard bands in rm V_2O_3. Work in this dissertation was performed

  14. A metallic mosaic phase and the origin of Mott-insulating state in 1T-TaS2

    PubMed Central

    Ma, Liguo; Ye, Cun; Yu, Yijun; Lu, Xiu Fang; Niu, Xiaohai; Kim, Sejoong; Feng, Donglai; Tománek, David; Son, Young-Woo; Chen, Xian Hui; Zhang, Yuanbo

    2016-01-01

    Electron–electron and electron–phonon interactions are two major driving forces that stabilize various charge-ordered phases of matter. In layered compound 1T-TaS2, the intricate interplay between the two generates a Mott-insulating ground state with a peculiar charge-density-wave (CDW) order. The delicate balance also makes it possible to use external perturbations to create and manipulate novel phases in this material. Here, we study a mosaic CDW phase induced by voltage pulses, and find that the new phase exhibits electronic structures entirely different from that of the original Mott ground state. The mosaic phase consists of nanometre-sized domains characterized by well-defined phase shifts of the CDW order parameter in the topmost layer, and by altered stacking relative to the layers underneath. We discover that the nature of the new phase is dictated by the stacking order, and our results shed fresh light on the origin of the Mott phase in 1T-TaS2. PMID:26961788

  15. Doping-driven evolution of the superconducting state from a doped Mott insulator: Cluster dynamical mean-field theory

    NASA Astrophysics Data System (ADS)

    Civelli, M.

    2009-05-01

    In this paper we investigate the zero-temperature doping-driven evolution of a superconductor toward the Mott insulator in a two-dimensional electron model, relevant for high-temperature superconductivity. To this purpose we use a cluster extension of dynamical mean-field theory. Our results show that a standard d -wave superconductor, realized at high doping, is driven into the Mott insulator via an intermediate superconducting state displaying unconventional physical properties. By restoring the translational invariance of the lattice, we give an interpretation of these findings in momentum space. In particular, we show that at a finite doping a strong momentum-space differentiation takes place: non-Fermi liquid and insulatinglike (pseudogap) characters rise in some regions (antinodes), while Fermi liquid quasiparticles survive in other regions (nodes) of momentum space. We describe the consequence of these happenings on the spectral properties, stressing in particular the behavior of the superconducting gap, which reveals two distinct nodal and antinodal energy scales as a function of doping, detected in photoemission and Raman spectroscopy experiments. We study and compare with experimental results the doping-dependent behavior of other physical quantities, such as for instance, the nodal quasiparticle velocity (extracted in angle-resolved photoemission) and the low-energy slopes of the local density of states and of the Raman scattering response. We then propose a description of the evolution of the electronic structure while approaching the Mott transition. We show that, within our formalism, a strong asymmetry naturally arises in the local density of states, measured in scanning tunneling spectroscopy. We investigate in detail the doping evolution of the electronic bands, focusing on the kinklike quasiparticle dispersion observed with angle-resolved photoemission in specific cuts of the momentum-energy space. We finally show the consequences of the

  16. Emergent ``super-solitons'' following an interaction strength quantum quench across a Luttinger liquid-Mott insulating phase boundary

    NASA Astrophysics Data System (ADS)

    Foster, Matthew; Yuzbashyan, Emil

    2010-03-01

    Rapid progress in cold atom experiments has motivated the study of non-equilibrium many-body dynamics following a sudden deformation of the system Hamiltonian (a ``quantum quench''). Here, we consider the dynamics of localized excitations produced via a quench across a quantum phase boundary separating critical Luttinger liquid and gapped Mott insulating states. Our initial liquid ground state is labeled by a Luttinger interaction parameter K, and subject to a density-inhomogeneity forming external potential. For the Mott insulator, we employ the quantum Sine Gordon model at the Luther-Emery (LE) point. We find that over a wide range of initial K values, the quench induces the production of relativistic, non-dispersive traveling density waves, which we dub ``super-solitons.'' The super-solitons are generated from generic antecedent localized density lumps, and appear to be a robust feature of the post-quench dynamics. An isolated exception occurs for the case of K = KLE; here, the density dynamics are generically dispersive, and depend sensitively upon the shape of the initial inhomogeneity. We show that the super-solitons do not interact, and we demonstrate that an inhomogeneous Luttinger parameter K can be used to produce super-solitons with different characteristics in the same system.

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

    PubMed

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

    2014-03-18

    A(1-x)Fe(2-y)Se2 (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.

  18. Slater to Mott Crossover in the Metal to Insulator Transition of Nd2Ir2O7

    NASA Astrophysics Data System (ADS)

    Nakayama, M.; Kondo, Takeshi; Tian, Z.; Ishikawa, J. J.; Halim, M.; Bareille, C.; Malaeb, W.; Kuroda, K.; Tomita, T.; Ideta, S.; Tanaka, K.; Matsunami, M.; Kimura, S.; Inami, N.; Ono, K.; Kumigashira, H.; Balents, L.; Nakatsuji, S.; Shin, S.

    2016-07-01

    We present an angle-resolved photoemission study of the electronic structure of the three-dimensional pyrochlore iridate Nd2Ir2O7 through its magnetic metal-insulator transition. Our data reveal that metallic Nd2Ir2O7 has a quadratic band, touching the Fermi level at the Γ point, similar to that of Pr2Ir2O7 . The Fermi node state is, therefore, a common feature of the metallic phase of the pyrochlore iridates. Upon cooling below the transition temperature, this compound exhibits a gap opening with an energy shift of quasiparticle peaks like a band gap insulator. The quasiparticle peaks are strongly suppressed, however, with further decrease of temperature, and eventually vanish at the lowest temperature, leaving a nondispersive flat band lacking long-lived electrons. We thereby identify a remarkable crossover from Slater to Mott insulators with decreasing temperature. These observations explain the puzzling absence of Weyl points in this material, despite its proximity to the zero temperature metal-insulator transition.

  19. Slater to Mott Crossover in the Metal to Insulator Transition of Nd_{2}Ir_{2}O_{7}.

    PubMed

    Nakayama, M; Kondo, Takeshi; Tian, Z; Ishikawa, J J; Halim, M; Bareille, C; Malaeb, W; Kuroda, K; Tomita, T; Ideta, S; Tanaka, K; Matsunami, M; Kimura, S; Inami, N; Ono, K; Kumigashira, H; Balents, L; Nakatsuji, S; Shin, S

    2016-07-29

    We present an angle-resolved photoemission study of the electronic structure of the three-dimensional pyrochlore iridate Nd_{2}Ir_{2}O_{7} through its magnetic metal-insulator transition. Our data reveal that metallic Nd_{2}Ir_{2}O_{7} has a quadratic band, touching the Fermi level at the Γ point, similar to that of Pr_{2}Ir_{2}O_{7}. The Fermi node state is, therefore, a common feature of the metallic phase of the pyrochlore iridates. Upon cooling below the transition temperature, this compound exhibits a gap opening with an energy shift of quasiparticle peaks like a band gap insulator. The quasiparticle peaks are strongly suppressed, however, with further decrease of temperature, and eventually vanish at the lowest temperature, leaving a nondispersive flat band lacking long-lived electrons. We thereby identify a remarkable crossover from Slater to Mott insulators with decreasing temperature. These observations explain the puzzling absence of Weyl points in this material, despite its proximity to the zero temperature metal-insulator transition. PMID:27517783

  20. Effects of higher-order energy bands and temperature on the bosonic Mott insulator in a periodically modulated lattice

    NASA Astrophysics Data System (ADS)

    Sajna, A. S.

    2016-10-01

    We show that a certain class of higher-order excitations in ultracold atoms experiments can be described by straightforward extension of the standard strong coupling approach in the coherent state path integral formalism. It is achieved by theoretical analysis of energy absorption spectroscopy in the three-dimensional system of strongly correlated bosons described by the Bose-Hubbard model. In particular, for unit filling, an explicit form of the single-particle Mott insulator Green function at finite temperatures is derived which goes beyond the standard Hubbard bands description. Moreover, for relevant densities, we calculated the energy absorption rate and performed thermometry on rubidium atomic cloud gas by using previously obtained experimental data. Within the local density approximation, we explain that in such systems the nature of absorption spectrum depends significantly on local chemical potential: (a) the crossover region between lobes is characterized by different types of particle-hole excitations from neighboring Mott lobes and (b) origin of higher-order energy excitations changes from hole type to particle type for higher bosonic densities.

  1. Optical conductivity measurements of GaTa4Se8 under high pressure: evidence of a bandwidth-controlled insulator-to-metal Mott transition.

    PubMed

    Ta Phuoc, V; Vaju, C; Corraze, B; Sopracase, R; Perucchi, A; Marini, C; Postorino, P; Chligui, M; Lupi, S; Janod, E; Cario, L

    2013-01-18

    The optical properties of a GaTa(4)Se(8) single crystal are investigated under high pressure. At ambient pressure, the optical conductivity exhibits a charge gap of ≈0.12 eV and a broad midinfrared band at ≈0.55 eV. As pressure is increased, the low energy spectral weight is strongly enhanced and the optical gap is rapidly filled, pointing to an insulator to metal transition around 6 GPa. The overall evolution of the optical conductivity demonstrates that GaTa(4)Se(8) is a Mott insulator which undergoes a bandwidth-controlled Mott metal-insulator transition under pressure, in remarkably good agreement with theory. With the use of our optical data and ab initio band structure calculations, our results were successfully compared to the (U/D, T/D) phase diagram predicted by dynamical mean field theory for strongly correlated systems.

  2. Superconductor to Mott insulator transition in YBa2Cu3O7/LaCaMnO3 heterostructures

    PubMed Central

    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.

    2016-01-01

    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. PMID:27627855

  3. 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

    2016-01-01

    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. PMID:27627855

  4. Superconductor to Mott insulator transition in YBa2Cu3O7/LaCaMnO3 heterostructures

    DOE PAGES

    Gray, B. A.; Middey, S.; Conti, G.; Gray, A. X.; Kuo, C. -T.; Kaiser, A. M.; Ueda, S.; Kobayashi, K.; Meyers, D.; Kareev, M.; et al

    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 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, leadingmore » 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

  5. Superconductor to Mott insulator transition in YBa2Cu3O7/LaCaMnO3 heterostructures

    NASA Astrophysics Data System (ADS)

    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.

    2016-09-01

    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.

  6. 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

    2016-01-01

    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.

  7. The electronic structure of the Mott insulator VO2: the strongly correlated metal state is screened by impurity band

    NASA Astrophysics Data System (ADS)

    Kim, Hyun-Tak

    A Mott insulator VO2 (3d1) has a direct gap (Δdirect ~Vdirect) of 0.6 eV and an indirect gap of Δact ~Vdirect ~ 0.15 eV coming from impurity indirect band. At Tc, Δdirect =Δact = O is satisfied and the insulator-to-metal transition (IMT) occurs. The metallic carriers near core region can be trapped when a critical onsite Coulomb Uc exists. Then, a potential energy is defined as Vg =Vdirect +Uc +Vindirect = - (2 2 3) EF (1 + e (NtotNtotntot) (1 - exp (-Δact-ΔactkB T))) +Uc kB T))) +Uc ntot) (1 - exp (-Δact-ΔactkB T))) +Uc kB T))) +Uc 3) EF (1 + e (NtotNtotntot) (1 - exp (-Δact-ΔactkB T))) +Uc kB T))) +Uc ntot) (1 - exp (-Δact-ΔactkB T))) +Uc kB T))) +Uc , where Vdirect = - (2 2 3 3) EF is the screened Coulomb pseudopotential at K = 0. Δρ =NtotNtotntot ~ 0 . 018 % ntot ~ 0 . 018 % [1] is defined as the critical doping quantity, where ntot is the carrier density in the direct band and Ntot is the carrier density in the impurity band. In Uc < (2

  8. Anion effects on electronic structure and electrodynamic properties of the Mott insulator κ -(BEDT-TTF ) 2Ag2(CN) 3

    NASA Astrophysics Data System (ADS)

    Pinterić, M.; Lazić, P.; Pustogow, A.; Ivek, T.; Kuveždić, M.; Milat, O.; Gumhalter, B.; Basletić, M.; Čulo, M.; Korin-Hamzić, B.; Löhle, A.; Hübner, R.; Sanz Alonso, M.; Hiramatsu, T.; Yoshida, Y.; Saito, G.; Dressel, M.; Tomić, S.

    2016-10-01

    The Mott insulator κ -(BEDT-TTF ) 2Ag2(CN) 3 forms a highly-frustrated triangular lattice of S =1 /2 dimers with a possible quantum-spin-liquid state. Our experimental and numerical studies reveal the emergence of a slight charge imbalance between crystallographically inequivalent sites, relaxor dielectric response, and hopping dc transport. In a broader perspective we conclude that the universal properties of strongly-correlated charge-transfer salts with spin liquid state are an anion-supported valence band and cyanide-induced quasidegenerate electronic configurations in the relaxed state. The generic low-energy excitations are caused by charged domain walls rather than by fluctuating electric dipoles. They give rise to glassy dynamics characteristic of dimerized Mott insulators, including the sibling compound κ -(BEDT-TTF)2Cu2 (CN )3.

  9. Defects, Disorder, and Strong Electron Correlations in Orbital Degenerate, Doped Mott Insulators

    NASA Astrophysics Data System (ADS)

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

    2015-11-01

    We elucidate the effects of defect disorder and e -e interaction on the spectral density of the defect states emerging in the Mott-Hubbard gap of doped transition-metal oxides, such as Y1 -xCaxVO3. A soft gap of kinetic origin develops in the defect band and survives defect disorder for e -e interaction strengths comparable to the defect potential and hopping integral values above a doping dependent threshold; otherwise only a pseudogap persists. These two regimes naturally emerge in the statistical distribution of gaps among different defect realizations, which turns out to be of Weibull type. Its shape parameter k determines the exponent of the power-law dependence of the density of states at the chemical potential (k -1 ) and hence distinguishes between the soft gap (k ≥2 ) and the pseudogap (k <2 ) regimes. Both k and the effective gap scale with the hopping integral and the e -e interaction in a wide doping range. The motion of doped holes is confined by the closest defect potential and the overall spin-orbital structure. Such a generic behavior leads to complex nonhydrogenlike defect states that tend to preserve the underlying C -type spin and G -type orbital order and can be detected and analyzed via scanning tunneling microscopy.

  10. Direct probe of Mott-Hubbard to charge-transfer insulator transition and electronic structure evolution in transition-metal systems

    SciTech Connect

    Olalde-Velasco, P; Jimenez-Mier, J; Denlinger, JD; Hussain, Z; Yang, WL

    2011-07-11

    We report the most direct experimental verification of Mott-Hubbard and charge-transfer insulators through x-ray emission spectroscopy in transition-metal (TM) fluorides. The p-d hybridization features in the spectra allow a straightforward energy alignment of the anion-2p and metal-3d valence states, which visually shows the difference between the two types of insulators. Furthermore, in parallel with the theoretical Zaanen-Sawatzky-Allen diagram, a complete experimental systematics of the 3d Coulomb interaction and the 2p-3d charge-transfer energy is reported and could serve as a universal experimental trend for other TM systems including oxides.

  11. Fractional Mott insulator-to-superfluid transition of Bose-Hubbard model in a trimerized Kagomé optical lattice

    NASA Astrophysics Data System (ADS)

    Chen, Qi-Hui; Li, Peng; Su, Haibin

    2016-06-01

    By generalizing the traditional single-site strong coupling expansion approach to a cluster one, we study the zero-temperature phase diagram of bosonic atoms in a trimerized Kagomé optical lattice. Some new features are present in this system. Due to the strong intra-trimer hopping interaction, there will be a new Mott insulator (MI), which is by definition incompressible but with a fractional filling per trimer. This is different from the traditional MI, which has an integral filling and originates only from the repulsive interaction between particles. We investigate the MI-to-superfluid transition and the nature of the fractional MI by calculating the critical exponents of phase transitions and the low-lying energy excitation spectra of quasiparticles (quasihole). We will show how the low-energy properties of this system can be understood qualitatively as a Bose-Hubbard model in triangular lattice from the point of view of the cluster strong coupling expansion. We also discuss how our results are related to experiment by studying the Bragg spectroscopy.

  12. Fractional Mott insulator-to-superfluid transition of Bose–Hubbard model in a trimerized Kagomé optical lattice

    NASA Astrophysics Data System (ADS)

    Chen, Qi-Hui; Li, Peng; Su, Haibin

    2016-06-01

    By generalizing the traditional single-site strong coupling expansion approach to a cluster one, we study the zero-temperature phase diagram of bosonic atoms in a trimerized Kagomé optical lattice. Some new features are present in this system. Due to the strong intra-trimer hopping interaction, there will be a new Mott insulator (MI), which is by definition incompressible but with a fractional filling per trimer. This is different from the traditional MI, which has an integral filling and originates only from the repulsive interaction between particles. We investigate the MI-to-superfluid transition and the nature of the fractional MI by calculating the critical exponents of phase transitions and the low-lying energy excitation spectra of quasiparticles (quasihole). We will show how the low-energy properties of this system can be understood qualitatively as a Bose–Hubbard model in triangular lattice from the point of view of the cluster strong coupling expansion. We also discuss how our results are related to experiment by studying the Bragg spectroscopy.

  13. Magnetic properties in the Mott-insulating iron oxychalcogenides La2 O 2 Fe 2 OSe 2

    NASA Astrophysics Data System (ADS)

    Zhu, Jian-Xin; Yu, Rong; Si, Qimiao

    2011-03-01

    The role of electron correlation and magnetism in high-temperature superconductivity of the iron pnictides has been a topic of discussion. It has also motivated interest to compare related compounds with the iron pnictides and chalcogenides. Recently both electronic structure calculations and experimental measurements have indicated that the iron oxychalcogenides La 2 O2 Fe 2 OSe 2 , which contains an Fe square lattice with an enlarged unit cell, has a larger U/t and is a Mott insulator. We focus here on the understanding of the magnetism of this system. Within the density functional theory, we consider the magnetic phase diagram. Using an effective frustrating spin-exchange model in a doubled checker-board lattice, we study the magnetic excitation spectrum. Our theoretical results are compared with the emerging elastic and inelastic neutron scattering data in this compound. This work was supported by the NNSA of the U.S. DOE at LANL under Contract No. DE-AC52-06NA25396 (J.X.Z), the NSF Grant No. DMR-0706625, the Robert A. Welch Foundation Grant No. C-1411, and the W. M. Keck Foundation (R.Y. and Q.S.).

  14. 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

  15. Pressure-dependent relaxation in the photoexcited mott insulator ET-F2TCNQ: influence of hopping and correlations on quasiparticle recombination rates.

    PubMed

    Mitrano, M; Cotugno, G; Clark, S R; Singla, R; Kaiser, S; Stähler, J; Beyer, R; Dressel, M; Baldassarre, L; Nicoletti, D; Perucchi, A; Hasegawa, T; Okamoto, H; Jaksch, D; Cavalleri, A

    2014-03-21

    We measure the ultrafast recombination of photoexcited quasiparticles (holon-doublon pairs) in the one dimensional Mott insulator ET-F(2)TCNQ as a function of external pressure, which is used to tune the electronic structure. At each pressure value, we first fit the static optical properties and extract the electronic bandwidth t and the intersite correlation energy V. We then measure the recombination times as a function of pressure, and we correlate them with the corresponding microscopic parameters. We find that the recombination times scale differently than for metals and semiconductors. A fit to our data based on the time-dependent extended Hubbard Hamiltonian suggests that the competition between local recombination and delocalization of the Mott-Hubbard exciton dictates the efficiency of the recombination.

  16. Nonlocal Order Parameters for the 1D Hubbard Model

    NASA Astrophysics Data System (ADS)

    Montorsi, Arianna; Roncaglia, Marco

    2012-12-01

    We characterize the Mott-insulator and Luther-Emery phases of the 1D Hubbard model through correlators that measure the parity of spin and charge strings along the chain. These nonlocal quantities order in the corresponding gapped phases and vanish at the critical point Uc=0, thus configuring as hidden order parameters. The Mott insulator consists of bound doublon-holon pairs, which in the Luther-Emery phase turn into electron pairs with opposite spins, both unbinding at Uc. The behavior of the parity correlators is captured by an effective free spinless fermion model.

  17. Pressure-induced electronic and magnetic phase transitions in a Mott insulator: Ti-doped C a3R u2O7 bilayer ruthenate

    NASA Astrophysics Data System (ADS)

    Zou, T.; Cao, H. B.; Liu, G. Q.; Peng, J.; Gottschalk, M.; Zhu, M.; Zhao, Y.; Leão, J. B.; Tian, W.; Mao, Z. Q.; Ke, X.

    2016-07-01

    We report the hydrostatic pressure-induced electronic and magnetic phase transitions in a Mott insulator, a bilayer ruthenate C a3(Ru0.97Ti0.03 ) 2O7 , via electronic transport and single crystal neutron diffraction measurements. The system undergoes an insulator-metal transition at a very small hydrostatic pressure ≈0.04 GPa, followed by a magnetic phase transition around 0.3 GPa, suggesting that the low energy charge fluctuation and magnetic ordering couple to the pressure separately in this compound. The a b initio calculations show that the suppressed Ru O6 flattening induced by the pressure reduces the orbital polarization and gives rise to an insulator-metal transition preceding the magnetic phase transition.

  18. 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.

  19. 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. PMID:27159018

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

    DOE PAGES

    Dean, M. P. M.; Cao, Y.; Liu, X.; Wall, S.; Zhu, D.; Mankowsky, R.; Thampy, V.; Chen, X. M.; Vale, J. G.; Casa, D.; et al

    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 superconductivity1, 2, 3, 4. Recently, photo-excitation has been used to induce similarly exotic states transiently5, 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 Sr2IrO4. We find that the non-equilibrium state, 2 ps after the excitation,more » 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

  1. A new route to the Mott-Hubbard metal-insulator transition: Strong correlations effects in Pr0.7Ca0.3MnO3

    PubMed Central

    Lee, Hong Sub; Choi, Sun Gyu; Park, Hyung-Ho; Rozenberg, M. J.

    2013-01-01

    Resistive random access memory based on the resistive switching phenomenon is emerging as a strong candidate for next generation non-volatile memory. So far, the resistive switching effect has been observed in many transition metal oxides, including strongly correlated ones, such as, cuprate superconductors, colossal magnetoresistant manganites and Mott insulators. However, up to now, no clear evidence of the possible relevance of strong correlation effects in the mechanism of resistive switching has been reported. Here, we study Pr0.7Ca0.3MnO3, which shows bipolar resistive switching. Performing micro-spectroscopic studies on its bare surface we are able to track the systematic electronic structure changes in both, the low and high resistance state. We find that a large change in the electronic conductance is due to field-induced oxygen vacancies, which drives a Mott metal-insulator transition at the surface. Our study demonstrates that strong correlation effects may be incorporated to the realm of the emerging oxide electronics.

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

    NASA Astrophysics Data System (ADS)

    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.

  3. Angle Resolved Photoemission Spectroscopy Studies of the Mott Insulator to Superconductor Evolution in Ca2-xNaxCuO2Cl2

    SciTech Connect

    Shen, Kyle Michael

    2005-09-02

    It is widely believed that many of the exotic physical properties of the high-T{sub c} cuprate superconductors arise from the proximity of these materials to the strongly correlated, antiferromagnetic Mott insulating state. Therefore, one of the fundamental questions in the field of high-temperature superconductivity is to understand the insulator-to-superconductor transition and precisely how the electronic structure of Mott insulator evolves as the first holes are doped into the system. This dissertation presents high-resolution, doping dependent angle-resolved photoemission (ARPES) studies of the cuprate superconductor Ca{sub 2-x}Na{sub x}CuO{sub 2}Cl{sub 2}, spanning from the undoped parent Mott insulator to a high-temperature superconductor with a T{sub c} of 22 K. A phenomenological model is proposed to explain how the spectral lineshape, the quasiparticle band dispersion, and the chemical potential all progress with doping in a logical and self-consistent framework. This model is based on Franck-Condon broadening observed in polaronic systems where strong electron-boson interactions cause the quasiparticle residue, Z, to be vanishingly small. Comparisons of the low-lying states to different electronic states in the valence band strongly suggest that the coupling of the photohole to the lattice (i.e. lattice polaron formation) is the dominant broadening mechanism for the lower Hubbard band states. Combining this polaronic framework with high-resolution ARPES measurements finally provides a resolution to the long-standing controversy over the behavior of the chemical potential in the high-T{sub c} cuprates. This scenario arises from replacing the conventional Fermi liquid quasiparticle interpretation of the features in the Mott insulator by a Franck-Condon model, allowing the reassignment of the position of the quasiparticle pole. As a function of hole doping, the chemical potential shifts smoothly into the valence band while spectral weight is transferred

  4. Finite-temperature fluid-insulator transition of strongly interacting 1D disordered bosons.

    PubMed

    Michal, Vincent P; Aleiner, Igor L; Altshuler, Boris L; Shlyapnikov, Georgy V

    2016-08-01

    We consider the many-body localization-delocalization transition for strongly interacting one-dimensional disordered bosons and construct the full picture of finite temperature behavior of this system. This picture shows two insulator-fluid transitions at any finite temperature when varying the interaction strength. At weak interactions, an increase in the interaction strength leads to insulator [Formula: see text] fluid transition, and, for large interactions, there is a reentrance to the insulator regime. It is feasible to experimentally verify these predictions by tuning the interaction strength with the use of Feshbach or confinement-induced resonances, for example, in (7)Li or (39)K. PMID:27436894

  5. Strong lattice correlation of non-equilibrium quasiparticles in a pseudospin-1/2 Mott insulator Sr2IrO4

    DOE PAGES

    Li, Yuelin; Schaller, Richard D.; Zhu, Mengze; Walko, Donald A.; Kim, Jungho; Ke, Xianglin; Miao, Ludi; Mao, Z. Q.

    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 Sr2IrO4 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 Sr2IrO4 and cuprates to a new dimension ofmore » electron-phonon coupling which persists under highly non-equilibrium conditions.« less

  6. Strong lattice correlation of non-equilibrium quasiparticles in a pseudospin-1/2 Mott insulator Sr2IrO4

    PubMed Central

    Li, Yuelin; Schaller, Richard D.; Zhu, Mengze; Walko, Donald A.; Kim, Jungho; Ke, Xianglin; Miao, Ludi; Mao, Z. Q.

    2016-01-01

    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 Sr2IrO4 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. Due to the unique electronic configuration of the quasiparticles, the strong lattice correlation is unexpected but extends the similarity between Sr2IrO4 and cuprates to a new dimension of electron-phonon coupling which persists under highly non-equilibrium conditions. PMID:26787094

  7. Photoinduced switching to metallic states in the two-dimensional organic Mott insulator dimethylphenazine-tetrafluorotetracyanoquinodimethane with anisotropic molecular stacks

    NASA Astrophysics Data System (ADS)

    Matsuzaki, Hiroyuki; Ohkura, Masa-aki; Ishige, Yu; Nogami, Yoshio; Okamoto, Hiroshi

    2015-06-01

    A photoinduced phase transition was investigated in an organic charge-transfer (CT) complex M2P -TCNQ F4 , [M2P : 5,10-dihydro-5,10-dimethylphenazine, donor (D) molecule; TCNQ F4 : 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane, acceptor (A) molecule] by means of femtosecond pump-probe reflection spectroscopy. This is an ionic compound and has a peculiar two-dimensional (2D) molecular arrangement; the same A (or D) molecules arrange along the [100] direction, and A and D molecules alternately arrange along the [111] direction. It results in a strongly anisotropic two-dimensional electronic structure. This compound shows a structural and magnetic phase transition at 122 K below which the two neighboring molecules are dimerized along both the [100] and [111] directions. We demonstrate that two kinds of photoinduced phase transitions occur by irradiation of a femtosecond laser pulse; in the high-temperature lattice-uniform phase, a quasi-one-dimensional (1D) metallic state along the AA(DD) stack is generated, and in the low-temperature lattice-dimerized phase, a quasi-2D metallic state is initially produced and molecular dimerizations are subsequently released. Mixed-stack CT compounds consisting of DA stacks are generally insulators or semiconductors in the ground state. Here, such a dynamical metallization in the DA stack is demonstrated. The release of the dimerizations drives several kinds of coherent oscillations which play an important role in the stabilization of the lattice-dimerized phase. The mechanisms of those photoinduced phase transitions are discussed in terms of the magnitudes of the anisotropic bandwidths and molecular dimerizations along two different directions of the molecular stacks.

  8. 1-D Modes on Step-edges of the Putative Weak Topological Insulator BI2TeI

    NASA Astrophysics Data System (ADS)

    Avraham, Nurit; Norris, Andrew; Pan, Lin; Wu, Shu-Chun; Felser, Claudia; Yan, Binghai; Beidenkopf, Haim

    Weak topological insulators are layered materials that possess surfaces with an even number of Dirac cones and surfaces that are fully gapped. This inherent anisotropy provides them with unique properties such as sensitivity to the parity of the number of layers and absence of localization of their surface states. We use scanning tunneling microscopy to study the topological properties of stacked Bi2TeI, a promising candidate for weak topological insulator. We report the observation of the bulk energy gap on terraces perpendicular to the stacking direction and signatures of 1D intra-gap topological edge states along step-edges. The rich structure of quasi 2D terraces and Islands obtained on such cleaved Bi2TeI surfaces provides an excellent playground to explore some of the most fundamental concepts of TIs such as their Z2 classification, ``partner switching'' of Kramer's degenerate pairs, and helical modes along dislocation lines.

  9. Finite-temperature fluid–insulator transition of strongly interacting 1D disordered bosons

    NASA Astrophysics Data System (ADS)

    Michal, Vincent P.; Aleiner, Igor L.; Altshuler, Boris L.; Shlyapnikov, Georgy V.

    2016-08-01

    We consider the many-body localization–delocalization transition for strongly interacting one-dimensional disordered bosons and construct the full picture of finite temperature behavior of this system. This picture shows two insulator–fluid transitions at any finite temperature when varying the interaction strength. At weak interactions, an increase in the interaction strength leads to insulator → fluid transition, and, for large interactions, there is a reentrance to the insulator regime. It is feasible to experimentally verify these predictions by tuning the interaction strength with the use of Feshbach or confinement-induced resonances, for example, in 7Li or 39K.

  10. Nature of the magnetic correlations in photo-doped and chemically-doped spin-orbit Mott insulator Sr2IrO4

    NASA Astrophysics Data System (ADS)

    Dean, Mark P. M.

    In the iridates, competition between spin-orbit coupling, crystal field, and electronic correlation has lead to the observation of several novel states. Particularly notable is the spin-orbit Mott insulating state in Sr2IrO4 which has close analogies to the high temperature superconducting cuprates. This talk will describe the nature of the magnetic correlations in Sr2IrO4 and how the magnetic correlations can be modified by two different doping schemes. I will first describe doping via photo-excitation in which we use femtosecond infrared pulses to excite carriers across the Mott gap. After excitation, we probe the resulting magnetic state as a function of time delay using the first implementation of magnetic resonant inelastic X-ray scattering at a free electron laser. We find that the non-equilibrium state 2 ps after the excitation has strongly suppressed long-range magnetic order, but hosts photo-carriers that induce strong, non-thermal magnetic correlations. The magnetism recovers its two-dimensional in-plane Néel correlations on a timescale of a few ps, while the three-dimensional long range magnetic order is restored over a far longer, fluence-dependent timescale of a few 100 ps. In the second part of the talk I will describe chemical doping via Ir-Ru substitution. In this situation, we find that with increased Ru concentration, the dispersive magnetic excitations in the parent compound become almost momentum-independent, opening a magnetic gap > 150 meV. We attribute this gap to the combined effects of disorder and Ir-Ru interactions. Work performed at Brookhaven National Laboratory was supported by the US Department of Energy, Division of Materials Science, under Contract No. DE-AC02-98CH10886.

  11. Thermal Instability of Edge States in a 1D Topological Insulator

    NASA Astrophysics Data System (ADS)

    Viyuela, Oscar; Rivas, Angel; Martin-Delgado, Miguel Angel

    2013-03-01

    The stability of topological phases of matter, also known as topological orders, against thermal noise has provided several surprising results in the context of topological codes used in topological quantum information. However, very little is known about the behavior of a topological insulator (TI) subjected to the disturbing thermal effect of its surrounding environment. This is of great relevance if we want to address key questions such as the robustness of TIs to thermal noise, existence of thermalization processes, use of TIs as platforms for quantum computation, etc. In this work, we have studied the dynamical thermal effects on the protected edge states of a TI when it is considered as an open quantum system in interaction with a noisy environment at a certain temperature T. Let us recall that stable edge states are a defining signature of topological insulators. Outstandingly, we find that the usual protection of edge states against quantum perturbations and randomness is lost in the case of thermal effects, despite the fermion-boson interaction with the thermal environment respects chiral symmetry, which is the symmetry responsible for the protection (robustness) of the edge states in this TI. We are able to compute decay rates for practical implementations. PRB (2012) Phys. Rev. B 86, 155140 (2012)

  12. 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

  13. Emergence of superconductivity, valence bond order, and Mott insulators in Pd[(dmit)2] based organic salts.

    PubMed

    Rau, Jeffrey G; Kee, Hae-Young

    2011-02-01

    The EtMe(3)P and EtMe(3)Sb triangular organic salts are distinguished from other Pd[(dmit)(2)] based salts, as they display valence bond and no long-range order, respectively. Under pressure, a superconducting phase is revealed in EtMe(3)P near the boundary of valence bond order. We use slave-rotor theory with an enlarged unit cell to study competition between uniform and broken translational symmetry states, offering a theoretical framework capturing the superconducting, valence bond order, spin liquid, and metallic phases on an isotropic triangular lattice. Our finite temperature phase diagram manifests a remarkable resemblance to the phase diagram of the EtMe(3)P salt, where the reentrant transition of insulator-metal-insulator type can be explained by an entropy difference between the metal and U(1) spin liquid. We predict different temperature dependence of the specific heat between the spin liquid and metal.

  14. Quantitative mapping of phase coexistence in Mott-Peierls insulator during electronic and thermally driven phase transition.

    PubMed

    Madan, Himanshu; Jerry, Matthew; Pogrebnyakov, Alexej; Mayer, Theresa; Datta, Suman

    2015-02-24

    Quantitative impedance mapping of the spatially inhomogeneous insulator-to-metal transition (IMT) in vanadium dioxide (VO2) is performed with a lateral resolution of 50 nm through near-field scanning microwave microscopy (SMM) at 16 GHz. SMM is used to measure spatially resolved electronic properties of the phase coexistence in an unstrained VO2 film during the electrically as well as thermally induced IMT. A quantitative impedance map of both the electrically driven filamentary conduction and the thermally induced bulk transition is established. This was modeled as a 2-D heterogeneous resistive network where the distribution function of the IMT temperature across the sample is captured. Applying the resistive network model for the electrically induced IMT case, we reproduce the filamentary nature of electronically induced IMT, which elucidates a cascading avalanche effect triggered by the local electric field across nanoscale insulating and metallic domains.

  15. Emergence of superconductivity, valence bond order, and Mott insulators in Pd[(dmit)2] based organic salts.

    PubMed

    Rau, Jeffrey G; Kee, Hae-Young

    2011-02-01

    The EtMe(3)P and EtMe(3)Sb triangular organic salts are distinguished from other Pd[(dmit)(2)] based salts, as they display valence bond and no long-range order, respectively. Under pressure, a superconducting phase is revealed in EtMe(3)P near the boundary of valence bond order. We use slave-rotor theory with an enlarged unit cell to study competition between uniform and broken translational symmetry states, offering a theoretical framework capturing the superconducting, valence bond order, spin liquid, and metallic phases on an isotropic triangular lattice. Our finite temperature phase diagram manifests a remarkable resemblance to the phase diagram of the EtMe(3)P salt, where the reentrant transition of insulator-metal-insulator type can be explained by an entropy difference between the metal and U(1) spin liquid. We predict different temperature dependence of the specific heat between the spin liquid and metal. PMID:21405417

  16. Fate of Spinons at the Mott Point

    NASA Astrophysics Data System (ADS)

    Lee, Tsung-Han; Florens, Serge; Dobrosavljević, Vladimir

    2016-09-01

    Gapless spin liquids have recently been observed in several frustrated Mott insulators, with elementary spin excitations—"spinons"—reminiscent of degenerate Fermi systems. However, their precise role at the Mott point, where charge fluctuations begin to proliferate, remains controversial and ill understood. Here we present the simplest theoretical framework that treats the dynamics of emergent spin and charge excitations on the same footing, providing a new physical picture of the Mott metal-to-insulator transition at half filing. We identify a generic orthogonality mechanism leading to strong damping of spinons, arising as soon as the Mott gap closes. Our results indicate that spinons should not play a significant role within the high-temperature quantum critical regime above the Mott point—in striking agreement with all available experiments.

  17. Sudden slowing down of charge carrier dynamics at the Mott metal-insulator transition in kappa-(D{sub 8}-BEDT-TTF){sub 2}Cu[N(CN){sub 2}]Br.

    SciTech Connect

    Brandenburg, J.; Muller, J.; Schlueter, J. A.

    2012-02-01

    We investigate the dynamics of correlated charge carriers in the vicinity of the Mott metal-insulator (MI) transition in the quasi-two-dimensional organic charge-transfer salt {kappa}-(D{sub 8}-BEDT-TTF){sub 2}Cu[N(CN){sub 2}]Br by means of fluctuation (noise) spectroscopy. The observed 1/f-type fluctuations are quantitatively very well described by a phenomenological model based on the concept of non-exponential kinetics. The main result is a correlation-induced enhancement of the fluctuations accompanied by a substantial shift of spectral weight to low frequencies in the vicinity of the Mott critical endpoint. This sudden slowing down of the electron dynamics, observed here in a pure Mott system, may be a universal feature of MI transitions. Our findings are compatible with an electronic phase separation in the critical region of the phase diagram and offer an explanation for the not yet understood absence of effective mass enhancement when crossing the Mott transition.

  18. Mott transitions in the periodic Anderson model.

    PubMed

    Logan, David E; Galpin, Martin R; Mannouch, Jonathan

    2016-11-16

    The periodic Anderson model (PAM) is studied within the framework of dynamical mean-field theory, with particular emphasis on the interaction-driven Mott transition it contains, and on resultant Mott insulators of both Mott-Hubbard and charge-transfer type. The form of the PAM phase diagram is first deduced on general grounds using two exact results, over the full range of model parameters and including metallic, Mott, Kondo and band insulator phases. The effective low-energy model which describes the PAM in the vicinity of a Mott transition is then shown to be a one-band Hubbard model, with effective hoppings that are not in general solely nearest neighbour, but decay exponentially with distance. This mapping is shown to have a range of implications for the physics of the problem, from phase boundaries to single-particle dynamics; all of which are confirmed and supplemented by NRG calculations. Finally we consider the locally degenerate, non-Fermi liquid Mott insulator, to describe which requires a two-self-energy description. This is shown to yield a number of exact results for the associated local moment, charge, and interaction-renormalised levels, together with a generalisation of Luttinger's theorem to the Mott insulator.

  19. Mott transitions in the periodic Anderson model

    NASA Astrophysics Data System (ADS)

    Logan, David E.; Galpin, Martin R.; Mannouch, Jonathan

    2016-11-01

    The periodic Anderson model (PAM) is studied within the framework of dynamical mean-field theory, with particular emphasis on the interaction-driven Mott transition it contains, and on resultant Mott insulators of both Mott-Hubbard and charge-transfer type. The form of the PAM phase diagram is first deduced on general grounds using two exact results, over the full range of model parameters and including metallic, Mott, Kondo and band insulator phases. The effective low-energy model which describes the PAM in the vicinity of a Mott transition is then shown to be a one-band Hubbard model, with effective hoppings that are not in general solely nearest neighbour, but decay exponentially with distance. This mapping is shown to have a range of implications for the physics of the problem, from phase boundaries to single-particle dynamics; all of which are confirmed and supplemented by NRG calculations. Finally we consider the locally degenerate, non-Fermi liquid Mott insulator, to describe which requires a two-self-energy description. This is shown to yield a number of exact results for the associated local moment, charge, and interaction-renormalised levels, together with a generalisation of Luttinger’s theorem to the Mott insulator.

  20. Mott transitions in the periodic Anderson model.

    PubMed

    Logan, David E; Galpin, Martin R; Mannouch, Jonathan

    2016-11-16

    The periodic Anderson model (PAM) is studied within the framework of dynamical mean-field theory, with particular emphasis on the interaction-driven Mott transition it contains, and on resultant Mott insulators of both Mott-Hubbard and charge-transfer type. The form of the PAM phase diagram is first deduced on general grounds using two exact results, over the full range of model parameters and including metallic, Mott, Kondo and band insulator phases. The effective low-energy model which describes the PAM in the vicinity of a Mott transition is then shown to be a one-band Hubbard model, with effective hoppings that are not in general solely nearest neighbour, but decay exponentially with distance. This mapping is shown to have a range of implications for the physics of the problem, from phase boundaries to single-particle dynamics; all of which are confirmed and supplemented by NRG calculations. Finally we consider the locally degenerate, non-Fermi liquid Mott insulator, to describe which requires a two-self-energy description. This is shown to yield a number of exact results for the associated local moment, charge, and interaction-renormalised levels, together with a generalisation of Luttinger's theorem to the Mott insulator. PMID:27618214

  1. Dimensional decoupling at continuous quantum critical Mott transitions

    NASA Astrophysics Data System (ADS)

    Zou, Liujun; Senthil, T.

    2016-09-01

    For continuous Mott metal-insulator transitions in layered two-dimensional systems, we demonstrate the phenomenon of dimensional decoupling: the system behaves as a three-dimensional metal in the Fermi-liquid side but as a stack of decoupled two-dimensional layers in the Mott insulator. We show that the dimensional decoupling happens at the Mott quantum critical point itself. We derive the temperature dependence of the interlayer electric conductivity in various crossover regimes near such a continuous Mott transition, and discuss experimental implications.

  2. New method for the controlled creation of sub-15 nm aluminum nanowires to probe the 1D superconductor-insulator transition

    NASA Astrophysics Data System (ADS)

    Morgan-Wall, Tyler; Hughes, Hannah; Hartman, Nik; McQueen, Tyrell; Markovic, Nina

    2014-03-01

    We have developed a new method for the creation of sub-15 nm aluminum nanostructures using a sodium bicarbonate solution. Using PMMA masks patterned with e-beam lithography, we can controllably etch lithographically-produced nanostructures while measuring their resistances in-situ using a 4-probe measurement. This technique allows for precise control over the final resistance and thus can be used to create a wide variety of nanodevices. In particular, this technique allows for the creation of nanowires to probe the superconductor-insulator transition in 1D.

  3. Magnetic and orbital orders coupled to negative thermal expansion in Mott insulators, Ca2Ru1--xM xO4 (M = 3d transition metal ion)

    NASA Astrophysics Data System (ADS)

    Qi, Tongfei

    Ca2RuO4 is a structurally-driven Mott insulator with a metal-insulator (MI) transition at TMI = 357K, followed by a well-separated antiferromagnetic order at T N = 110 K. Slightly substituting Ru with a 3d transition metal ion M effectively shifts TMI and induces exotic magnetic behavior below TN. Moreover, M doping for Ru produces negative thermal expansion in Ca2Ru1-- xMxO4 (M = Cr, Mn, Fe or Cu); the lattice volume expands on cooling with a total volume expansion ratio, DeltaV/V, reaching as high as 1%. The onset of the negative thermal expansion closely tracks TMI and TN, sharply contrasting classic negative thermal expansion that shows no relevance to electronic properties. In addition, the observed negative thermal expansion occurs near room temperature and extends over a wide temperature interval. These findings underscores new physics driven by a complex interplay between orbital, spin and lattice degrees of freedom. These materials constitute a new class of Negative Thermal Expansion (NTE) materials with novel electronic and magnetic functions. KEYWORDS: Transition Metal Oxide, Ruthenate, Negative Thermal Expansion, Single crystal XRD, Invar Effect, Orbital Ordering, Magnetic Ordering, Jahn-Teller Effect.

  4. Tuning directional dependent metal–insulator transitions in quasi-1D quantum wires with spin–orbit density wave instability

    NASA Astrophysics Data System (ADS)

    Das, Tanmoy

    2016-07-01

    We study directional dependent band gap evolutions and metal–insulator transitions (MITs) in model quantum wire systems within the spin–orbit density wave (SODW) model. The evolution of MIT is studied as a function of varying anisotropy between the intra-wire hopping ({{t}\\parallel} ) and inter-wire hopping ({{t}\\bot} ) with Rashba spin–orbit coupling. We find that as long as the anisotropy ratio (β ={{t}\\bot}/{{t}\\parallel} ) remains below 0.5, and the Fermi surface nesting is tuned to {{\\mathbf{Q}}1}=≤ft(π,0\\right) , an exotic SODW induced MIT easily develops, with its critical interaction strength increasing with increasing anisotropy. As β \\to 1 (2D system), the nesting vector switches to {{\\mathbf{Q}}2}=≤ft(π,π \\right) , making this state again suitable for an isotropic MIT. Finally, we discuss various physical consequences and possible applications of the directional dependent MIT.

  5. Holography and Mottness: A Discrete Marriage

    NASA Astrophysics Data System (ADS)

    Phillips, Philip

    2012-02-01

    Gauge-gravity duality has allowed us to solve the physics of certain strongly coupled quantum mechanical systems using gravity. I will show how a space-time consisting of a charged black hole and a bulk Pauli coupling corresponds to a boundary theory with a dynamically generated gap (with no obvious symmetry breaking) and a massive rearrangement of the spectral weight as in classic Mott systems such as VO2. In this holographic set-up, the gap opens only when discrete scale invariance is present. This raises the possibility that the elusive symmetry that might be broken in Mott insulators, in general, might pertain to scale invariance. The relevance of this claim to recent theories of Mott systems that possess massless charged bosons is explored.

  6. Universality class of the mott transition.

    PubMed

    Abdel-Jawad, M; Kato, R; Watanabe, I; Tajima, N; Ishii, Y

    2015-03-13

    Pressure dependence of the conductivity and thermoelectric power is measured through the Mott transition in the layer organic conductor EtMe_{3}P[Pd(dmit)_{2}]_{2}. The critical behavior of the thermoelectric effect provides a clear and objective determination of the Mott-Hubbard transition during the isothermal pressure sweep. Above the critical end point, the metal-insulator crossing, determined by the thermoelectric effect minimum value, is not found to coincide with the maximum of the derivative of the conductivity as a function of pressure. We show that the critical exponents of the Mott-Hubbard transition fall within the Ising universality class regardless of the dimensionality of the system. PMID:25815951

  7. 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

  8. Unusual Mott transition in multiferroic PbCrO 3

    DOE PAGES

    Wang, Shanmin; Zhu, Jinlong; Zhang, Yi; Yu, Xiaohui; Zhang, Jianzhong; Wang, Wendan; Bai, Ligang; Qian, Jiang; Yin, Liang; Sullivan, Neil S.; et al

    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

  9. Unusual Mott transition in multiferroic PbCrO3.

    PubMed

    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

    2015-12-15

    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

  10. Nonequilibrium gap collapse near a first-order Mott transition

    NASA Astrophysics Data System (ADS)

    Sandri, Matteo; Fabrizio, Michele

    2015-03-01

    We study the nonequilibrium dynamics of a simple model for V2O3 that consists of a quarter-filled Hubbard model for two orbitals that are split by a weak crystal field. Peculiarities of this model are (1) a Mott insulator whose gap corresponds to transferring an electron from the occupied lower orbital to the empty upper one, rather than from the lower to the upper Hubbard subbands; (2) a Mott transition generically of first order even at zero temperature. We simulate by means of time-dependent Gutzwiller approximation the evolution within the insulating phase of an initial state endowed by a nonequilibrium population of electrons in the upper orbital and holes in the lower one. We find that the excess population may lead, above a threshold, to a gap collapse and drive the insulator into the metastable metallic phase within the coexistence region around the Mott transition. This result foresees a nonthermal pathway to revert a Mott insulator into a metal. Even though this physical scenario is uncovered in a very specific toy model, we argue it might apply to other Mott insulating materials that share similar features.

  11. Mixed Bose-Fermi Mott Phases and Phase Transitions

    NASA Astrophysics Data System (ADS)

    Altman, Ehud

    2012-02-01

    A recent experiment with an ultra-cold mixture of ^174Yb and ^173Yb atoms in an optical lattice [S. Sugawa e. al. Nature Physics 7, 642 (2011)] found a remarkable quantum phase that can be described as a mixed Mott insulator. Such a an incompressible state established at integer combined filling of the two species, must have residual low energy Fermionic degrees of freedom associated with relative motion of the two species. I will discuss the novel quantum states formed by the composite Fermions in the mixed Mott insulator as well as the unconventional phase transitions separating these states from the compressible Bose-Fermi mixture established at weak interactions. Finally I will propose to utilize the mixed Mott insulator as a quantum simulator for models of the doped Mott insulator relevant to high Tc superconductivity. The new approach, where the bosonic atoms play the role of doped holes offers significant advantages over direct simulation of the Hubbard model. In particular the mixed Mott plateau naturally provides a flat trap potential to the doped holes, while the hole doping is easily tuned by varying the relative fraction of the bosons.

  12. Photoheat-induced Schottky nanojunction and indirect Mott transition in VO2: photocurrent analysis

    NASA Astrophysics Data System (ADS)

    Kim, Hyun-Tak; Kim, Minjung; Sohn, Ahrum; Slusar, Tetiana; Seo, Giwan; Cheong, Hyeonsik; Kim, Dong-Wook

    2016-03-01

    In order to elucidate a mechanism of the insulator-to-metal transition (IMT) for a Mott insulator VO2 (3d 1), we present Schottky nanojunctions and the structural phase transition (SPT) by simultaneous nanolevel measurements of photocurrent and Raman scattering in microlevel devices. The Schottky nanojunction with the monoclinic metallic phase between the monoclinic insulating phases is formed by the photoheat-induced IMT not accompanied with the SPT. The temperature dependence of the Schottky junction reveals that the Mott insulator has an electronic structure of an indirect subband between the main Hubbard d bands. The IMT as reverse process of the Mott transition occurs by temperature-induced excitation of bound charges in the indirect semiconductor band, most likely formed by impurities such as oxygen deficiency. The metal band (3d 1) for the Mott insulator is screened (trapped) by the indirect band (impurities).

  13. Spectral functions in the 1D and 2D Bose Hubbard model

    NASA Astrophysics Data System (ADS)

    Ivancic, Robert; Duchon, Eric; Trivedi, Nandini

    2014-03-01

    We use state of the art numerical techniques including quantum Monte Carlo and maximum entropy methods to obtain the low energy excitation spectra in the superfluid and Mott-insulator phases of the Bose Hubbard model. These results are checked in 1D against Bethe Ansatz and tDMRG results and extended to 2D where such approaches are impossible. In the superfluid, we find linearly dispersing Bogoliubov sound modes as well as additional gapped modes broadened by interaction effects. In the Mott insulator, we find evidence for a finite gap and well defined quasiparticle excitations. We examine properties such as the excitation lifetime, density of states, and speed of sound as the system is tuned across the quantum phase transition that separates the superfluid and Mott states. These results provide an important theoretical framework for upcoming ultracold atom experiments in one and two dimensions. We acknowledge support from the NSF DMR-0907275 (R.I., E.D. and N.T.).

  14. Structural, magnetic, and electronic properties of GdTiO{sub 3} Mott insulator thin films grown by pulsed laser deposition

    SciTech Connect

    Grisolia, M. N.; Bruno, F. Y.; Sando, D.; Jacquet, E.; Barthélémy, A.; Bibes, M.; Zhao, H. J.; Chen, X. M.; Bellaiche, L.

    2014-10-27

    We report on the optimization process to synthesize epitaxial thin films of GdTiO{sub 3} on SrLaGaO{sub 4} substrates by pulsed laser deposition. Optimized films are free of impurity phases and are fully strained. They possess a magnetic Curie temperature T{sub C} = 31.8 K with a saturation magnetization of 4.2 μ{sub B} per formula unit at 10 K. Transport measurements reveal an insulating response, as expected. Optical spectroscopy indicates a band gap of ∼0.7 eV, comparable to the bulk value. Our work adds ferrimagnetic orthotitanates to the palette of perovskite materials for the design of emergent strongly correlated states at oxide interfaces using a versatile growth technique such as pulsed laser deposition.

  15. Electrolyte-gated charge transport in molecularly linked gold nanoparticle films: The transition from a Mott insulator to an exotic metal with strong electron-electron interactions

    NASA Astrophysics Data System (ADS)

    Tie, M.; Dhirani, A.-A.

    2016-09-01

    Strong electron-electron interactions experienced by electrons as they delocalize are widely believed to play a key role in a range of remarkable phenomena such as high Tc superconductivity, colossal magnetoresistance, and others. Strongly correlated electrons are often described by the Hubbard model, which is the simplest description of a correlated system and captures important gross features of phase diagrams of strongly correlated materials. However, open challenges in this field include experimentally mapping correlated electron phenomena beyond those captured by the Hubbard model, and extending the model accordingly. Here we use electrolyte gating to study a metal-insulator transition (MIT) in a new class of strongly correlated material, namely, nanostructured materials, using 1,4-butanedithiol-linked Au nanoparticle films (NPFs) as an example. Electrolyte gating provides a means for tuning the chemical potential of the materials over a wide range, without significantly modifying film morphology. On the insulating side of the transition, we observe Efros-Shklovskii variable range hopping and a soft Coulomb gap, evidencing the importance of Coulomb barriers. On the metallic side of the transition, we observe signatures of strong disorder mediated electron-electron correlations. Gating films near MIT also reveal a zero-bias conductance peak, which we attribute to a resonance at the Fermi level predicted by the Hubbard and Anderson impurity models when electrons delocalize and experience strong Coulomb electron-electron interactions. This study shows that by enabling large changes in carrier density, electrolyte gating of Au NPFs is a powerful means for tuning through the Hubbard MIT in NPFs. By revealing the range of behaviours that strongly correlated electrons can exhibit, this platform can guide the development of an improved understanding of correlated materials.

  16. Electrolyte-gated charge transport in molecularly linked gold nanoparticle films: The transition from a Mott insulator to an exotic metal with strong electron-electron interactions.

    PubMed

    Tie, M; Dhirani, A-A

    2016-09-14

    Strong electron-electron interactions experienced by electrons as they delocalize are widely believed to play a key role in a range of remarkable phenomena such as high Tc superconductivity, colossal magnetoresistance, and others. Strongly correlated electrons are often described by the Hubbard model, which is the simplest description of a correlated system and captures important gross features of phase diagrams of strongly correlated materials. However, open challenges in this field include experimentally mapping correlated electron phenomena beyond those captured by the Hubbard model, and extending the model accordingly. Here we use electrolyte gating to study a metal-insulator transition (MIT) in a new class of strongly correlated material, namely, nanostructured materials, using 1,4-butanedithiol-linked Au nanoparticle films (NPFs) as an example. Electrolyte gating provides a means for tuning the chemical potential of the materials over a wide range, without significantly modifying film morphology. On the insulating side of the transition, we observe Efros-Shklovskii variable range hopping and a soft Coulomb gap, evidencing the importance of Coulomb barriers. On the metallic side of the transition, we observe signatures of strong disorder mediated electron-electron correlations. Gating films near MIT also reveal a zero-bias conductance peak, which we attribute to a resonance at the Fermi level predicted by the Hubbard and Anderson impurity models when electrons delocalize and experience strong Coulomb electron-electron interactions. This study shows that by enabling large changes in carrier density, electrolyte gating of Au NPFs is a powerful means for tuning through the Hubbard MIT in NPFs. By revealing the range of behaviours that strongly correlated electrons can exhibit, this platform can guide the development of an improved understanding of correlated materials. PMID:27634270

  17. 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…

  18. Bose and Mott glass phases in dimerized quantum antiferromagnets

    NASA Astrophysics Data System (ADS)

    Thomson, S. J.; Krüger, F.

    2015-11-01

    We examine the effects of disorder on dimerized quantum antiferromagnets in a magnetic field, using the mapping to a lattice gas of hard-core bosons with finite-range interactions. Combining a strong-coupling expansion, the replica method, and a one-loop renormalization-group analysis, we investigate the nature of the glass phases formed. We find that away from the tips of the Mott lobes, the transition is from a Mott insulator to a compressible Bose glass, however the compressibility at the tips is strongly suppressed. We identify this finding with the presence of a rare Mott glass phase and demonstrate that the inclusion of replica symmetry breaking is vital to correctly describe the glassy phases. This result suggests that the formation of Bose and Mott glass phases is not simply a weak localization phenomenon but is indicative of much richer physics. We discuss our results in the context of both ultracold atomic gases and spin-dimer materials.

  19. 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.

  20. Superfluid--Insulator Transition in Commensurate One-Dimensional Bosonic System with Off-Diagonal Disorder

    NASA Astrophysics Data System (ADS)

    Balabanyan, Karén; Prokof'ev, Nikolay; Svistunov, Boris

    2005-03-01

    We analyze the superfluid--insulator transition in a system of one-dimensional (1D) lattice bosons with off-diagonal disorder in the limit of large commensurate filling. We argue---in contrast to the recent prediction (E. Altman, Y. Kafri, A. Polkovnikov, and G. Refael, cond-mat/0402177) of strong- randomness fixed point for this system---that at any strength of disorder the universality class of the transition on the superfluid side coincides with that of the superfluid--Mott- insulator transition in a pure system. We present results of Monte Carlo simulations for two strongly disordered models that are in excellent agreement with the advocated scenario.

  1. Drude and Superconducting Weights and Mott Transitions in Variation Theory

    NASA Astrophysics Data System (ADS)

    Tamura, Shun; Yokoyama, Hisatoshi

    2015-06-01

    The Drude weight (D) is a useful measure for distinguishing a metal from an insulator. However, D has not been justifiably estimated using variation theory for a long time, since Millis and Coppersmith [Phys. Rev. B 43, 13770 (1991)] pointed out that the variational wave function ΨQ, which includes the key ingredient (doublon-holon binding effect) for a Mott transition, yields a positive D (namely, metallic) even in the Mott insulating regime. We argue that, to obtain a correct D, an imaginary part must exist in the wave function. By introducing a configuration-dependent phase factor Pθ to ΨQ, Mott transitions are successfully represented by D (D = 0 for U > Uc) for normal and d-wave pairing states; thus, the problem of Millis and Coppersmith is solved. Generally, Pθ plays a pivotal role in describing current-carrying states in the regime of Mott physics. On the other hand, we show using perturbation theory that the one-body (mean-field) part of the wave function should be complex for band insulators such as antiferromagnetic states in hypercubic lattices.

  2. Unusual Mott transition in multiferroic PbCrO 3

    SciTech Connect

    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

    2015-11-24

    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. 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 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.

  3. 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.

  4. Influence of spinons fluctuations near the spin liquid Mott transition

    NASA Astrophysics Data System (ADS)

    Lee, Tsung-Han; Florens, Serge; Dobrosavljevic, Vladimir

    We investigate the metal to Mott-insulator transition (MIT) in the Hubbard-Heisenberg model using the slave-rotor technique, which allows to combine for the first time the dynamical mean field theory (DMFT) with the Resonating Valence Bond (RVB) approach. In the spin-liquid phase at large Coulomb repulsion, the system shows a RVB transition from a trivial paramagnetic Mott insulator towards a low temperature insulating state with long lived spinons, as seen by the emergence of a linear specific heat. This quenching of the entropy in the spin liquid phase provides strong modifications in the shape of the standard DMFT phase diagram for the MIT occurring at intermediate values of the Coulomb repulsion. We find that the RVB transition happens concomitantly with the first order MIT lines at low temperature. This implies that the Mott insulator always accommodates a spinon Fermi surface, even in the coexistence regime of the MIT, and that the metallic state always stays a Fermi-liquid as it rejects the presence of free spinons, due to their strong scattering onto the holons.

  5. Random Field Driven Spatial Complexity at the Mott Transition in VO2

    NASA Astrophysics Data System (ADS)

    Carlson, Erica; Liu, Shuo; Phillabaum, Benjamin; Dahmen, Karin; Vidhyadhiraja, Narsimhamurthy; Qazilbash, Mumtaz; Basov, Dimitri

    We report the first application of critical cluster techniques to the Mott metal-insulator transition in vanadium dioxide. We show that the geometric properties of the metallic and insulating puddles observed by scanning near-field infrared microscopy are consistent with the system passing near criticality of the random field Ising model as temperature is varied. The resulting large barriers to equilibrium may be the source of the unusually robust hysteresis phenomena associated with the metal-insulator transition in this system.

  6. Mott Physics in lightly doped (Sr1-xLax)3Ir2O7

    NASA Astrophysics Data System (ADS)

    Affeldt, Gregory; Hogan, Tom; Smallwood, Christopher; Das, Tanmoy; Denlinger, Jonathan; Mo, Sung-Kwan; Wilson, Stephen; Lanzara, Alessandra

    The layered perovskite iridates Sr2IrO4 and Sr3Ir2O7 exhibit a spin-orbit Mott insulating state that becomes metallic upon sufficient carrier doping. While Sr2IrO4 presents striking similarities to cuprates upon electron doping, Sr3Ir2O7 appears to be a correlated metal. We show a detailed doping and temperature-dependent ARPES study which reveals important similarities between (Sr1-xLax)3Ir2O7 and doped Sr2IrO4, as well as other doped Mott insulators.

  7. Characteristics of a Mott field-effect transistor (MottFET) based on La1-xSrxMnO3

    NASA Astrophysics Data System (ADS)

    Lee, Suyoun; Lee, Keundong; Gwon, Hyojin; Baek, Seung-Hyub; Park, Baeho; Kim, Jin-Sang

    2013-03-01

    Recently, the metal-insulator transition (MIT) phenomenon shown in transition metal oxides has attracted much interest due to its superior characteristics such as fast switching speed (~ femtoseconds), high on/off ratio, and low power consumption. One example is the MottFET, which utilizes the MIT modulated by electric field through the band-filling in a Mott insulator. In this work, we examined MottFET devices based on La1-xSrxMnO3(LSMO), which is one of the mostly studied Mott insulators and attractive for the potential application in spintronic devices due to its intriguing properties such as colossal magnetoresistance (CMR) and half-metallicity. For the devices with the composition near the boundary of the metal-insulator transition, we confirmed that the conductivity of the channel could be modulated by a gate electric field of moderate strength. In addition, for the future application in spintronic devices, we investigated the dependence of device characteristics on the magnetic field. As the applied magnetic field increased, we found that the current-voltage characteristic showed anomalous behavior, which might be attributed to the electron-electron interaction, spin ordering, and the magnetic impurities in the channel. This work was supported by KIST Grant 2E22731 from Ministry of Educational Science and Technology.

  8. Doping induced Mott transition in the two dimensional Hubbard model

    NASA Astrophysics Data System (ADS)

    Sordi, Giovanni; Tremblay, A.-M. S.

    2010-03-01

    The description of the Mott transition by single-site dynamical mean-field theory is exact in infinite dimensions but, in two dimensions, substantial deviations from those results have been found for the interaction driven transition [1]. In addition, the experimentally relevant transition for layered systems such as the high-Tc cuprates is doping driven. We thus study this transition in the two dimensional Hubbard model on the square lattice using cluster dynamical mean-field theory with continuous-time quantum Monte Carlo in the hybridization expansion [2]. We find that the Mott transition is strongly influenced by the inclusion of short-range antiferromagnetic correlations. Doping of the Mott insulating state occurs gradually in the different momentum sectors, as found in previous studies [3], but in addition we find a first order transition between an incoherent metal and an insulator or between two incoherent metals, depending on interaction strength. Short range spin correlations create a pseudogap in a doping range that increases with interaction. [1] H. Park et al., PRL 101, 186403 (2008) [2] K. Haule, PRB 75, 155113 (2007) [3] E. Gull et al., arXiv:0909.1795 (2009)

  9. Fractional quantum Hall states in the vicinity of Mott plateaus

    SciTech Connect

    Umucalilar, R. O.; Mueller, Erich J.

    2010-05-15

    We perform variational Monte Carlo calculations to show that bosons in a rotating optical lattice will form analogs of fractional quantum Hall states when the tunneling is sufficiently weak compared to the interactions, and the deviation of density from an integer is commensurate with the effective magnetic field. We compare the energies of superfluid and correlated states to one another and to the energies found in full configuration-interaction calculations on small systems. We look at overlaps between our variational states and the exact ground state, characterizing the ways in which fractional quantum Hall effect correlations manifest themselves near the Mott insulating state. We explore the experimental signatures of these states.

  10. Pressure-Induced Mott Transition Followed by a 24-K Superconducting Phase in BaFe2S3

    NASA Astrophysics Data System (ADS)

    Yamauchi, Touru; Hirata, Yasuyuki; Ueda, Yutaka; Ohgushi, Kenya

    2015-12-01

    We performed high-pressure study for a Mott insulator BaFe2S3 , by measuring dc resistivity and ac susceptibility up to 15 GPa. We found that the antiferromagnetic insulating state at the ambient pressure is transformed into a metallic state at the critical pressure, Pc=10 GPa , and the superconductivity with the optimum Tc=24 K emerges above Pc. Furthermore, we found that the metal-insulator transition (Mott transition) boundary terminates at a critical point around 10 GPa and 75 K. The obtained pressure-temperature (P -T ) phase diagram is similar to those of the organic and fullerene compounds; namely, BaFe2S3 is the first inorganic superconductor in the vicinity of bandwidth control type Mott transition.

  11. A scalable neuristor built with Mott memristors.

    PubMed

    Pickett, Matthew D; Medeiros-Ribeiro, Gilberto; Williams, R Stanley

    2013-02-01

    The Hodgkin-Huxley model for action potential generation in biological axons is central for understanding the computational capability of the nervous system and emulating its functionality. Owing to the historical success of silicon complementary metal-oxide-semiconductors, spike-based computing is primarily confined to software simulations and specialized analogue metal-oxide-semiconductor field-effect transistor circuits. However, there is interest in constructing physical systems that emulate biological functionality more directly, with the goal of improving efficiency and scale. The neuristor was proposed as an electronic device with properties similar to the Hodgkin-Huxley axon, but previous implementations were not scalable. Here we demonstrate a neuristor built using two nanoscale Mott memristors, dynamical devices that exhibit transient memory and negative differential resistance arising from an insulating-to-conducting phase transition driven by Joule heating. This neuristor exhibits the important neural functions of all-or-nothing spiking with signal gain and diverse periodic spiking, using materials and structures that are amenable to extremely high-density integration with or without silicon transistors. PMID:23241533

  12. A scalable neuristor built with Mott memristors

    NASA Astrophysics Data System (ADS)

    Pickett, Matthew D.; Medeiros-Ribeiro, Gilberto; Williams, R. Stanley

    2013-02-01

    The Hodgkin-Huxley model for action potential generation in biological axons is central for understanding the computational capability of the nervous system and emulating its functionality. Owing to the historical success of silicon complementary metal-oxide-semiconductors, spike-based computing is primarily confined to software simulations and specialized analogue metal-oxide-semiconductor field-effect transistor circuits. However, there is interest in constructing physical systems that emulate biological functionality more directly, with the goal of improving efficiency and scale. The neuristor was proposed as an electronic device with properties similar to the Hodgkin-Huxley axon, but previous implementations were not scalable. Here we demonstrate a neuristor built using two nanoscale Mott memristors, dynamical devices that exhibit transient memory and negative differential resistance arising from an insulating-to-conducting phase transition driven by Joule heating. This neuristor exhibits the important neural functions of all-or-nothing spiking with signal gain and diverse periodic spiking, using materials and structures that are amenable to extremely high-density integration with or without silicon transistors.

  13. Random Field Driven Spatial Complexity at the Mott Transition in VO2

    NASA Astrophysics Data System (ADS)

    Liu, Shuo; Phillabaum, B.; Carlson, E. W.; Dahmen, K. A.; Vidhyadhiraja, N. S.; Qazilbash, M. M.; Basov, D. N.

    2016-01-01

    We report the first application of critical cluster techniques to the Mott metal-insulator transition in vanadium dioxide. We show that the geometric universal properties of the metallic and insulating puddles observed by scanning near-field infrared microscopy are consistent with the system passing near criticality of the random field Ising model as temperature is varied. The resulting large barriers to equilibrium may be the source of the unusually robust hysteresis phenomena associated with the metal-insulator transition in this system.

  14. Concept of a multichannel spin-resolving electron analyzer based on Mott scattering

    PubMed Central

    Strocov, Vladimir N.; Petrov, Vladimir N.; Dil, J. Hugo

    2015-01-01

    The concept of a multichannel electron spin detector based on optical imaging principles and Mott scattering (iMott) is presented. A multichannel electron image produced by a standard angle-resolving (photo) electron analyzer or microscope is re-imaged by an electrostatic lens at an accelerating voltage of 40 kV onto the Au target. Quasi-elastic electrons bearing spin asymmetry of the Mott scattering are imaged by magnetic lenses onto position-sensitive electron CCDs whose differential signals yield the multichannel spin asymmetry image. Fundamental advantages of this concept include acceptance of inherently divergent electron sources from the electron analyzer or microscope focal plane as well as small aberrations achieved by virtue of high accelerating voltages, as demonstrated by extensive ray-tracing analysis. The efficiency gain compared with the single-channel Mott detector can be a factor of more than 104 which opens new prospects of spin-resolved spectroscopies in application not only to standard bulk and surface systems (Rashba effect, topological insulators, etc.) but also to buried heterostructures. The simultaneous spin detection combined with fast CCD readout enables efficient use of the iMott detectors at X-ray free-electron laser facilities. PMID:25931087

  15. Experimental consequences of Mottness in high-temperature copper-oxide superconductors

    NASA Astrophysics Data System (ADS)

    Chakraborty, Shiladitya

    It has been more than two decades since the copper-oxide high temperature superconductors were discovered. However, building a satisfactory theoretical framework to study these compounds still remains one of the major challenges in condensed matter physics. In addition to the mechanism of superconductivity, understanding the properties of the normal state is a major puzzle in itself. As these materials are doped Mott insulators, the interaction between electrons is particularly strong. The strong electron correlations are responsible for the breakdown of Fermi-liquid behavior in the normal state. A variety of experimental probes reveal anomalous features in these materials. Such anomalies are reflected in the photoemission spectra as well as transport coefficients such as resistivity, optical conductivity, Hall coefficient, thermoelectric power etc. The objective of this dissertation is to understand the anomalous features as universal features of doped Mott insulators arising entirely as a consequence of strong electron correlations, using the two-dimensional square lattice Hubbard model as the model Hamiltonian. This dissertation is organized into eight chapters. Chapter 1 is an introductory chapter that discusses some key issues. A brief introduction to the superconducting cuprates and their anomalous physical properties is given. Also included is an outline on Mott insulators and the concept of Mottness. Chapter 2 contains a discussion on Cluster Dynamical Mean Field Theory (CDMFT), the principal numerical technique to be implemented in this dissertation. Chapter 3 describes the exact low-energy theory of doped Mott insulators, which largely provides a theoretical framework to this dissertation. In Chapter 4, we compute the spectral function of the two-dimensional Hubbard model using CDMFT and study the origin of the kink feature observed in the electron dispersion measured by ARPES (Angle Resolved Photoemission Spectroscopy). In Chapter 5, the origin of the

  16. Extended dynamic Mott transition in the two-band Hubbard model out of equilibrium

    NASA Astrophysics Data System (ADS)

    Behrmann, Malte; Fabrizio, Michele; Lechermann, Frank

    2013-07-01

    We reformulate the time-dependent Gutzwiller approximation by M. Schiró and M. Fabrizio, [Phys. Rev. Lett.PRLTAO0031-900710.1103/PhysRevLett.105.076401 105, 076401 (2010)] in the framework of slave-boson mean-field theory, which is used to investigate the dynamical Mott transition of the generic two-band Hubbard model at half filling upon an interaction quench. Interorbital fluctuations lead to notable changes with respect to the single-band case. The singular dynamical transition is replaced by a broad regime of long-lived fluctuations between metallic and insulating states, accompanied by intriguing precursor behavior. A mapping to a spin model proves helpful to analyze the different regions in terms of the evolution of an Ising-like order parameter. Contrary to the static case, singlet occupations remain vital in the Mott-insulating regime with finite Hund's exchange.

  17. Mott physics and spin fluctuations: A functional viewpoint

    NASA Astrophysics Data System (ADS)

    Ayral, Thomas; Parcollet, Olivier

    2016-06-01

    We present a formalism for strongly correlated systems with fermions coupled to bosonic modes. We construct the three-particle irreducible functional K by successive Legendre transformations of the free energy of the system. We derive a closed set of equations for the fermionic and bosonic self-energies for a given K . We then introduce a local approximation for K , which extends the idea of dynamical mean-field theory (DMFT) approaches from two- to three-particle irreducibility. This approximation entails the locality of the three-leg electron-boson vertex Λ (i ω ,i Ω ) , which is self-consistently computed using a quantum impurity model with dynamical charge and spin interactions. This local vertex is used to construct frequency- and momentum-dependent electronic self-energies and polarizations. By construction, the method interpolates between the spin-fluctuation or G W approximations at weak coupling and the atomic limit at strong coupling. We apply it to the Hubbard model on two-dimensional square and triangular lattices. We complement the results of [T. Ayral and O. Parcollet, Phys. Rev. B 92, 115109 (2015), 10.1103/PhysRevB.92.115109] by (i) showing that, at half-filling, as DMFT, the method describes the Fermi-liquid metallic state and the Mott insulator, separated by a first-order interaction-driven Mott transition at low temperatures, (ii) investigating the influence of frustration, and (iii) discussing the influence of the bosonic decoupling channel.

  18. Mott Insulating Ground State on a Triangular Surface Lattice

    SciTech Connect

    Weitering, H.; Shi, X.; Weitering, H.; Johnson, P.; Chen, J.; DiNardo, N.; DiNardo, N.; Kempa, K.

    1997-02-01

    Momentum-resolved direct and inverse photoemission spectra of the K/Si(111)-({radical}(3){times}{radical}(3))R30{degree}-B interface reveals the presence of strongly localized surface states. The K overlayer remains nonmetallic up to the saturation coverage. This system most likely presents the first experimental realization of a frustrated spin 1/2 Heisenberg antiferromagnet on a two-dimensional triangular lattice. {copyright} {ital 1997} {ital The American Physical Society}

  19. Large Seebeck coefficient in frustrated doped Mott insulators

    NASA Astrophysics Data System (ADS)

    Arsenault, Louis-François; Shastry, B. Sriram; Sémon, Patrick; Tremblay, André-Marie

    2011-03-01

    Since calculations based on the standard Kubo formula have proven extremely difficult for electric and thermal transport, Shastry and co-workers suggested two novel approximate ways to obtain the thermopower (S) in interacting systems. One method is based on the high-frequency limit. The other, based on ideas of Kelvin, is purely thermodynamical. With these we study the Hubbard model on a 3d FCC lattice, a frustrated lattice. The high dimensionality of the problem justifies the use of dynamical mean field theory (DMFT). CTQMC in the hybridization expansion and the fast IPT are the impurity solver. The Seebeck coefficient is obtained as a function of doping and temperature for different U. Within DMFT, vertex corrections vanish for transports coefficients, hence the bubble suffices. This enables us to further assess how both approximate methods compare with each other and with the DC Kubo approach. At low T, results can be interpreted in terms of effective Fermi temperatures and carrier number.

  20. Orbital-selective Mott phase of Cu-substituted iron-based superconductors

    NASA Astrophysics Data System (ADS)

    Liu, Yang; Zhao, Yang-Yang; Song, Yun

    2016-07-01

    We study the phase transition in Cu-substituted iron-based superconductors with a new developed real-space Green’s function method. We find that Cu substitution has strong effect on the orbital-selective Mott transition introduced by the Hund’s rule coupling. The redistribution of the orbital occupancy which is caused by the increase of the Hund’s rule coupling, gives rise to the Mott-Hubbard metal-insulator transition in the half-filled d xy orbital. We also find that more and more electronic states appear inside that Mott gap of the d xy orbital with the increase of Cu substitution, and the in-gap states around the Fermi level are strongly localized at some specific lattice sites. Further, a distinctive phase diagram, obtained for the Cu-substituted Fe-based superconductors, displays an orbital-selective insulating phase, as a result of the cooperative effect of the Hund’s rule coupling and the impurity-induced disorder.

  1. Three-dimensional dynamics of a fermionic Mott wedding-cake in clean and disordered optical lattices

    PubMed Central

    Kartsev, A.; Karlsson, D.; Privitera, A.; Verdozzi, C.

    2013-01-01

    Non-equilibrium quantum phenomena are ubiquitous in nature. Yet, theoretical predictions on the real-time dynamics of many-body quantum systems remain formidably challenging, especially for high dimensions, strong interactions or disordered samples. Here we consider a notable paradigm of strongly correlated Fermi systems, the Mott phase of the Hubbard model, in a setup resembling ultracold-gases experiments. We study the three-dimensional expansion of a cloud into an optical lattice after removing the confining potential. We use time-dependent density-functional theory combined with dynamical mean-field theory, considering interactions below and above the Mott threshold, as well as disorder effects. At strong coupling, we observe multiple timescales in the melting of the Mott wedding-cake structure, as the Mott plateau persist orders of magnitude longer than the band insulating core. We also show that disorder destabilises the Mott plateau and that, compared to a clean setup, localisation can decrease, creating an interesting dynamic crossover during the expansion. PMID:23999144

  2. 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.

  3. Mott glass to superfluid transition for random bosons in two dimensions

    NASA Astrophysics Data System (ADS)

    Iyer, S.; Pekker, D.; Refael, G.

    2012-03-01

    We study the zero-temperature superfluid-insulator transition for a two-dimensional model of interacting, lattice bosons in the presence of quenched disorder and particle-hole symmetry. We follow the approach of a recent series of papers by Altman, Kafri, Polkovnikov, and Refael, in which the strong disorder renormalization group is used to study disordered bosons in one dimension. Adapting this method to two dimensions, we study several different species of disorder and uncover universal features of the superfluid-insulator transition. In particular, we locate an unstable finite disorder fixed point that governs the transition between the superfluid and a gapless, glassy insulator. We present numerical evidence that this glassy phase is the incompressible Mott glass and that the transition from this phase to the superfluid is driven by a percolation-type process. Finally, we provide estimates of the critical exponents governing this transition.

  4. A Mott Glass to Superfluid Transition for Random Bosons in Two Dimensions

    NASA Astrophysics Data System (ADS)

    Pekker, David; Iyer, Shankar; Refael, Gil

    2012-02-01

    We study the zero temperature superfluid-insulator transition for a two-dimensional model of interacting, lattice bosons in the presence of quenched disorder and particle-hole symmetry. We follow the approach of a recent series of papers by Altman, Kafri, Polkovnikov, and Refael, in which the strong disorder renormalization group is used to study disordered bosons in one dimension. Adapting this method to two dimensions, we study several different species of disorder and uncover universal features of the superfluid-insulator transition. In particular, we locate an unstable finite disorder fixed point that governs the transition between the superfluid and a gapless, glassy insulator. We present numerical evidence that this glassy phase is the incompressible Mott glass and that the transition from this phase to the superfluid is driven by percolation-type process. Finally, we provide estimates of the critical exponents governing this transition.

  5. Hallmarks of Metal Insulator transition in Doped Sr2IrO4

    NASA Astrophysics Data System (ADS)

    Cao, Yue; Wang, Qiang; Dhaka, Rajendra; Waugh, Justin; Reber, Theodore; Li, Haoxiang; Parham, Stephen; Zhou, Xiaoqing; Park, Seung Ryong; Qi, Tongfei; Korneta, Oleksandr; Plumb, Nicholas; Bostwick, Aaron; Rotenberg, Eli; Denlinger, Jonathan; Hermele, Michael; Cao, Gang; Dessau, Daniel

    2014-03-01

    How Mott insulators acquire metallicity upon the introduction of extra carriers lies at the heart of correlated electron physics. The evolution of the electronic structure and low energy dynamics in the ultra-low doped region where the Mottness begins to break down is a critical place to study this physics. We report ARPES studies of the Rh and La doped Sr2IrO4 and show the appearance and evolution of a pseudogap and Fermi arcs. Further more we present evidence how the Mott gap breaks down with a profound change in the band structure. The experimental results in the doped iridates resemble those observed in the cuprate systems, which are prototype Mott insulators, and suggest we could establish a series of signatures that occur in the metal insulator transition. Now at Los Alamos National Lab.

  6. Strong-coupling approach to Mott transition of massless and massive Dirac fermions on honeycomb lattice

    NASA Astrophysics Data System (ADS)

    Adibi, Elaheh; Jafari, S. Akbar

    2016-02-01

    Phase transitions in the Hubbard model and ionic Hubbard model at half-filling on the honeycomb lattice are investigated in the strong-coupling perturbation theory which corresponds to an expansion in powers of the hopping t around the atomic limit. Within this formulation we find analytic expressions for the single-particle spectrum, whereby the calculation of the insulating gap is reduced to a simple root finding problem. This enables high-precision determination of the insulating gap that does not require any extrapolation procedure. The critical value of Mott transition on the honeycomb lattice is obtained to be Uc≈2.38 t . Studying the ionic Hubbard model at the lowest order, we find two insulating states, one with Mott character at large U and another with single-particle gap character at large ionic potential Δ . The present approach gives a critical gapless state at U =2 Δ at lowest order. By systematically improving on the perturbation expansion, the density of states around this critical gapless phase reduces.

  7. Metal-insulator transitions in IZO, IGZO, and ITZO films

    SciTech Connect

    Makise, Kazumasa; Hidaka, Kazuya; Ezaki, Syohei; Asano, Takayuki; Shinozaki, Bunju; Tomai, Shigekazu; Yano, Koki; Nakamura, Hiroaki

    2014-10-21

    In this study, we measured the low-temperature resistivity of amorphous two- and three-dimensional (2D and 3D) indium-zinc oxide, indium-gallium-zinc oxide, and indium-tin-zinc oxide films with a wide range of carrier densities. To determine their critical characteristics at the metal-insulator transition (MIT), we used the Ioffe–Regel criterion. We found that the MIT occurs in a narrow range between k{sub F}ℓ =0.13 and k{sub F}ℓ =0.25, where k{sub F} and ℓ are the Fermi wave number and electron mean free path, respectively. For films in the insulating region, we analyzed ρ(T) using a procedure proposed by Zabrodskii and Zinov'eva. This analysis confirmed the occurrence of Mott and Efros–Shklovskii (ES) variable-range hopping. The materials studied show crossover behavior from exp(T{sub Mott}/T){sup 1/4} or exp(T{sub Mott}/T){sup 1/3} for Mott hopping conduction to exp(T{sub ES}/T){sup 1/2} for ES hopping conduction with decreasing temperature. For both 2D and 3D materials, we found that the relationship between T{sub Mott} and T{sub ES} satisfies T{sub ES}∝T{sub Mott}{sup 2/3}.

  8. 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.

  9. Strongly Correlated Superconductivity close to a Mott transition in orbitally degenerate models

    NASA Astrophysics Data System (ADS)

    Capone, Massimo; Fabrizio, Michele; Castellani, Claudio; Tosatti, Erio

    2004-03-01

    Recently a novel strongly correlated superconductivity (SCS) scenario has been proposed [1] which deals with the question whether and under which conditions Cooper-pairing may get enhanced by strong electron repulsion close to a Mott transition. The core of the SCS proposal is that the effective repulsion between quasiparticles vanishes close to the Mott transition, whereas any pairing attraction will remain unrenormalized if it acts inside the spin channel. This scenario was originally demonstrated through a Dynamical Mean Field Theory (DMFT) solution of a model for doped fullerenes, but it is believed to be far more general. Very recently, a twofold orbitally degenerate model with inverted Hund rule exchange has been proposed as a new candidate for SCS [2]. We report fresh DMFT work that fully confirms this expectation, and provides an extremely appealing phase diagram, where superconductivity arises by doping the Mott insulator, out of an unstable a pseudogapped metal, very much as it happens in cuprates. [1] M. Capone, M. Fabrizio, C. Castellani, and E. Tosatti, Science 296, 2364 (2002). [2] M. Fabrizio, A.F. Ho, L. De Leo, and G. Santoro, Phys. Rev. Lett., to appear; L. De Leo and M. Fabrizio, unpublished.

  10. Synthesis, characterization, and physical properties of 1D nanostructures

    NASA Astrophysics Data System (ADS)

    Marley, Peter Mchael

    The roster of materials exhibiting metal---insulator transitions with sharply discontinuous switching of electrical conductivity close to room temperature remains rather sparse despite the fundamental interest in the electronic instabilities manifested in such materials and the plethora of potential technological applications, ranging from frequency-agile metamaterials to electrochromic coatings and Mott field-effect transistors. Vanadium oxide bronzes with the general formula MxV2O 5, provide a wealth of compositions and frameworks where strong electron correlation can be systematically (albeit thus far only empirically) tuned. Charge fluctuations along the quasi-1D frameworks of MxV 2O5 bronzes have evinced much recent interest owing to the manifestation of colossal metal---insulator transitions and superconductivity. We start with a general review on the phase transitions, both electronic and structural, of vanadium oxide bronzes in Chapter 1. In Chapter 2, we demonstrate an unprecedented reversible transformation between double-layered (delta) and tunnel (beta) quasi-1D geometries for nanowires of a divalent vanadium bronze CaxV2O5 (x ˜0.23) upon annealing-induced dehydration and hydrothermally-induced hydration. Such a facile hydration/dehydration-induced interconversion between two prominent quasi-1D structures (accompanied by a change in charge ordering motifs) has not been observed in the bulk and is posited to result from the ease of propagation of crystallographic slip processes across the confined nanowire widths for the delta→beta conversion and the facile diffusion of water molecules within the tunnel geometries for the beta→delta reversion. We demonstrate in Chapter 3 unprecedented pronounced metal-insulator transitions induced by application of a voltage for nanowires of a vanadium oxide bronze with intercalated divalent cations, beta-PbxV 2O5 (x ˜0.33). The induction of the phase transition through application of an electric field at room

  11. Synthesis, characterization, and physical properties of 1D nanostructures

    NASA Astrophysics Data System (ADS)

    Marley, Peter Mchael

    The roster of materials exhibiting metal---insulator transitions with sharply discontinuous switching of electrical conductivity close to room temperature remains rather sparse despite the fundamental interest in the electronic instabilities manifested in such materials and the plethora of potential technological applications, ranging from frequency-agile metamaterials to electrochromic coatings and Mott field-effect transistors. Vanadium oxide bronzes with the general formula MxV2O 5, provide a wealth of compositions and frameworks where strong electron correlation can be systematically (albeit thus far only empirically) tuned. Charge fluctuations along the quasi-1D frameworks of MxV 2O5 bronzes have evinced much recent interest owing to the manifestation of colossal metal---insulator transitions and superconductivity. We start with a general review on the phase transitions, both electronic and structural, of vanadium oxide bronzes in Chapter 1. In Chapter 2, we demonstrate an unprecedented reversible transformation between double-layered (delta) and tunnel (beta) quasi-1D geometries for nanowires of a divalent vanadium bronze CaxV2O5 (x ˜0.23) upon annealing-induced dehydration and hydrothermally-induced hydration. Such a facile hydration/dehydration-induced interconversion between two prominent quasi-1D structures (accompanied by a change in charge ordering motifs) has not been observed in the bulk and is posited to result from the ease of propagation of crystallographic slip processes across the confined nanowire widths for the delta→beta conversion and the facile diffusion of water molecules within the tunnel geometries for the beta→delta reversion. We demonstrate in Chapter 3 unprecedented pronounced metal-insulator transitions induced by application of a voltage for nanowires of a vanadium oxide bronze with intercalated divalent cations, beta-PbxV 2O5 (x ˜0.33). The induction of the phase transition through application of an electric field at room

  12. NMR Study of the Superconducting Gap Variation near the Mott Transition in Cs3C60

    NASA Astrophysics Data System (ADS)

    Wzietek, P.; Mito, T.; Alloul, H.; Pontiroli, D.; Aramini, M.; Riccò, M.

    2014-02-01

    Former extensive studies of superconductivity in the A3C60 compounds, where A is an alkali metal, have led one to consider that Bardeen-Cooper-Schrieffer electron-phonon pairing prevails in those compounds, though the incidence of electronic Coulomb repulsion has been highly debated. The discovery of two isomeric fulleride compounds Cs3C60 which exhibit a transition with pressure from a Mott insulator (MI) to a superconducting (SC) state clearly reopens that question. Using pressure (p) as a single control parameter of the C60 balls lattice spacing, one can now study the progressive evolution of the SC properties when the electronic correlations are increased towards the critical pressure pc of the Mott transition. We have used C13 and Cs133 NMR measurements on the cubic phase A15-Cs3C60 just above pc=5.0(3) kbar, where the SC transition temperature Tc displays a dome shape with decreasing cell volume. From the T dependence below Tc of the nuclear spin lattice relaxation rate (T1)-1 we determine the electronic excitations in the SC state, that is 2Δ, the gap value. The latter is found to be largely enhanced with respect to the Bardeen-Cooper-Schrieffer value established in the case of dense A3C60 compounds. It even increases slightly with decreasing p towards pc, where Tc decreases on the SC dome, so that 2Δ /kBTc increases regularly upon approaching the Mott transition. These results bring clear evidence that the increasing correlations near the Mott transition are not significantly detrimental to superconductivity. They rather suggest that repulsive electron interactions might even reinforce elecron-phonon superconductivity, being then partly responsible for the large Tc values, as proposed by theoretical models taking the electronic correlations as a key ingredient.

  13. Nature of strong hole pairing in doped Mott antiferromagnets.

    PubMed

    Zhu, Zheng; Jiang, Hong-Chen; Sheng, D N; Weng, Zheng-Yu

    2014-06-24

    Cooper pairing instability in a Fermi liquid is well understood by the BCS theory, but pairing mechanism for doped Mott insulators still remains elusive. Previously it has been shown by density matrix renormalization group (DMRG) method that a single doped hole is always self-localized due to the quantum destructive interference of the phase string signs hidden in the t-J ladders. Here we report a DMRG investigation of hole binding in the same model, where a novel pairing-glue scheme beyond the BCS realm is discovered. Specifically, we show that, in addition to spin pairing due to superexchange interaction, the strong frustration of the phase string signs on the kinetic energy gets effectively removed by pairing the charges, which results in strong binding of two holes. By contrast, if the phase string signs are "switched off" artificially, the pairing strength diminishes significantly even if the superexchange coupling remains the same. In the latter, unpaired holes behave like coherent quasiparticles with pairing drastically weakened, whose sole origin may be attributed to the resonating-valence-bond (RVB) pairing of spins. Such non-BCS pairing mechanism is therefore beyond the RVB picture and may shed important light on the high-T(c) cuprate superconductors.

  14. Nature of strong hole pairing in doped Mott antiferromagnets

    NASA Astrophysics Data System (ADS)

    Zhu, Zheng; Jiang, Hong-Chen; Sheng, D. N.; Weng, Zheng-Yu

    2014-06-01

    Cooper pairing instability in a Fermi liquid is well understood by the BCS theory, but pairing mechanism for doped Mott insulators still remains elusive. Previously it has been shown by density matrix renormalization group (DMRG) method that a single doped hole is always self-localized due to the quantum destructive interference of the phase string signs hidden in the t-J ladders. Here we report a DMRG investigation of hole binding in the same model, where a novel pairing-glue scheme beyond the BCS realm is discovered. Specifically, we show that, in addition to spin pairing due to superexchange interaction, the strong frustration of the phase string signs on the kinetic energy gets effectively removed by pairing the charges, which results in strong binding of two holes. By contrast, if the phase string signs are ``switched off'' artificially, the pairing strength diminishes significantly even if the superexchange coupling remains the same. In the latter, unpaired holes behave like coherent quasiparticles with pairing drastically weakened, whose sole origin may be attributed to the resonating-valence-bond (RVB) pairing of spins. Such non-BCS pairing mechanism is therefore beyond the RVB picture and may shed important light on the high-Tc cuprate superconductors.

  15. Nature of strong hole pairing in doped Mott antiferromagnets.

    PubMed

    Zhu, Zheng; Jiang, Hong-Chen; Sheng, D N; Weng, Zheng-Yu

    2014-01-01

    Cooper pairing instability in a Fermi liquid is well understood by the BCS theory, but pairing mechanism for doped Mott insulators still remains elusive. Previously it has been shown by density matrix renormalization group (DMRG) method that a single doped hole is always self-localized due to the quantum destructive interference of the phase string signs hidden in the t-J ladders. Here we report a DMRG investigation of hole binding in the same model, where a novel pairing-glue scheme beyond the BCS realm is discovered. Specifically, we show that, in addition to spin pairing due to superexchange interaction, the strong frustration of the phase string signs on the kinetic energy gets effectively removed by pairing the charges, which results in strong binding of two holes. By contrast, if the phase string signs are "switched off" artificially, the pairing strength diminishes significantly even if the superexchange coupling remains the same. In the latter, unpaired holes behave like coherent quasiparticles with pairing drastically weakened, whose sole origin may be attributed to the resonating-valence-bond (RVB) pairing of spins. Such non-BCS pairing mechanism is therefore beyond the RVB picture and may shed important light on the high-T(c) cuprate superconductors. PMID:24957467

  16. Classification of interacting electronic topological insulators in three dimensions.

    PubMed

    Wang, Chong; Potter, Andrew C; Senthil, T

    2014-02-01

    A fundamental open problem in condensed-matter physics is how the dichotomy between conventional and topological band insulators is modified in the presence of strong electron interactions. We show that there are six interacting electronic topological insulators that have no noninteracting counterpart. Combined with the previously known band insulators, these produce a total of eight topologically distinct phases. Two of the six interacting topological insulators can be described as Mott insulators in which the electron spins form spin analogs of the topological band insulator. The remaining phases are obtained as combinations of these two "topological paramagnets" and the topological band insulator. We prove that these eight phases form a complete list of all possible interacting topological insulators and discuss their experimental signatures.

  17. Singlet Mott state simulating the bosonic Laughlin wave function

    NASA Astrophysics Data System (ADS)

    Lian, Biao; Zhang, Shoucheng

    2014-01-01

    We study properties of a class of spin-singlet Mott states for arbitrary spin S bosons on a lattice, with particle number per cite n =S/l+1, where l is a positive integer. We show that such a singlet Mott state can be mapped to a bosonic Laughlin wave function on a sphere with a finite number of particles at filling ν =1/2l. Spin, particle, and hole excitations in the Mott state are discussed, among which the hole excitation can be mapped to the quasihole of the bosonic Laughlin wave function. We show that this singlet Mott state can be realized in a cold-atom system on an optical lattice and can be identified using Bragg spectroscopy and Stern-Gerlach techniques. This class of singlet Mott states may be generalized to map to bosonic Laughlin states with filling ν =q/2l.

  18. Singlet Mott State Simulating the Bosonic Laughlin Wave Function

    NASA Astrophysics Data System (ADS)

    Lian, Biao; Zhang, Shou-Cheng

    2014-03-01

    We study properties of a class of spin singlet Mott states for arbitrary spin S bosons on a lattice, with particle number per cite n = S / l + 1 , where l is a positive integer. We show that such a singlet Mott state can be mapped to a bosonic Laughlin wave function on the sphere with a finite number of particles at filling ν = 1 / 2 l . Bosonic spinons, particle and hole excitations in the Mott state are discussed, among which the hole excitation can be mapped to the quasi-hole of the bosonic Laughlin wave function. We show that this singlet Mott state can be realized in a cold atom system on optical lattice, and can be identified using Bragg spectroscopy and Stern-Gerlach techniques. This class of singlet Mott states may be generalized to simulate bosonic Laughlin states with filling ν = q / 2 l .

  19. MOTT FOUNDATION PROJECTS MOTT PROGRAM--FLINT PUBLIC SCHOOLS, SUMMARY REPORTS JULY 1, 1964 TO JUNE 30, 1965.

    ERIC Educational Resources Information Center

    BRIGGS, LARRY; AND OTHERS

    ONE-PAGE REPORTS ARE PRESENTED, SUMMARIZING EACH OF THE PROJECTS IN THE MOTT PROGRAM FOR THE FLINT PUBLIC SCHOOLS--WORKSHOPS AND VISITATIONS, ADULT EDUCATION, GRADUATE TRAINING, YOUTH PROGRAMS, THE MOTT CAMP, RECREATION, A BETTER TOMORROW FOR THE URBAN CHILD, THE PERSONALIZED CURRICULUM PROGRAM, MEDICAL-DENTAL HEALTH, INTERUNIVERSITY CLINICAL…

  20. Z2 slave-spin theory of a strongly correlated Chern insulator

    NASA Astrophysics Data System (ADS)

    Prychynenko, Diana; Huber, Sebastian D.

    2016-01-01

    We calculate the phase diagram of the topological honeycomb model in the presence of strong interactions. We concentrate on half filling and employ a Z2 slave-spin method to find a band insulator with staggered density, a spin-density-wave and a Mott insulating phase. Both the band insulator and the spin-density wave come in various topological varieties. Finally, we calculate the response function relevant for lattice modulation spectroscopy with cold atomic gases in optical lattices.

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

    PubMed

    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. PMID:26565588

  2. 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.

  3. Electrically driven reversible insulator-metal phase transition in 1T-TaS2.

    PubMed

    Hollander, Matthew J; Liu, Yu; Lu, Wen-Jian; Li, Li-Jun; Sun, Yu-Ping; Robinson, Joshua A; Datta, Suman

    2015-03-11

    In this work, we demonstrate abrupt, reversible switching of resistance in 1T-TaS2 using dc and pulsed sources, corresponding to an insulator-metal transition between the insulating Mott and equilibrium metallic states. This transition occurs at a constant critical resistivity of 7 mohm-cm regardless of temperature or bias conditions and the transition time is significantly smaller than abrupt transitions by avalanche breakdown in other small gap Mott insulating materials. Furthermore, this critical resistivity corresponds to a carrier density of 4.5 × 10(19) cm(-3), which compares well with the critical carrier density for the commensurate to nearly commensurate charge density wave transition. These results suggest that the transition is facilitated by a carrier driven collapse of the Mott gap in 1T-TaS2, which results in fast (3 ns) switching.

  4. Oxygen-doped Mott-Hubbard cuprate superconductor La1.85Y0.15CuO4-δ from transport measurements

    NASA Astrophysics Data System (ADS)

    Yu, W.; Liang, B.; Li, P.; Fujino, S.; Murakami, T.; Takeuchi, I.; Greene, R. L.

    2007-01-01

    We report resistivity, Hall effect, Nernst effect, and magnetoresistance measurements on T' -phase La1.85Y0.15CuO4-δ (LYCO) films prepared by pulsed laser deposition under different oxygen conditions. Our results show that superconductivity in LYCO originates from an oxygen-doped Mott-like insulator and not from a weakly correlated, half-filled band metal as proposed previously.

  5. Quasiparticle Dynamics in a Bose Insulator Probed by Interband Bragg Spectroscopy

    NASA Astrophysics Data System (ADS)

    Fabbri, N.; Huber, S. D.; Clément, D.; Fallani, L.; Fort, C.; Inguscio, M.; Altman, E.

    2012-08-01

    We investigate experimentally and theoretically the dynamical properties of a Mott insulator in decoupled one-dimensional chains. Using a theoretical analysis of the Bragg excitation scheme, we show that the spectrum of interband transitions holds information on the single-particle Green’s function of the insulator. In particular, the existence of particle-hole coherence due to quantum fluctuations in the Mott state is clearly seen in the Bragg spectra and quantified. Finally, we propose a scheme to directly measure the full, momentum-resolved spectral function as obtained in the angle-resolved photoemission spectroscopy of solids.

  6. Unified understanding of superconductivity and Mott transition in alkali-doped fullerides from first principles.

    PubMed

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

    2015-08-01

    Alkali-doped fullerides A 3C60 (A = K, Rb, Cs) are surprising materials where conventional phonon-mediated superconductivity and unconventional Mott physics meet, leading to a remarkable phase diagram as a function of volume per C60 molecule. We address these materials with a state-of-the-art calculation, where we construct a realistic low-energy model from first principles without using a priori information other than the crystal structure and solve it with an accurate many-body theory. Remarkably, our scheme comprehensively reproduces the experimental phase diagram including the low-spin Mott-insulating phase next to the superconducting phase. More remarkably, the critical temperatures T c's calculated from first principles quantitatively reproduce the experimental values. The driving force behind the surprising phase diagram of A 3C60 is a subtle competition between Hund's coupling and Jahn-Teller phonons, which leads to an effectively inverted Hund's coupling. Our results establish that the fullerides are the first members of a novel class of molecular superconductors in which the multiorbital electronic correlations and phonons cooperate to reach high T c s-wave superconductivity.

  7. Charge-ordering cascade with spin-orbit Mott dimer states in metallic iridium ditelluride.

    PubMed

    Ko, K-T; Lee, H-H; Kim, D-H; Yang, J-J; Cheong, S-W; Eom, M J; Kim, J S; Gammag, R; Kim, K-S; Kim, H-S; Kim, T-H; Yeom, H-W; Koo, T-Y; Kim, H-D; Park, J-H

    2015-01-01

    Spin-orbit coupling results in technologically-crucial phenomena underlying magnetic devices like magnetic memories and energy-efficient motors. In heavy element materials, the strength of spin-orbit coupling becomes large to affect the overall electronic nature and induces novel states such as topological insulators and spin-orbit-integrated Mott states. Here we report an unprecedented charge-ordering cascade in IrTe2 without the loss of metallicity, which involves localized spin-orbit Mott states with diamagnetic Ir(4+)-Ir(4+) dimers. The cascade in cooling, uncompensated in heating, consists of first order-type consecutive transitions from a pure Ir(3+) phase to Ir(3+)-Ir(4+) charge-ordered phases, which originate from Ir 5d to Te 5p charge transfer involving anionic polymeric bond breaking. Considering that the system exhibits superconductivity with suppression of the charge order by doping, analogously to cuprates, these results provide a new electronic paradigm of localized charge-ordered states interacting with itinerant electrons through large spin-orbit coupling. PMID:26059464

  8. Unified understanding of superconductivity and Mott transition in alkali-doped fullerides from first principles

    PubMed Central

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

    2015-01-01

    Alkali-doped fullerides A3C60 (A = K, Rb, Cs) are surprising materials where conventional phonon-mediated superconductivity and unconventional Mott physics meet, leading to a remarkable phase diagram as a function of volume per C60 molecule. We address these materials with a state-of-the-art calculation, where we construct a realistic low-energy model from first principles without using a priori information other than the crystal structure and solve it with an accurate many-body theory. Remarkably, our scheme comprehensively reproduces the experimental phase diagram including the low-spin Mott-insulating phase next to the superconducting phase. More remarkably, the critical temperatures Tc’s calculated from first principles quantitatively reproduce the experimental values. The driving force behind the surprising phase diagram of A3C60 is a subtle competition between Hund’s coupling and Jahn-Teller phonons, which leads to an effectively inverted Hund’s coupling. Our results establish that the fullerides are the first members of a novel class of molecular superconductors in which the multiorbital electronic correlations and phonons cooperate to reach high Tc s-wave superconductivity. PMID:26601242

  9. Low dimensional Mott material: Transport in ultra thin epitaxial LaNiO3

    NASA Astrophysics Data System (ADS)

    Son, Junwoo; Moetakef, Pouya; Lebeau, James M.; Ouellette, Daniel; Balents, Leon; Allen, S. James; Stemmer, Susanne

    2010-03-01

    Ultrathin Mott materials, close to a metal-insulator transition, are expected to be sensitive to local bonding, coordination, strain and dimensionality. LaNiO3 films have recently attracted interest because of theoretical predictions of antiferromagnetism and high-temperature superconductivity in superlattices. We have grown ultrathin, epitaxial LaNiO3 on different substrates, (LaAlO3)0.3(Sr2AlTaO6)0.7 (LSAT) and LaAlO3 (LAO). High oxygen pressures were required for stoichiometric films. Atomic resolution Z-contrast imaging confirmed that all LaNiO3 films were epitaxial and continuous down to 2.5 nm. Resistivity, magnetoresistance, Hall coefficient and mobility were measured between 2 and 300 K. The resistivity (< 200 μφ cm) was comparable to bulk for films down to 5 nm on LSAT and 3 nm on LAO, indicating good oxygen stoichiometry. All films showed temperature dependent Hall coefficients indicative of both electron and hole contributions. For 4 nm films on LSAT and 2.5 nm films on LAO, weak localization was observed. Films below 4 nm on LSAT (tensile stress) were strongly localized while those on LAO (compressive stress) remained metallic at thicknesses down to 2.5 nm. We will discuss these results in the context of confinement in ultrathin Mott materials.

  10. Correlation effects in two-dimensional topological insulators.

    PubMed

    Hohenadler, M; Assaad, F F

    2013-04-10

    Topological insulators have become one of the most active research areas in condensed matter physics. This article reviews progress on the topic of electronic correlation effects in the two-dimensional case, with a focus on systems with intrinsic spin-orbit coupling and numerical results. Topics addressed include an introduction to the noninteracting case, an overview of theoretical models, correlated topological band insulators, interaction-driven phase transitions, topological Mott insulators and fractional topological states, correlation effects on helical edge states, and topological invariants of interacting systems.

  11. Magnetic correlations in a classic Mott system

    SciTech Connect

    Bao, W.; Broholm, C.; Aeppli, G.; Carter, S.A.; Dai, D.; Frost, C.D.; Honig, J.M.; Metcalf, P.

    1997-07-01

    The metal-insulator transition in V{sub 2}O{sub 3} causes a fundamental change in its magnetism. While the antiferromagnetic insulator (AFI) is a Heisenberg localized spin system, the antiferromagnetism in the strongly correlated metal is determined by a Fermi surface instability. Paramagnetic fluctuations in the metal and insulator represent similar spatial spin correlations, but are unrelated to the long range order in the AFI. The phase transition to the AFI induces an abrupt switching of magnetic correlations to a different magnetic wave vector. The AFI transition, therefore, is not a conventional spin order-disorder transition. Instead it is accounted for by an ordering in the occupation of the two degenerate d-orbitals at the Fermi level.

  12. Surface Effects on the Mott-Hubbard Transition in Archetypal V{2}O{3}.

    PubMed

    Lantz, G; Hajlaoui, M; Papalazarou, E; Jacques, V L R; Mazzotti, A; Marsi, M; Lupi, S; Amati, M; Gregoratti, L; Si, L; Zhong, Z; Held, K

    2015-12-01

    We present an experimental and theoretical study exploring surface effects on the evolution of the metal-insulator transition in the model Mott-Hubbard compound Cr-doped V{2}O{3}. We find a microscopic domain formation that is clearly affected by the surface crystallographic orientation. Using scanning photoelectron microscopy and x-ray diffraction, we find that surface defects act as nucleation centers for the formation of domains at the temperature-induced isostructural transition and favor the formation of microscopic metallic regions. A density-functional theory plus dynamical mean-field theory study of different surface terminations shows that the surface reconstruction with excess vanadyl cations leads to doped, and hence more metallic, surface states, which explains our experimental observations. PMID:26684133

  13. Surface Effects on the Mott-Hubbard Transition in Archetypal V2O3

    NASA Astrophysics Data System (ADS)

    Lantz, G.; Hajlaoui, M.; Papalazarou, E.; Jacques, V. L. R.; Mazzotti, A.; Marsi, M.; Lupi, S.; Amati, M.; Gregoratti, L.; Si, L.; Zhong, Z.; Held, K.

    2015-12-01

    We present an experimental and theoretical study exploring surface effects on the evolution of the metal-insulator transition in the model Mott-Hubbard compound Cr-doped V2O3. We find a microscopic domain formation that is clearly affected by the surface crystallographic orientation. Using scanning photoelectron microscopy and x-ray diffraction, we find that surface defects act as nucleation centers for the formation of domains at the temperature-induced isostructural transition and favor the formation of microscopic metallic regions. A density-functional theory plus dynamical mean-field theory study of different surface terminations shows that the surface reconstruction with excess vanadyl cations leads to doped, and hence more metallic, surface states, which explains our experimental observations.

  14. Low-temperature fabrication of VO2 thin film on ITO glass with a Mott transition

    NASA Astrophysics Data System (ADS)

    Lin, Tiegui; Wang, Langping; Wang, Xiaofeng; Zhang, Yufen

    2016-09-01

    Polycrystalline Vanadium dioxide (VO2) thin film can be fabricated on glass substrates by high power impulse magnetron sputtering at a relative high temperature. In order to apply an effective bias voltage on substrate and control the energy of the ions impinged to the substrate, conductive indium-tin oxide (ITO) glass was used as the substrate. UV-visible-near IR transmittance spectra and X-ray diffraction (XRD) patterns of the as-deposited films exhibited that M-VO2 thin film with a metal-insulator transition temperature of 37∘C was fabricated successfully at 300∘C with a bias voltage of ‑200V, and the calculated average crystalline size of this film was about 12nm. XRD patterns at varied temperatures showed that the structural change of MIT of the VO2 thin film was suppressed during the phase transition process, and a pure Mott transition was obtained.

  15. Excitonic correlation in the Mott crossover regime in Ge

    NASA Astrophysics Data System (ADS)

    Sekiguchi, Fumiya; Shimano, Ryo

    2015-04-01

    Exciton Mott transition (EMT) in Ge was investigated by using optical-pump and terahertz-probe spectroscopy. From the quantitative analysis of optical conductivity and dielectric function, we evaluated the densities of unbound electron-hole pairs and excitons after the photoexcitation, from which we determined the ionization ratio of excitons α. The Mott crossover density region in Ge was elucidated from the density dependence of α in the temperature range above the critical temperature of electron-hole droplets. The 1 s -2 p excitonic transition energy hardly shifted with increasing density toward the EMT. Combined with the similar results recently observed in bulk Si, we suggest that the robustness of excitonic correlation against the Coulomb screening is a universal feature in bulk semiconductors in the Mott crossover regime.

  16. Renormalization for insulating states of matter

    NASA Astrophysics Data System (ADS)

    Hong, Seungmin

    In this thesis, we study three cases of insulating states of matter in terms of the renormalization procedure where the conventional renormalization group scheme is not simply applicable. The first subject is the spectral weight structure of hole-doped Mott insulators. As the mixing between two separate Hubbard bands is dynamically generated, additional charge degrees of freedom is required to give a proper description to the relevant low-energy physics. On this account, we first discuss how the low-energy Hubbard band should be partitioned to account for the extra degrees of freedom. Following the exact integration procedure of the upper Hubbard band, we explicitly demonstrate that the conserved charge cannot be exhausted by counting quasiparticles. In addition, we argue that it is the existence of dynamically generated charge degrees of freedom that gives rise to the coexistence of poles and zeroes in the single-particle Green function. In comparison to the Fermi arc structure, which is intrinsic to cuperate phenomenology, we suggest that the suppression of the spectral weight at the back side of the arc is a consequence of composite excitations, arising from dynamical mixing. The second topic we study is the nature of the transition between two insulating states of matter in a weakly disordered bosonic system. In particular, we investigate the instabilities of the Mott-insulating phase within a renormalization group analysis of the replica field theory obtained by a strong-coupling expansion around the atomic limit. To this end, we identify a new order parameter and associated correlation length scale that are capable of capturing the transition from a state with zero compressibility, the Mott insulator, to another insulating state with finite compressibility, the Bose glass. The order parameter is the relative variance of the disorder-induced mass distribution. From its distinctive behavior on each phase, we find that the divergence of the relative variance in

  17. 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. PMID:23006401

  18. Spontaneous Spin Textures in Multiorbital Mott Systems

    NASA Astrophysics Data System (ADS)

    Kuneš, J.; Geffroy, D.

    2016-06-01

    Spin textures in k -space arising from spin-orbit coupling in noncentrosymmetric crystals find numerous applications in spintronics. We present a mechanism that leads to the appearance of k -space spin texture due to spontaneous symmetry breaking driven by electronic correlations. Using dynamical mean-field theory we show that doping a spin-triplet excitonic insulator provides a means of creating new thermodynamic phases with unique properties. The numerical results are interpreted using analytic calculations within a generalized double-exchange framework.

  19. Spontaneous Spin Textures in Multiorbital Mott Systems.

    PubMed

    Kuneš, J; Geffroy, D

    2016-06-24

    Spin textures in k-space arising from spin-orbit coupling in noncentrosymmetric crystals find numerous applications in spintronics. We present a mechanism that leads to the appearance of k-space spin texture due to spontaneous symmetry breaking driven by electronic correlations. Using dynamical mean-field theory we show that doping a spin-triplet excitonic insulator provides a means of creating new thermodynamic phases with unique properties. The numerical results are interpreted using analytic calculations within a generalized double-exchange framework. PMID:27391736

  20. Pseudogap and superconductivity in two-dimensional doped charge-transfer insulators

    NASA Astrophysics Data System (ADS)

    Fratino, L.; Sémon, P.; Sordi, G.; Tremblay, A.-M. S.

    2016-06-01

    High-temperature superconductivity emerges upon doping a state of matter that is insulating because of interactions. A widely studied model considers one orbital per CuO2 unit cell on a square lattice with a strong intraorbital repulsion that leads to a so-called Mott-Hubbard insulator. Here we solve a model that takes into account, within each unit cell, two oxygen orbitals where there is no electron-electron repulsion and a copper orbital with strong electron-electron repulsion. The insulating phase is a so-called charge-transfer insulator, not a Mott-Hubbard insulator. Using cluster dynamical mean-field theory with continuous-time quantum Monte Carlo as an impurity solver and 12 atoms per cluster, we report the normal and superconducting phase diagram of this model as a function of doping, interaction strength, and temperature. As expected, the three-orbital model is consistent with the experimental observation that doped holes are located predominantly on oxygens, a result that goes beyond the one-orbital model. Nevertheless, the phase boundary between pseudogap and correlated metal, the Widom line, and the origin of the pairing energy (kinetic vs potential) are similar to the one-orbital model, demonstrating that these are emergent phenomena characteristic of doped Mott insulators, independently of many microscopic details. Broader implications are discussed.

  1. Cellulose Insulation

    NASA Technical Reports Server (NTRS)

    1980-01-01

    Fire retardant cellulose insulation is produced by shredding old newspapers and treating them with a combination of chemicals. Insulating material is blown into walls and attics to form a fiber layer which blocks the flow of air. All-Weather Insulation's founders asked NASA/UK-TAP to help. They wanted to know what chemicals added to newspaper would produce an insulating material capable of meeting federal specifications. TAP researched the query and furnished extensive information. The information contributed to successful development of the product and helped launch a small business enterprise which is now growing rapidly.

  2. 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.

  3. 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.

  4. 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. PMID:27376190

  5. Stabilizing the false vacuum. Mott skyrmions

    DOE PAGES

    Kanász-Nagy, M.; Dóra, B.; Demler, E. A.; Zaránd, G.

    2015-01-13

    Topological excitations keep fascinating physicists since many decades. While individual vortices and solitons emerge and have been observed in many areas of physics, their most intriguing higher dimensional topological relatives, skyrmions (smooth, topologically stable textures) and magnetic monopoles emerging almost necessarily in any grand unified theory and responsible for charge quantization remained mostly elusive. Here we propose that loading a three-component nematic superfluid such as 23Na into a deep optical lattice and thereby creating an insulating core, one can create topologically stable skyrmion textures. The skyrmion’s extreme stability and its compact geometry enable one to investigate the skyrmion’s structure, andmore » the interplay of topology and excitations in detail. In particular, the superfluid’s excitation spectrum as well as the quantum numbers are demonstrated to change dramatically due to the skyrmion, and reflect the presence of a trapped monopole, as imposed by the skyrmion’s topology.« less

  6. Stabilizing the false vacuum: Mott skyrmions

    PubMed Central

    Kanász-Nagy, M.; Dóra, B.; Demler, E. A.; Zaránd, G.

    2015-01-01

    Topological excitations keep fascinating physicists since many decades. While individual vortices and solitons emerge and have been observed in many areas of physics, their most intriguing higher dimensional topological relatives, skyrmions (smooth, topologically stable textures) and magnetic monopoles emerging almost necessarily in any grand unified theory and responsible for charge quantization remained mostly elusive. Here we propose that loading a three-component nematic superfluid such as 23Na into a deep optical lattice and thereby creating an insulating core, one can create topologically stable skyrmion textures. The skyrmion's extreme stability and its compact geometry enable one to investigate the skyrmion's structure, and the interplay of topology and excitations in detail. In particular, the superfluid's excitation spectrum as well as the quantum numbers are demonstrated to change dramatically due to the skyrmion, and reflect the presence of a trapped monopole, as imposed by the skyrmion's topology. PMID:25582915

  7. Stabilizing the false vacuum. Mott skyrmions

    SciTech Connect

    Kanász-Nagy, M.; Dóra, B.; Demler, E. A.; Zaránd, G.

    2015-01-13

    Topological excitations keep fascinating physicists since many decades. While individual vortices and solitons emerge and have been observed in many areas of physics, their most intriguing higher dimensional topological relatives, skyrmions (smooth, topologically stable textures) and magnetic monopoles emerging almost necessarily in any grand unified theory and responsible for charge quantization remained mostly elusive. Here we propose that loading a three-component nematic superfluid such as 23Na into a deep optical lattice and thereby creating an insulating core, one can create topologically stable skyrmion textures. The skyrmion’s extreme stability and its compact geometry enable one to investigate the skyrmion’s structure, and the interplay of topology and excitations in detail. In particular, the superfluid’s excitation spectrum as well as the quantum numbers are demonstrated to change dramatically due to the skyrmion, and reflect the presence of a trapped monopole, as imposed by the skyrmion’s topology.

  8. Dielectric breakdown and avalanches at nonequilibrium metal-insulator transitions.

    PubMed

    Shekhawat, Ashivni; Papanikolaou, Stefanos; Zapperi, Stefano; Sethna, James P

    2011-12-30

    Motivated by recent experiments on the finite temperature Mott transition in VO(2) films, we propose a classical coarse-grained dielectric breakdown model where each degree of freedom represents a nanograin which transitions from insulator to metal with increasing temperature and voltage at random thresholds due to quenched disorder. We describe the properties of the resulting nonequilibrium metal-insulator transition and explain the universal characteristics of the resistance jump distribution. We predict that by tuning voltage, another critical point is approached, which separates a phase of boltlike avalanches from percolationlike ones.

  9. Metal-Insulator Transition of Dirac Fermions: Variational Cluster Study

    NASA Astrophysics Data System (ADS)

    Ebato, Masaki; Kaneko, Tatsuya; Ohta, Yukinori

    2015-04-01

    A comparative study is made on the metal-insulator transition of Dirac fermions in the honeycomb and π-flux Hubbard models at half filling by means of the variational cluster approximation and cluster dynamical impurity approximation. Paying particular attention to the choice of the geometry of solver clusters and the inclusion of particle-bath sites, we show that the direct transition from the Dirac semimetallic state to the antiferromagnetic Mott insulator state occurs in these models, and therefore, the spin liquid phase is absent in the intermediate region, in agreement with recent quantum-Monte-Carlo-based calculations.

  10. Metal-insulator transition and novel magnetism driven by Coulomb interactions, spin-orbit coupling and disorder

    NASA Astrophysics Data System (ADS)

    Meetei, Oinam Nganba

    Strong interactions in transition metal oxides can lead to spectacular phenomena like high Tc superconductivity and colossal magnetoresistance which have dominated materials research in the past decades. The goal of this thesis is to examine the interplay of strong correlations with additional degrees of freedom, like spin orbit coupling (SOC), multiple transition metal ions and disorder. We start with a discussion of Mott insulators, with the transition metal in the d4 configuration, where the competition between superexchange interaction and SOC leads to a novel ferromagnetic insulator. In recent years SOC has been at the center stage of condensed matter research because it can produce band insulators in uncorrelated materials with non-trivial topological properties. Here, we focus on the dual role of SOC and strong interactions, naturally realized in 4d/5dd transition metal oxides. We show that in d4 Mott insulators, the local moment can be altered by varying the relative strength of SOC and superexchange, both of which are small parameters compared to the interaction energy scale. In fact, a phase transition from a non-magnetic insulator with J=0 singlets at every site to an orbitally entangled ferromagnetic insulator occurs with decreasing SOC. Our results challenge the commonly held notion that local moments are robust in a Mott insulator. We identify candidate materials and present predictions for Resonant X-ray Scattering (RXS) signatures of the unusual magnetism in d4 Mott insulators. Next we focus on the double perovskite material Sr2 CrOsO6 which is an insulator and has the highest ferromagnetic Tc among all perovskites with a net moment. It presents several puzzles which we address systematically. Its insulating behavior cannot be explained from a band theory point of view or from a naive consideration of Mott physics. Additionally, the net moment at low temperature, M(0)=0.75 μΒ ,is unusual for half-filled bands where anti-ferromagnetism is expected

  11. T-shaped GaAs quantum-wire lasers and the exciton Mott transition.

    PubMed

    Yoshita, M; Liu, S M; Okano, M; Hayamizu, Y; Akiyama, H; Pfeiffer, L N; West, K W

    2007-07-25

    T-shaped GaAs quantum-wire (T-wire) lasers fabricated by the cleaved-edge overgrowth method with molecular beam epitaxy on the interface improved by a growth-interrupt high-temperature anneal are measured to study the laser device physics and fundamental many-body physics in clean one-dimensional (1D) systems. A current-injection T-wire laser that has 20 periods of T-wires in the active region and a 0.5 mm long cavity with high-reflection coatings shows a low threshold current of 0.27 mA at 30 K. The origin of the laser gain above the lasing threshold is studied with the high-quality T-wire lasers by means of optical pumping. The lasing energy is about 5 meV below the photoluminescence (PL) peak of free excitons, and is on the electron-hole (e-h) plasma PL band at a high e-h carrier density. The observed energy shift excludes the laser gain due to free excitons, and it suggests a contribution from the e-h plasma instead. A systematic micro-PL study reveals that the PL evolves with the e-h density from a sharp exciton peak, via a biexciton peak, to an e-h-plasma PL band. The data demonstrate an important role of biexcitons in the exciton Mott transition. Comparison with microscopic theories points out some problems in the picture of the exciton Mott transition.

  12. Fitting of m*/m with Divergence Curve for He3 Fluid Monolayer using Hole-driven Mott Transition

    NASA Astrophysics Data System (ADS)

    Kim, Hyun-Tak

    2012-02-01

    The electron-electron interaction for strongly correlated systems plays an important role in formation of an energy gap in solid. The breakdown of the energy gap is called the Mott metal-insulator transition (MIT) which is different from the Peierls MIT induced by breakdown of electron-phonon interaction generated by change of a periodic lattice. It has been known that the correlated systems are inhomogeneous. In particular, He3 fluid monolayer [1] and La1-xSrxTiO3 [2] are representative strongly correlated systems. Their doping dependence of the effective mass of carrier in metal, m*/m, indicating the magnitude of correlation (Coulomb interaction) between electrons has a divergence behavior. However, the fitting remains unfitted to be explained by a Mott-transition theory with divergence. In the case of He3 regarded as the Fermi system with one positive charge (2 electrons + 3 protons), the interaction between He3 atoms is regarded as the correlation in strongly correlated system. In this presentation, we introduce a Hole-driven MIT with a divergence near the Mott transition [3] and fit the m*/m curve in He3 [1] and La1-xSrxTiO3 systems with the Hole-driven MIT with m*/m=1/(1-ρ^4) where ρ is band filling. Moreover, it is shown that the physical meaning of the effective mass with the divergence is percolation in which m*/m increases with increasing doping concentration, and that the magnitude of m*/m is constant.[4pt] [1] Phys. Rev. Lett. 90, 115301 (2003).[0pt] [2] Phys. Rev. Lett. 70, 2126 (1993).[0pt] [3] Physica C 341-348, 259 (2000); Physica C 460-462, 1076 (2007).

  13. Mott Criticality and Pseudogap in Bose-Fermi Mixtures

    NASA Astrophysics Data System (ADS)

    Altman, Ehud; Demler, Eugene; Rosch, Achim

    2012-12-01

    We study the Mott transition of a mixed Bose-Fermi system of ultracold atoms in an optical lattice, where the number of (spinless) fermions and bosons adds up to one atom per lattice, nF+nB=1. For weak interactions, a Fermi surface coexists with a Bose-Einstein condensate while for strong interaction the system is incompressible but still characterized by a Fermi surface of composite fermions. At the critical point, the spectral function of the fermions A(k,ω) exhibits a pseudogapped behavior, rising as |ω| at the Fermi momentum, while in the Mott phase it is fully gapped. Taking into account the interaction between the critical modes leads at very low temperatures either to p-wave pairing or the transition is driven weakly first order. The same mechanism should also be important in antiferromagnetic metals with a small Fermi surface.

  14. Constitutive relations associated with the Mott-Smith distribution function

    USGS Publications Warehouse

    Nathenson, M.; Baganoff, D.

    1973-01-01

    It is shown that the distribution function assumed by Mott-Smith determines a unique relation between heat flux, stress, and fluid velocity given by q = (3/2)??u, i.e., it provides a constitutive relation for heat flux, and it also determines a simple expression for this ratio of third-order central moments Q = . These expressions allow the equation of transfer for c x2 to be cast in a form that yields a nonlinear constitutive relation for stress. The results obtained from the Mott-Smith ansatz are compared with the theory of Baganoff and Nathenson and results from a numerical solution of the Boltzmann equation for shock-wave structure obtained by Hicks and Yen.

  15. Automotive Insulation

    NASA Technical Reports Server (NTRS)

    1997-01-01

    Under a Space Act Agreement between Boeing North America and BSR Products, Space Shuttle Thermal Protection System (TPS) materials are now used to insulate race cars. BSR has created special TPS blanket insulation kits for use on autos that take part in NASCAR events, and other race cars through its nationwide catalog distribution system. Temperatures inside a race car's cockpit can soar to a sweltering 140 to 160 degrees, with the extreme heat coming through the engine firewall, transmission tunnel, and floor. It is common for NASCAR drivers to endure blisters and burns due to the excessive heat. Tests on a car insulated with the TPS material showed a temperature drop of some 50 degrees in the driver's cockpit. BSR-TPS Products, Inc. now manufactures insulation kits for distribution to race car teams around the world.

  16. Mott scattering in an elliptically polarized laser field

    SciTech Connect

    Attaourti, Y.; Manaut, B.; Taj, S.

    2004-08-01

    We study Mott scattering in the presence of a strong elliptically polarized field. Using the first Born approximation and the Dirac-Volkov states for the electron, we obtain an analytic formula for the unpolarized differential cross section. This generalizes the results found for the linearly polarized field by Li et al. [ 67, 063409 (2003)] and for the circularly polarized field by Attaourti and Manaut [ 68, 067401 (2003)].

  17. 5 MeV Mott Polarimeter Development at Jefferson Lab

    SciTech Connect

    Price, J. S.; Sinclair, C. K.; Cardman, L. S.; Haanskneccht, J.; Mack, D. J.; Piot, P.; Assamagan, K. A.; Grames, J.

    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.

  18. Thermal Insulation

    NASA Technical Reports Server (NTRS)

    1984-01-01

    Commercially known as Solimide, Temptronics, Inc.'s thermal insulation has application in such vehicles as aircraft, spacecraft and surface transportation systems (i.e. rapid transit cars, trains, buses, and ships) as acoustical treatment for door, wall, and ceiling panels, as a means of reducing vibrations, and as thermal insulation (also useful in industrial equipment). Product originated from research conducted by Johnson Space Center on advanced flame-resistant materials for minimizing fire hazard in the Shuttle and other flight vehicles.

  19. 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.

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

    PubMed

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

    2015-11-01

    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

  1. 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

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

    PubMed

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

    2015-11-01

    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.

  3. Phase fluctuation in overdoped cuprates? Superconducting dome due to Mott-ness of the tightly bound preformed pairs

    NASA Astrophysics Data System (ADS)

    Ku, Wei; Yang, Fan

    2015-03-01

    In contrast to the current lore, we demonstrate that even the overdoped cuprates suffer from superconducting phase fluctuation in the strong binding limit. Specifically, the Mott-ness of the underlying doped holes dictates naturally a generic optimal doping around 15% and nearly complete loss of phase coherence around 25%, giving rise to a dome shape of superconducting transition temperature in excellent agreement with experimental observations of the cuprates. We verify this effect with a simple estimation using Gutzwiller approximation of the preformed pairs, obtained through variational Monte Carlo calculation. This realization suggests strongly the interesting possibility that the high-temperature superconductivity in the cuprates might be mostly described by Bose-Einstein condensation, without crossing over to amplitude fluctuating Cooper pairs. Supported by Department of Energy, Office of Basic Energy Science DE-AC02-98CH10886.

  4. Large epitaxial bi-axial strain induces a Mott-like phase transition in VO{sub 2}

    SciTech Connect

    Kittiwatanakul, Salinporn; Wolf, Stuart A.; Lu, Jiwei

    2014-08-18

    The metal insulator transition (MIT) in vanadium dioxide (VO{sub 2}) has been an important topic for recent years. It has been generally agreed upon that the mechanism of the MIT in bulk VO{sub 2} is considered to be a collaborative Mott-Peierls transition, however, the effect of strain on the phase transition is much more complicated. In this study, the effect of the large strain on the properties of VO{sub 2} films was investigated. One remarkable result is that highly strained epitaxial VO{sub 2} thin films were rutile in the insulating state as well as in the metallic state. These highly strained VO{sub 2} films underwent an electronic phase transition without the concomitant Peierls transition. Our results also show that a very large tensile strain along the c-axis of rutile VO{sub 2} resulted in a phase transition temperature of ∼433 K, much higher than in any previous report. Our findings elicit that the metal insulator transition in VO{sub 2} can be driven by an electronic transition alone, rather the typical coupled electronic-structural transition.

  5. James C. McGroddy Prize for New Materials Talk: What is new in multiferroicity?: Mott ferroelectrics!

    NASA Astrophysics Data System (ADS)

    Cheong, Sang-Wook

    2010-03-01

    Multiferroicity is an old topic. For example, linear magnetoelectric effect in materials such as Cr2O3 with broken time reversal and space inversion symmetry has been known since 1960's. However, giant cross-coupling effects such as flipping polarization or enormous change of dielectric constant by applied magnetic fields have been recently observed in systems such as Tb(Dy)MnO3 and Tb(Dy)Mn2O5 [1-3]. The important ingredient for these giant magnetoelectric effects turns out to be associated with the presence of non-zero d electrons and their mutual interactions, leading to the Mott-insulator-type charge gap, magnetism, and collective phase transitions. Particularly, the collective nature of simultaneous magnetic-ferroelectric phase transitions results in the giant magnetoelectric effects. In addition, fascinating charge transport properties such as a switchable photovoltaic effect and characteristic conduction properties at domain walls stem from the (carrier-doped) Mott insulating nature of compounds such as BiFeO3 and hexagonal YMnO3 [4,5]. [4pt] [1] Kimura, T. et al. Magnetic control of ferroelectric polarization. Nature 426, 55--58 (2003).[0pt] [2] Hur, N. et al. Electric polarization reversal and memory in a multiferroic material induced by magnetic fields. Nature 429, 392--395 (2004).[0pt] [3] Cheong, S.-W. & Mostovoy, M. Multiferroics: a magnetic twist for ferroelectricity. Nature Mater. 6, 13--20 (2007).[0pt] [4] Seidel, J. et al. Conduction at domain walls in oxide multiferroics. Nature Mater. 8, 229--234 (2009).[0pt] [5] Choi, T., Lee, S., Choi, Y.J., Kiryukhin, V. & Cheong, S.-W. Switchable ferroelectric diode and photovoltaic effect in BiFeO3. Science 324, 63--66 (2009)

  6. Mott transition in CaFe2O4 at around 50 GPa

    NASA Astrophysics Data System (ADS)

    Greenberg, Eran; Rozenberg, Gregory Kh.; Xu, Weiming; Pasternak, Moshe P.; McCammon, Catherine; Glazyrin, Konstantin; Dubrovinsky, Leonid S.

    2013-12-01

    Electrical transport and magnetic properties of CaFe2O4 have been studied at pressures up to 70 GPa using Fe57 Mössbauer spectroscopy (MS), Raman spectroscopy, and electrical resistance measurements. These studies have shown the onset of the Mott transition (MT) at a pressure of around 50 GPa, leading to the collapse of Fe3+ magnetic moments and to the insulator-metal (IM) transition. The observed onset of the MT corroborates with the recently reported isostructural transition accompanied by a 12% decrease in the Fe polyhedral volume. An analysis of the alterations of the electrical transport, magnetic, and structural properties with pressure increase and at the transition range suggests that the coinciding IM transition, magnetic moment, and volume collapse at around 50 GPa are caused by the closure of the Hubbard gap driven by the high-spin to low-spin (HS-LS) transition. At that, since MS did not reveal any evidence of a preceding LS state, it could be inferred that the HS-LS transition immediately leads to an IM transition and complete collapse of magnetism.

  7. Direct Probing of the Mott Crossover in the SU (N ) Fermi-Hubbard Model

    NASA Astrophysics Data System (ADS)

    Hofrichter, Christian; Riegger, Luis; Scazza, Francesco; Höfer, Moritz; Fernandes, Diogo Rio; Bloch, Immanuel; Fölling, Simon

    2016-04-01

    We report on a detailed experimental investigation of the equation of state (EoS) of the three-dimensional Fermi-Hubbard model (FHM) in its generalized SU (N ) -symmetric form, using a degenerate ytterbium gas in an optical lattice. In its more common spin-1 /2 form, the FHM is a central model of condensed-matter physics. The generalization to N >2 was first used to describe multi-orbital materials and is expected to exhibit novel many-body phases in a complex phase diagram. By realizing and locally probing the SU (N ) FHM with ultracold atoms, we obtain model-free access to thermodynamic quantities. The measurement of the EoS and the local compressibility allows us to characterize the crossover from a compressible metal to an incompressible Mott insulator. We reach specific entropies above Néel order but below that of uncorrelated spins. Having access to the EoS of such a system represents an important step towards probing predicted novel SU (N ) phases.

  8. Ambient organic molecular passivation of Si yields near-ideal, Schottky-Mott limited, junctions

    NASA Astrophysics Data System (ADS)

    Har-Lavan, Rotem; Yaffe, Omer; Joshi, Pranav; Kazaz, Roy; Cohen, Hagai; Cahen, David

    2012-03-01

    We report near-perfect transfer of the electrical properties of oxide-free Si surface, modified by a molecular monolayer, to the interface of a junction made with that modified Si surface. Such behavior is highly unusual for a covalent, narrow bandgap semiconductor, such as Si. Short, ambient atmosphere, room temperature treatment of oxide-free Si(100) in hydroquinone (HQ)/alkyl alcohol solutions, fully passivates the Si surface, while allowing controlled change of the resulting surface potential. The junctions formed, upon contacting such surfaces with Hg, a metal that does not chemically interact with Si, follow the Schottky-Mott model for metal-semiconductor junctions closer than ever for Si-based junctions. Two examples of such ideal behavior are demonstrated: a) Tuning the molecular surface dipole over 400 mV, with only negligible band bending, by changing the alkyl chain length. Because of the excellent passivation this yields junctions with Hg with barrier heights that follow the change in the Si effective electron affinity nearly ideally. b) HQ/ methanol passivation of Si is accompanied by a large surface dipole, which suffices, as interface dipole, to drive the Si into strong inversion as shown experimentally via its photovoltaic effect. With only ˜0.3 nm molecular interlayer between the metal and the Si, our results proves that it is passivation and prevention of metal-semiconductor interactions that allow ideal metal-semiconductor junction behavior, rather than an insulating transport barrier.

  9. Radiation Insulation

    NASA Technical Reports Server (NTRS)

    1995-01-01

    The Apollo and subsequent spacecraft have had highly effective radiation barriers; made of aluminized polymer film, they bar or let in heat to maintain consistent temperatures inside. Tech 2000, formerly Quantum International Corporation used the NASA technology in its insulating materials, Super "Q" Radiant Barrier, for home, industry and mobile applications. The insulation combines industrial aluminum foil overlaid around a core of another material, usually propylene or mylar. The outer layer reflects up to 97 percent of heat; the central layer creates a thermal break in the structure and thus allows low radiant energy emission. The Quantum Cool Wall, used in cars and trucks, takes up little space while providing superior insulation, thus reducing spoilage and costs. The panels can also dampen sound and engine, exhaust and solar heat.

  10. Insulation Material

    NASA Technical Reports Server (NTRS)

    1984-01-01

    Manufactured by Hitco Materials Division of Armco, Inc. a ceramic fiber insulation material known as Refrasil has been used extensively as a heat-absorbing ablative reinforcement for such space systems as rocket motor nozzles, combustion chambers, and re-entry shields. Refrasil fibers are highly porous and do not melt or vaporize until fibers exceed 3,100 degrees Fahrenheit. Due to these and other properties, Refrasil has found utility in a number of industrial high temperature applications where glass, asbestos and other materials fail. Hitco used this insulation to assist Richardson Co., Inc. in the manufacturing of hard rubber and plastic molded battery cases.

  11. Theory of a competitive spin liquid state for weak Mott insulators on the triangular lattice.

    PubMed

    Mishmash, Ryan V; Garrison, James R; Bieri, Samuel; Xu, Cenke

    2013-10-11

    We propose a novel quantum spin liquid state that can explain many of the intriguing experimental properties of the low-temperature phase of the organic spin liquid candidate materials κ-(BEDT-TTF)2Cu2(CN)3 and EtMe3Sb[Pd(dmit)2]2. This state of paired fermionic spinons preserves all symmetries of the system, and it has a gapless excitation spectrum with quadratic bands that touch at momentum k[over →]=0. This quadratic band touching is protected by symmetries. Using variational Monte Carlo techniques, we show that this state has highly competitive energy in the triangular lattice Heisenberg model supplemented with a realistically large ring-exchange term.

  12. Optical anisotropy of the Jeff=1 /2 Mott insulator Sr2IrO4

    NASA Astrophysics Data System (ADS)

    Pröpper, D.; Yaresko, A. N.; Höppner, M.; Matiks, Y.; Mathis, Y.-L.; Takayama, T.; Matsumoto, A.; Takagi, H.; Keimer, B.; Boris, A. V.

    2016-07-01

    We report the complex dielectric function along and perpendicular to the IrO2 planes in the layered perovskite Sr2IrO4 determined by spectroscopic ellipsometry in the spectral range from 12 meV to 6 eV. Thin high-quality single crystals were stacked to measure the c -axis optical conductivity. In the phonon response, we identified ten infrared-active modes polarized within the basal plane and only four modes polarized along the c axis, which we assign according to first-principles lattice dynamics calculations. We also observed a strong optical anisotropy in the near-infrared spectra. It arises from direct transitions between Ir 5 d t2 g Jeff=1 /2 and Jeff=3 /2 bands, whose transition probability is highly suppressed for light polarized along the c axis. The spectra are analyzed and discussed in terms of relativistic local spin-density approximation (LSDA)+U band structure calculations.

  13. Block Magnetic Excitations in the Orbitally Selective Mott Insulator BaFe2Se3

    NASA Astrophysics Data System (ADS)

    Mourigal, M.; Wu, Shan; Stone, M. B.; Neilson, J. R.; Caron, J. M.; McQueen, T. M.; Broholm, C. L.

    2015-07-01

    Iron pnictides and selenides display a variety of unusual magnetic phases originating from the interplay between electronic, orbital, and lattice degrees of freedom. Using powder inelastic neutron scattering on the two-leg ladder BaFe2Se3 , we fully characterize the static and dynamic spin correlations associated with the Fe4 block state, an exotic magnetic ground state observed in this low-dimensional magnet and in Rb0.89Fe1.58Se2 . All the magnetic excitations of the Fe4 block state predicted by an effective Heisenberg model with localized spins are observed below 300 meV and quantitatively reproduced. However, the data only account for 16 (3 )μB2 per Fe2 + , approximatively 2 /3 of the total spectral weight expected for localized S =2 moments. Our results highlight how orbital degrees of freedom in iron-based magnets can conspire to stabilize an exotic magnetic state.

  14. Photoinduced phase transitions in narrow-gap Mott insulators: the case of VO2

    NASA Astrophysics Data System (ADS)

    He, Zhuoran; Millis, Andrew

    The nonequilibrium dynamics of strongly correlated electrons in photoexcited VO2 is studied using the quantum Boltzmann equation and nonequilibrium Hartree-Fock methods applied to a band structure given by extended density functional theory (DFT+ U+ V) and realistic dynamical interactions. The initial equilibration of electrons occurs in hundreds of femtoseconds. For physically reasonable parameters, our Hartree-Fock calculation sustains a new metastable M1 metal phase that is qualitatively consistent with the recent experiment of Morrison et al. The long-term stability of the M1 metal phase will also be considered This work is supported by the Department of Energy under Grant Number DE-SC0012375.

  15. Metal-Insulator Transition in VO_{2}: A DFT+DMFT Perspective.

    PubMed

    Brito, W H; Aguiar, M C O; Haule, K; Kotliar, G

    2016-07-29

    We present a theoretical investigation of the electronic structure of rutile (metallic) and M_{1} and M_{2} monoclinic (insulating) phases of VO_{2} employing a fully self-consistent combination of density functional theory and embedded dynamical mean field theory calculations. We describe the electronic structure of the metallic and both insulating phases of VO_{2}, and propose a distinct mechanism for the gap opening. We show that Mott physics plays an essential role in all phases of VO_{2}: undimerized vanadium atoms undergo classical Mott transition through local moment formation (in the M_{2} phase), while strong superexchange within V dimers adds significant dynamic intersite correlations, which remove the singularity of self-energy for dimerized V atoms. The resulting transition from rutile to dimerized M_{1} phase is adiabatically connected to the Peierls-like transition, but is better characterized as the Mott transition in the presence of strong intersite exchange. As a consequence of Mott physics, the gap in the dimerized M_{1} phase is temperature dependent. The sole increase of electronic temperature collapses the gap, reminiscent of recent experiments. PMID:27517782

  16. Metal-Insulator Transition in VO2 : A DFT +DMFT Perspective

    NASA Astrophysics Data System (ADS)

    Brito, W. H.; Aguiar, M. C. O.; Haule, K.; Kotliar, G.

    2016-07-01

    We present a theoretical investigation of the electronic structure of rutile (metallic) and M1 and M2 monoclinic (insulating) phases of VO2 employing a fully self-consistent combination of density functional theory and embedded dynamical mean field theory calculations. We describe the electronic structure of the metallic and both insulating phases of VO2 , and propose a distinct mechanism for the gap opening. We show that Mott physics plays an essential role in all phases of VO2 : undimerized vanadium atoms undergo classical Mott transition through local moment formation (in the M2 phase), while strong superexchange within V dimers adds significant dynamic intersite correlations, which remove the singularity of self-energy for dimerized V atoms. The resulting transition from rutile to dimerized M1 phase is adiabatically connected to the Peierls-like transition, but is better characterized as the Mott transition in the presence of strong intersite exchange. As a consequence of Mott physics, the gap in the dimerized M1 phase is temperature dependent. The sole increase of electronic temperature collapses the gap, reminiscent of recent experiments.

  17. Superfluid and Insulating Phases of Fermion Mixtures in Optical Lattices

    NASA Astrophysics Data System (ADS)

    Iskin, M.; de Melo, C. A. R. Sá

    2007-08-01

    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 the FPI phase is particular to the Fermi nature of the constituent atoms of the mixture.

  18. Probing the excitations of a one dimensional topological Bose insulator

    NASA Astrophysics Data System (ADS)

    Dalla Torre, Emanuele G.; Berg, Erez; Altman, Ehud

    2008-03-01

    We investigate the dynamic response of a system of ultracold dipolar atoms or molecules in the one dimensional Haldane Bose insulator phase. This phase, which was recently predicted theoretically [1], is characterized by non-local string order and its elementary excitations are domain walls in this order. We compute experimentally relevant response functions and we derive asymptotically exact expressions near the quantum critical points separating the Haldane insulator from the conventional Mott and density wave insulators. In particular, we predict a narrow absorption peak in Bragg spectroscopy experiments, due to the excitation of a single domain wall in the string order. [1] E.G. Dalla Torre, E. Berg, E. Altman, Phys. Rev Lett. 97, 260401 (2006)

  19. Thermodynamic and topological phase diagrams of correlated topological insulators

    NASA Astrophysics Data System (ADS)

    Zdulski, Damian; Byczuk, Krzysztof

    2015-09-01

    A definition of topological phases of density matrices is presented. The topological invariants in case of both noninteracting and interacting systems are extended to nonzero temperatures. The influence of electron interactions on topological insulators at finite temperatures is investigated. A correlated topological insulator is described by the Kane-Mele model, which is extended by the interaction term of the Falicov-Kimball type. Within the Hartree-Fock and the Hubbard I approximations, thermodynamic and topological phase diagrams are determined where the long-range order is included. The results show that correlation effects lead to a strong suppression of the existence of the nontrivial topological phase. In the homogeneous phase, we find a purely correlation driven phase transition into the topologically trivial Mott insulator.

  20. Mott scattering of polarized electrons in a strong laser field

    SciTech Connect

    Manaut, B.; Taj, S.; Attaourti, Y.

    2005-04-01

    We present analytical and numerical results of the relativistic calculation of the transition matrix element S{sub fi} and differential cross sections for Mott scattering of initially polarized Dirac particles (electrons) in the presence of a strong laser field with linear polarization. We use exact Dirac-Volkov wave functions to describe the dressed electrons and the collision process is treated in the first Born approximation. The influence of the laser field on the degree of polarization of the scattered electron is reported.

  1. Superfluid - Mott transition in the presence of artificial gauge fields

    NASA Astrophysics Data System (ADS)

    Vasic, Ivana; Petrescu, Alex; Le Hur, Karyn; Hofstetter, Walter

    2014-05-01

    Several recent cold atom experiments reported implementation of artificial gauge fields in optical lattice systems, paving the way toward observation of new phases of matter. Here we study the tight-binding model on the honeycomb lattice introduced by Haldane, for lattice bosons. We analyze the ground state topology and quasiparticle properties in the Mott phase by applying bosonic dynamical mean field theory, strong-coupling perturbation theory and exact diagonalization. The phase diagram also contains two different superfluid phases. The quasiparticle dynamics, number fluctuations, and local currents are measurable in cold atom experiments.

  2. Cabrera-Mott kinetics of oxidation of metal nanowires

    NASA Astrophysics Data System (ADS)

    Zhdanov, Vladimir P.; Kasemo, Bengt

    2012-06-01

    The Cabrera-Mott model, implying that oxidation of a metal is limited by the field-facilitated activated jumps of metal ions at the metal-oxide interface, was originally proposed to interpret growth of thin oxide films on planar metal surfaces. Recently, the model was used to describe oxidation of spherical nanoparticles with small radius of curvature. Here, we analyze oxidation of nanowires. The increase of the oxide thickness with increasing time for a nanowire is shown to be slower than that for a nanoparticle with the same radius, but faster than in the case of a planar surface.

  3. 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.

  4. 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…

  5. Novel electronic structures of self-organized 1D surface nanostructures

    NASA Astrophysics Data System (ADS)

    Yeom, Han Woong

    2002-03-01

    Recently we have searched for the exotic physical properties of the nanostructures formed on semiconductor surfaces by STM and photoelectron spectroscopy [1]. The major objects have been the 1D chains of metal adsorbates on Si or SiC surfaces. It now seems obvious that such (sub)nanometer-scale atomic chains possess significant technological implications for the future device technology. Furthermore those systems provide very attractive and unprecedented opportunity to study exotic physical properties of 1D electronic systems in detail, such as Peierls instability, charge density wave (CDW), electron correlation, non-Fermi liquid behavior, and interplay of defects with 1D excitations (1D solitons, 1D domain walls and etc). The present talk focuses on the recent experimental and theoretical studies for the novel electronic properties of the 1D atomic chain systems on the Si(111) surface such as Si(111)4x1-In [2], Si(111)5x2-Au [3], Si(557)5x2-Au [4], and Si(111)3x2-Ba(or Ca) [5]. These systems have well defined one dimensional electronic bands, which exhibit intriguing properties challenging our present understanding. The major points of debates right now are the origin of the periodicity-doubling phase transition of Si(111)4x1-In in relation to 1D CDW [2], the nature of the band gap (or pseudo gap) of Si(111)5x2-Au (also related to 1D CDW idea) [3], the Si(111)3x2-Ba (or Ca) surface (1D Mott-Hubbard system ?) [5], and the nature of the band dispersion of the Si(557)5x2-Au surface (any Luttinger liquid behavior ?) [4]. Some new aspects of these systems are introduced such as the doping dependence of the 1D CDW system and the transport measurements across the 1D CDW transition. References [1] For a recent review, see H. W. Yeom, J. Electron Spectro. and Rel. Phenom., 114-116, 283 (2001). [2] H.W. Yeom et al., Phys. Rev. Lett. 82, 4898 (1999); C. Kumpf et al, Phys. Rev. Lett. 85, 4916 (2001); H.W. Yeom et al., submitted; G. Le Lay et al., submitted; J.-H. Cho et al

  6. Metal-insulator transitions in LaTiO3 / CaTiO3 superlattices

    NASA Astrophysics Data System (ADS)

    Seo, Sung Seok A.; Lee, Ho Nyung

    2010-03-01

    Strongly correlated electrons at an interface of complex oxide heterostructures often show interesting behaviors that require an introduction of new physical concepts. For example, the metallic transport behavior found in the superlattices of a Mott insulator LaTiO3 and a band insulator SrTiO3 (STO) has established the concept of interfacial electronic reconstruction. In this work, we have studied the transport property of a new type of Mott/band insulator LaTiO3/CaTiO3 (LTO/CTO) superlattices grown by pulsed laser deposition (PLD). In order to rule out concerns about the PLD plume-triggered oxygen vacancies generated in STO substrates, which might influence transport measurement, and to investigate the effect of epitaxial strain, we have used insulating NdGaO3 substrates. While both LTO and CTO single films are highly insulating, we have observed intriguing metal-insulator transitions (MIT) in the LTO/CTO superlattices depending on the global LTO/CTO thickness ratio and temperature. (Note that LTO/STO superlattices are metallic at all temperatures (2-300 K)). In this talk, we will discuss the origin of the MIT in the scheme of self compensation mechanism of d-electrons at the hetero-interface between LTO and CTO.

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

    DOE PAGES

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

    2016-01-21

    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 exhibitsmore » interfacial charge transfer from Ti to Ni sites, giving rise to an insulating ground state with orbital polarization and eg 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

  8. 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

  9. 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.

  10. Crossover from Mott to Efros-Shklovskii variable-range-hopping conductivity in InxOy films

    NASA Astrophysics Data System (ADS)

    Rosenbaum, Ralph

    1991-08-01

    Crossover from Mott variable-range-hopping conductivity to the Coulomb-gap Efros-Shklovskii (ES) variable-range-hopping conductivity has been observed in amorphous indium oxide films. The hopping exponent x~=0.56 in the activated Coulomb-gap regime is greater than the x=0.50 value predicted by Efros and Shklovskii. The experimental value of x~=0.56 is in excellent agreement with the computational calculations of Mobius and Richter, who suggest that x=0.55. The experimental ratios for TMott/TES~=54 are in close agreement with the prediction of Castner that TMott/TES=81. Experimental values for the crossover temperatures, which separate the two hopping regimes, are consistent with predicted values. The Coulomb-gap energy ΔCG is estimated to range from a few tenths of a meV for films close to the metal-insulator transition to several meV's for films quite deep in the insulating regime.

  11. Mott Multiferroics and Ferroelectric Metals from Dynamical Mean-Field Theory combined with Density-Functional Theory

    NASA Astrophysics Data System (ADS)

    Capone, Massimo

    2015-03-01

    Multiferroic materials, in which ferroelectricity and long-range magnetic ordering coexist, are natural candidates for applications. In this perspective, the most promising compounds are those in which the two phenomena do not simply coexist, but they influence each other through a magnetoelectric coupling. We present different applications of Density Functional Theory combined with Dynamical Mean-Field Theory in which electron-electron correlation effects are crucial in the stabilization of multiferroic behavior and in the magnetoelectric coupling. Within this wide family we can distinguish different cases. In Sr0.5Ba0.5MnO3 the multiferroic behavior is associated with a Mott insulating state in which the Mn half-filled t2g orbitals are responsible of the magnetic properties and the value of the polarization is strongly affected by the magnetic state. LiOsO3 shares the same electronic configuration with half-filled Os t2g orbitals. Despite this configuration enhances the effect of electron-electron interactions, the material remains metallic and represents a peculiar ferroelectric metal. We propose however how to turn this non-magnetic polar metal into a multiferroic through the design of a superlattice, which increases the degree of correlation, leading to Mott localization of the Os orbitals. In completely different systems, such as organic crystals like (TMTTF)2-X, strong correlations can lead to multiferroicity in organic crystals such as (TMTTF)2-X, where charge ordering promotes a polarization which is favored by an antiferromagnetic ordering. We finally discuss how strong correlations can play a major role away from half-filling when the Hund's coupling is sizable in compounds with a nominal valence of, e.g., two electrons in the three t2g orbitals. Such ``Hund's metals'' are correlated despite being far from Mott localization. This physical regime can be a fertile ground to obtain other ferroelectric metals. This work is supported by ERC/FP7 through the

  12. Nature of Pressure-induced Insulating States in Simple Metals

    NASA Astrophysics Data System (ADS)

    Naumov, Ivan; Hemley, Russell

    As experimentally established, all the alkali metals and heavy alkaline earth metals (Ca, Sr and Ba) become progressively less conductive on compression, at least up to some critical limit over a broad pressure range. Of these metals, Li and Na clearly undergo pressure-induced metal-insulator transitions, which may also be called reverse Mott transitions. Here, using group theory arguments and first-principles calculations, we show that such transitions can be understood in terms of band representations introduced by Zak. The valence bands in the insulating states are described by simple and composite band representations constructed from localized Wannier functions centered on points unoccupied by atoms. The character of the Wannier functions is closely related to the degree of s-p(-d) hybridization and reflects multi-center chemical bonding in these insulating states. The conditions under which an insulating state is allowed for structures having an integer number of atoms per primitive unit cell as well as re-entrant (i.e., metal-insulator-metal) transition sequences are detailed, resulting in predictions of semimetallic phases with flat surface states. The general principles developed are tested and applied to the alkali and alkaline earth metals, including elements where high-pressure insulating phases have been identified or reported (e.g., Li, Na, and Ca). This research was supported by EFree, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Basic Energy Sciences under Award DESC0001057.

  13. Probing non local order parameters in highly correlated Bose insulators

    NASA Astrophysics Data System (ADS)

    Altman, Ehud

    2008-03-01

    Ground states of integer spin chains are known since the late 80's to sustain highly non local order described by infinite string operators of the spins. Such states defy the usual Landau theory description and can be considered simple prototypes of topological order. Recently we showed that spinless Bose insulators with nearest neighbor or longer range repulsion in one dimension can exhibit similar string order in terms of the boson density [1]. The tunability of cold atomic systems would allow much more flexibility in probing the non local order than spin systems do. For example the bosons can be tuned across a quantum phase transition between the exotic insulator, which we term Haldane insulator, and the usual Mott insulator. Investigating how the transition responds to external perturbations lends direct access to properties of the string order parameter. I will demonstrate this with several new results obtained from a field theoretic description of the phases and confirmed by numerical calculations using DMRG. Particularly revealing of the unusual character of the string order is the prediction that any external perturbation, which breaks the lattice inversion symmetry, would eliminate the distinction between the Haldane and Mott phases and allow a fully gapped adiabatic connection between them. This is remarkable given that neither phase involves spontaneous breaking of lattice inversion symmetry. We also predict that inter-chain tunneling destroys the direct phase transition between the two insulators by establishing an intermediate superfluid phase. Finally I will discuss how the new phases and phase transitions may be realized and probed in actual experiments with ultra cold atoms or polar molecules. [1] E. G. Dalla Torre, E. Berg and E. Altman, Phys. Rev. Lett. 97, 260401 (2006)

  14. Wannier-Mott excitons in semiconductors with a superlattice

    SciTech Connect

    Suris, R. A.

    2015-06-15

    The effect of the motion of a Wannier-Mott exciton in semiconductors with a superlattice formed by heterojunctions on the exciton binding energy and wave function is analyzed. This effect arises as a result of the fact that the dispersion laws of the electron and hole that form an exciton in a superlattice differ from the quadratic law. The investigated one-dimensional superlattice consists of alternating semiconductor layers with different energy positions of the conduction and valence bands, i.e., with one-dimensional wells and barriers. The exciton state in a superlattice consisting of quantum dots is analyzed. It is demonstrated that the closer the electron and hole effective masses, the greater the dependence of the binding energy on the exciton quasi-momentum. The possibility of replacing the tunneling excitation transfer between superlattice cells with the dipole-dipole one at certain exciton quasi-wave vector values is investigated.

  15. Slowdown of the Electronic Relaxation Close to the Mott Transition.

    PubMed

    Sayyad, Sharareh; Eckstein, Martin

    2016-08-26

    We investigate the time-dependent reformation of the quasiparticle peak in a correlated metal near the Mott transition, after the system is quenched into a hot electron state and equilibrates with an environment which is colder than the Fermi-liquid crossover temperature. Close to the transition, we identify a purely electronic bottleneck time scale, which depends on the spectral weight around the Fermi energy in the bad metallic phase in a nonlinear way. This time scale can be orders of magnitude larger than the bare and renormalized electronic hopping time, so that a separation of electronic and lattice time scales may break down. The results are obtained using nonequilibrium dynamical mean-field theory and a slave-rotor representation of the Anderson impurity model. PMID:27610867

  16. Ge doping of GaN beyond the Mott transition

    NASA Astrophysics Data System (ADS)

    Ajay, A.; Schörmann, J.; Jiménez-Rodriguez, M.; Lim, C. B.; Walther, F.; Rohnke, M.; Mouton, I.; Amichi, L.; Bougerol, C.; Den Hertog, M. I.; Eickhoff, M.; Monroy, E.

    2016-11-01

    We present a study of germanium as n-type dopant in wurtzite GaN films grown by plasma-assisted molecular-beam epitaxy, reaching carrier concentrations of up to 6.7  ×  1020 cm‑3 at 300 K, well beyond the Mott density. The Ge concentration and free carrier density were found to scale linearly with the Ge flux in the studied range. All the GaN:Ge layers present smooth surface morphology with atomic terraces, without trace of pits or cracks, and the mosaicity of the samples has no noticeable dependence on the Ge concentration. The variation of the GaN:Ge band gap with the carrier concentration is consistent with theoretical calculations of the band gap renormalization due to electron–electron and electron–ion interaction, and Burstein–Moss effect.

  17. Slowdown of the Electronic Relaxation Close to the Mott Transition

    NASA Astrophysics Data System (ADS)

    Sayyad, Sharareh; Eckstein, Martin

    2016-08-01

    We investigate the time-dependent reformation of the quasiparticle peak in a correlated metal near the Mott transition, after the system is quenched into a hot electron state and equilibrates with an environment which is colder than the Fermi-liquid crossover temperature. Close to the transition, we identify a purely electronic bottleneck time scale, which depends on the spectral weight around the Fermi energy in the bad metallic phase in a nonlinear way. This time scale can be orders of magnitude larger than the bare and renormalized electronic hopping time, so that a separation of electronic and lattice time scales may break down. The results are obtained using nonequilibrium dynamical mean-field theory and a slave-rotor representation of the Anderson impurity model.

  18. A cylindrically symmetric "micro-Mott" electron polarimeter.

    PubMed

    Clayburn, N B; Brunkow, E; Burtwistle, S J; Rutherford, G H; Gay, T J

    2016-05-01

    A small, novel, cylindrically symmetric Mott electron polarimeter is described. The effective Sherman function, Seff, or analyzing power, for 20 kV Au target bias with a 1.3 keV energy loss window is 0.16 ± 0.01, where uncertainty in the measurement is due primarily to uncertainty in the incident electron polarization. For an energy loss window of 0.5 keV, Seff reaches its maximum value of 0.24 ± 0.02. The device's maximum efficiency, I/Io, defined as the detected count rate divided by the incident particle rate, is 3.7 ± 0.2 × 10(-4) at 20 keV. The figure-of-merit of the device, η, is defined as Seff (2)IIo and equals 9.0 ± 1.6 × 10(-6). Potential sources of false asymmetries due to detector electronic asymmetry and beam misalignment have been investigated. The new polarimeter's performance is compared to published results for similar compact retarding-field Mott polarimeters, and it is concluded that this device has a relatively large Seff and low efficiency. SIMION(®) electron trajectory simulations and Sherman function calculations are presented to explain the differences in performance between this device and previous designs. This design has an Seff that is insensitive to spatial beam fluctuations and, for an energy loss window >0.5 keV, negligible background due to spurious ion and X-ray production at the target. PMID:27250409

  19. A cylindrically symmetric "micro-Mott" electron polarimeter

    NASA Astrophysics Data System (ADS)

    Clayburn, N. B.; Brunkow, E.; Burtwistle, S. J.; Rutherford, G. H.; Gay, T. J.

    2016-05-01

    A small, novel, cylindrically symmetric Mott electron polarimeter is described. The effective Sherman function, Seff, or analyzing power, for 20 kV Au target bias with a 1.3 keV energy loss window is 0.16 ± 0.01, where uncertainty in the measurement is due primarily to uncertainty in the incident electron polarization. For an energy loss window of 0.5 keV, Seff reaches its maximum value of 0.24 ± 0.02. The device's maximum efficiency, I/Io, defined as the detected count rate divided by the incident particle rate, is 3.7 ± 0.2 × 10-4 at 20 keV. The figure-of-merit of the device, η, is defined as Seff2I/Io and equals 9.0 ± 1.6 × 10-6. Potential sources of false asymmetries due to detector electronic asymmetry and beam misalignment have been investigated. The new polarimeter's performance is compared to published results for similar compact retarding-field Mott polarimeters, and it is concluded that this device has a relatively large Seff and low efficiency. SIMION® electron trajectory simulations and Sherman function calculations are presented to explain the differences in performance between this device and previous designs. This design has an Seff that is insensitive to spatial beam fluctuations and, for an energy loss window >0.5 keV, negligible background due to spurious ion and X-ray production at the target.

  20. Broken Symmetry Bond Order Phase Transitions in 1D Generalized Ionic Hubbard Models

    NASA Astrophysics Data System (ADS)

    Wilkens, Tim; Martin, Richard M.

    2000-03-01

    An ionic Hubbard model at half filling is expected to undergo a transition from a band insulator (BI) at U=0 to a Mott insulator (MI) like the usual Hubbard model at large U. In previous numerical work this was found to occur at a metallic point with an abrupt change of 1/2 in the electronic polarization(R.Resta and S.Sorella, PRL 74) 4738 (1995); G.Ortiz et al, PRB 54 13515 (1996).; however, this left open questions about the transition since a topological variable cannot be a valid order parameter for a true phase transition. Recent theoretical work has predicted the existence of a Bond Ordered (BO) phase between the BI and MI phases(M.Fabrizio et al, PRL 83) 2014 (1999) . We report the results of Quantum Monte Carlo (QMC) calculations that determine the spontaneous BO order parameter and polarization showing a second order quantum phase transition at a critical U. Studies at large U and/or small ionicity lead to our conclusion that the MI is unstable to the BO phase at any non-zero ionicity. These results further suggest interesting conclusions about quantized charge transport in these correlated systems.

  1. Tank Insulation

    NASA Technical Reports Server (NTRS)

    1979-01-01

    For NASA's Apollo program, McDonnell Douglas Astronautics Company, Huntington Beach, California, developed and built the S-IVB, uppermost stage of the three-stage Saturn V moonbooster. An important part of the development task was fabrication of a tank to contain liquid hydrogen fuel for the stage's rocket engine. The liquid hydrogen had to be contained at the supercold temperature of 423 degrees below zero Fahrenheit. The tank had to be perfectly insulated to keep engine or solar heat from reaching the fuel; if the hydrogen were permitted to warm up, it would have boiled off, or converted to gaseous form, reducing the amount of fuel available to the engine. McDonnell Douglas' answer was a supereffective insulation called 3D, which consisted of a one-inch thickness of polyurethane foam reinforced in three dimensions with fiberglass threads. Over a 13-year development and construction period, the company built 30 tanks and never experienced a failure. Now, after years of additional development, an advanced version of 3D is finding application as part of a containment system for transporting Liquefied Natural Gas (LNG) by ship.

  2. Orbitally driven trimerization in LiVO2 and LiVS2: a ``partial Mott transition''

    NASA Astrophysics Data System (ADS)

    Wu, Hua; Khomskii, D. I.

    2011-03-01

    Layered triangular-lattice transition-metal compounds often display interesting magnetic and electronic properties. Here we studied the formation of the trimerized spin-singlet state of the V3+ (S = 1) in vanadates Li VO2 and Li VS2 and their electronic structure with a special orbital order, using constrained LSDA+ U calculations combined with lattice optimization. The obtained results show that the trimerization distortion in Li VO2 increases as the effective U decreases, and the calculated distortion of ~ 0.3 AA at the small U = 1 eV agrees well with the experiments, indicating that Li VO2 is close to a metal-insulator transition. The corresponding distortion in Li VS2 is even stronger, being ~ 0.4 AA at the U = 1 eV, which is due to enhanced electron delocalization via increased V-S covalency, in spite of a lattice expansion. This agrees with the experimental finding that Li VS2 has a metal-insulator transition. The calculated energy gain associated with the trimerization well accounts for the observed structural phase transition temperature in Li VO2 and Li VS2 . We conclude that the trimerization in Li VO2 and Li VS2 is due to a partial delocalization of the orbitally ordered electrons---a ``partial Mott transition,'' occurring not in the whole system but in small clusters (here in trimers). This situation is contrasted with that in Na VO2 , which is further away from the localized-itinerant crossover and thus remains insulating with different orbital ordering.

  3. Insulators for high voltages

    SciTech Connect

    Looms, J.S.T.

    1987-01-01

    This book describes electrical insulators for high voltage applications. Topics considered include the insulating materials, the manufacture of wet process porcelain, the manufacture of tempered glass, the glass-fibre core, the polymeric housing, the common problem - terminating an insulator, mechanical constraints, the physics of pollution flashover, the physics of contamination, testing of insulators, conclusions from testing, remedies for flashover, insulators for special cases, interference and noise, and the insulator of the future.

  4. Metallic and Insulating Phases of Interacting Fermions in a 3D Optical Lattice

    NASA Astrophysics Data System (ADS)

    Hackermueller, Lucia

    2010-03-01

    Ultracold fermions in optical lattices are a promising tool to simulate solid state physics, since they represent an ideal and highly tunable implementation of the Hubbard Hamiltonian. A proof of principle is to demonstrate a Mott insulating state, where repulsive interactions between the atoms lead to an insulating behavior in a half-filled conduction band. In our experiments we study repulsively and attractively interacting ^40K atoms within the combination of a red-detuned dipole trap and a blue detuned lattice. This setup allows us to gradually transform the system from metallic to Mott-insulating and band insulating states. We measure the phase of the system by analyzing the system size and the number of doubly occupied sites and compare our findings to DMFT theory. In addition we investigate the dynamical behavior of interacting fermionic mixtures. We prepare a band insulating system and suddenly release it into a homogenous lattice. We detect a symmetric behavior from a ballistic expansion for non-interacting clouds to a strongly suppressed expansion due to the formation of attractively or repulsively bound pairs. This experiment allows us to study transport properties of the Hubbard model. This work was done together with U.Schneider, S. Will, Th. Best, S. Braun, I. Bloch and with theoretical support from T.A. Costi, R.W. Helmes, D. Rasch, A.Rosch, B. Paredes, M. Moreno-Cardoner, T. Kitagawa, E.Demler.

  5. Insulator-metal transition in highly compressed NiO.

    PubMed

    Gavriliuk, Alexander G; Trojan, Ivan A; Struzhkin, Viktor V

    2012-08-24

    The insulator-metal transition was observed experimentally in nickel monoxide (NiO) at very high pressures of ~240 GPa. The sample resistance becomes measurable at about 130 GPa and decreases substantially with the pressure increase to ~240 GPa. A sharp drop in resistance by about 3 orders of magnitude has been observed at ~240 GPa with a concomitant change of the resistance type from semiconducting to metallic. This is the first experimental observation of an insulator-metal transition in NiO, which was anticipated by Mott decades ago. From simple multielectron consideration, the metallic phase of NiO forms when the effective Hubbard energy U(eff) is almost equal to the estimated full bandwidth 2W. PMID:23002762

  6. Metal-insulator transition in films of doped semiconductor nanocrystals.

    PubMed

    Chen, Ting; Reich, K V; Kramer, Nicolaas J; Fu, Han; Kortshagen, Uwe R; Shklovskii, B I

    2016-03-01

    To fully deploy the potential of semiconductor nanocrystal films as low-cost electronic materials, a better understanding of the amount of dopants required to make their conductivity metallic is needed. In bulk semiconductors, the critical concentration of electrons at the metal-insulator transition is described by the Mott criterion. Here, we theoretically derive the critical concentration nc for films of heavily doped nanocrystals devoid of ligands at their surface and in direct contact with each other. In the accompanying experiments, we investigate the conduction mechanism in films of phosphorus-doped, ligand-free silicon nanocrystals. At the largest electron concentration achieved in our samples, which is half the predicted nc, we find that the localization length of hopping electrons is close to three times the nanocrystals diameter, indicating that the film approaches the metal-insulator transition.

  7. Mott behavior of ultrathin epitaxial LaNiO3 films and interfaces via hard x-ray and standing-wave excited photoemission

    NASA Astrophysics Data System (ADS)

    Gray, Alexander; Kaiser, Alexander; Son, Junwoo; Janotti, Anderson; Yang, See-Hun; Bostwick, Aaron; Ueda, Shigenori; Kobayashi, Keisuke; van de Walle, Chris; Stemmer, Susanne; Fadley, Charles

    2012-02-01

    In this study we apply several emerging x-ray photoemission techniques to study Mott behavior of ultrathin LaNiO3 films and interfaces in a depth-resolved manner. In order to understand the effects of thickness and strain on the electronic structure, we apply hard x-ray photoemission (HAXPES) at 6 keV to epitaxial LaNiO3 films of varying thickness under compressive and tensile strain. Mott metal-to-insulator transition is observed for the thinnest films. Furthermore, standing-wave-excited photoemission is used to study the electronic structure of ultrathin LaNiO3 in a SrTiO3/LaNiO3 superlattice. Standing-wave measurements of core-level and valence band spectra are used to derive layer-resolved densities of states, revealing a suppression of electronic states near the Fermi level in the multilayer as compared to bulk LaNiO3. Further analysis shows that the suppression of these states is not homogeneously distributed over the LaNiO3 layers but is more pronounced near the interfaces.

  8. Metal-insulator transitions in IZO, IGZO, and ITZO films

    NASA Astrophysics Data System (ADS)

    Makise, Kazumasa; Hidaka, Kazuya; Ezaki, Syohei; Asano, Takayuki; Shinozaki, Bunju; Tomai, Shigekazu; Yano, Koki; Nakamura, Hiroaki

    2014-10-01

    In this study, we measured the low-temperature resistivity of amorphous two- and three-dimensional (2D and 3D) indium-zinc oxide, indium-gallium-zinc oxide, and indium-tin-zinc oxide films with a wide range of carrier densities. To determine their critical characteristics at the metal-insulator transition (MIT), we used the Ioffe-Regel criterion. We found that the MIT occurs in a narrow range between k F ℓ = 0.13 and k F ℓ = 0.25, where k F and ℓ are the Fermi wave number and electron mean free path, respectively. For films in the insulating region, we analyzed ρ ( T ) using a procedure proposed by Zabrodskii and Zinov'eva. This analysis confirmed the occurrence of Mott and Efros-Shklovskii (ES) variable-range hopping. The materials studied show crossover behavior from exp(TMott/T)1/4 or exp(TMott/T)1/3 for Mott hopping conduction to exp(TES/T)1/2 for ES hopping conduction with decreasing temperature. For both 2D and 3D materials, we found that the relationship between TMott and TES satisfies TES ∝ TMott2/3.

  9. Zero finite-temperature charge stiffness within the half-filled 1D Hubbard model

    SciTech Connect

    Carmelo, J.M.P.; Gu, Shi-Jian; Sacramento, P.D.

    2013-12-15

    Even though the one-dimensional (1D) Hubbard model is solvable by the Bethe ansatz, at half-filling its finite-temperature T>0 transport properties remain poorly understood. In this paper we combine that solution with symmetry to show that within that prominent T=0 1D insulator the charge stiffness D(T) vanishes for T>0 and finite values of the on-site repulsion U in the thermodynamic limit. This result is exact and clarifies a long-standing open problem. It rules out that at half-filling the model is an ideal conductor in the thermodynamic limit. Whether at finite T and U>0 it is an ideal insulator or a normal resistor remains an open question. That at half-filling the charge stiffness is finite at U=0 and vanishes for U>0 is found to result from a general transition from a conductor to an insulator or resistor occurring at U=U{sub c}=0 for all finite temperatures T>0. (At T=0 such a transition is the quantum metal to Mott–Hubbard-insulator transition.) The interplay of the η-spin SU(2) symmetry with the hidden U(1) symmetry beyond SO(4) is found to play a central role in the unusual finite-temperature charge transport properties of the 1D half-filled Hubbard model. -- Highlights: •The charge stiffness of the half-filled 1D Hubbard model is evaluated. •Its value is controlled by the model symmetry operator algebras. •We find that there is no charge ballistic transport at finite temperatures T>0. •The hidden U(1) symmetry controls the U=0 phase transition for T>0.

  10. Upstream Design and 1D-CAE

    NASA Astrophysics Data System (ADS)

    Sawada, Hiroyuki

    Recently, engineering design environment of Japan is changing variously. Manufacturing companies are being challenged to design and bring out products that meet the diverse demands of customers and are competitive against those produced by rising countries(1). In order to keep and strengthen the competitiveness of Japanese companies, it is necessary to create new added values as well as conventional ones. It is well known that design at the early stages has a great influence on the final design solution. Therefore, design support tools for the upstream design is necessary for creating new added values. We have established a research society for 1D-CAE (1 Dimensional Computer Aided Engineering)(2), which is a general term for idea, methodology and tools applicable for the upstream design support, and discuss the concept and definition of 1D-CAE. This paper reports our discussion about 1D-CAE.

  11. Multiple density layered insulator

    DOEpatents

    Alger, Terry W.

    1994-01-01

    A multiple density layered insulator for use with a laser is disclosed wh provides at least two different insulation materials for a laser discharge tube, where the two insulation materials have different thermoconductivities. The multiple layer insulation materials provide for improved thermoconductivity capability for improved laser operation.

  12. Multiple density layered insulator

    DOEpatents

    Alger, T.W.

    1994-09-06

    A multiple density layered insulator for use with a laser is disclosed which provides at least two different insulation materials for a laser discharge tube, where the two insulation materials have different thermoconductivities. The multiple layer insulation materials provide for improved thermoconductivity capability for improved laser operation. 4 figs.

  13. Calcium silicate insulation structure

    DOEpatents

    Kollie, Thomas G.; Lauf, Robert J.

    1995-01-01

    An insulative structure including a powder-filled evacuated casing utilizes a quantity of finely divided synthetic calcium silicate having a relatively high surface area. The resultant structure-provides superior thermal insulating characteristics over a broad temperature range and is particularly well-suited as a panel for a refrigerator or freezer or the insulative barrier for a cooler or a insulated bottle.

  14. 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

  15. Magnetic-field induced crossover of superconducting percolation regimes in the layered organic Mott system {kappa}-(BEDT-TTF){sub 2}Cu[N(CN){sub 2}]Cl.

    SciTech Connect

    Mueller, J.; Brandenberg, J.; Schlueter, J. A.; Materials Science Division; Max Planck Inst. for Chemical Physics of Solids

    2009-01-01

    Fluctuation spectroscopy is used to investigate the organic bandwidth-controlled Mott system {kappa}-(BEDT-TTF){sub 2}Cu[N(CN){sub 2}]Cl. We find evidence for percolative-type superconductivity in the spatially inhomogeneous coexistence region of antiferromagnetic insulating and superconducting states. When the superconducting transition is driven by a magnetic field, percolation seems to be dominated by instable superconducting clusters upon approaching T{sub c}(B) from above, before a 'classical' type of percolation is resumed at low fields, dominated by the fractional change of superconducting clusters. The 1/f noise is resolved into Lorentzian spectra in the crossover region, where the action of an individual fluctuator is enhanced, pointing to a mesoscopic phase separation.

  16. DESIGN PACKAGE 1D SYSTEM SAFETY ANALYSIS

    SciTech Connect

    L.R. Eisler

    1995-02-02

    The purpose of this analysis is to systematically identify and evaluate hazards related to the Yucca Mountain Project Exploratory Studies Facility (ESF) Design Package 1D, Surface Facilities, (for a list of design items included in the package 1D system safety analysis see section 3). This process is an integral part of the systems engineering process; whereby safety is considered during planning, design, testing, and construction. A largely qualitative approach was used since a radiological System Safety analysis is not required. The risk assessment in this analysis characterizes the accident scenarios associated with the Design Package 1D structures/systems/components in terms of relative risk and includes recommendations for mitigating all identified risks. The priority for recommending and implementing mitigation control features is: (1) Incorporate measures to reduce risks and hazards into the structure/system/component (S/S/C) design, (2) add safety devices and capabilities to the designs that reduce risk, (3) provide devices that detect and warn personnel of hazardous conditions, and (4) develop procedures and conduct training to increase worker awareness of potential hazards, on methods to reduce exposure to hazards, and on the actions required to avoid accidents or correct hazardous conditions. The scope of this analysis is limited to the Design Package 1D structures/systems/components (S/S/Cs) during normal operations excluding hazards occurring during maintenance and ''off normal'' operations.

  17. Metal-insulator transitions of bulk and domain-wall states in pyrochlore iridates

    NASA Astrophysics Data System (ADS)

    Ueda, Kentaro

    A family of pyrochlore iridates R2Ir2O7 offers an ideal platform to explore intriguing phases such as topological Mott insulator and Weyl semimetal. Here we report transport and spectroscopic studies on the metal-insulator transition (MIT) induced by the modulations of effective electron correlation and magnetic structures, which is finely tuned by external pressure, chemical substitutions (R = Nd1-x Prx and SmyNd1-y) , and magnetic field. A reentrant insulator-metal-insulator transition is observed near the paramagnetic insulator-metal phase boundary reminiscent of a first-order Mott transition for R = SmyNd1-y compounds (y~0.8). The metallic states on the magnetic domain walls (DWs), which are observed for R = Nd in real space as well as in transport properties, is simultaneously turned into the insulating one. These findings imply that the DW electronic state is intimately linked to the bulk states. For the mixed R = Nd1-x Prx compounds, the divergent behavior of resistivity with antiferromagnetic order is significantly suppressed by applying a magnetic field along [001] direction. It is attributed to the phase transition from the antiferromagnetic insulating state to the novel Weyl (semi-)metal state accompanied by the change of magnetic structure. The present study combined with experiment and theory suggests that there are abundant exotic phases with physical parameters such as electron correlation and Ir-5 d magnetic order pattern. Work performed in collaboration with J. Fujioka, B.-J. Yang, C. Terakura, N. Nagaosa, Y. Tokura (University of Tokyo, RIKEN CEMS), J. Shiogai, A. Tsukazaki, S. Nakamura, S. Awaji (Tohoku University). 1This work was supported by JSPS FIRST Program and Grant-in-Aid for Scientific Research (Grants No. 80609488 and No. 24224009).

  18. Topological crystalline insulators.

    PubMed

    Fu, Liang

    2011-03-11

    The recent discovery of topological insulators has revived interest in the band topology of insulators. In this Letter, we extend the topological classification of band structures to include certain crystal point group symmetry. We find a class of three-dimensional "topological crystalline insulators" which have metallic surface states with quadratic band degeneracy on high symmetry crystal surfaces. These topological crystalline insulators are the counterpart of topological insulators in materials without spin-orbit coupling. Their band structures are characterized by new topological invariants. We hope this work will enlarge the family of topological phases in band insulators and stimulate the search for them in real materials.

  19. Effective field theory and integrability in two-dimensional Mott transition

    SciTech Connect

    Bottesi, Federico L.; Zemba, Guillermo R.

    2011-08-15

    Highlights: > Mott transition in 2d lattice fermion model. > 3D integrability out of 2D. > Effective field theory for Mott transition in 2d. > Double Chern-Simons. > d-Density waves. - Abstract: We study the Mott transition in a two-dimensional lattice spinless fermion model with nearest neighbors density-density interactions. By means of a two-dimensional Jordan-Wigner transformation, the model is mapped onto the lattice XXZ spin model, which is shown to possess a quantum group symmetry as a consequence of a recently found solution of the Zamolodchikov tetrahedron equation. A projection (from three to two space-time dimensions) property of the solution is used to identify the symmetry of the model at the Mott critical point as U{sub q}(sl(2)-circumflex)xU{sub q}(sl(2)-circumflex), with deformation parameter q = -1. Based on this result, the low-energy effective field theory for the model is obtained and shown to be a lattice double Chern-Simons theory with coupling constant k = 1 (with the standard normalization). By further employing the effective filed theory methods, we show that the Mott transition that arises is of topological nature, with vortices in an antiferromagnetic array and matter currents characterized by a d-density wave order parameter. We also analyze the behavior of the system upon weak coupling, and conclude that it undergoes a quantum gas-liquid transition which belongs to the Ising universality class.

  20. Centrosome Positioning in 1D Cell Migration

    NASA Astrophysics Data System (ADS)

    Adlerz, Katrina; Aranda-Espinoza, Helim

    During cell migration, the positioning of the centrosome and nucleus define a cell's polarity. For a cell migrating on a two-dimensional substrate the centrosome is positioned in front of the nucleus. Under one-dimensional confinement, however, the centrosome is positioned behind the nucleus in 60% of cells. It is known that the centrosome is positioned by CDC42 and dynein for cells moving on a 2D substrate in a wound-healing assay. It is currently unknown, however, if this is also true for cells moving under 1D confinement, where the centrosome position is often reversed. Therefore, centrosome positioning was studied in cells migrating under 1D confinement, which mimics cells migrating through 3D matrices. 3 to 5 μm fibronectin lines were stamped onto a glass substrate and cells with fluorescently labeled nuclei and centrosomes migrated on the lines. Our results show that when a cell changes directions the centrosome position is maintained. That is, when the centrosome is between the nucleus and the cell's trailing edge and the cell changes direction, the centrosome will be translocated across the nucleus to the back of the cell again. A dynein inhibitor did have an influence on centrosome positioning in 1D migration and change of directions.

  1. Metal-insulator transitions due to self-doping

    SciTech Connect

    Blawid, S.; Tuan, H.A.; Yanagisawa, T.; Fulde, P.

    1996-09-01

    We investigate the influence of an unoccupied band on the transport properties of a strongly correlated electron system. For that purpose, additional orbitals are coupled to a Hubbard model via hybridization. The filling is one electron per site. Depending on the position of the additional band, both a metal-to-insulator and an insulator-to-metal transition occur with increasing hybridization. The latter transition from a Mott insulator into a metal via {open_quote}{open_quote}self-doping{close_quote}{close_quote} was recently proposed to explain the low carrier concentration in Yb{sub 4}As{sub 3}. We suggest a restrictive parameter regime for this transition, making use of exact results in various limits. The predicted absence of the self-doping transition for nested Fermi surfaces is confirmed by means of an unrestricted Hartree-Fock approximation and an exact diagonalization study in one dimension. In the general case metal-insulator phase diagrams are obtained within the slave-boson mean-field and the alloy-analog approximations. {copyright} {ital 1996 The American Physical Society.}

  2. 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

  3. Silica reusable surface insulation

    NASA Technical Reports Server (NTRS)

    Goldstein, H. E.; Smith, M.; Leiser, D. B. (Inventor)

    1976-01-01

    A reusable silica surface insulation material is provided by bonding amorphous silica fibers with colloidal silica at an elevated temperature. The surface insulation is ordinarily manufactured in the form of blocks (i.e., tiles).

  4. Percolative Metal-Insulator transition in the doped Hubbard-Holstein model with the Gutzwiller Approach

    NASA Astrophysics Data System (ADS)

    Moradi Kurdestany, Jamshid; Satpathy, Sashi

    Motivated by the recent progress in understanding of Mott insulators away from half filling, observed in many perovskite oxides, we study the metal-insulator transition in the Hubbard-Holstein model, which contains both the Coulomb and the electron-lattice (Jahn Teller) interactions by using the Gutzwiller variational method. We find that strong electron-lattice Interaction leads to phase separation, which however can be frustrated due to the long-range Coulomb interaction, resulting in a mixed phase consisting of puddles of metallic phases embedded in an insulating matrix. When the dopant concentration exceeds a threshold value xc , the metallic part forms a percolating network leading to metallic conduction. Depending on the strength of the electron-lattice interaction, xc can be of the order of 0.05 - 0.20 or so, which is the typical value observed in the perovskites.

  5. Ultrahigh-resolution spin-resolved photoemission spectrometer with a mini Mott detector.

    PubMed

    Souma, S; Takayama, A; Sugawara, K; Sato, T; Takahashi, T

    2010-09-01

    We have developed an ultrahigh-resolution spin-resolved photoemission spectrometer with a highly efficient mini Mott detector and an intense xenon plasma discharge lamp. The spectrometer achieves the energy resolutions of 0.9 and 8 meV for non-spin-resolved and spin-resolved modes, respectively. Three-dimensional spin-polarization is determined by using a 90° electron deflector situated before the Mott detector. The performance of spectrometer is demonstrated by observation of a clear Rashba splitting of the Bi(111) surface states.

  6. Ultrahigh-resolution spin-resolved photoemission spectrometer with a mini Mott detector

    SciTech Connect

    Souma, S.; Sugawara, K.; Takayama, A.; Sato, T.; Takahashi, T.

    2010-09-15

    We have developed an ultrahigh-resolution spin-resolved photoemission spectrometer with a highly efficient mini Mott detector and an intense xenon plasma discharge lamp. The spectrometer achieves the energy resolutions of 0.9 and 8 meV for non-spin-resolved and spin-resolved modes, respectively. Three-dimensional spin-polarization is determined by using a 90 deg. electron deflector situated before the Mott detector. The performance of spectrometer is demonstrated by observation of a clear Rashba splitting of the Bi(111) surface states.

  7. Shrinking of the Cooper Pair Insulator Phase in Thin Films with Ultrasmall Superconducting Islands

    NASA Astrophysics Data System (ADS)

    Joy, J. C.; Zhang, X.; Zhao, C.; Valles, J. M., Jr.; Fernandes, G.; Xu, J. M.

    The ubiquity of the bosonic Cooper Pair Insulator (CPI) phase near the two-dimensional superconductor to insulator transition (SIT) is a long standing question. While a number of two dimensional materials exhibit bosonic insulating phases similar to the Mott Insulator in arrays of ultrasmall, Josephson coupled superconducting islands, others show behaviors consistent with a fermionic insulating phase. Utilizing specially prepared anodized aluminum oxide substrates, we are able to fabricate films reminiscent of arrays of superconducting islands whose properties are tunable by varying the substrate morphology. Our recent work has focused on arrays of islands which possess an energy level spacing comparable to the mean field superconducting gap, where one expects pair breaking followed by fermionic Anderson Localization as the dominant mechanism by which superconductivity is destroyed. Early results show that the paradigmatic bosonic insulator exists only very near the disorder tuned SIT, while films only marginally deeper in the insulating phase exhibit transport distinct from the CPI's reentrant, activated transport. We are grateful for the support of NSF Grant No. DMR-1307290, the AFOSR, and the AOARD. Currently at Northwestern Polytechnical University, Xian, China.

  8. A 1-D dusty plasma photonic crystal

    SciTech Connect

    Mitu, M. L.; Ticoş, C. M.; Toader, D.; Banu, N.; Scurtu, A.

    2013-09-21

    It is demonstrated numerically that a 1-D plasma crystal made of micron size cylindrical dust particles can, in principle, work as a photonic crystal for terahertz waves. The dust rods are parallel to each other and arranged in a linear string forming a periodic structure of dielectric-plasma regions. The dispersion equation is found by solving the waves equation with the boundary conditions at the dust-plasma interface and taking into account the dielectric permittivity of the dust material and plasma. The wavelength of the electromagnetic waves is in the range of a few hundred microns, close to the interparticle separation distance. The band gaps of the 1-D plasma crystal are numerically found for different types of dust materials, separation distances between the dust rods and rod diameters. The distance between levitated dust rods forming a string in rf plasma is shown experimentally to vary over a relatively wide range, from 650 μm to about 1350 μm, depending on the rf power fed into the discharge.

  9. Cubic topological Kondo insulators.

    PubMed

    Alexandrov, Victor; Dzero, Maxim; Coleman, Piers

    2013-11-27

    Current theories of Kondo insulators employ the interaction of conduction electrons with localized Kramers doublets originating from a tetragonal crystalline environment, yet all Kondo insulators are cubic. Here we develop a theory of cubic topological Kondo insulators involving the interaction of Γ(8) spin quartets with a conduction sea. The spin quartets greatly increase the potential for strong topological insulators, entirely eliminating the weak topological phases from the diagram. We show that the relevant topological behavior in cubic Kondo insulators can only reside at the lower symmetry X or M points in the Brillouin zone, leading to three Dirac cones with heavy quasiparticles.

  10. Antiferromagnetic Metal and Mott Transition on Shastry-Sutherland Lattice

    PubMed Central

    Liu, Hai-Di; Chen, Yao-Hua; Lin, Heng-Fu; Tao, Hong-Shuai; Liu, Wu-Ming

    2014-01-01

    The Shastry-Sutherland lattice, one of the simplest systems with geometrical frustration, which has an exact eigenstate by putting singlets on diagonal bonds, can be realized in a group of layered compounds and raises both theoretical and experimental interest. Most of the previous studies on the Shastry-Sutherland lattice are focusing on the Heisenberg model. Here we opt for the Hubbard model to calculate phase diagrams over a wide range of interaction parameters, and show the competing effects of interaction, frustration and temperature. At low temperature, frustration is shown to favor a paramagnetic metallic ground state, while interaction drives the system to an antiferromagnetic insulator phase. Between these two phases, there are an antiferromagnetic metal phase and a paramagnetic insulator phase (which should consist of a small plaquette phase and a dimer phase) resulting from the competition of the frustration and the interaction. Our results may shed light on more exhaustive studies about quantum phase transitions in geometrically frustrated systems. PMID:24777282

  11. Insulated solar storage tanks

    SciTech Connect

    Eldighidy, S.M. )

    1991-01-01

    This paper presents the theoretical and experimental investigation of an insulated parallelepiped, outdoor solar, water-filled storage tank of size 1 m {times} 0.5 m {times} 0.3 m, that is made from galvanized iron. The absorption coefficient of the insulating material has been determined. The effects of plastic covers and insulation thickness on the water temperature and the energy gained or lost by water are investigated. Moreover, the effects of insulation thickness on the temperature profiles of the insulating material are discussed. The results show that the absorption coefficient decreases as the insulation thickness increases. Also, it is found that the glass wool insulation of 2.5 cm thickness has the best results compared with the other thicknesses (5 cm, 7.5 cm, and 10 cm) as far as the water temperature and the energy gained by water are concerned.

  12. 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.

  13. Brane parity orders in the insulating state of Hubbard ladders

    NASA Astrophysics Data System (ADS)

    Degli Esposti Boschi, Cristian; Montorsi, Arianna; Roncaglia, Marco

    2016-08-01

    The Mott insulating state of the Hubbard model at half filling could be depicted as a spin liquid of singly occupied sites with holon-doublon quantum fluctuations localized in pairs. In one dimension the behavior is captured by a finite value of the charge parity string correlator, which fails to remain finite when generalized to higher dimensions. We recover a definition of parity brane correlator which may remain nonvanishing in the presence of interchain coupling, by assigning an appropriate fractional phase to the parity breaking fluctuations. In the case of Hubbard ladders at half filling, we find that the charge parity brane is nonzero at any repulsive value of interaction. The spin-parity brane instead becomes nonvanishing in the even-leg case, in correspondence to the onset of the spin gapped D-Mott phase, which is absent in the odd-leg case. The behavior of the parity correlators is also analyzed by means of a numerical DMRG analysis of the one- and two-leg ladder.

  14. 1D fast coded aperture camera.

    PubMed

    Haw, Magnus; Bellan, Paul

    2015-04-01

    A fast (100 MHz) 1D coded aperture visible light camera has been developed as a prototype for imaging plasma experiments in the EUV/X-ray bands. The system uses printed patterns on transparency sheets as the masked aperture and an 80 channel photodiode array (9 V reverse bias) as the detector. In the low signal limit, the system has demonstrated 40-fold increase in throughput and a signal-to-noise gain of ≈7 over that of a pinhole camera of equivalent parameters. In its present iteration, the camera can only image visible light; however, the only modifications needed to make the system EUV/X-ray sensitive are to acquire appropriate EUV/X-ray photodiodes and to machine a metal masked aperture. PMID:25933861

  15. 1D fast coded aperture camera.

    PubMed

    Haw, Magnus; Bellan, Paul

    2015-04-01

    A fast (100 MHz) 1D coded aperture visible light camera has been developed as a prototype for imaging plasma experiments in the EUV/X-ray bands. The system uses printed patterns on transparency sheets as the masked aperture and an 80 channel photodiode array (9 V reverse bias) as the detector. In the low signal limit, the system has demonstrated 40-fold increase in throughput and a signal-to-noise gain of ≈7 over that of a pinhole camera of equivalent parameters. In its present iteration, the camera can only image visible light; however, the only modifications needed to make the system EUV/X-ray sensitive are to acquire appropriate EUV/X-ray photodiodes and to machine a metal masked aperture.

  16. 1D-VAR Retrieval Using Superchannels

    NASA Technical Reports Server (NTRS)

    Liu, Xu; Zhou, Daniel; Larar, Allen; Smith, William L.; Schluessel, Peter; Mango, Stephen; SaintGermain, Karen

    2008-01-01

    Since modern ultra-spectral remote sensors have thousands of channels, it is difficult to include all of them in a 1D-var retrieval system. We will describe a physical inversion algorithm, which includes all available channels for the atmospheric temperature, moisture, cloud, and surface parameter retrievals. Both the forward model and the inversion algorithm compress the channel radiances into super channels. These super channels are obtained by projecting the radiance spectra onto a set of pre-calculated eigenvectors. The forward model provides both super channel properties and jacobian in EOF space directly. For ultra-spectral sensors such as Infrared Atmospheric Sounding Interferometer (IASI) and the NPOESS Airborne Sounder Testbed Interferometer (NAST), a compression ratio of more than 80 can be achieved, leading to a significant reduction in computations involved in an inversion process. Results will be shown applying the algorithm to real IASI and NAST data.

  17. Promising Breakthroughs: Initial Results of the Charles Stewart Mott Foundation's Breaking Through Initiative. In Brief

    ERIC Educational Resources Information Center

    Bragg, Debra D.; Barnett, Elisabeth A.

    2008-01-01

    The Breaking Through (BT) initiative of the Charles Stewart Mott Foundation seeks to prepare low-skilled adults, adult learners who are below college-level in reading, writing and/or mathematics, often lacking a high school diploma, and frequently low-income, to be successful in college and the labor market by strengthening and expanding policies…

  18. 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.

  19. Position Paper on International Studies Program at C. S. Mott Community College.

    ERIC Educational Resources Information Center

    Joseph, Wise B.

    This descriptive report outlines the history and operation of the International Studies Program at Charles Stewart Mott Community College (MCC). First, introductory material discusses the growing importance of international studies in the nation's community colleges. Next, the need for an international studies and international trade program at…

  20. Time-dependent Mott transition in the periodic Anderson model with nonlocal hybridization

    NASA Astrophysics Data System (ADS)

    Hofmann, Felix; Potthoff, Michael

    2016-08-01

    The time-dependent Mott transition in a periodic Anderson model with off-site, nearest-neighbor hybridization is studied within the framework of nonequilibrium self-energy functional theory. Using the two-site dynamical-impurity approximation, we compute the real-time dynamics of the optimal variational parameter and of different observables initiated by sudden quenches of the Hubbard-U and identify the critical interaction. The time-dependent transition is orbital selective, i.e., in the final state, reached in the long-time limit after the quench to the critical interaction, the Mott gap opens in the spectral function of the localized orbitals only. We discuss the dependence of the critical interaction and of the final-state effective temperature on the hybridization strength and point out the various similarities between the nonequilibrium and the equilibrium Mott transition. It is shown that these can also be smoothly connected to each other by increasing the duration of a U-ramp from a sudden quench to a quasi-static process. The physics found for the model with off-site hybridization is compared with the dynamical Mott transition in the single-orbital Hubbard model and with the dynamical crossover found for the real-time dynamics of the conventional Anderson lattice with on-site hybridization.

  1. THE MOTT FOUNDATION CHILDREN'S HEALTH CENTER--THE WORLD OF STEPHEN SHAKER.

    ERIC Educational Resources Information Center

    Flint Board of Education, MI.

    THE C.S. MOTT FOUNDATION CHILDREN'S HEALTH CENTER WAS BUILT TO SERVE CHILDREN OF THOSE BORDERLINE FAMILIES WHOSE INCOMES PROHIBIT PRIVATE MEDICAL CARE YET MAKE THEM INELIGIBLE FOR DIRECT RELIEF OF ANY KIND. THE NEED FOR SUCH A CENTER WAS PROVED BY THE CHILDREN'S 18,000 VISITS ANNUALLY FOR HEALTH CARE. WHILE PROVIDING CARE FOR CHILDREN WAS THE MAIN…

  2. From Romantic Idealism to Enlightenment Rationalism: Lucretia Coffin Mott Responds to Richard Henry Dana, Sr.

    ERIC Educational Resources Information Center

    Sillars, Malcolm O.

    1995-01-01

    Suggests that the contrast between speeches by Richard Henry Dana Sr. and Lucretia Coffin Mott lies not only in their two views of the woman's place and role in society but also in the respective orientation toward Romantic idealism and Enlightenment rationalism. (TB)

  3. Computational design of axion insulators based on 5d spinel compounds.

    PubMed

    Wan, Xiangang; Vishwanath, Ashvin; Savrasov, Sergey Y

    2012-04-01

    Based on density functional calculation using the local density approximation+U method, we predict that osmium compounds such as CaOs(2)O(4) and SrOs(2)O(4) can be stabilized in the geometrically frustrated spinel crystal structure. They show ferromagnetic order in a reasonable range of the on-site Coulomb correlation U and exotic electronic properties, in particular, a large magnetoelectric coupling characteristic of axion electrodynamics. Depending on U, other electronic phases including a 3D Weyl semimetal and Mott insulator are also shown to occur. PMID:22540814

  4. On metal-insulator transition in cubic fullerides

    NASA Astrophysics Data System (ADS)

    Iwahara, Naoya; Chibotaru, Liviu

    The interplay between degenerate orbital and electron correlation is a key to characterize the electronic phases in, for example, transition metal compounds and alkali-doped fullerides. Besides, the degenerate orbital couples to spin and lattice degrees of freedom ,giving rise to exotic phenomena. Here, we develop the self-consistent Gutzwiller approach for the simultaneous treatment of the Jahn-Teller effect and electron correlation, and apply the methodology to reveal the nature of the ground electronic state of fullerides. For small Coulomb repulsion on site U, the fulleride is quasi degenerate correlated metal. With increase of U, we found the quantum phase transition from the metallic phase to JT split phase. In the latter, the Mott transition (MT) mainly develops in the half-filled subband, whereas the empty and the completely filled subbands are almost uninvolved. Therefore, we can qualify the metal-insulator transition in fullerides as an orbital selective MT induced by JT effect.

  5. Quantum critical transport at a continuous metal-insulator transition

    NASA Astrophysics Data System (ADS)

    Haldar, P.; Laad, M. S.; Hassan, S. R.

    2016-08-01

    In contrast to the first-order correlation-driven Mott metal-insulator transition, continuous disorder-driven transitions are intrinsically quantum critical. Here, we investigate transport quantum criticality in the Falicov-Kimball model, a representative of the latter class in the strong disorder category. Employing cluster-dynamical mean-field theory, we find clear and anomalous quantum critical scaling behavior manifesting as perfect mirror symmetry of scaling curves on both sides of the MIT. Surprisingly, we find that the beta function β (g ) scales as log(g ) deep into the bad-metallic phase as well, providing a sound unified basis for these findings. We argue that such strong localization quantum criticality may manifest in real three-dimensional systems where disorder effects are more important than electron-electron interactions.

  6. Delocalization of Weakly Interacting Bosons in a 1D Quasiperiodic Potential

    NASA Astrophysics Data System (ADS)

    Michal, V. P.; Altshuler, B. L.; Shlyapnikov, G. V.

    2014-07-01

    We consider weakly interacting bosons in a 1D quasiperiodic potential (Aubry-Azbel-Harper model) in the regime where all single-particle states are localized. We show that the interparticle interaction may lead to the many-body delocalization and we obtain the finite-temperature phase diagram. Counterintuitively, in a wide range of parameters the delocalization requires stronger coupling as the temperature increases. This means that the system of bosons can undergo a transition from a fluid to insulator (glass) state under heating.

  7. Scratched-XY Universality and Phase Diagram of Disordered 1D Bosons in Optical Lattice

    NASA Astrophysics Data System (ADS)

    Yao, Zhiyuan; Pollet, Lode; Prokof'ev, Nikolay; Svistunov, Boris

    The superfluid-insulator quantum phase transition in a 1D system with weak links belongs to the so-called scratched-XY universality class, provided the irrenormalizable exponent ζ characterizing the distribution of weak links is smaller than 2 / 3 . With a combination of worm-algorithm Monte Carlo simulations and asymptotically exact analytics, we accurately trace the position of the scratched-XY critical line on the ground-state phase diagram of bosonic Hubbard model at unity filling. In particular, we reveal the location of the tricritical point separating the scratched-XY criticality from the Giamarchi-Schulz one.

  8. On the theory of current passage via an ideal insulator

    SciTech Connect

    Elesin, V. F.

    2015-01-15

    An analytic solution to the problem of current passage via an ideal insulator in the case of monopolar hole injection has been found. The current-voltage (J-V) characteristics have been obtained for the first time in a broad range of parameters (insulator length, hole concentrations at boundaries, temperature, etc.) and applied voltages. It is shown that the Mott-Gurney quadratic J-V relation is valid only in a certain interval of currents between J{sub 1} and J{sub 2}. For J < J{sub 1}, the current linearly depends on voltage V to within V{sup 3} terms. A new mode has been found for J > J{sub 2}, where the J-V characteristic also becomes linear because the insulator is completely filled with injected holes. The integration constants are determined in the entire range of parameters and currents. Analytic expressions for the spatial electric-field and hole-concentration distributions are derived.

  9. Interaction effects and quantum phase transitions in topological insulators

    SciTech Connect

    Varney, Christopher N.; Sun Kai; Galitski, Victor; Rigol, Marcos

    2010-09-15

    We study strong correlation effects in topological insulators via the Lanczos algorithm, which we utilize to calculate the exact many-particle ground-state wave function and its topological properties. We analyze the simple, noninteracting Haldane model on a honeycomb lattice with known topological properties and demonstrate that these properties are already evident in small clusters. Next, we consider interacting fermions by introducing repulsive nearest-neighbor interactions. A first-order quantum phase transition was discovered at finite interaction strength between the topological band insulator and a topologically trivial Mott insulating phase by use of the fidelity metric and the charge-density-wave structure factor. We construct the phase diagram at T=0 as a function of the interaction strength and the complex phase for the next-nearest-neighbor hoppings. Finally, we consider the Haldane model with interacting hard-core bosons, where no evidence for a topological phase is observed. An important general conclusion of our work is that despite the intrinsic nonlocality of topological phases their key topological properties manifest themselves already in small systems and therefore can be studied numerically via exact diagonalization and observed experimentally, e.g., with trapped ions and cold atoms in optical lattices.

  10. Nature of the Insulating Ground State of the Two-Dimensional Sn Atom Lattice on SiC(0001)

    NASA Astrophysics Data System (ADS)

    Yi, Seho; Lee, Hunpyo; Choi, Jin-Ho; Cho, Jun-Hyung

    2016-07-01

    Semiconductor surfaces with narrow surface bands provide unique playgrounds to search for Mott-insulating state. Recently, a combined experimental and theoretical study of the two-dimensional (2D) Sn atom lattice on a wide-gap SiC(0001) substrate proposed a Mott-type insulator driven by strong on-site Coulomb repulsion U within a single-band Hubbard model. However, our systematic density-functional theory (DFT) study with local, semilocal, and hybrid exchange-correlation functionals shows that the Sn dangling-bond state largely hybridizes with the substrate Si 3p and C 2p states to split into three surface bands due to the crystal field. Such a hybridization gives rise to the stabilization of the antiferromagnetic order via superexchange interactions. The band gap and the density of states predicted by the hybrid DFT calculation agree well with photoemission data. Our findings not only suggest that the Sn/SiC(0001) system can be represented as a Slater-type insulator driven by long-range magnetism, but also have an implication that taking into account long-range interactions beyond the on-site interaction would be of importance for properly describing the insulating nature of Sn/SiC(0001).

  11. Interaction-Driven Topological Insulator in Fermionic Cold Atoms on an Optical Lattice: A Design with a Density Functional Formalism.

    PubMed

    Kitamura, Sota; Tsuji, Naoto; Aoki, Hideo

    2015-07-24

    We design an interaction-driven topological insulator for fermionic cold atoms in an optical lattice; that is, we pose the question of whether we can realize in a continuous space a spontaneous symmetry breaking induced by the interatom interaction into a topological Chern insulator. Such a state, sometimes called a "topological Mott insulator," has yet to be realized in solid-state systems, since this requires, in the tight-binding model, large off-site interactions on top of a small on-site interaction. Here, we overcome the difficulty by introducing a spin-dependent potential, where a spin-selective occupation of fermions in A and B sublattices makes the on-site interaction Pauli forbidden, while a sizeable intersite interaction is achieved by a shallow optical potential with a large overlap between neighboring Wannier orbitals. This puts the system away from the tight-binding model, so that we adopt density functional theory for cold atoms, here extended to accommodate noncollinear spin structures emerging in the topological regime, to quantitatively demonstrate the phase transition to the topological Mott insulator.

  12. Nature of the Insulating Ground State of the Two-Dimensional Sn Atom Lattice on SiC(0001).

    PubMed

    Yi, Seho; Lee, Hunpyo; Choi, Jin-Ho; Cho, Jun-Hyung

    2016-01-01

    Semiconductor surfaces with narrow surface bands provide unique playgrounds to search for Mott-insulating state. Recently, a combined experimental and theoretical study of the two-dimensional (2D) Sn atom lattice on a wide-gap SiC(0001) substrate proposed a Mott-type insulator driven by strong on-site Coulomb repulsion U within a single-band Hubbard model. However, our systematic density-functional theory (DFT) study with local, semilocal, and hybrid exchange-correlation functionals shows that the Sn dangling-bond state largely hybridizes with the substrate Si 3p and C 2p states to split into three surface bands due to the crystal field. Such a hybridization gives rise to the stabilization of the antiferromagnetic order via superexchange interactions. The band gap and the density of states predicted by the hybrid DFT calculation agree well with photoemission data. Our findings not only suggest that the Sn/SiC(0001) system can be represented as a Slater-type insulator driven by long-range magnetism, but also have an implication that taking into account long-range interactions beyond the on-site interaction would be of importance for properly describing the insulating nature of Sn/SiC(0001). PMID:27465057

  13. Interacting weak topological insulators and their transition to Dirac semimetal phases

    NASA Astrophysics Data System (ADS)

    Sangiovanni, Giorgio; Hanke, Werner; Li, Gang; Trauzettel, Bjoern

    Topological insulators in the presence of strong Coulomb interaction constitute novel phases of matter. Transitions between these phases can be driven by single-particle or many-body effects. On the basis of ab-initio calculations, we identify a concrete material, i.e. Ca2PtO4, that turns out to be a hole-doped weak topological insulator. Interestingly, the Pt- d orbitals in this material are relevant for the band inversion that gives rise to the topological phase. Therefore, Coulomb interaction should be of importance in Ca2PtO4. To study the influence of interactions on the weak topological insulating phase, we look at a toy model corresponding to a layer-stacked 3D version of the Bernevig-Hughes-Zhang model with local interactions. For small to intermediate interaction strength, we discover novel interaction-driven topological phase transitions between the weak topological insulator and two Dirac semimetal phases. The latter correspond to gapless topological phases. For strong interactions, the system eventually becomes a Mott insulator. DFG Grant No. Ha 1537/23-1 within the Forschergruppe FOR 1162, SPP Grant Ha 1537/24-2, SFB 1170 ``ToCoTronics'', SPP 1666, the Helmholtz Foundation (VITI), the ``Elitenetzwerk Bayern'' (ENB graduate school on ``Topological insulators'').

  14. Multilayer Insulation Material Guidelines

    NASA Technical Reports Server (NTRS)

    Finckenor, M. M.; Dooling, D.

    1999-01-01

    Multilayer Insulation Material Guidelines provides data on multilayer insulation materials used by previous spacecraft such as Spacelab and the Long-Duration Exposure Facility and outlines other concerns. The data presented in the document are presented for information only. They can be used as guidelines for multilayer insulation design for future spacecraft provided the thermal requirements of each new design and the environmental effects on these materials are taken into account.

  15. Topological crystalline insulator nanostructures.

    PubMed

    Shen, Jie; Cha, Judy J

    2014-11-01

    Topological crystalline insulators are topological insulators whose surface states are protected by the crystalline symmetry, instead of the time reversal symmetry. Similar to the first generation of three-dimensional topological insulators such as Bi₂Se₃ and Bi₂Te₃, topological crystalline insulators also possess surface states with exotic electronic properties such as spin-momentum locking and Dirac dispersion. Experimentally verified topological crystalline insulators to date are SnTe, Pb₁-xSnxSe, and Pb₁-xSnxTe. Because topological protection comes from the crystal symmetry, magnetic impurities or in-plane magnetic fields are not expected to open a gap in the surface states in topological crystalline insulators. Additionally, because they have a cubic structure instead of a layered structure, branched structures or strong coupling with other materials for large proximity effects are possible, which are difficult with layered Bi₂Se₃ and Bi₂Te₃. Thus, additional fundamental phenomena inaccessible in three-dimensional topological insulators can be pursued. In this review, topological crystalline insulator SnTe nanostructures will be discussed. For comparison, experimental results based on SnTe thin films will be covered. Surface state properties of topological crystalline insulators will be discussed briefly.

  16. Composite Flexible Blanket Insulation

    NASA Technical Reports Server (NTRS)

    Kourtides, Demetrius A. (Inventor); Pitts, William C. (Inventor); Goldstein, Howard E. (Inventor); Sawko, Paul M. (Inventor)

    1991-01-01

    Composite flexible multilayer insulation systems (MLI) were evaluated for thermal performance and compared with the currently used fibrous silica (baseline) insulation system. The systems described are multilayer insulations consisting of alternating layers of metal foil and scrim ceramic cloth or vacuum metallized polymeric films quilted together using ceramic thread. A silicon carbide thread for use in the quilting and the method of making it are also described. These systems are useful in providing lightweight insulation for a variety of uses, particularly on the surface of aerospace vehicles subject to very high temperatures during flight.

  17. Insulated waterproof drainage material

    SciTech Connect

    Tarko, P.L.

    1988-03-15

    An insulative waterproof drainage material is described comprising: a sheet of rigid material having hills and valleys therein to define a core having opposed surfaces; permeable fabric material attached to one of the opposed surfaces; and a layer of thermally insulative material on the other of the opposed surfaces. The insulative material has first surface covering the hills and valleys and a second surface oppositely disposed from the first surface defining an outer surface. The outer surface is spaced a preselected distance D from the hills of the core. The pre-selected distance D define an insulative material thickness corresponding to a pre-selected thermal value.

  18. Alternator insulation evaluation tests

    NASA Technical Reports Server (NTRS)

    Penn, W. B.; Schaefer, R. F.; Balke, R. L.

    1972-01-01

    Tests were conducted to predict the remaining electrical insulation life of a 60 KW homopolar inductor alternator following completion of NASA turbo-alternator endurance tests for SNAP-8 space electrical power systems application. The insulation quality was established for two alternators following completion of these tests. A step-temperature aging test procedure was developed for insulation life prediction and applied to one of the two alternators. Armature winding insulation life of over 80,000 hours for an average winding temperature of 248 degrees C was predicted using the developed procedure.

  19. Loose-fill insulations

    SciTech Connect

    1995-05-01

    Whether you are increasing the insulation levels in your current home or selecting insulation for a new home, choosing the right insulation material can be challenging. Fibrous loose-fill insulations such as cellulose, fiberglass, and rock wool are options you may wish to consider. This publication will introduce you to these materials--what they are, how they are applied, how they compare with each other, and other considerations regarding their use--so that you can decide whether loose fills are right for your home.

  20. Ultrafast dynamics of localized magnetic moments in the unconventional Mott insulator Sr2IrO4.

    PubMed

    Krupin, O; Dakovski, G L; Kim, B J; Kim, J W; Kim, Jungho; Mishra, S; Chuang, Yi-De; Serrao, C R; Lee, W-S; Schlotter, W F; Minitti, M P; Zhu, D; Fritz, D; Chollet, M; Ramesh, R; Molodtsov, S L; Turner, J J

    2016-08-17

    We report a time-resolved study of the ultrafast dynamics of the magnetic moments formed by the [Formula: see text] states in Sr2IrO4 by directly probing the localized iridium 5d magnetic state through resonant x-ray diffraction. Using optical pump-hard x-ray probe measurements, two relaxation time scales were determined: a fast fluence-independent relaxation is found to take place on a time scale of 1.5 ps, followed by a slower relaxation on a time scale of 500 ps-1.5 ns. PMID:27310659

  1. Ultrafast dynamics of localized magnetic moments in the unconventional Mott insulator Sr2IrO4

    NASA Astrophysics Data System (ADS)

    Krupin, O.; Dakovski, G. L.; Kim, B. J.; Kim, J. W.; Kim, Jungho; Mishra, S.; Chuang, Yi-De; Serrao, C. R.; Lee, W.-S.; Schlotter, W. F.; Minitti, M. P.; Zhu, D.; Fritz, D.; Chollet, M.; Ramesh, R.; Molodtsov, S. L.; Turner, J. J.

    2016-08-01

    We report a time-resolved study of the ultrafast dynamics of the magnetic moments formed by the {{J}\\text{eff}}=1/2 states in Sr2IrO4 by directly probing the localized iridium 5d magnetic state through resonant x-ray diffraction. Using optical pump–hard x-ray probe measurements, two relaxation time scales were determined: a fast fluence-independent relaxation is found to take place on a time scale of 1.5 ps, followed by a slower relaxation on a time scale of 500 ps–1.5 ns.

  2. Gas insulated transmission line with insulators having field controlling recesses

    DOEpatents

    Cookson, Alan H.; Pederson, Bjorn O.

    1984-01-01

    A gas insulated transmission line having a novel insulator for supporting an inner conductor concentrically within an outer sheath. The insulator has a recess contiguous with the periphery of one of the outer and inner conductors. The recess is disposed to a depth equal to an optimum gap for the dielectric insulating fluid used for the high voltage insulation or alternately disposed to a large depth so as to reduce the field at the critical conductor/insulator interface.

  3. 1D-1D Coulomb drag in a 6 Million Mobility Bi-layer Heterostructure

    NASA Astrophysics Data System (ADS)

    Bilodeau, Simon; Laroche, Dominique; Xia, Jian-Sheng; Lilly, Mike; Reno, John; Pfeiffer, Loren; West, Ken; Gervais, Guillaume

    We report Coulomb drag measurements in vertically-coupled quantum wires. The wires are fabricated in GaAs/AlGaAs bilayer heterostructures grown from two different MBE chambers: one at Sandia National Laboratories (1.2M mobility), and the other at Princeton University (6M mobility). The previously observed positive and negative drag signals are seen in both types of devices, demonstrating the robustness of the result. However, attempts to determine the temperature dependence of the drag signal in the 1D regime proved challenging in the higher mobility heterostructure (Princeton), in part because of difficulties in aligning the wires within the same transverse subband configuration. Nevertheless, this work, performed at the Microkelvin laboratory of the University of Florida, is an important proof-of-concept for future investigations of the temperature dependence of the 1D-1D drag signal down to a few mK. Such an experiment could confirm the Luttinger charge density wave interlocking predicted to occur in the wires. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under Contract DE-AC04-94AL8500.

  4. Thermal insulation blanket material

    NASA Technical Reports Server (NTRS)

    Pusch, R. H.

    1982-01-01

    A study was conducted to provide a tailorable advanced blanket insulation based on a woven design having an integrally woven core structure. A highly pure quartz yarn was selected for weaving and the cells formed were filled with a microquartz felt insulation.

  5. Insulation Fact Sheet.

    ERIC Educational Resources Information Center

    Conservation and Renewable Energy Inquiry and Referral Service (DOE), Silver Spring, MD.

    Heating and cooling account for 50-70% of the energy consumed in the average American home. Heating water accounts for another 20%. A poorly insulated home loses much of this energy, causing drafty rooms and high energy bills. This fact sheet discusses how to determine if your home needs more insulation, the additional thermal resistance (called…

  6. Breakdown of organic insulators

    NASA Technical Reports Server (NTRS)

    Cuddihy, E. F.

    1983-01-01

    Solar cells and their associated electrical interconnects and leads were encapsulated in transparent elastomeric materials. Their purpose in a photovoltaic module, one of the most important for these elastomeric encapsulation materials, is to function as electrical insulation. This includes internal insulation between adjacent solar cells, between other encapsulated electrical parts, and between the total internal electrical circuitry and external metal frames, grounded areas, and module surfaces. Catastrophic electrical breakdown of the encapsulant insulation materials or electrical current through these materials or module edges to external locations can lead to module failure and can create hazards to humans. Electrical insulation stability, advanced elastomeric encapsulation materials are developed which are intended to be intrinsically free of in-situ ionic impurities, have ultralow water absorption, be weather-stable (UV, oxygen), and have high mechanical flexibility. Efforts to develop a method of assessing the life potential of organic insulation materials in photovoltaic modules are described.

  7. Topological Kondo Insulators

    NASA Astrophysics Data System (ADS)

    Dzero, Maxim; Xia, Jing; Galitski, Victor; Coleman, Piers

    2016-03-01

    This article reviews recent theoretical and experimental work on a new class of topological material -- topological Kondo insulators, which develop through the interplay of strong correlations and spin-orbit interactions. The history of Kondo insulators is reviewed along with the theoretical models used to describe these heavy fermion compounds. The Fu-Kane method of topological classification of insulators is used to show that hybridization between the conduction electrons and localized f electrons in these systems gives rise to interaction-induced topological insulating behavior. Finally, some recent experimental results are discussed, which appear to confirm the theoretical prediction of the topological insulating behavior in samarium hexaboride, where the long-standing puzzle of the residual low-temperature conductivity has been shown to originate from robust surface states.

  8. Obesity-related abnormalities couple environmental triggers with genetic susceptibility in adult-onset T1D.

    PubMed

    Nguyen, K Hoa; Ande, Sudharsana R; Mishra, Suresh

    2016-01-29

    The incidence of adult-onset T1D in low-risk non-HLA type has increased several folds, whereas the contemporaneous incidence in high-risk HLA-type remains stable. Various factors behind this selective increase in T1D in young adults remain unclear. Obesity and its associated abnormalities appear to be an important determinant; however, the underlying mechanism involved is not understood. Recently, we have developed two novel transgenic obese mice models, Mito-Ob and m-Mito-Ob, by expressing a pleiotropic protein prohibitin (PHB) and a phospho mutant form of PHB (Y114F-PHB or m-PHB) from the aP2 gene promoter, respectively. Both mice models develop obesity in a sex-neutral manner, independent of diet; but obesity associated chronic low-grade inflammation and insulin resistance in a male sex-specific manner. Interestingly, on a high fat diet (HFD) only male m-Mito-Ob mice displayed marked mononuclear cell infiltration in pancreas and developed insulitis that mimic adult-onset T1D. Male Mito-Ob mice that share the metabolic phenotype of male m-Mito-Ob mice, and female m-Mito-Ob that harbor m-PHB similar to male m-Mito-Ob mice, did not develop insulitis. Thus, insulitis development in male m-Mito-Ob in response to HFD requires both, obesity-related abnormalities and m-PHB. Collectively, this data provides a proof-of-concept that obesity-associated abnormalities couple environmental triggers with genetic susceptibility in adult-onset T1D and reveals PHB as a potential susceptibility gene for T1D.

  9. Mott lobes evolution of the spin-1 Bose-Hubbard model

    NASA Astrophysics Data System (ADS)

    Hincapie-F, A. F.; Franco, R.; Silva-Valencia, J.

    2016-02-01

    We study spin-1 bosons confined in a one-dimensional optical lattice, taking into consideration both ferromagnetic and antiferromagnetic interaction. Using the density matrix renormalization group, we determine the phase diagram for the two firsts lobes and report the evolution of the first and second Mott lobes with respect to the spin-exchange interaction parameter (U 2). We determine that for the antiferromagnetic case, the first lobe is suppressed while the second grows as |U 2| increases. For the ferromagnetic case, the first and second Mott lobes are suppressed by the spin-exchange interaction parameter. We propose an expresion to describe the evolution of the critical point with the increase in |U 2| for both cases.

  10. Detection of spin-resolved electronic structures from a buried ferromagnetic layer utilizing forward Mott scattering

    SciTech Connect

    Ueda, S.; Mizuguchi, M.; Kojima, T.; Takanashi, K.; Ishimaru, S.; Tsujikawa, M.; Shirai, M.

    2014-03-31

    We report ultrahigh-resolution spin-resolved hard X-ray photoemission (HAXPES) for a buried FeNi alloy film. By utilizing the forward Mott scattering in a Au layer on FeNi, our spin-resolved HAXPES method does not require a standard spin detector and allows us to use the multi-channel electron detection system for the high-efficient electron detection as used in conventional photoemission spectroscopy. A combination of the forward Mott scattering and multi-channel detection leads us to measure a clear spin polarization as well as spin-resolved majority and minority states in the Fe 2p core-level spectra without using the standard spin detector. This method enables us to measure spin-resolved core-level spectra for buried ferromagnetic materials.

  11. Coexistence of Midgap Antiferromagnetic and Mott States in Undoped, Hole- and Electron-Doped Ambipolar Cuprates.

    PubMed

    Yin, Xinmao; Zeng, Shengwei; Das, Tanmoy; Baskaran, G; Asmara, Teguh Citra; Santoso, Iman; Yu, Xiaojiang; Diao, Caozheng; Yang, Ping; Breese, Mark B H; Venkatesan, T; Lin, Hsin; Ariando; Rusydi, Andrivo

    2016-05-13

    We report the first observation of the coexistence of a distinct midgap state and a Mott state in undoped and their evolution in electron and hole-doped ambipolar Y_{0.38}La_{0.62}(Ba_{0.82}La_{0.18})_{2}Cu_{3}O_{y} films using spectroscopic ellipsometry and x-ray absorption spectroscopies at the O K and Cu L_{3,2} edges. Supported by theoretical calculations, the midgap state is shown to originate from antiferromagnetic correlation. Surprisingly, while the magnetic state collapses and its correlation strength weakens with dopings, the Mott state in contrast moves toward a higher energy and its correlation strength increases. Our result provides important clues to the mechanism of electronic correlation strengths and superconductivity in cuprates. PMID:27232036

  12. Extension of the radiative lifetime of Wannier-Mott excitons in semiconductor nanoclusters

    SciTech Connect

    Kukushkin, V. A.

    2015-01-15

    The purpose of the study is to calculate the radiative lifetime of Wannier-Mott excitons in three-dimensional potential wells formed of direct-gap narrow-gap semiconductor nanoclusters in wide-gap semiconductors and assumed to be large compared to the exciton radius. Calculations are carried out for the InAs/GaAs heterosystem. It is shown that, as the nanocluster dimensions are reduced to values on the order of the exciton radius, the exciton radiative lifetime becomes several times longer compared to that in a homogeneous semiconductor. The increase in the radiative lifetime is more pronounced at low temperatures. Thus, it is established that the placement of Wannier-Mott excitons into direct-gap semiconductor nanoclusters, whose dimensions are of the order of the exciton radius, can be used for considerable extension of the exciton radiative lifetime.

  13. 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.

  14. Bosons with Artificial Gauge Fields and Mott Physics on the Honeycomb Lattice

    NASA Astrophysics Data System (ADS)

    Vidanovic, Ivana; Petrescu, Alexandru; Le Hur, Karyn; Hofstetter, Walter

    2014-03-01

    We study bosons in the tight-binding model on the honeycomb lattice introduced by Haldane. We analyze the ground state topology and quasiparticle properties in the Mott phase by applying bosonic dynamical mean field theory, strong-coupling perturbation theory, exact diagonalization and numerical evaluations of sample Hall conductivity. The phase diagram also contains two different superfluid phases. The quasiparticle dynamics, number fluctuations, and local currents are measurable in cold atom experiments.

  15. Competing ground states of strongly correlated bosons in the Harper-Hofstadter-Mott model

    NASA Astrophysics Data System (ADS)

    Natu, Stefan S.; Mueller, Erich J.; Das Sarma, S.

    2016-06-01

    Using an efficient cluster approach, we study the physics of two-dimensional lattice bosons in a strong magnetic field in the regime where the tunneling is much weaker than the on-site interaction strength. We study both the dilute, hard-core bosons at filling factors much smaller than unity occupation per site and the physics in the vicinity of the superfluid-Mott lobes as the density is tuned away from unity. For hard-core bosons, we carry out extensive numerics for a fixed flux per plaquette ϕ =1 /5 and ϕ =1 /3 . At large flux, the lowest-energy state is a strongly correlated superfluid, analogous to He-4, in which the order parameter is dramatically suppressed, but nonzero. At filling factors ν =1 /2 ,1 , we find competing incompressible states which are metastable. These appear to be commensurate density wave states. For small flux, the situation is reversed and the ground state at ν =1 /2 is an incompressible density wave solid. Here, we find a metastable lattice supersolid phase, where superfluidity and density wave order coexist. We then perform careful numerical studies of the physics near the vicinity of the Mott lobes for ϕ =1 /2 and ϕ =1 /4 . At ϕ =1 /2 , the superfluid ground state has commensurate density wave order. At ϕ =1 /4 , incompressible phases appear outside the Mott lobes at densities n =1.125 and n =1.25 , corresponding to filling fractions ν =1 /2 and 1, respectively. These phases, which are absent in single-site mean-field theory, are metastable and have slightly higher energy than the superfluid, but the energy difference between them shrinks rapidly with increasing cluster size, suggestive of an incompressible ground state. We thus explore the interplay between Mott physics, magnetic Landau levels, and superfluidity, finding a rich phase diagram of competing compressible and incompressible states.

  16. Microsphere plate detectors used with a compact Mott polarimeter for time-of-flight studies

    SciTech Connect

    Snell, G.; Viefhaus, J.; Dunning, F. B.; Berrah, N.

    2000-06-01

    A compact retarding-potential Mott polarimeter combined with microsphere plates (MSP) as electron detectors was built to perform spin-resolved time-of-flight electron spectroscopy. The comparison of the performance of MSP and channeltron detectors shows that the MSP detector has a better time resolution but a lower efficiency. The overall time resolution of the system was determined to be 350 ps using synchrotron radiation pulses. (c) 2000 American Institute of Physics.

  17. 5f-electron localization in the actinide metals: thorides, actinides and the Mott transition

    NASA Astrophysics Data System (ADS)

    Lawson, A. C.

    2016-03-01

    For the light actinides Ac-Cm, the numbers of localized and itinerant 5f-electrons are determined by comparing various estimates of the f-electron counts. At least one itinerant f-electron is found for each element, Pa-Cm. These results resolve certain disagreements among electron counts determined by different methods and are consistent with the Mott transition model and with the picture of the 5f-electrons' dual nature.

  18. Quantum and classical solutions for statically screened two-dimensional Wannier-Mott excitons

    SciTech Connect

    Makowski, Adam J.

    2011-08-15

    Quantum solutions and classical orbits are discussed for statically screened Wannier-Mott excitons for two closely related potentials: the Stern-Howard potential and a suggested simple focusing one. Bound states and exact ''quantized'' values of screening are obtained as well. For the suggested potential, the scattering matrix, the Regge poles, and the transmission coefficient are calculated exactly. We argue that the simple potential can be utilized in applications instead of the Stern-Howard potential, which is difficult to handle.

  19. Criticality in the (2+1)-dimensional compact Higgs model and fractionalized insulators.

    PubMed

    Sudbø, A; Smørgrav, E; Smiseth, J; Nogueira, F S; Hove, J

    2002-11-25

    We use a novel method of computing the third moment M3 of the action of the (2+1)-dimensional compact Higgs model in the adjoint representation with q=2 to extract correlation length and specific heat exponents nu and alpha without invoking hyperscaling. Finite-size scaling analysis of M3 yields the ratios (1+alpha)/nu and 1/nu separately. We find that alpha and nu vary along the critical line of the theory, which however exhibits a remarkable resilience of Z2 criticality. We propose this novel universality class to be that of the quantum phase transition from a Mott-Hubbard insulator to a charge-fractionalized insulator in two spatial dimensions. PMID:12485087

  20. Raman study of the metal-insulator transition in pyrochlore Mo oxides

    NASA Astrophysics Data System (ADS)

    Taniguchi, K.; Katsufuji, T.; Iguchi, S.; Taguchi, Y.; Takagi, H.; Tokura, Y.

    2004-09-01

    Raman scattering spectra have been investigated for the correlated 4d -electron system, R2Mo2O7 ( R=Nd , Sm , Gd , Tb , Dy , Nd1-xDyx ), which undergoes a metal-insulator transition with changing the rare-earth ion R , or equivalently the one-electron bandwidth. It is found that several phonon peaks modulating the Mo-O-Mo bond angle appear in the metallic phase ( R=Nd , Sm , Gd , Nd1-xDyx ), whereas they are remarkably suppressed in intensity in the insulating phase ( R=Tb , Dy ). This result indicates that the phonon modes of R2Mo2O7 are coupled with the electron-hole excitation across the Fermi level, thus probing sensitively the low-energy charge dynamics in the vicinity of the bandwidth-control Mott transition.

  1. Mott Transitions and Staggered Orders in the Three-Component Fermionic System: Variational Cluster Approach

    NASA Astrophysics Data System (ADS)

    Hasunuma, Takumi; Kaneko, Tatsuya; Miyakoshi, Shohei; Ohta, Yukinori

    2016-07-01

    The variational cluster approximation is used to study the ground-state properties and single-particle spectra of the three-component fermionic Hubbard model defined on the two-dimensional square lattice at half filling. First, we show that either a paired Mott state or color-selective Mott state is realized in the paramagnetic system, depending on the anisotropy in the interaction strengths, except around the SU(3) symmetric point, where a paramagnetic metallic state is maintained. Then, by introducing Weiss fields to observe spontaneous symmetry breakings, we show that either a color-density-wave state or color-selective antiferromagnetic state is realized depending on the interaction anisotropy and that the first-order phase transition between these two states occurs at the SU(3) point. We moreover show that these staggered orders originate from the gain in potential energy (or Slater mechanism) near the SU(3) point but originate from the gain in kinetic energy (or Mott mechanism) when the interaction anisotropy is strong. The staggered orders near the SU(3) point disappear when the next-nearest-neighbor hopping parameters are introduced, indicating that these orders are fragile, protected only by the Fermi surface nesting.

  2. Superconductivity close to the Mott state: From condensed-matter systems to superfluidity in optical lattices

    SciTech Connect

    Le Hur, Karyn Maurice Rice, T.

    2009-07-15

    Since the discovery of high-temperature superconductivity in 1986 by Bednorz and Mueller, great efforts have been devoted to finding out how and why it works. From the d-wave symmetry of the order parameter, the importance of antiferromagnetic fluctuations, and the presence of a mysterious pseudogap phase close to the Mott state, one can conclude that high-T{sub c} superconductors are clearly distinguishable from the well-understood BCS superconductors. The d-wave superconducting state can be understood through a Gutzwiller-type projected BCS wavefunction. In this review article, we revisit the Hubbard model at half-filling and focus on the emergence of exotic superconductivity with d-wave symmetry in the vicinity of the Mott state, starting from ladder systems and then studying the dimensional crossovers to higher dimensions. This allows to confirm that short-range antiferromagnetic fluctuations can mediate superconductivity with d-wave symmetry. Ladders are also nice prototype systems allowing to demonstrate the truncation of the Fermi surface and the emergence of a Resonating Valence Bond (RVB) state with preformed pairs in the vicinity of the Mott state. In two dimensions, a similar scenario emerges from renormalization group arguments. We also discuss theoretical predictions for the d-wave superconducting phase as well as the pseudogap phase, and address the crossover to the overdoped regime. Finally, cold atomic systems with tunable parameters also provide a complementary insight into this outstanding problem.

  3. A low-voltage retarding-field Mott polarimeter for photocathode characterization

    NASA Astrophysics Data System (ADS)

    McCarter, J. L.; Stutzman, M. L.; Trantham, K. W.; Anderson, T. G.; Cook, A. M.; Gay, T. J.

    2010-06-01

    Nuclear physics experiments at Thomas Jefferson National Accelerator Facility's CEBAF rely on high polarization electron beams. We describe a recently commissioned system for prequalifying and studying photocathodes for CEBAF with a load-locked, low-voltage polarized electron source coupled to a compact retarding-field Mott polarimeter. The polarimeter uses simplified electrode structures and operates from 5 to 30 kV. The effective Sherman function for this device has been calibrated by comparison with the CEBAF 5 MeV Mott polarimeter. For elastic scattering from a thick gold target at 20 keV, the effective Sherman function is 0.201(5). Its maximum efficiency at 20 keV, defined as the detected count rate divided by the incident particle current, is 5.4(2)×10 -4, yielding a figure-of-merit, or analyzing power squared times efficiency, of 1.0(1)×10 -5. The operating parameters of this new polarimeter design are compared to previously published data for other compact Mott polarimeters of the retarding-field type.

  4. A low-voltage retarding-field Mott polarimeter for photocathode characterization

    SciTech Connect

    McCarter, J. L.; Stutzman, M. L.; Trantham, K. W.; Anderson, T. G.; Cook, A. M.; Gay, T. J.

    2010-02-26

    Nuclear physics experiments at Thomas Jefferson National Accelerator Facility's CEBAF rely on high polarization electron beams. We describe a recently commissioned system for prequalifying and studying photocathodes for CEBAF with a load-locked, low-voltage polarized electron source coupled to a compact retarding-field Mott polarimeter. The polarimeter uses simplified electrode structures and operates from 5 to 30 kV. The effective Sherman function for this device has been calibrated by comparison with the CEBAF 5 MeV Mott polarimeter. For elastic scattering from a thick gold target at 20 keV, the effective Sherman function is 0.201(5). Its maximum efficiency at 20 keV, defined as the detected count rate divided by the incident particle current, is 5.4(2)×10-4, yielding a figure-of-merit, or analyzing power squared times efficiency, of 1.0(1)×10-5. The operating parameters of this new polarimeter design are compared to previously published data for other compact Mott polarimeters of the retarding-field type.

  5. 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. PMID:25272476

  6. Cooper Pair Insulators

    NASA Astrophysics Data System (ADS)

    Valles, James

    One of the recent advances in the field of the Superconductor to Insulator Transition (SIT) has been the discovery and characterization of the Cooper Pair Insulator phase. This bosonic insulator, which consists of localized Cooper pairs, exhibits activated transport and a giant magneto-resistance peak. These features differ markedly from the weakly localized transport that emerges as pairs break at a ``fermionic'' SIT. I will describe how our experiments on films nano-patterned with a nearly triangular array of holes have enabled us to 1) distinguish bosonic insulators from fermionic insulators, 2) show that Cooper pairs, rather than quasi-particles dominate the transport in the Cooper Pair insulator phase, 3) demonstrate that very weak, sub nano-meter thickness inhomogeneities control whether a bosonic or fermionic insulator forms at an SIT and 4) reveal that Cooper pairs disintegrate rather than becoming more tightly bound deep in the localized phase. We have also developed a method, using a magnetic field, to tune flux disorder reversibly in these films. I will present our latest results on the influence of magnetic flux disorder and random gauge fields on phenomena near bosonic SITs. This work was performed in collaboration with M. D. Stewart, Jr., Hung Q. Nguyen, Shawna M. Hollen, Jimmy Joy, Xue Zhang, Gustavo Fernandez, Jeffrey Shainline and Jimmy Xu. It was supported by NSF Grants DMR 1307290 and DMR-0907357.

  7. Interacting topological insulator and emergent grand unified theory

    NASA Astrophysics Data System (ADS)

    You, Yi-Zhuang; Xu, Cenke

    2015-03-01

    Motivated by the Pati-Salam grand unified theory [J. C. Pati and A. Salam, Phys. Rev. D 10, 275 (1974), 10.1103/PhysRevD.10.275], we study (4 +1 )d topological insulators with SU (4 ) ×SU (2) 1×SU (2) 2 symmetry, whose (3 +1 )d boundary has 16 flavors of left-chiral fermions, which form representations (4 ,2 ,1 ) and (4 ¯,1 ,2 ) . The key result we obtain is that, without any interaction, this topological insulator has a Z classification, namely, any quadratic fermion mass operator at the (3 +1 )d boundary is prohibited by the symmetries listed above; while under interaction, this system becomes trivial, namely, its (3 +1 )d boundary can be gapped out by a properly designed short-range interaction without generating nonzero vacuum expectation value of any fermion bilinear mass, or in other words, its (3 +1 )d boundary can be driven into a "strongly-coupled symmetric gapped (SCSG) phase." Based on this observation, we propose that after coupling the system to a dynamical SU (4 ) ×SU (2) 1×SU (2) 2 lattice gauge field, the Pati-Salam GUT can be fully regularized as the boundary states of a (4 +1 )d topological insulator with a thin fourth spatial dimension, the thin fourth dimension makes the entire system generically a (3 +1 )d system. The mirror sector on the opposite boundary will not interfere with the desired GUT, because the mirror sector is driven to the SCSG phase by a carefully designed interaction and is hence decoupled from the GUT.

  8. Universal Quantum Criticality in the Metal-Insulator Transition of Two-Dimensional Interacting Dirac Electrons

    NASA Astrophysics Data System (ADS)

    Otsuka, Yuichi; Yunoki, Seiji; Sorella, Sandro

    2016-01-01

    The metal-insulator transition has been a subject of intense research since Mott first proposed that the metallic behavior of interacting electrons could turn to an insulating one as electron correlations increase. Here, we consider electrons with massless Dirac-like dispersion in two spatial dimensions, described by the Hubbard models on two geometrically different lattices, and perform numerically exact calculations on unprecedentedly large systems that, combined with a careful finite-size scaling analysis, allow us to explore the quantum critical behavior in the vicinity of the interaction-driven metal-insulator transition. Thereby, we find that the transition is continuous, and we determine the quantum criticality for the corresponding universality class, which is described in the continuous limit by the Gross-Neveu model, a model extensively studied in quantum field theory. Furthermore, we discuss a fluctuation-driven scenario for the metal-insulator transition in the interacting Dirac electrons: The metal-insulator transition is triggered only by the vanishing of the quasiparticle weight, not by the Dirac Fermi velocity, which instead remains finite near the transition. This important feature cannot be captured by a simple mean-field or Gutzwiller-type approximate picture but is rather consistent with the low-energy behavior of the Gross-Neveu model.

  9. Nature of the insulating ground state of the 5d postperovskite CaIrO3

    DOE PAGES

    Kim, Sun -Woo; Liu, Chen; Kim, Hyun -Jung; Lee, Jun -Ho; Yao, Yongxin; Ho, Kai -Ming; Cho, Jun -Hyung

    2015-08-26

    In this study, the insulating ground state of the 5d transition metal oxide CaIrO3 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 t2g 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 Ir4+ spins. Furthermore, the spin-orbit coupling (SOC) hybridizes the t2g states to open an insulating gap. These results indicate thatmore » CaIrO3 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

  10. Cryogenic insulation development

    NASA Technical Reports Server (NTRS)

    Leonhard, K. E.

    1972-01-01

    Multilayer insulations for long term cryogenic storage are described. The development effort resulted in an insulation concept using lightweight radiation shields, separated by low conductive Dacron fiber tufts. The insulation is usually referred to as Superfloc. The fiber tufts are arranged in a triangular pattern and stand about .040 in. above the radiation shield base. Thermal and structural evaluation of Superfloc indicated that this material is a strong candidate for the development of high performance thermal protection systems because of its high strength, purge gas evacuation capability during boost, its density control and easy application to a tank.

  11. Internal insulation system development

    NASA Technical Reports Server (NTRS)

    Gille, J. P.

    1973-01-01

    The development of an internal insulation system for cryogenic liquids is described. The insulation system is based on a gas layer concept in which capillary or surface tension effects are used to maintain a stable gas layer within a cellular core structure between the tank wall and the contained cryogen. In this work, a 1.8 meter diameter tank was insulated and tested with liquid hydrogen. Ability to withstand cycling of the aluminum tank wall to 450 K was a design and test condition.

  12. Insulation fact sheet

    SciTech Connect

    1997-08-01

    Electricity bills, oil bills, gas bills - all homeowners pay for one or more of these utilities, and wish they paid less. Often many of us do not really know how to control or reduce our utility bills. We resign ourselves to high bills because we think that is the price we have to pay for a comfortable home. We encourage our children to turn off the lights and appliances, but may not recognize the benefits of insulating the attic. This publication provides facts relative to home insulation. It discusses where to insulate, what products to use, the decision making process, installation options, and sources of additional information.

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

    SciTech Connect

    Biswas, Abhijit; Jeong, Yoon Hee; Kim, Ki-Seok

    2014-12-07

    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 found 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.

  14. Dimensional phase transition from an array of 1D Luttinger liquids to a 3D Bose-Einstein condensate.

    PubMed

    Vogler, Andreas; Labouvie, Ralf; Barontini, Giovanni; Eggert, Sebastian; Guarrera, Vera; Ott, Herwig

    2014-11-21

    We study the thermodynamic properties of a 2D array of coupled one-dimensional Bose gases. The system is realized with ultracold bosonic atoms loaded in the potential tubes of a two-dimensional optical lattice. For negligible coupling strength, each tube is an independent weakly interacting 1D Bose gas featuring Tomonaga Luttinger liquid behavior. By decreasing the lattice depth, we increase the coupling strength between the 1D gases and allow for the phase transition into a 3D condensate. We extract the phase diagram for such a system and compare our results with theoretical predictions. Because of the high effective mass across the periodic potential and the increased 1D interaction strength, the phase transition is shifted to large positive values of the chemical potential. Our results are prototypical to a variety of low-dimensional systems, where the coupling between the subsystems is realized in a higher spatial dimension such as coupled spin chains in magnetic insulators.

  15. Human serotonin 1D receptor is encoded by a subfamily of two distinct genes: 5-HT1D alpha and 5-HT1D beta.

    PubMed Central

    Weinshank, R L; Zgombick, J M; Macchi, M J; Branchek, T A; Hartig, P R

    1992-01-01

    The serotonin 1D (5-HT1D) receptor is a pharmacologically defined binding site and functional receptor site. Observed variations in the properties of 5-HT1D receptors in different tissues have led to the speculation that multiple receptor proteins with slightly different properties may exist. We report here the cloning, deduced amino acid sequences, pharmacological properties, and second-messenger coupling of a pair of human 5-HT1D receptor genes, which we have designated 5-HT1D alpha and 5-HT1D beta due to their strong similarities in sequence, pharmacological properties, and second-messenger coupling. Both genes are free of introns in their coding regions, are expressed in the human cerebral cortex, and can couple to inhibition of adenylate cyclase activity. The pharmacological binding properties of these two human receptors are very similar, and match closely the pharmacological properties of human, bovine, and guinea pig 5-HT1D sites. Both receptors exhibit high-affinity binding of sumatriptan, a new anti-migraine medication, and thus are candidates for the pharmacological site of action of this drug. Images PMID:1565658

  16. Reversible interconversion of a divalent vanadium bronze between δ and β quasi-1D structures.

    PubMed

    Marley, Peter M; Banerjee, Sarbajit

    2012-05-01

    Charge fluctuations along the quasi-1D frameworks of M(x)V(2)O(5) bronzes have evinced much recent interest owing to the manifestation of colossal metal-insulator transitions and superconductivity. Depending upon the nature of the intercalating cation (M), distinctive geometries of the V(2)O(5) framework are accessible. Herein, we demonstrate an unprecedented reversible transformation between double-layered (δ) and tunnel (β) quasi-1D geometries for nanowires of a divalent vanadium bronze, Ca(x)V(2)O(5) (x ≈ 0.23), upon annealing-induced dehydration and hydrothermally induced hydration. Such a facile hydration/dehydration-induced interconversion between two prominent quasi-1D structures (accompanied by a change in charge-ordering motifs) has not been observed in the bulk and is posited to result from the ease of propagation of crystallographic slip processes across the confined nanowire widths for the δ → β conversion and the facile diffusion of water molecules within the tunnel geometries for the β → δ reversion.

  17. Realizing 1-D conducting channel between oppositely gated regions in bilayer graphene

    NASA Astrophysics Data System (ADS)

    Lee, Janghee; Watanabe, Kenji; Taniguchi, Takashi; Lee, Hu-Jong

    The band gap of bilayer graphene (BLG) can be tuned by applying an external electric field perpendicular to the plane of a BLG sheet. If direction of the electric fields in two adjacent regions in BLG are opposite, one-dimensional (1-D) conducting channel emerges at the boundary between two regions with chiral nature. In this presentation, we introduce a method for fabricating two pairs of split-gates attached to BLG, which is sandwiched between two atomically clean hexagonal boron nitride (h-BN) single crystals and thus allows ballistic transport of carriers at least within the device size. Current-voltage characteristics show a large transport gap, which is comparable to the results obtained from optical measurements and numerical calculations. Opening the band gap in two adjacent regions of the BLG flake by oppositely gated electric fields, we observed metallic behavior in transport characteristics along the boundary between the two regions although the resistance of two gapped regions are a few hundreds of k Ω. These results indicate that a 1-D conducting channel formed between the two regions where the induced band gaps were inverted to each other. The formation of this 1-D conducting channel mimics the topological edge conducting channels emerging at the boundary of a two-dimensional topological insulator and may be utilized for applying BLG to valleytronics

  18. Cooper Pairs in Insulators?!

    SciTech Connect

    James Valles

    2008-07-23

    Nearly 50 years elapsed between the discovery of superconductivity and the emergence of the microscopic theory describing this zero resistance state. The explanation required a novel phase of matter in which conduction electrons joined in weakly bound pairs and condensed with other pairs into a single quantum state. Surprisingly, this Cooper pair formation has also been invoked to account for recently uncovered high-resistance or insulating phases of matter. To address this possibility, we have used nanotechnology to create an insulating system that we can probe directly for Cooper pairs. I will present the evidence that Cooper pairs exist and dominate the electrical transport in these insulators and I will discuss how these findings provide new insight into superconductor to insulator quantum phase transitions. 

  19. Cooper Pairs in Insulators?!

    ScienceCinema

    James Valles

    2016-07-12

    Nearly 50 years elapsed between the discovery of superconductivity and the emergence of the microscopic theory describing this zero resistance state. The explanation required a novel phase of matter in which conduction electrons joined in weakly bound pairs and condensed with other pairs into a single quantum state. Surprisingly, this Cooper pair formation has also been invoked to account for recently uncovered high-resistance or insulating phases of matter. To address this possibility, we have used nanotechnology to create an insulating system that we can probe directly for Cooper pairs. I will present the evidence that Cooper pairs exist and dominate the electrical transport in these insulators and I will discuss how these findings provide new insight into superconductor to insulator quantum phase transitions. 

  20. Composite flexible blanket insulation

    NASA Technical Reports Server (NTRS)

    Kourtides, Demetrius A. (Inventor); Lowe, David M. (Inventor)

    1994-01-01

    An improved composite flexible blanket insulation is presented comprising top silicon carbide having an interlock design, wherein the reflective shield is composed of single or double aluminized polyimide and wherein the polyimide film has a honeycomb pattern.

  1. Repairing ceramic insulating tiles

    NASA Technical Reports Server (NTRS)

    Dunn, B. R.; Laymance, E. L.

    1980-01-01

    Fused-silica tiles containing large voids or gauges are repaired without adhesives by plug insertion method. Tiles are useful in conduits for high-temperature gases, in furnaces, and in other applications involving heat insulation.

  2. Improved Sprayable Insulation

    NASA Technical Reports Server (NTRS)

    Hill, W. F.; Sharpe, M. H.; Lester, C. N.; Echols, Sherman; Simpson, W. G.; Lambert, J. D.; Norton, W. F.; Mclemore, J. P.; Patel, A. K.; Patel, S. V.; Shockney, C. H.; Adams, G. R.; Kelly, M. R.; White, W. T.

    1992-01-01

    MSA-2 and MSA-2A, two similar improved versions of Marshall sprayable ablator, insulating material developed at Marshall Space Flight Center to replace both sheets of cork and MSA-1. Suitable for use on large vehicles and structures exposed to fire or other sources of heat by design or accident. Ablative insulation turns into strong char when exposed to high temperature; highly desireable property in original spacecraft application and possibly in some terrestrial applications.

  3. Insulator for laser housing

    DOEpatents

    Duncan, D.B.

    1992-12-29

    The present invention provides a heat-resistant electrical insulator adapted for joining laser housing portions, which insulator comprises: an annulus; a channel in the annulus traversing the circumference and length of the housing; at least two ports, each communicating with the channel and an outer surface of the housing; and an attachment for securely attaching each end of the annulus to a laser housing member. 3 figs.

  4. Photonic Floquet topological insulators.

    PubMed

    Rechtsman, Mikael C; Zeuner, Julia M; Plotnik, Yonatan; Lumer, Yaakov; Podolsky, Daniel; Dreisow, Felix; Nolte, Stefan; Segev, Mordechai; Szameit, Alexander

    2013-04-11

    Topological insulators are a new phase of matter, with the striking property that conduction of electrons occurs only on their surfaces. In two dimensions, electrons on the surface of a topological insulator are not scattered despite defects and disorder, providing robustness akin to that of superconductors. Topological insulators are predicted to have wide-ranging applications in fault-tolerant quantum computing and spintronics. Substantial effort has been directed towards realizing topological insulators for electromagnetic waves. One-dimensional systems with topological edge states have been demonstrated, but these states are zero-dimensional and therefore exhibit no transport properties. Topological protection of microwaves has been observed using a mechanism similar to the quantum Hall effect, by placing a gyromagnetic photonic crystal in an external magnetic field. But because magnetic effects are very weak at optical frequencies, realizing photonic topological insulators with scatter-free edge states requires a fundamentally different mechanism-one that is free of magnetic fields. A number of proposals for photonic topological transport have been put forward recently. One suggested temporal modulation of a photonic crystal, thus breaking time-reversal symmetry and inducing one-way edge states. This is in the spirit of the proposed Floquet topological insulators, in which temporal variations in solid-state systems induce topological edge states. Here we propose and experimentally demonstrate a photonic topological insulator free of external fields and with scatter-free edge transport-a photonic lattice exhibiting topologically protected transport of visible light on the lattice edges. Our system is composed of an array of evanescently coupled helical waveguides arranged in a graphene-like honeycomb lattice. Paraxial diffraction of light is described by a Schrödinger equation where the propagation coordinate (z) acts as 'time'. Thus the helicity of the

  5. Insulator for laser housing

    DOEpatents

    Duncan, David B.

    1992-01-01

    The present invention provides a heat-resistant electrical insulator adapted for joining laser housing portions, which insulator comprises: an annulus; a channel in the annulus traversing the circumference and length of the housing; at least two ports, each communicating with the channel and an outer surface of the housing; and an attachment for securely attaching each end of the annulus to a laser housing member.

  6. Vacuum foil insulation system

    DOEpatents

    Hanson, John P.; Sabolcik, Rudolph E.; Svedberg, Robert C.

    1976-11-16

    In a multifoil thermal insulation package having a plurality of concentric cylindrical cups, means are provided for reducing heat loss from the penetration region which extends through the cups. At least one cup includes an integral skirt extending from one end of the cup to intersection with the penetration means. Assembly of the insulation package with the skirted cup is facilitated by splitting the cup to allow it to be opened up and fitted around the other cups during assembly.

  7. Photonic Floquet topological insulators.

    PubMed

    Rechtsman, Mikael C; Zeuner, Julia M; Plotnik, Yonatan; Lumer, Yaakov; Podolsky, Daniel; Dreisow, Felix; Nolte, Stefan; Segev, Mordechai; Szameit, Alexander

    2013-04-11

    Topological insulators are a new phase of matter, with the striking property that conduction of electrons occurs only on their surfaces. In two dimensions, electrons on the surface of a topological insulator are not scattered despite defects and disorder, providing robustness akin to that of superconductors. Topological insulators are predicted to have wide-ranging applications in fault-tolerant quantum computing and spintronics. Substantial effort has been directed towards realizing topological insulators for electromagnetic waves. One-dimensional systems with topological edge states have been demonstrated, but these states are zero-dimensional and therefore exhibit no transport properties. Topological protection of microwaves has been observed using a mechanism similar to the quantum Hall effect, by placing a gyromagnetic photonic crystal in an external magnetic field. But because magnetic effects are very weak at optical frequencies, realizing photonic topological insulators with scatter-free edge states requires a fundamentally different mechanism-one that is free of magnetic fields. A number of proposals for photonic topological transport have been put forward recently. One suggested temporal modulation of a photonic crystal, thus breaking time-reversal symmetry and inducing one-way edge states. This is in the spirit of the proposed Floquet topological insulators, in which temporal variations in solid-state systems induce topological edge states. Here we propose and experimentally demonstrate a photonic topological insulator free of external fields and with scatter-free edge transport-a photonic lattice exhibiting topologically protected transport of visible light on the lattice edges. Our system is composed of an array of evanescently coupled helical waveguides arranged in a graphene-like honeycomb lattice. Paraxial diffraction of light is described by a Schrödinger equation where the propagation coordinate (z) acts as 'time'. Thus the helicity of the

  8. Wrapped Multilayer Insulation

    NASA Technical Reports Server (NTRS)

    Dye, Scott A.

    2015-01-01

    New NASA vehicles, such as Earth Departure Stage (EDS), Orion, landers, and orbiting fuel depots, need improved cryogenic propellant transfer and storage for long-duration missions. Current cryogen feed line multilayer insulation (MLI) performance is 10 times worse per area than tank MLI insulation. During each launch, cryogenic piping loses approximately 150,000 gallons (equivalent to $300,000) in boil-off during transfer, chill down, and ground hold. Quest Product Development Corp., teaming with Ball Aerospace, developed an innovative advanced insulation system, Wrapped MLI (wMLI), to provide improved thermal insulation for cryogenic feed lines. wMLI is high-performance multilayer insulation designed for cryogenic piping. It uses Quest's innovative discrete-spacer technology to control layer spacing/ density and reduce heat leak. The Phase I project successfully designed, built, and tested a wMLI prototype with a measured heat leak 3.6X lower than spiral-wrapped conventional MLI widely used for piping insulation. A wMLI prototype had a heat leak of 7.3 W/m2, or 27 percent of the heat leak of conventional MLI (26.7 W/m2). The Phase II project is further developing wMLI technology with custom, molded polymer spacers and advancing the product toward commercialization via a rigorous testing program, including developing advanced vacuuminsulated pipe for ground support equipment.

  9. Wrapped Multilayer Insulation

    NASA Technical Reports Server (NTRS)

    Dye, Scott A.

    2015-01-01

    New NASA vehicles, such as Earth Departure Stage (EDS), Orion, landers, and orbiting fuel depots, need improved cryogenic propellant transfer and storage for long-duration missions. Current cryogen feed line multilayer insulation (MLI) performance is 10 times worse per area than tank MLI insulation. During each launch, cryogenic piping loses approximately 150,000 gallons (equivalent to $300,000) in boil-off during transfer, chill down, and ground hold. Quest Product Development Corp., teaming with Ball Aerospace, developed an innovative advanced insulation system, Wrapped MLI (wMLI), to provide improved thermal insulation for cryogenic feed lines. wMLI is high-performance multilayer insulation designed for cryogenic piping. It uses Quest's innovative discrete-spacer technology to control layer spacing/ density and reduce heat leak. The Phase I project successfully designed, built, and tested a wMLI prototype with a measured heat leak 3.6X lower than spiral-wrapped conventional MLI widely used for piping insulation. A wMLI prototype had a heat leak of 7.3 W/sq m, or 27 percent of the heat leak of conventional MLI (26.7 W/sq m). The Phase II project is further developing wMLI technology with custom, molded polymer spacers and advancing the product toward commercialization via a rigorous testing program, including developing advanced vacuuminsulated pipe for ground support equipment.

  10. Perioperative thermal insulation.

    PubMed

    Bräuer, Anselm; Perl, Thorsten; English, Michael J M; Quintel, Michael

    2007-01-01

    Perioperative hypothermia remains a common problem during anesthesia and surgery. Unfortunately, the implementation of new minimally invasive surgical procedures has not lead to a reduction of this problem. Heat losses from the skin can be reduced by thermal insulation to avoid perioperative hypothermia. However, only a small amount of information is available regarding the physical properties of insulating materials used in the Operating Room (OR). Therefore, several materials using validated manikins were tested. Heat loss from the surface of the manikin can be described as:"Q = h . DeltaT . A" where Q = heat flux, h = heat exchange coefficient, DeltaT = temperature gradient between the environment and surface, and A = covered area. Heat flux per unit area and surface temperature were measured with calibrated heat flux transducers. Environmental temperature was measured using a thermoanemometer. The temperature gradient between the surface and environment (DeltaT) was varied and "h" was determined by linear regression analysis as the slope of "DeltaT" versus heat flux per unit area. The reciprocal of the heat exchange coefficient defines the insulation. The insulation values of the materials varied between 0.01 Clo (plastic bag) to 2.79 Clo (2 layers of a hospital duvet). Given the range of insulating materials available for outdoor activities, significant improvement in insulation of patients in the OR is both possible and desirable.

  11. Brady 1D seismic velocity model ambient noise prelim

    DOE Data Explorer

    Mellors, Robert J.

    2013-10-25

    Preliminary 1D seismic velocity model derived from ambient noise correlation. 28 Green's functions filtered between 4-10 Hz for Vp, Vs, and Qs were calculated. 1D model estimated for each path. The final model is a median of the individual models. Resolution is best for the top 1 km. Poorly constrained with increasing depth.

  12. Sauter-Schwinger-like tunneling in tilted Bose-Hubbard lattices in the Mott phase

    NASA Astrophysics Data System (ADS)

    Queisser, Friedemann; Navez, Patrick; Schützhold, Ralf

    2012-03-01

    We study the Mott phase of the Bose-Hubbard model on a tilted lattice. On the (Gutzwiller) mean-field level, the tilt has no effect, but quantum fluctuations entail particle-hole pair creation via tunneling. For small potential gradients (long-wavelength limit), we derive a quantitative analogy to the Sauter-Schwinger effect, i.e., electron-positron pair creation out of the vacuum by an electric field. For large tilts, we obtain resonant tunneling reminiscent of Bloch oscillations.

  13. Enhanced Thermoelectric Power in Graphene: Violation of the Mott Relation by Inelastic Scattering.

    PubMed

    Ghahari, Fereshte; Xie, Hong-Yi; Taniguchi, Takashi; Watanabe, Kenji; Foster, Matthew S; Kim, Philip

    2016-04-01

    We report the enhancement of the thermoelectric power (TEP) in graphene with extremely low disorder. At high temperature we observe that the TEP is substantially larger than the prediction of the Mott relation, approaching to the hydrodynamic limit due to strong inelastic scattering among the charge carriers. However, closer to room temperature the inelastic carrier-optical-phonon scattering becomes more significant and limits the TEP below the hydrodynamic prediction. We support our observation by employing a Boltzmann theory incorporating disorder, electron interactions, and optical phonons. PMID:27081996

  14. Enhanced Thermoelectric Power in Graphene: Violation of the Mott Relation by Inelastic Scattering

    NASA Astrophysics Data System (ADS)

    Ghahari, Fereshte; Xie, Hong-Yi; Taniguchi, Takashi; Watanabe, Kenji; Foster, Matthew S.; Kim, Philip

    2016-04-01

    We report the enhancement of the thermoelectric power (TEP) in graphene with extremely low disorder. At high temperature we observe that the TEP is substantially larger than the prediction of the Mott relation, approaching to the hydrodynamic limit due to strong inelastic scattering among the charge carriers. However, closer to room temperature the inelastic carrier-optical-phonon scattering becomes more significant and limits the TEP below the hydrodynamic prediction. We support our observation by employing a Boltzmann theory incorporating disorder, electron interactions, and optical phonons.

  15. Equations for the Cabrera-Mott kinetics of oxidation for spherical nanoparticles

    NASA Astrophysics Data System (ADS)

    Ermoline, Alexandre; Dreizin, Edward L.

    2011-03-01

    Equations describing formation of a spherical oxide shell according to the Cabrera-Mott mechanism are presented. Two different configurations of metal and oxidizer are considered: oxidation of a spherical metal particle in surrounding oxidizer, and reduction of a spherical oxide inclusion in a metal matrix. Equations for the former configuration were reported earlier but did not explicitly account for volume changes in the growing oxide shell and shrinking central core. For aluminum oxidation, the correction for these volume changes is significant for spherical particles with diameters less than 10 nm.

  16. Thermal insulated glazing unit

    DOEpatents

    Selkowitz, Stephen E.; Arasteh, Dariush K.; Hartmann, John L.

    1991-01-01

    An improved insulated glazing unit is provided which can attain about R5 to about R10 thermal performance at the center of the glass while having dimensions about the same as those of a conventional double glazed insulated glazing unit. An outer glazing and inner glazing are sealed to a spacer to form a gas impermeable space. One or more rigid, non-structural glazings are attached to the inside of the spacer to divide the space between the inner and outer glazings to provide insulating gaps between glazings of from about 0.20 inches to about 0.40 inches. One or more glazing surfaces facing each thermal gap are coated with a low emissivity coating. Finally, the thermal gaps are filled with a low conductance gas such as krypton gas.

  17. Thermal insulated glazing unit

    DOEpatents

    Selkowitz, S.E.; Arasteh, D.K.; Hartmann, J.L.

    1988-04-05

    An improved insulated glazing unit is provided which can attain about R5 to about R10 thermal performance at the center of the glass while having dimensions about the same as those of a conventional double glazed insulated glazing unit. An outer glazing and inner glazing are sealed to a spacer to form a gas impermeable space. One or more rigid, non-structural glazings are attached to the inside of the spacer to divide the space between the inner and outer glazings to provide insulating gaps between glazings of from about 0.20 inches to about 0.40 inches. One or more glazing surfaces facing each thermal gap are coated with a low emissivity coating. Finally, the thermal gaps are filled with a low conductance gas such as krypton gas. 2 figs.

  18. Reusable Surface Insulation

    NASA Technical Reports Server (NTRS)

    1997-01-01

    Advanced Flexible Reusable Surface Insulation, developed by Ames Research Center, protects the Space Shuttle from the searing heat that engulfs it on reentry into the Earth's atmosphere. Initially integrated into the Space Shuttle by Rockwell International, production was transferred to Hi-Temp Insulation Inc. in 1974. Over the years, Hi-Temp has created many new technologies to meet the requirements of the Space Shuttle program. This expertise is also used commercially, including insulation blankets to cover aircrafts parts, fire barrier material to protect aircraft engine cowlings and aircraft rescue fire fighter suits. A Fire Protection Division has also been established, offering the first suit designed exclusively by and for aircraft rescue fire fighters. Hi-Temp is a supplier to the Los Angeles City Fire Department as well as other major U.S. civil and military fire departments.

  19. Insulation bonding test system

    NASA Technical Reports Server (NTRS)

    Beggs, J. M.; Johnston, G. D.; Coleman, A. D.; Portwood, J. N.; Saunders, J. M.; Redmon, J. W.; Porter, A. C. (Inventor)

    1984-01-01

    A method and a system for testing the bonding of foam insulation attached to metal is described. The system involves the use of an impacter which has a calibrated load cell mounted on a plunger and a hammer head mounted on the end of the plunger. When the impacter strikes the insulation at a point to be tested, the load cell measures the force of the impact and the precise time interval during which the hammer head is in contact with the insulation. This information is transmitted as an electrical signal to a load cell amplifier where the signal is conditioned and then transmitted to a fast Fourier transform (FFT) analyzer. The FFT analyzer produces energy spectral density curves which are displayed on a video screen. The termination frequency of the energy spectral density curve may be compared with a predetermined empirical scale to determine whether a igh quality bond, good bond, or debond is present at the point of impact.

  20. Endoplasmic Reticulum Glycoprotein Quality Control Regulates CD1d Assembly and CD1d-mediated Antigen Presentation*

    PubMed Central

    Kunte, Amit; Zhang, Wei; Paduraru, Crina; Veerapen, Natacha; Cox, Liam R.; Besra, Gurdyal S.; Cresswell, Peter

    2013-01-01

    The non-classical major histocompatibility complex (MHC) homologue CD1d presents lipid antigens to innate-like lymphocytes called natural-killer T (NKT) cells. These cells, by virtue of their broad cytokine repertoire, shape innate and adaptive immune responses. Here, we have assessed the role of endoplasmic reticulum glycoprotein quality control in CD1d assembly and function, specifically the role of a key component of the quality control machinery, the enzyme UDP glucose glycoprotein glucosyltransferase (UGT1). We observe that in UGT1-deficient cells, CD1d associates prematurely with β2-microglobulin (β2m) and is able to rapidly exit the endoplasmic reticulum. At least some of these CD1d-β2m heterodimers are shorter-lived and can be rescued by provision of a defined exogenous antigen, α-galactosylceramide. Importantly, we show that in UGT1-deficient cells the CD1d-β2m heterodimers have altered antigenicity despite the fact that their cell surface levels are unchanged. We propose that UGT1 serves as a quality control checkpoint during CD1d assembly and further suggest that UGT1-mediated quality control can shape the lipid repertoire of newly synthesized CD1d. The quality control process may play a role in ensuring stability of exported CD1d-β2m complexes, in facilitating presentation of low abundance high affinity antigens, or in preventing deleterious responses to self lipids. PMID:23615906

  1. Interaction of environmental contaminants with zebrafish organic anion transporting polypeptide, Oatp1d1 (Slco1d1)

    SciTech Connect

    Popovic, Marta; Zaja, Roko; Fent, Karl; Smital, Tvrtko

    2014-10-01

    Polyspecific transporters from the organic anion transporting polypeptide (OATP/Oatp) superfamily mediate the uptake of a wide range of compounds. In zebrafish, Oatp1d1 transports conjugated steroid hormones and cortisol. It is predominantly expressed in the liver, brain and testes. In this study we have characterized the transport of xenobiotics by the zebrafish Oatp1d1 transporter. We developed a novel assay for assessing Oatp1d1 interactors using the fluorescent probe Lucifer yellow and transient transfection in HEK293 cells. Our data showed that numerous environmental contaminants interact with zebrafish Oatp1d1. Oatp1d1 mediated the transport of diclofenac with very high affinity, followed by high affinity towards perfluorooctanesulfonic acid (PFOS), nonylphenol, gemfibrozil and 17α-ethinylestradiol; moderate affinity towards carbaryl, diazinon and caffeine; and low affinity towards metolachlor. Importantly, many environmental chemicals acted as strong inhibitors of Oatp1d1. A strong inhibition of Oatp1d1 transport activity was found by perfluorooctanoic acid (PFOA), chlorpyrifos-methyl, estrone (E1) and 17β-estradiol (E2), followed by moderate to low inhibition by diethyl phthalate, bisphenol A, 7-acetyl-1,1,3,4,4,6-hexamethyl-1,2,3,4 tetrahydronapthalene and clofibrate. In this study we identified Oatp1d1 as a first Solute Carrier (SLC) transporter involved in the transport of a wide range of xenobiotics in fish. Considering that Oatps in zebrafish have not been characterized before, our work on zebrafish Oatp1d1 offers important new insights on the understanding of uptake processes of environmental contaminants, and contributes to the better characterization of zebrafish as a model species. - Highlights: • We optimized a novel assay for determination of Oatp1d1 interactors • Oatp1d1 is the first SLC characterized fish xenobiotic transporter • PFOS, nonylphenol, diclofenac, EE2, caffeine are high affinity Oatp1d1substrates • PFOA, chlorpyrifos

  2. Perioperative thermal insulation.

    PubMed

    Sessler, D I; McGuire, J; Sessler, A M

    1991-05-01

    To determine the efficacy of passive insulators advocated for prevention of cutaneous heat loss, we determined heat loss in unanesthetized volunteers covered by one of the following: a cloth "split sheet" surgical drape; a Convertors disposable-paper split sheet; a Thermadrape disposable laparotomy sheet; an unheated Bair Hugger patient-warming blanket; 1.5-mil-thick plastic hamper bags; and a prewarmed, cotton hospital blanket. Cutaneous heat loss was measured using 10 area-weighted thermal flux transducers while volunteers were exposed to a 20.6 degrees C environment for 1 h. Heat loss decreased significantly from 100 +/- 3 W during the control periods to 69 +/- 6 W (average of all covers) after 1 h of treatment. Heat losses from volunteers insulated by the Thermadrape (61 +/- 6 W) and Bair Hugger covers (64 +/- 5 W) were significantly less than losses from those insulated by plastic bags (77 +/- 11 W). The paper drape (67 +/- 7 W) provided slightly, but not significantly, better insulation than the cloth drape (70 +/- 4 W). Coverage by prewarmed cotton blankets initially resulted in the least heat loss (58 +/- 8 W), but after 40 min, resulted in heat loss significantly greater than that for the Thermadrape (71 +/- 7 W). Regional heat loss was roughly proportional to surface area, and the distribution of regional heat loss remained similar with all covers. These data suggest that cost and convenience should be major factors when choosing among passive perioperative insulating covers. It is likely that the amount of skin surface covered is more important than the choice of skin region covered or the choice of insulating material. PMID:2021204

  3. Quantum Monte Carlo study of strange correlator in interacting topological insulators

    NASA Astrophysics Data System (ADS)

    Wu, Han-Qing; He, Yuan-Yao; You, Yi-Zhuang; Xu, Cenke; Meng, Zi Yang; Lu, Zhong-Yi

    2015-10-01

    Distinguishing the nontrivial symmetry-protected topological (SPT) phase from the trivial insulator phase in the presence of electron-electron interaction is an urgent question to the study of topological insulators, due to the fact that most of the topological indices defined for free electron systems are very likely unsuitable for interacting cases. In this work, we demonstrate that the strange correlator is a sensitive diagnosis to detect SPT states in interacting systems. Employing large-scale quantum Monte Carlo (QMC) simulations, we investigate the interaction-driven quantum phase transition in the Kane-Mele-Hubbard model. The transition from the quantum spin Hall insulator at weak interaction to an antiferromagnetic Mott insulator at strong interaction can be readily detected by the momentum space behavior of the strange correlator in single-particle, spin, and pairing sectors. The interaction effects on the symmetry-protected edge states in various sectors, i.e., the helical Luttinger liquid behavior, are well captured in the QMC measurements of strange correlators. Moreover, we demonstrate that the strange correlator is technically easier to implement in QMC and more robust in performance than other proposed numerical diagnoses for interacting topological states, as only static correlations are needed. The attempt in this work paves the way for using the strange correlator to study interaction-driven topological phase transitions in fermionic as well as bosonic systems.

  4. Quantum Monte Carlo study of strange correlator in interacting topological insulators

    NASA Astrophysics Data System (ADS)

    Wu, Han-Qing; He, Yuan-Yao; You, Yi-Zhuang; Xu, Cenke; Meng, Zi Yang; Lu, Zhong-Yi

    Distinguishing the nontrivial symmetry-protected topological (SPT) phase from the trivial insulator phase in the presence of electron-electron interaction is an urgent question to the study of topological insulators. In this work, we demonstrate that the strange correlator is a sensitive diagnosis to detect SPT states in interacting systems. Employing large-scale quantum Monte Carlo (QMC) simulations, we investigate the interaction-driven quantum phase transition in the Kane-Mele-Hubbard model. The transition from the quantum spin Hall insulator at weak interaction to an antiferromagnetic Mott insulator at strong interaction can be readily detected by the momentum space behavior of the strange correlator in single-particle, spin, and pairing sectors. The interaction e?ects on the symmetry-protected edge states in various sectors are well captured in the QMC measurements of strange correlators. Moreover, we demonstrate that the strange correlator is technically easier to implement in QMC and more robust in performance than other proposed numerical diagnoses for interacting topological states, as only static correlations are needed. The attempt in this work paves the way for using the strange correlator to study interaction-driven topological phase transitions.

  5. Measuring Building Insulation

    NASA Astrophysics Data System (ADS)

    Parks, Beth

    2013-03-01

    Currently, the only way for homeowners to learn about the effectiveness of their home insulation is to hire an energy auditor. This difficulty deters homeowners from taking action to improve energy efficiency. In principle, measuring the temperature difference between a wall surface and the interior of a home is sufficient to determine the wall insulation, but in practice, temperature cycles from the heating system make a single measurement unreliable. I will describe a simple and inexpensive thermocouple-based device to measure this temperature difference and report results obtained by monitoring this temperature difference over multiple heating cycles in a range of buildings. Patent application 12/555371

  6. Thermal insulation protection means

    NASA Technical Reports Server (NTRS)

    Dotts, R. L.; Smith, J. A.; Strouhal, G. (Inventor)

    1979-01-01

    A system for providing thermal insulation for portions of a spacecraft which do not exceed 900 F during ascent or reentry relative to the earth's atmosphere is described. The thermal insulation is formed of relatively large flexible sheets of needled Nomex felt having a flexible waterproof coating. The thickness of the felt is sized to protect against projected temperatures and is attached to the structure by a resin adhesive. Vent holes in the sheets allow ventilation while maintaining waterproofing. The system is heat treated to provide thermal stability.

  7. D1/D5 dopamine receptors modulate spatial memory formation.

    PubMed

    da Silva, Weber C N; Köhler, Cristiano C; Radiske, Andressa; Cammarota, Martín

    2012-02-01

    We investigated the effect of the intra-CA1 administration of the D1/D5 receptor antagonist SCH23390 and the D1/D5 receptor agonist SKF38393 on spatial memory in the water maze. When given immediately, but not 3h after training, SCH23390 hindered long-term spatial memory formation without affecting non-spatial memory or the normal functionality of the hippocampus. On the contrary, post-training infusion of SKF38393 enhanced retention and facilitated the spontaneous recovery of the original spatial preference after reversal learning. Our findings demonstrate that hippocampal D1/D5 receptors play an essential role in spatial memory processing.

  8. Ripple modulated electronic structure of a 3D topological insulator

    NASA Astrophysics Data System (ADS)

    Madhavan, Vidya

    2013-03-01

    Many of the unusual properties of topological insulators can only be realized through a delicate tuning of the Dirac surface state rendering their detection thus far elusive. We have discovered that the surface state dispersion of a prototypical topological insulator can be continuously tuned via a novel topographical route. STM images of Bi2Te3 show one-dimensional (striped) ripples with 100nm periodicity. By combining information from Landau level spectra and Fourier transform of interference patterns we show that the ripples induce spatial modulations in the surface state dispersion. We describe how the ripples create topological channels for chiral spin modes at the boundaries such that placing the Fermi energy between the Landau levels of these periodic stripes would result in the first experimental realization of the ideal 1D dissipationless quantum wire. This ability to tune the surface state dispersion locally opens the door to a host of new phenomena in topological insulators.

  9. Self-Healing Wire Insulation

    NASA Technical Reports Server (NTRS)

    Parrish, Clyde F. (Inventor)

    2012-01-01

    A self-healing system for an insulation material initiates a self-repair process by rupturing a plurality of microcapsules disposed on the insulation material. When the plurality of microcapsules are ruptured, reactants within the plurality of microcapsules react to form a replacement polymer in a break of the insulation material. This self-healing system has the ability to repair multiple breaks in a length of insulation material without exhausting the repair properties of the material.

  10. Bias activated dielectric response of excitons and excitonic Mott transition in quantum confined lasers structures.

    NASA Astrophysics Data System (ADS)

    Bhunia, Amit; Bansal, Kanika; Datta, Shouvik; Alshammari, Marzook S.; Henini, Mohamed

    In contrast to the widely reported optical techniques, there are hardly any investigations on corresponding electrical signatures of condensed matter physics of excitonic phenomena. We studied small signal steady state capacitance response in III-V materials based multi quantum well (AlGaInP) and MBE grown quantum dot (InGaAs) laser diodes to identify signatures of excitonic presence. Conductance activation by forward bias was probed using frequency dependent differential capacitance response (fdC/df), which changes characteristically with the onset of light emission indicating the occurrence of negative activation energy. Our analysis shows that it is connected with a steady state population of exciton like bound states. Calculated average energy of this bound state matches well with the binding energy of weakly confined excitons in this type of structures. Further increase in charge injection decreases the differential capacitive response in AlGaInP based diodes, indicating a gradual Mott transition of excitonic states into electron hole plasma. This electrical description of excitonic Mott transition is fully supplemented by standard optical spectroscopic signatures of band gap renormalization and phase space filling effects.

  11. Nonequilibrium self-energy functional approach to the dynamical Mott transition

    NASA Astrophysics Data System (ADS)

    Hofmann, Felix; Eckstein, Martin; Potthoff, Michael

    2016-06-01

    The real-time dynamics of the Fermi-Hubbard model, driven out of equilibrium by quenching or ramping the interaction parameter, is studied within the framework of the nonequilibrium self-energy functional theory. A dynamical impurity approximation with a single auxiliary bath site is considered as a reference system, and the time-dependent hybridization is optimized as prescribed by the variational principle. The dynamical two-site approximation turns out to be useful to study the real-time dynamics on short and intermediate time scales. Depending on the strength of the interaction in the final state, two qualitatively different response regimes are observed. For both weak and strong couplings, qualitative agreement with previous results of nonequilibrium dynamical mean-field theory is found. The two regimes are sharply separated by a critical point at which the low-energy bath degree of freedom decouples in the course of time. We trace the dependence of the critical interaction of the dynamical Mott transition on the duration of the interaction ramp from sudden quenches to adiabatic dynamics and therewith link the dynamical to the equilibrium Mott transition.

  12. Tuning a strain-induced orbital selective Mott transition in epitaxial VO2

    NASA Astrophysics Data System (ADS)

    Mukherjee, Shantanu; Quackenbush, N. F.; Paik, H.; Schlueter, C.; Lee, T.-L.; Schlom, D. G.; Piper, L. F. J.; Lee, Wei-Cheng

    2016-06-01

    We present evidence of strain-induced modulation of electron correlation effects and increased orbital anisotropy in the rutile phase of epitaxial VO2/TiO2 films from hard x-ray photoelectron spectroscopy and soft V L-edge x-ray absorption spectroscopy, respectively. By using the U(1) slave spin formalism, we further argue that the observed anisotropic correlation effects can be understood by a model of orbital selective Mott transition at a filling that is noninteger but close to the half filling. Because the overlaps of wave functions between d orbitals are modified by the strain, orbital-dependent renormalizations of the bandwidths and the onsite energy occur. These renormalizations generally result in different occupation numbers in different orbitals. We find that if the system has a noninteger filling number near the half filling such as for VO2, certain orbitals could reach an occupation number closer to half filling under the strain, resulting in a strong reduction in the quasiparticle weight Zα of that orbital. Our work demonstrates that such an orbital selective Mott transition, defined as the case with Zα=0 in some but not all orbitals, could be accessed by epitaxial-strain engineering of correlated electron systems.

  13. Anderson-Mott transition in arrays of a few dopant atoms in a silicon transistor.

    PubMed

    Prati, Enrico; Hori, Masahiro; Guagliardo, Filippo; Ferrari, Giorgio; Shinada, Takahiro

    2012-07-01

    Dopant atoms are used to control the properties of semiconductors in most electronic devices. Recent advances such as single-ion implantation have allowed the precise positioning of single dopants in semiconductors as well as the fabrication of single-atom transistors, representing steps forward in the realization of quantum circuits. However, the interactions between dopant atoms have only been studied in systems containing large numbers of dopants, so it has not been possible to explore fundamental phenomena such as the Anderson-Mott transition between conduction by sequential tunnelling through isolated dopant atoms, and conduction through thermally activated impurity Hubbard bands. Here, we observe the Anderson-Mott transition at low temperatures in silicon transistors containing arrays of two, four or six arsenic dopant atoms that have been deterministically implanted along the channel of the device. The transition is induced by controlling the spacing between dopant atoms. Furthermore, at the critical density between tunnelling and band transport regimes, we are able to change the phase of the electron system from a frozen Wigner-like phase to a Fermi glass by increasing the temperature. Our results open up new approaches for the investigation of coherent transport, band engineering and strongly correlated systems in condensed-matter physics.

  14. A human serotonin 1D receptor variant (5HT1D beta) encoded by an intronless gene on chromosome 6.

    PubMed Central

    Demchyshyn, L; Sunahara, R K; Miller, K; Teitler, M; Hoffman, B J; Kennedy, J L; Seeman, P; Van Tol, H H; Niznik, H B

    1992-01-01

    An intronless gene encoding a serotonin receptor (5HT1D beta) has been cloned and functionally expressed in mammalian fibroblast cultures. Based on the deduced amino acid sequence, the gene encodes a 390-amino acid protein displaying considerable homology, within putative transmembrane domains (approximately 75% identity) to the canine and human 5HT1D receptors. Membranes prepared from CHO cells stably expressing the receptor bound [3H]serotonin with high affinity (Kd 4 nM) and displayed a pharmacological profile consistent, but not identical, with that of the characterized serotonin 5HT1D receptor. Most notably, metergoline and serotonergic piperazine derivatives, as a group, display 3- to 8-fold lower affinity for the 5HT1D beta receptor than for the 5HT1D receptor, whereas both receptors display similar affinities for tryptamine derivatives, including the antimigraine drug sumatriptan. Northern blot analysis revealed an mRNA of approximately 5.5 kilobases expressed in human and monkey frontal cortex, medulla, striatum, hippocampus and amygdala but not in cerebellum, olfactory tubercle, and pituitary. The 5HT1D beta gene maps to human chromosome 6. The existence of multiple neuronal 5HT1D-like receptors may help account for some of the complexities associated with [3H]serotonin binding patterns in native membranes. Images PMID:1351684

  15. Improved insulation material

    NASA Technical Reports Server (NTRS)

    1976-01-01

    Multilayer material consisting of embossed, silver-coated Mylar, nylon net, and silk net is useful for thermal-protection systems and cryogenic containers. Embossing serves two purposes: helps separate radiation barriers and controls radiant energy diffusion. Insulation requires no maintenance after installation.

  16. Alaska Pipeline Insulation

    NASA Technical Reports Server (NTRS)

    1979-01-01

    Crude oil moving through the 800-mile Trans-Alaska Pipeline must be kept at a relatively high temperature, about 180 degrees Fahrenheit, to maintain the fluidity of the oil. In Arctic weather, that demands highly effective insulation. General Electric Co.'s Space Division, Valley Forge, Pennsylvania, provided it with a spinoff product called Therm-O-Trol. Shown being installed on the pipeline, Therm-O-Trol is a metal-bonded polyurethane foam especially formulated for Arctic insulation. A second GE spinoff product, Therm-O-Case, solved a related problem involved in bringing hot crude oil from 2,000-foot-deep wells to the surface without transferring oil heat to the surrounding permafrost soil; heat transfer could melt the frozen terrain and cause dislocations that might destroy expensive well casings. Therm-O-Case is a double-walled oil well casing with multi-layered insulation which provides an effective barrier to heat transfer. Therm-O-Trol and Therm-O-Case are members of a family of insulating products which stemmed from technology developed by GE Space Division in heat transferlthermal control work on Gemini, Apollo and other NASA programs.

  17. Photonic topological insulators.

    PubMed

    Khanikaev, Alexander B; Mousavi, S Hossein; Tse, Wang-Kong; Kargarian, Mehdi; MacDonald, Allan H; Shvets, Gennady

    2013-03-01

    Recent progress in understanding the topological properties of condensed matter has led to the discovery of time-reversal-invariant topological insulators. A remarkable and useful property of these materials is that they support unidirectional spin-polarized propagation at their surfaces. Unfortunately topological insulators are rare among solid-state materials. Using suitably designed electromagnetic media (metamaterials) we theoretically demonstrate a photonic analogue of a topological insulator. We show that metacrystals-superlattices of metamaterials with judiciously designed properties-provide a platform for designing topologically non-trivial photonic states, similar to those that have been identified for condensed-matter topological insulators. The interfaces of the metacrystals support helical edge states that exhibit spin-polarized one-way propagation of photons, robust against disorder. Our results demonstrate the possibility of attaining one-way photon transport without application of external magnetic fields or breaking of time-reversal symmetry. Such spin-polarized one-way transport enables exotic spin-cloaked photon sources that do not obscure each other.

  18. Insulated ECG electrodes

    NASA Technical Reports Server (NTRS)

    Portnoy, W. M.; David, R. M.

    1973-01-01

    Insulated, capacitively coupled electrode does not require electrolyte paste for attachment. Other features of electrode include wide range of nontoxic material that may be employed for dielectric because of sputtering technique used. Also, electrode size is reduced because there is no need for external compensating networks with FET operational amplifier.

  19. Preassembly Of Insulating Tiles

    NASA Technical Reports Server (NTRS)

    Izu, Y. D.; Yoshioka, E. N.; Rosario, T.

    1988-01-01

    Concept for preassembling high-temperature insulating tiles speeds and simplifies installation and repair and reduces damage from handling. Preassembly concept facilitates placement of tiles on gently contoured surfaces as well as on flat ones. Tiles bonded to nylon mesh with room-temperature-vulcanizing silicon rubber. Spacing between tiles is 0.03 in. Applications include boilers, kilns, and furnaces.

  20. The Polar Insulation Investigation

    ERIC Educational Resources Information Center

    Urban-Rich, Juanita

    2006-01-01

    In this article, the author developed an activity called "The Polar Insulation Investigation." This activity builds on students' natural interest in "things polar" and introduces them to animal adaptations in a unique way. The aim of the exploration is to determine the role of animal coverings (e.g., blubber, fur, and feathers) and to see which is…

  1. Erosion of polyurethane insulation.

    NASA Technical Reports Server (NTRS)

    Kraus, S.

    1973-01-01

    Detailed description of the test program in which erosion of the spray foam insulation used in the S-II stage of the Saturn-V Apollo launch vehicle was investigated. The behavior of the spray foam was investigated at the elevated temperature and static pressure appropriate to the S-II stage environment, but in the absence of the aerodynamic shear stress.

  2. THERMAL INSULATION SYSTEMS

    NASA Technical Reports Server (NTRS)

    Augustynowicz, Stanislaw D. (Inventor); Fesmire, James E. (Inventor)

    2005-01-01

    Thermal insulation systems and with methods of their production. The thermal insulation systems incorporate at least one reflection layer and at least one spacer layer in an alternating pattern. Each spacer layer includes a fill layer and a carrier layer. The fill layer may be separate from the carrier layer, or it may be a part of the carrier layer, i.e., mechanically injected into the carrier layer or chemically formed in the carrier layer. Fill layers contain a powder having a high surface area and low bulk density. Movement of powder within a fill layer is restricted by electrostatic effects with the reflection layer combined with the presence of a carrier layer, or by containing the powder in the carrier layer. The powder in the spacer layer may be compressed from its bulk density. The thermal insulation systems may further contain an outer casing. Thermal insulation systems may further include strips and seams to form a matrix of sections. Such sections serve to limit loss of powder from a fill layer to a single section and reduce heat losses along the reflection layer.

  3. Lightweight Electrical Insulation

    NASA Technical Reports Server (NTRS)

    Schroeder, J. E.

    1985-01-01

    Hollow plastic spheres expanded and fused together. Hollow, gasfilled plastic spheres piled in mold. Heating in vacuum softens and expands spheres, forcing them together into nearly regular hexagonal close packing. Foam used as lightweight, electrically insulating material in place of solid ceramic, glass, or polymer. Padding to protect against mechanical shocks another application for such dense, regular foam.

  4. 60. BOILER CHAMBER No. 1, D LOOP STEAM GENERATOR AND ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    60. BOILER CHAMBER No. 1, D LOOP STEAM GENERATOR AND MAIN COOLANT PUMP LOOKING NORTHEAST (LOCATION OOO) - Shippingport Atomic Power Station, On Ohio River, 25 miles Northwest of Pittsburgh, Shippingport, Beaver County, PA

  5. Severe Hypertriglyceridemia in Glut1D on Ketogenic Diet.

    PubMed

    Klepper, Joerg; Leiendecker, Baerbel; Heussinger, Nicole; Lausch, Ekkehart; Bosch, Friedrich

    2016-04-01

    High-fat ketogenic diets are the only treatment available for Glut1 deficiency (Glut1D). Here, we describe an 8-year-old girl with classical Glut1D responsive to a 3:1 ketogenic diet and ethosuximide. After 3 years on the diet a gradual increase of blood lipids was followed by rapid, severe asymptomatic hypertriglyceridemia (1,910 mg/dL). Serum lipid apheresis was required to determine liver, renal, and pancreatic function. A combination of medium chain triglyceride-oil and a reduction of the ketogenic diet to 1:1 ratio normalized triglyceride levels within days but triggered severe myoclonic seizures requiring comedication with sultiam. Severe hypertriglyceridemia in children with Glut1D on ketogenic diets may be underdiagnosed and harmful. In contrast to congenital hypertriglyceridemias, children with Glut1D may be treated effectively by dietary adjustments alone. PMID:26902182

  6. 1D Nanostructures: Controlled Fabrication and Energy Applications

    SciTech Connect

    Hu, Michael Z.

    2013-01-01

    Jian Wei, Xuchun Song, Chunli Yang, and Michael Z. Hu, 1D Nanostructures: Controlled Fabrication and Energy Applications, Journal of Nanomaterials, published special issue (http://www.hindawi.com/journals/jnm/si/197254/) (2013).

  7. High voltage variable diameter insulator

    DOEpatents

    Vanacek, D.L.; Pike, C.D.

    1982-07-13

    A high voltage feedthrough assembly having a tubular insulator extending between the ground plane ring and the high voltage ring. The insulator is made of Pyrex and decreases in diameter from the ground plane ring to the high voltage ring, producing equipotential lines almost perpendicular to the wall of the insulator to optimize the voltage-holding capability of the feedthrough assembly.

  8. Peg supported thermal insulation panel

    DOEpatents

    Nowobilski, Jeffert J.; Owens, William J.

    1985-01-01

    A thermal insulation panel which is lightweight, load bearing, accommodates thermal stress, and has excellent high temperature insulation capability comprising high performance insulation between thin metal walls supported by high density, high strength glass pegs made in compliance with specified conditions of time, temperature and pressure.

  9. Peg supported thermal insulation panel

    DOEpatents

    Nowobilski, J.J.; Owens, W.J.

    1985-04-30

    A thermal insulation panel which is lightweight, load bearing, accommodates thermal stress, and has excellent high temperature insulation capability comprises high performance insulation between thin metal walls supported by high density, high strength glass pegs made in compliance with specified conditions of time, temperature and pressure. 2 figs.

  10. Multilayer High-Gradient Insulators

    SciTech Connect

    Harris, J R

    2006-08-16

    Multilayer High-Gradient Insulators are vacuum insulating structures composed of thin, alternating layers of dielectric and metal. They are currently being developed for application to high-current accelerators and related pulsed power systems. This paper describes some of the High-Gradient Insulator research currently being conducted at Lawrence Livermore National Laboratory.

  11. Transcription Independent Insulation at TFIIIC-Dependent Insulators

    PubMed Central

    Valenzuela, Lourdes; Dhillon, Namrita; Kamakaka, Rohinton T.

    2009-01-01

    Chromatin insulators separate active from repressed chromatin domains. In yeast the RNA pol III transcription machinery bound to tRNA genes function with histone acetylases and chromatin remodelers to restrict the spread of heterochromatin. Our results collectively demonstrate that binding of TFIIIC is necessary for insulation but binding of TFIIIB along with TFIIIC likely improves the probability of complex formation at an insulator. Insulation by this transcription factor occurs in the absence of RNA polymerase III or polymerase II but requires specific histone acetylases and chromatin remodelers. This analysis identifies a minimal set of factors required for insulation. PMID:19596900

  12. TBC1D24 genotype–phenotype correlation

    PubMed Central

    Balestrini, Simona; Milh, Mathieu; Castiglioni, Claudia; Lüthy, Kevin; Finelli, Mattea J.; Verstreken, Patrik; Cardon, Aaron; Stražišar, Barbara Gnidovec; Holder, J. Lloyd; Lesca, Gaetan; Mancardi, Maria M.; Poulat, Anne L.; Repetto, Gabriela M.; Banka, Siddharth; Bilo, Leonilda; Birkeland, Laura E.; Bosch, Friedrich; Brockmann, Knut; Cross, J. Helen; Doummar, Diane; Félix, Temis M.; Giuliano, Fabienne; Hori, Mutsuki; Hüning, Irina; Kayserili, Hulia; Kini, Usha; Lees, Melissa M.; Meenakshi, Girish; Mewasingh, Leena; Pagnamenta, Alistair T.; Peluso, Silvio; Mey, Antje; Rice, Gregory M.; Rosenfeld, Jill A.; Taylor, Jenny C.; Troester, Matthew M.; Stanley, Christine M.; Ville, Dorothee; Walkiewicz, Magdalena; Falace, Antonio; Fassio, Anna; Lemke, Johannes R.; Biskup, Saskia; Tardif, Jessica; Ajeawung, Norbert F.; Tolun, Aslihan; Corbett, Mark; Gecz, Jozef; Afawi, Zaid; Howell, Katherine B.; Oliver, Karen L.; Berkovic, Samuel F.; Scheffer, Ingrid E.; de Falco, Fabrizio A.; Oliver, Peter L.; Striano, Pasquale; Zara, Federico

    2016-01-01

    Objective: To evaluate the phenotypic spectrum associated with mutations in TBC1D24. Methods: We acquired new clinical, EEG, and neuroimaging data of 11 previously unreported and 37 published patients. TBC1D24 mutations, identified through various sequencing methods, can be found online (http://lovd.nl/TBC1D24). Results: Forty-eight patients were included (28 men, 20 women, average age 21 years) from 30 independent families. Eighteen patients (38%) had myoclonic epilepsies. The other patients carried diagnoses of focal (25%), multifocal (2%), generalized (4%), and unclassified epilepsy (6%), and early-onset epileptic encephalopathy (25%). Most patients had drug-resistant epilepsy. We detail EEG, neuroimaging, developmental, and cognitive features, treatment responsiveness, and physical examination. In silico evaluation revealed 7 different highly conserved motifs, with the most common pathogenic mutation located in the first. Neuronal outgrowth assays showed that some TBC1D24 mutations, associated with the most severe TBC1D24-associated disorders, are not necessarily the most disruptive to this gene function. Conclusions: TBC1D24-related epilepsy syndromes show marked phenotypic pleiotropy, with multisystem involvement and severity spectrum ranging from isolated deafness (not studied here), benign myoclonic epilepsy restricted to childhood with complete seizure control and normal intellect, to early-onset epileptic encephalopathy with severe developmental delay and early death. There is no distinct correlation with mutation type or location yet, but patterns are emerging. Given the phenotypic breadth observed, TBC1D24 mutation screening is indicated in a wide variety of epilepsies. A TBC1D24 consortium was formed to develop further research on this gene and its associated phenotypes. PMID:27281533

  13. Integrated Multilayer Insulation

    NASA Technical Reports Server (NTRS)

    Dye, Scott

    2009-01-01

    Integrated multilayer insulation (IMLI) is being developed as an improved alternative to conventional multilayer insulation (MLI), which is more than 50 years old. A typical conventional MLI blanket comprises between 10 and 120 metallized polymer films separated by polyester nets. MLI is the best thermal- insulation material for use in a vacuum, and is the insulation material of choice for spacecraft and cryogenic systems. However, conventional MLI has several disadvantages: It is difficult or impossible to maintain the desired value of gap distance between the film layers (and consequently, it is difficult or impossible to ensure consistent performance), and fabrication and installation are labor-intensive and difficult. The development of IMLI is intended to overcome these disadvantages to some extent and to offer some additional advantages over conventional MLI. The main difference between IMLI and conventional MLI lies in the method of maintaining the gaps between the film layers. In IMLI, the film layers are separated by what its developers call a micro-molded discrete matrix, which can be loosely characterized as consisting of arrays of highly engineered, small, lightweight, polymer (typically, thermoplastic) frames attached to, and placed between, the film layers. The term "micro-molded" refers to both the smallness of the frames and the fact that they are fabricated in a process that forms precise small features, described below, that are essential to attainment of the desired properties. The term "discrete" refers to the nature of the matrix as consisting of separate frames, in contradistinction to a unitary frame spanning entire volume of an insulation blanket.

  14. Spatial Correlations and the Insulating Phase of the High-Tc Cuprates: Insights from a Configuration-Interaction-Based Solver for Dynamical Mean Field Theory

    NASA Astrophysics Data System (ADS)

    Go, Ara; Millis, Andrew J.

    2015-01-01

    A recently proposed configuration-interaction-based impurity solver is used in combination with the single-site and four-site cluster dynamical mean field approximations to investigate the three-band copper oxide model believed to describe the electronic structure of high transition temperature copper-oxide superconductors. Use of the configuration interaction solver enables verification of the convergence of results with respect to the number of bath orbitals. The spatial correlations included in the cluster approximation substantially shift the metal-insulator phase boundary relative to the prediction of the single-site approximation and increase the predicted energy gap of the insulating phase by about 1 eV above the single-site result. Vertex corrections occurring in the four-site approximation act to dramatically increase the value of the optical conductivity near the gap edge, resulting in better agreement with the data. The calculations reveal two distinct correlated insulating states: the "magnetically correlated insulator," in which nontrivial intersite correlations play an essential role in stabilizing the insulating state, and the strongly correlated insulator, in which local physics suffices. Comparison of the calculations to the data places the cuprates in the magnetically correlated Mott insulator regime.

  15. Calculation of metallic and insulating phases of V{sub 2}O{sub 3} by hybrid density functionals

    SciTech Connect

    Guo, Yuzheng; Robertson, John; Clark, Stewart J.

    2014-02-07

    The electronic structure of vanadium sesquioxide V{sub 2}O{sub 3} in its different phases has been calculated using the screened exchange hybrid density functional. The hybrid functional accurately reproduces the experimental electronic properties of all three phases, the paramagnetic metal (PM) phase, the anti-ferromagnetic insulating phase, and the Cr-doped paramagnetic insulating (PI) phase. We find that a fully relaxed supercell model of the Cr-doped PI phase based on the corundum structure has a monoclinic-like local strain around the substitutional Cr atoms. This is found to drive the PI-PM transition, consistent with a Peierls-Mott transition. The PI phase has a calculated band gap of 0.15 eV, in good agreement with experiment.

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

    NASA Astrophysics Data System (ADS)

    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

    2016-03-01

    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.

  17. 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

  18. Superfluid-insulator transition in strongly disordered one-dimensional systems

    NASA Astrophysics Data System (ADS)

    Yao, Zhiyuan; Pollet, Lode; Prokof'ev, N.; Svistunov, B.

    2016-04-01

    We present an asymptotically exact renormalization-group theory of the superfluid-insulator transition in one-dimensional (1D) disordered systems, with emphasis on an accurate description of the interplay between the Giamarchi-Schulz (instanton-anti-instanton) and weak-link (scratched-XY) criticalities. Combining the theory with extensive quantum Monte Carlo simulations allows us to shed new light on the ground-state phase diagram of the 1D disordered Bose-Hubbard model at unit filling.

  19. Multilayer High-Gradient Insulators

    SciTech Connect

    Harris, J R; Anaya, R M; Blackfield, D; Chen, Y -; Falabella, S; Hawkins, S; Holmes, C; Paul, A C; Sampayan, S; Sanders, D M; Watson, J A; Caporaso, G J; Krogh, M

    2006-11-15

    High voltage systems operated in vacuum require insulating materials to maintain spacing between conductors held at different potentials, and may be used to maintain a nonconductive vacuum boundary. Traditional vacuum insulators generally consist of a single material, but insulating structures composed of alternating layers of dielectric and metal can also be built. These ''High-Gradient Insulators'' have been experimentally shown to withstand higher voltage gradients than comparable conventional insulators. As a result, they have application to a wide range of high-voltage vacuum systems where compact size is important. This paper describes ongoing research on these structures, as well as the current theoretical understanding driving this work.

  20. Nature of the insulating ground state of the 5d postperovskite CaIrO3

    SciTech Connect

    Kim, Sun -Woo; Liu, Chen; Kim, Hyun -Jung; Lee, Jun -Ho; Yao, Yongxin; Ho, Kai -Ming; Cho, Jun -Hyung

    2015-08-26

    In this study, the insulating ground state of the 5d transition metal oxide CaIrO3 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 t2g 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 Ir4+ spins. Furthermore, the spin-orbit coupling (SOC) hybridizes the t2g states to open an insulating gap. These results indicate that CaIrO3 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.