Showing papers on "Mott insulator published in 1998"
TL;DR: A review of the metal-insulator transition can be found in this article, where a pedagogical introduction to the subject is given, as well as a comparison between experimental results and theoretical achievements.
Abstract: Metal-insulator transitions are accompanied by huge resistivity changes, even over tens of orders of magnitude, and are widely observed in condensed-matter systems. This article presents the observations and current understanding of the metal-insulator transition with a pedagogical introduction to the subject. Especially important are the transitions driven by correlation effects associated with the electron-electron interaction. The insulating phase caused by the correlation effects is categorized as the Mott Insulator. Near the transition point the metallic state shows fluctuations and orderings in the spin, charge, and orbital degrees of freedom. The properties of these metals are frequently quite different from those of ordinary metals, as measured by transport, optical, and magnetic probes. The review first describes theoretical approaches to the unusual metallic states and to the metal-insulator transition. The Fermi-liquid theory treats the correlations that can be adiabatically connected with the noninteracting picture. Strong-coupling models that do not require Fermi-liquid behavior have also been developed. Much work has also been done on the scaling theory of the transition. A central issue for this review is the evaluation of these approaches in simple theoretical systems such as the Hubbard model and $t\ensuremath{-}J$ models. Another key issue is strong competition among various orderings as in the interplay of spin and orbital fluctuations. Experimentally, the unusual properties of the metallic state near the insulating transition have been most extensively studied in $d$-electron systems. In particular, there is revived interest in transition-metal oxides, motivated by the epoch-making findings of high-temperature superconductivity in cuprates and colossal magnetoresistance in manganites. The article reviews the rich phenomena of anomalous metallicity, taking as examples Ti, V, Cr, Mn, Fe, Co, Ni, Cu, and Ru compounds. The diverse phenomena include strong spin and orbital fluctuations, mass renormalization effects, incoherence of charge dynamics, and phase transitions under control of key parameters such as band filling, bandwidth, and dimensionality. These parameters are experimentally varied by doping, pressure, chemical composition, and magnetic fields. Much of the observed behavior can be described by the current theory. Open questions and future problems are also extracted from comparison between experimental results and theoretical achievements.
5,781 citations
TL;DR: In this paper, the Bose-Hubbard model was used to model the phase transition from the superfluid to the Mott insulator phase induced by varying the depth of the optical potential.
Abstract: The dynamics of an ultracold dilute gas of bosonic atoms in an optical lattice can be described by a Bose-Hubbard model where the system parameters are controlled by laser light We study the continuous (zero temperature) quantum phase transition from the superfluid to the Mott insulator phase induced by varying the depth of the optical potential, where the Mott insulator phase corresponds to a commensurate filling of the lattice (``optical crystal'') Examples for formation of Mott structures in optical lattices with a superimposed harmonic trap and in optical superlattices are presented
2,873 citations
TL;DR: In this article, it was shown that such a transition is eliminated if the zero-point energy of transverse stripe fluctuations is sufficiently large compared to the ordered charge-density-wave coupling between stripes.
Abstract: The character of the ground state of an antiferromagnetic insulator is fundamentally altered following addition of even a small amount of charge1. The added charge is concentrated into domain walls across which a π phase shift in the spin correlations of the host material is induced. In two dimensions, these domain walls are ‘stripes’ which can be insulating2,3 or conducting4,5,6 — that is, metallic ‘rivers’ with their own low-energy degrees of freedom. However, in arrays of one-dimensional metals, which occur in materials such as organic conductors7, interactions between stripes typically drive a transition to an insulating ordered charge-density-wave (CDW) state at low temperatures. Here it is shown that such a transition is eliminated if the zero-point energy of transverse stripe fluctuations is sufficiently large compared tothe CDW coupling between stripes. As a consequence, there should exist electronic quantum liquid-crystal phases, which constitute new states of matter, and which can be either high-temperature superconductors or two-dimensional anisotropic ‘metallic’ non-Fermi liquids. Neutron scattering and other experiments in the copper oxide superconductor La1.6−xNd0.4SrxCuO4 already provide evidence for the existence of these phases in at least one class of materials.
877 citations
TL;DR: In this paper, a field effect transistor fabricated with an oxide channel has been shown to demonstrate switching characteristics similar to conventional silicon metal oxide field effect transistors, operating via a Mott metal-insulator transition induced by the gate field, and offers a potential technology alternative for the regime beyond silicon scaling limitations.
Abstract: A field effect transistor fabricated with an oxide channel has been shown to demonstrate switching characteristics similar to conventional silicon metal oxide field effect transistors. This device is believed to operate via a Mott metal-insulator transition induced by the gate field, and offers a potential technology alternative for the regime beyond silicon scaling limitations.
234 citations
TL;DR: Results suggest that this d-wave-like dispersion of the insulator is the underlying reason for the pseudo gap in the underdoped regime.
Abstract: An angle-resolved photoemission study is reported on Ca2CuO2Cl2, a parent compound of high-Tc superconductors. Analysis of the electron occupation probability, n(k), from the spectra shows a steep drop in spectral intensity across a contour that is close to the Fermi surface predicted by the band calculation. This analysis reveals a Fermi surface remnant, even though Ca2CuO2Cl2 is a Mott insulator. The lowest energy peak exhibits a dispersion with approximately the |coskxa – coskya| form along this remnant Fermi surface. Together with the data from Dy-doped Bi2Sr2CaCu2O8+δ, these results suggest that this d-wave–like dispersion of the insulator is the underlying reason for the pseudo gap in the underdoped regime.
187 citations
TL;DR: The thermally induced insulator-metal transition (IMT) has been investigated for single crystals of undoped and lightly doped LaCoO by measurements of the optical-conductivity spectra, the resistivity, and the Hall coefficient up to 800 K as mentioned in this paper.
Abstract: The thermally induced insulator-metal transition (IMT) has been investigated for single crystals of undoped and lightly doped ${\mathrm{LaCoO}}_{3}$ by measurements of the optical-conductivity spectra, the resistivity, and the Hall coefficient up to 800 K. The IMT around 500 K, where the spin-state transition from the nonmagnetic $(S=0)$ ground state to the intermediate-spin $(S=1)$ state is nearly completed, is characterized by a large energy-scale change of the electronic structure as well as by a steep increase of carrier number up to a typical metallic value due to closing of the charge gap. These behaviors are strikingly parallel to those characteristic of the Mott transition.
155 citations
TL;DR: In this paper, the authors investigated the thermoelectric response of correlated electron systems near the density driven Mott transition using the dynamical mean field theory, and showed that the response of the correlated electron system near Mott is positively correlated with the mean field.
Abstract: We investigate the thermoelectric response of correlated electron systems near the density driven Mott transition using the dynamical mean field theory.
120 citations
TL;DR: In this article, the breakdown of the Mott insulator is studied when the dissipative tunneling into the environment is introduced to the system, and it is shown how such a breakdown occurs.
Abstract: The breakdown of the Mott insulator is studied when the dissipative tunneling into the environment is introduced to the system. By exactly solving the one-dimensional asymmetric Hubbard model, we show how such a breakdown of the Mott insulator occurs. As the effect of the tunneling is increased, the Hubbard gap is monotonically decreased and finally disappears, resulting in the insulator-metal transition. We discuss the origin of this quantum-phase transition in comparison with other non-Hermitian systems recently studied.
71 citations
TL;DR: In this paper, the evolution of the spectral function with progressive hole doping in a Mott insulator, La1-xCaxVO3 with x = 0.0-0.5, was studied.
Abstract: We study the evolution of the spectral function with progressive hole doping in a Mott insulator, La1-xCaxVO3 with x = 0.0-0.5. The spectral features indicate a bulk-to-surface metal-insulator transition in this system. Doping dependent changes in the bulk electronic structure are shown to be incompatible with existing theoretical predictions. An empirical description based on the single parameter U/W is shown to describe consistently the spectral evolution.
65 citations
TL;DR: In this paper, the change of the ground state energy under twisted boundary conditions using the density matrix renormalization group algorithm was studied. But the authors focused on the effect of spinless fermions in disordered mesoscopic rings.
Abstract: When a system of spinless fermions in a disordered mesoscopic ring becomes instable between the inhomogeneous configuration driven by the random potential (Anderson insulator) and the homogeneous one driven by repulsive interactions (Mott insulator), the persistent current can be enhanced by orders of magnitude. This is illustrated by a study of the change of the ground state energy under twisted boundary conditions using the density matrix renormalization group algorithm.
57 citations
TL;DR: In this paper, the role of electron-electron interactions, and also of electronphonon coupling, on the narrow surface state band originating from the dangling bond orbitals of the adsorbate was investigated.
TL;DR: In this article, it is shown that bipolaron formation leads to a d-wave charged Bose-Einstein condensate in cuprates, which is the bipolaron energy dispersion rather than a particular pairing interaction which is responsible for the dwave symmetry.
Abstract: Starting from the Hamiltonian, which describes holes in a doped Mott insulator with the strong electron–phonon and Coulomb interactions we show that bipolaron formation leads to a d-wave charged Bose–Einstein condensate in cuprates. It is the bipolaron energy dispersion rather than a particular pairing interaction which is responsible for the d-wave symmetry. Single-particle spectral density is derived taking into account realistic band structure and disorder in cuprates. The tunnelling and photoemission (PES) spectra are described, including the temperature independent gap observed both in the superconducting and normal states, the emission/injection asymmetry, the finite zero-bias conductance, the spectral shape in the gap region and its temperature and doping dependence, the dip–hump incoherent asymmetric features at high voltage (tunnelling) and large binding energy (PES). The interaction responsible for the high value of Tc is elucidated which is the Frohlich electron–phonon interaction.
TL;DR: In this paper, an angle-resolved photoemission study of the V $3d band of the Mott insulator was performed at room temperature, and the results reflect the one dimensionality of the electronic structure and indicate the existence of antiferromagnetic correlations or holon excitations.
Abstract: We have made an angle-resolved photoemission study of ${\mathrm{NaV}}_{2}{\mathrm{O}}_{5}$ at room temperature, i.e., in the paramagnetic phase well above the spin-Peierls transition temperature. The obtained results reflect the one dimensionality of the electronic structure. The lower binding energy side of the V $3d$ band shows a clear momentum-dependent modulation with the periodicity of $\ensuremath{\pi}$, indicating the existence of antiferromagnetic correlations or holon excitations in the one-dimensional Mott insulator. We compare the results with recent theoretical works on the one-dimensional Hubbard and $t$- $J$ models and discuss consistency between model parameters.
TL;DR: In this paper, the Luther-Emery model is used to describe 1D charge density wave systems with one gapless and one gapped degree of freedom, i.e. fermions with one Gapless and 1 gapped degrees of freedom.
Abstract: I construct the spectral function of the Luther-Emery model which describes one-dimensional fermions with one gapless and one gapped degree of freedom, i.e. superconductors and Peierls and Mott insulators, by using symmetries, relations to other models, and known limits. Depending on the relative magnitudes of the charge and spin velocities, and on whether a charge or a spin gap is present, I find spectral functions differing in the number of singularities and presence or absence of anomalous dimensions of fermion operators. I find, for a Peierls system, one singularity with anomalous dimension and one finite maximum; for a superconductor two singularities with anomalous dimensions; and for a Mott insulator one or two singularities without anomalous dimension. In addition, there are strong shadow bands. I generalize the construction to arbitrary dynamical multi-particle correlation functions. The main aspects of this work are in agreement with numerical and Bethe Ansatz calculations by others. I also discuss the application to photoemission experiments on 1D Mott insulators and on the normal state of 1D Peierls systems, and propose the Luther-Emery model as the generic description of 1D charge density wave systems with important electronic correlations.
TL;DR: In this article, the Luther-Emery model is used to describe 1D charge density wave systems with one gapless and one gapped degree of freedom, i.e. fermions with one Gapless and 1 gapped degrees of freedom.
Abstract: I construct the spectral function of the Luther-Emery model which describes one-dimensional fermions with one gapless and one gapped degree of freedom, i.e. superconductors and Peierls and Mott insulators, by using symmetries, relations to other models, and known limits. Depending on the relative magnitudes of the charge and spin velocities, and on whether a charge or a spin gap is present, I find spectral functions differing in the number of singularities and presence or absence of anomalous dimensions of fermion operators. I find, for a Peierls system, one singularity with anomalous dimension and one finite maximum; for a superconductor two singularities with anomalous dimensions; and for a Mott insulator one or two singularities without anomalous dimension. In addition, there are strong shadow bands. I generalize the construction to arbitrary dynamical multi-particle correlation functions. The main aspects of this work are in agreement with numerical and Bethe Ansatz calculations by others. I also discuss the application to photoemission experiments on 1D Mott insulators and on the normal state of 1D Peierls systems, and propose the Luther-Emery model as the generic description of 1D charge density wave systems with important electronic correlations.
TL;DR: In this article, the slave boson mean field studies of the ground state of the Hubbard model with correlated hopping were performed, and the results for the case of the hopping integral t equal to the correlated hopping integral X were recovered.
Abstract: The slave boson mean-field studies of the ground state of the Hubbard model with correlated hopping were performed. The approach qualitatively recovers the exact results for the case of the hopping integral t equal to the correlated hopping integral X. The phase diagram for the strongly correlated state with only singly occupied sites, the weakly correlated state, where single and double occupation is allowed, and for the superconducting state, was determined for any values of X and any electron concentration n. At the half-filled band (n=1) a direct transition from the superconductor to the Mott insulator was found. In the region of strong correlations the superconducting solution is stable for n close to 1, in contrast to the case of weak correlations, in which superconductivity occurs at n close to 0 and n close to 2. We found also that strong correlations change characteristics of the superconducting phase, e.g. the gap in the excitation spectrum has a nonexponential dependence close to the point of the phase transition.
TL;DR: In this article, the effects of randomness on interacting fermionic systems in one dimension are investigated by quantum Monte Carlo techniques, and the quantum phase transition due to randomness is observed associated with the collapse of the charge ordering.
Abstract: Effects of randomness on interacting fermionic systems in one dimension are investigated by quantum Monte Carlo techniques. At first, interacting spinless fermions are studied whose ground state shows charge ordering. Quantum phase transition due to randomness is observed associated with the collapse of the charge ordering. We also treat random Hubbard model focusing on the Mott gap. Although the randomness closes the Mott gap and low-lying states are created, which is observed in the charge compressibility, no (quasi-)Fermi-surface singularity is formed. It implies localized nature of the low-lying states.
TL;DR: In this article, a pseudo-one-dimensional charge transfer salt DMTSA-BF 4 was found to have high electrical conductivity (σ RT ≈500 Scm -1 ) and metallic temperature dependence down to ca. 160 K. This compound is the first metal among the 1:1 organic charge transfer salts.
Abstract: Pseudo-one-dimensional charge-transfer salt DMTSA-BF 4 shows high electrical conductivity (σ RT ≈500 Scm -1 ) and metallic temperature dependence down to ca. 160 K, in contrast to the conventional half-filled organic conductors which are regarded as Mott insulators. The pseudo-one-dimensionality is evidenced by the polarized reflectance spectra. The electrical resistivity, thermopower, magnetic susceptibility, and polarized reflectance spectrum suggest that DMTSA-BF 4 is a metal above ca. 150 K. This compound is the first metal among the 1:1 organic charge-transfer salts. The low-temperature reflectance spectrum suggests that the glide plane symmetry is broken below 150 K and the fluctuation of this broken symmetry is already observed at room temperature. The metal-insulator transition around 150 K is regarded as Peierls transition. The Hubbard parameter U / W is estimated to be <0.8, which may be the possible reason for the metallic nature in high-temperature phase.
TL;DR: In this paper, structural and transport properties of interacting localized flux lines in the Bose glass phase of irradiated superconductors are studied by means of Monte Carlo simulations near the matching field where the densities of vortices and columnar defects are equal.
Abstract: Structural and transport properties of interacting localized flux lines in the Bose glass phase of irradiated superconductors are studied by means of Monte Carlo simulations near the matching field ${B}_{\ensuremath{\Phi}},$ where the densities of vortices and columnar defects are equal. For a completely random columnar pin distribution in the $\mathrm{xy}$ plane transverse to the magnetic field, our results show that the repulsive vortex interactions destroy the Mott insulator phase which was predicted to occur at ${B=B}_{\ensuremath{\Phi}}.$ On the other hand, for ratios of the penetration depth to average defect distance $\ensuremath{\lambda}/d\ensuremath{\lesssim}1,$ characteristic remnants of the Mott insulator singularities remain visible in experimentally accessible quantities as the magnetization, the bulk modulus, and the magnetization relaxation, when $B$ is varied near ${B}_{\ensuremath{\Phi}}.$ For spatially more regular disorder, e.g., a nearly triangular defect distribution, we find that the Mott insulator phase can survive up to considerably large interaction range $\ensuremath{\lambda}/d,$ and may thus be observable in experiments.
TL;DR: In this article, the authors use renormalization-group theory to examine the quantum phase transitions upon exiting the insulating phase of a disordered, strongly interacting boson system, and they find a direct transition from this Mott insulator to the superfluid phase.
Abstract: We use renormalization-group theory to examine the quantum phase transitions upon exiting the insulating phase of a disordered, strongly interacting boson system. For weak disorder we find a direct transition from this Mott insulator to the superfluid phase. In $dg4$ a finite region around the particle-hole symmetric point supports this direct transition, whereas for $2l~dl4$ perturbative arguments suggest that the direct transition survives only precisely at commensurate filling. For strong disorder the renormalization trajectories pass next to two fixed points, describing a pair of distinct transitions; first from the Mott insulator to the Bose glass, and then from the Bose glass to the superfluid. The latter fixed point possesses statistical particle-hole symmetry and a dynamical exponent $z$, equal to the dimension $d$.
TL;DR: In this paper, the authors examined a two-dimensional Fermi liquid with a fermi surface which touched the Umklapp surface first at the four points as the electron density is increased.
Abstract: We examine a two-dimensional Fermi liquid with a Fermi surface which touches the Umklapp surface first at the four points as the electron density is increased. Umklapp processes at the four patches near lead the renormalization group equations to scale to strong coupling, resembling the behaviour of a two-leg ladder at half-filling. The incompressible character of the fixed point causes a breakdown of Landau theory at these patches. A further increase in density spreads the incompressible regions so that the open Fermi surface shrinks to four disconnected segments. This non-Landau state, in which parts of the Fermi surface are truncated to form an insulating spin liquid, has many features in common with phenomenological models recently proposed for the cuprate superconductors.
TL;DR: In this article, the anomalous metallic state (AMS) of doped Mott insulators is analyzed based on the slave-boson mean-field approximation to the t-J model.
TL;DR: In this paper, it was shown that for small transverse fields, the insulating phase is preserved, and the transverse field is exponentially screened away from the boundaries of the superconductor.
Abstract: The boson Hubbard model has been extensively studied as a model of the zero temperature superfluid/insulator transition in Helium-4 on periodic substrates. It can also serve as a model for vortex lines in superconductors with a magnetic field parallel to a periodic array of columnar pins, due to a formal analogy between the vortex lines and the statistical mechanics of quantum bosons. When the magnetic field has a component perpendicular to the pins, this analogy yields a non-Hermitian boson Hubbard model. At integer filling, we find that for small transverse fields, the insulating phase is preserved, and the transverse field is exponentially screened away from the boundaries of the superconductor. At larger transverse fields, a ``superfluid'' phase of tilted, entangled vortices appears. The universality class of the transition is found to be that of vortex lines entering the Meissner phase at H_{c1}, with the additional feature that the direction of the tilted vortices at the transition bears a non-trivial relationship to the direction of the applied magnetic field. The properties of the Mott Insulator and flux liquid phases with tilt are also discussed.
TL;DR: In this article, the authors show that the nature of the doping induced metal-insulator transition in the two-dimensional Hubbard model is radically altered by the inclusion of a term, $W$, which depends upon a square of a single-particle nearest-neighbor hopping.
Abstract: We show numerically that the nature of the doping induced metal-insulator transition in the two-dimensional Hubbard model is radically altered by the inclusion of a term, $W$, which depends upon a square of a single-particle nearest-neighbor hopping. This result is reached by computing the localization length, $\xi_l$, in the insulating state. At finite values of $W$ we find results consistent with $\xi_l \sim | \mu - \mu_c|^{- 1/2} $ where $\mu_c$ is the critical chemical potential. In contrast, $\xi_l \sim | \mu - \mu_c|^{-1/4}$ for the Hubbard model. At finite values of $W$, the presented numerical results imply that doping the antiferromagnetic Mott insulator leads to a $d_{x^2 - y ^2}$ superconductor.
TL;DR: In this paper, a dynamical mean-field theory approach was used to study the metal-insulator transition of a strongly correlated two-band Hubbard model using the Mott transition, which is characterized by the development of a ''Kondo-like'' peak near Fermi level.
Abstract: We report a study of metal-insulator transition of a strongly correlated two-band Hubbard model using a dynamical mean-field theory approach. We find that the Mott transition appears at half filling even at $T=0$ in contrast to the one-band Hubbard model. The transition is characterized by the development of a ``Kondo-like'' peak near Fermi level. We also find a signature of the coexistence of metallic and antiferromagnetic phases from the study of the single-particle Green's function and the magnetic long-range order due to the superexchange coupling between the correlated electrons. We then suggest the relevance of our results to the metal-insulator transition and the recent angle-resolved photoemission measurements of ${\mathrm{NiS}}_{2\ensuremath{-}x}{\mathrm{Se}}_{x}.$ We also study the effect of carrier doping and the comparison of our findings with the experimental results suggests the possible importance of departures from stoichiometry associated with the Se substitution. The relevance of our results to high-temperature superconductivity is also discussed.
TL;DR: In this paper, the effects of long-range Coulomb interaction on the onset of superconductivity were examined using the model of complex scalar fields with the Coulomb interactions studied first by Fisher and Grinstein.
Abstract: We reexamine the effects of long-range Coulomb interaction on the onset of superconductivity. We use the model of $N$ complex scalar fields with the Coulomb interaction studied first by Fisher and Grinstein (FG). We find that near $d=3$ space dimension, the system undergoes second order phase transition if $Ng~55.39,$ but undergoes possible fluctuation driven first order transition if $Nl55.39.$ We give the detailed derivation of the field theory renormalization group (RG) of this model to one loop. Our RG results disagree with those of FG near $d=3.$ A possible scenario at $d=2$ is proposed.
TL;DR: In this paper, the scaling theory for the metal-insulator transition with the critical enhancement of orbital correlations toward the staggered ordering of two e g orbitals such as 3 x 2 - r 2 and 3 y 2 -r 2 symmetries may lead to the critical exponents of D ∝δ u and γ∝ δ v with u =3/2 and v =0.
Abstract: Small Drude weight D together with small specific heat coefficient γ observed in the ferromagnetic phase of R 1- x A x MnO 3 (R=La, Pr, Nd, Sm; A=Ca, Sr, Ba) are analyzed in terms of a proximity effect of the Mott insulator. The scaling theory for the metal-insulator transition with the critical enhancement of orbital correlations toward the staggered ordering of two e g orbitals such as 3 x 2 - r 2 and 3 y 2 - r 2 symmetries may lead to the critical exponents of D ∝δ u and γ∝δ v with u =3/2 and v =0. The result agrees with the experimental indications.
TL;DR: In this article, the formation of a Mott insulator in periodic arrays of small Josephson junctions has been studied experimentally and the influence of interaction strength, bandwidth, sample geometry, and temperature on the stability of the Mott states has been explored.
Abstract: The quantum transport of vortices in very long and narrow arrays of small Josephson junctions is studied experimentally. We investigate the forming of a Mott insulator in periodic arrays. When the vortex density is commensurate with the one-dimensional periodic potential, the vortices localize due to the strong repulsive vortex-vortex interaction. We explore the influence of interaction strength, bandwidth, sample geometry, and temperature on the stability of the Mott states. @S0163-1829~98!01018-2#
TL;DR: In this article, the ground state properties of multi-orbital Hubbard models are investigated by the auxiliary field quantum Monte Carlo method, which contains non-trivial cases where the negative sign problem does not exist.
Abstract: Ground state properties of multi-orbital Hubbard models are investigated by the auxiliary field quantum Monte Carlo method. A Monte Carlo technique generalized to the multi-orbital systems is introduced and examined in detail. The algorithm contains non-trivial cases where the negative sign problem does not exist. We investigate one-dimensional systems with doubly degenerate orbitals by this new technique. Properties of the Mott insulating state are quantitatively clarified as the strongly correlated insulator, where the charge gap amplitude is much larger than the spin gap. The insulator-metal transitions driven by the chemical potential shows a universality class with the correlation length exponent ν=1/2, which is consistent with the scaling arguments. Increasing level split between two orbitals drives crossover from the Mott insulator with high spin state to the band insulator with low spin state, where the spin gap amplitude increases and becomes closer to the charge gap. Experimental relevance of ou...