Showing papers on "Mott insulator published in 1997"
TL;DR: In this paper, a generalization of the Local Density Approximation (LDA) method for the systems with strong Coulomb correlations is presented which gives a correct description of the Mott insulators.
Abstract: The generalization of the Local Density Approximation (LDA) method for the systems with strong Coulomb correlations is presented which gives a correct description of the Mott insulators. The LDA+U method is based on the model hamiltonian approach and allows to take into account the non-sphericity of the Coulomb and exchange interactions. parameters. Orbital-dependent LDA+U potential gives correct orbital polarization and corresponding Jahn-Teller distortion. To calculate the spectra of the strongly correlated systems the impurity Anderson model should be solved with a many-electron trial wave function. All parameters of the many-electron hamiltonian are taken from LDA+U calculations. The method was applied to NiO and has shown good agreement with experimental photoemission spectra and with the oxygen Kα X-ray emission spectrum.
3,331 citations
TL;DR: In this paper, a local density approximation (LDA) within the framework of the linearized muffin-tin orbitals (LMTO) method was used for investigating the electronic structure of strongly correlated electron systems.
Abstract: A recently developed dynamical mean-field theory, in the iterated perturbation theory approximation, was used as a basis for the construction of a `first-principles' calculation scheme for investigating the electronic structure of strongly correlated electron systems. This scheme is based on the local density approximation (LDA) within the framework of the linearized muffin-tin orbitals (LMTO) method. The classical example of the doped Mott insulator was studied by the new method, and the results showed qualitative improvement when compared with experimental photoemission spectra.
571 citations
TL;DR: In this paper, the authors showed that both phases of Ca 2 RuO 4 are Mott-Hubbard-type gap and showed that the decrease of the 4 d band width in comparison with that of Sr 2RuO 4, caused by distortions in the RuO 2 planes, leads to a MottHubbard type gap.
Abstract: Noncuprate layered perovskite Sr 2 RuO 4 is a highly correlated metal and exhibits superconductivity below T c ≈1.35 K. We have newly synthesized related layered ruthenates Ca 2 RuO 4 in two distinct structural phases with substantially different aspect ratios c / a . Electrical and magnetic measurements show that the two phases are insulating antiferromagnets. We argue that both phases of Ca 2 RuO 4 are Mott insulators. The decrease of the 4 d band width in comparison with that of Sr 2 RuO 4 , caused by distortions in the RuO 2 planes, leads to a Mott-Hubbard-type gap.
178 citations
TL;DR: In this paper, the phase diagram and critical properties of both Mott transitions at fixed filling and upon doping, as well as the DC and AC conductivity application of these results to organic conductors are discussed.
Abstract: I review some of the results on the Mott transition in one-dimensional systems obtained in Refs [1–3] I discuss the phase diagram and critical properties of both Mott transitions at fixed filling and upon doping, as well as the DC and AC conductivity Application of these results to organic conductors is discussed
123 citations
TL;DR: In this paper, a slave-boson representation for the degenerate Hubbard model is introduced, and the location of the metal-to-insulator transition that occurs at commensurate densities is shown to depend weakly on the band degeneracy.
Abstract: A slave-boson representation for the degenerate Hubbard model is introduced. The location of the metal-to-insulator transition that occurs at commensurate densities is shown to depend weakly on the band degeneracy $M$. The relative weights of the Hubbard subbands depend strongly on $M$, as well as the magnetic properties. It is also shown that a sizable Hund's rule coupling is required in order to have a ferromagnetic instability appearing. The metal-to-insulator transition driven by an increase in temperature is a strong function of it.
113 citations
TL;DR: In this paper, a simple E{circle_times}e Jahn-Teller model was proposed for non-magnetic insulators with Mott-like properties, with an interesting interplay between electron-electron repulsion and the Jahn Teller effect.
Abstract: Narrow-band conductors may turn insulating and magnetic as a consequence of strong electron-electron correlation. In molecular conductors, the concomitance of a strong Jahn-Teller coupling may give rise to the alternative possibility of a nonmagnetic insulator, with or without a static cooperative Jahn-Teller distortion. In the latter case the insulator has Mott-like properties, with an interesting interplay between electron-electron repulsion and the Jahn-Teller effect, which is dynamical. We study this kind of nonmagnetic insulator in a very simple E{circle_times}e Jahn-Teller model and we discuss its general properties in a more general context, also in connection with the insulating state of K{sub 4}C{sub 60} and Rb{sub 4}C{sub 60}. {copyright} {ital 1997} {ital The American Physical Society}
92 citations
TL;DR: In this article, it is argued that exchange interactions in Fermi liquids are normally purely ferromagnetic and that antiferromagnetic exchange and antiferromeagnetic fluctuations arise from the breakdown of the FermI-liquid theory as in the Mott insulator.
Abstract: Attempts to draw parallels between the ferromagnetic spin fluctuations of nearly ferromagnetic Fermi liquids, and the new concept of antiferromagnetic spin fluctuations in ‘nearly antiferromagnetic’ Fermi liquids are examined. It is argued that exchange interactions in Fermi liquids are normally purely ferromagnetic and that antiferromagnetic exchange and antiferromagnetic fluctuations arise from the breakdown of the Fermi-liquid theory as in the Mott insulator. Spin-density waves are a distinct phenomenon caused by umklapp effects, unrelated to local antiferromagnetic exchange interactions, and lead only to minor fluctuation effects. Experimental evidence is cited in favour of this dichotomy between two different causes for antiferromagnetism.
71 citations
TL;DR: In this paper, the authors study the two-dimensional disordered boson Hubbard model via Monte Carlo simulations and show that the probability distribution of the local susceptibility has a 1/\chi^2-tail in the Bose glass phase.
Abstract: We study the Villain representation of the two-dimensional disordered boson Hubbard model via Monte Carlo simulations. It is shown that the probability distribution of the local susceptibility has a 1/\chi^2-tail in the Bose glass phase. This gives rise to a divergence although particles are completely localized here as we prove with the help of the participation ratio. We demonstrate the presence of an incompressible Mott lobe within the Bose glass phase and show that a direct Mott-insulator to superfluid transition happens at the tip of the lobe. Here we find critical exponents z=1,
u~0.7$ and \eta~0.1, which are reminiscent of the pure three-dimensional classical XY model.
65 citations
TL;DR: The 1:1 composition organic conductor with a highly one-dimensional half-filled energy band exhibits metallic conductivity down to 1.5 K, but the spin susceptibility follows the onedimensional Heisenberg model from room temperature to 2 K, without any anomaly at 2 K as discussed by the authors.
Abstract: The title 1:1 composition organic conductor, with a highly one-dimensional half-filled energy band, exhibits metallic conductivity down to ${T}_{\mathrm{MI}}\ensuremath{\approx}160\mathrm{K}$, but the spin susceptibility follows the one-dimensional Heisenberg model from room temperature to 2 K, without any anomaly at ${T}_{\mathrm{MI}}$. The insulating state is regarded as a Mott insulator. The small $U$, related to the extended molecular structure, gives rise to the small charge gap and the high-temperature metallic conduction.
51 citations
TL;DR: In this paper, critical behaviors of generalized Mott transitions in perovskites have been discussed and a close interplay between the spin, charge and orbital degrees of freedom has been observed.
Abstract: Versatile metal-insulator phenomena arising from strong electron correlations show up in pseudo-cubic and layered perovskites of 3d transition metal oxide. Most of them are derived from the correlated insulators by controlling of the one-electron bandwidth, band filling and dimensionality. Overviews are presented on some critical behaviors of the generalized Mott transitions in the perovskites which show, in general, a close interplay between the spin, charge and orbital degrees of freedom.
27 citations
TL;DR: In this article, the authors investigated the Mott transition in infinite dimensions in the orbitally degenerate Hubbard model and found that the qualitative features of Mott transitions in the one-band model are also present in the orbital degenerate case.
Abstract: We investigate the Mott transition in infinite dimensions in the orbitally degenerate Hubbard model. We find that the qualitative features of the Mott transition found in the one-band model are also present in the orbitally degenerate case. Surprisingly, the quantitative aspects of the density driven Mott transition around density one are not very sensitive to orbital degeneracy, justifying the quantitative success of the one-band model which was previously applied to orbitally degenerate systems. We contrast this with quantities that have a sizeable dependence on the orbital degeneracy and comment on the role of the intra-atomic exchange J.
TL;DR: In this paper, a theory for the T = 0 Mott - Hubbard insulating phases of the Hubbard model at -filling, including both the antiferromagnetic (AF) and paramagnetic (P) insulators, is developed.
Abstract: A theory is developed for the T = 0 Mott - Hubbard insulating phases of the Hubbard model at -filling, including both the antiferromagnetic (AF) and paramagnetic (P) insulators. Local moments are introduced explicitly from the outset, enabling ready identification of the dominant low-energy scales for insulating spin-flip excitations. Dynamical coupling of single-particle processes to the spin-flip excitations leads to a renormalized self-consistent description of the single-particle propagators that is shown to be asymptotically exact in strong coupling, for both the AF and P phases. For the AF case, the resultant theory is applicable over the entire U-range, and is discussed in some detail. For the P phase, we consider in particular the destruction of the Mott insulator, the resultant critical behaviour of which is found to stem inherently from proper inclusion of the spin-flip excitations.
TL;DR: In this article, the perovskite system with a metal - insulator crossover was studied through measurements of x-ray diffraction, electrical resistivity, thermoelectric power, Hall coefficient and magnetization.
Abstract: Electronic states of the perovskite systems and with a metal - insulator crossover have been studied through measurements of x-ray diffraction, electrical resistivity, thermoelectric power, Hall coefficient and magnetization. The system that is pseudotetragonal for and cubic for is characterized as follows: (i) , variable-range hopping-like insulators; (ii) , highly correlated metals accompanied by a significant Jahn - Teller effect, a band dispersion anomaly and cant magnetism for ; (iii) , metals with a mean free path comparable with the Ti - Ti distance; (iv) x = 1, band insulators. The properties of against y are rather similar to those of against x, but larger random potentials due to the atomic deficiency in the former system give rise to strong electron localization. For the metallic state near the crossover between the Mott - Hubbard insulator and metal, both an enhancement of the conduction electron mass and the antiferromagnetic correlation effect should be considered.
TL;DR: In this paper, a theory for the T = 0 Mott-Hubbard insulating phases of the infinite-dimensional Hubbard model at half-filling, including both the antiferromagnetic (AF) and paramagnetic (P) insulators, is developed.
Abstract: A theory is developed for the T=0 Mott-Hubbard insulating phases of the infinite-dimensional Hubbard model at half-filling, including both the antiferromagnetic (AF) and paramagnetic (P) insulators. Local moments are introduced explicitly from the outset, enabling ready identification of the dominant low energy scales for insulating spin- flip excitations. Dynamical coupling of single-particle processes to the spin-flip excitations leads to a renormalized self-consistent description of the single-particle propagators that is shown to be asymptotically exact in strong coupling, for both the AF and P phases. For the AF case, the resultant theory is applicable over the entire U-range, and is discussed in some detail. For the P phase, we consider in particular the destruction of the Mott insulator, the resultant critical behaviour of which is found to stem inherently from proper inclusion of the spin-flip excitations.
TL;DR: In this article, the electronic state of a new group of DCNQI-metal complexes, (DI-DCNQIs 2 M (M=Li, Cu, Ag), has been studied by the electric resistance, R, magnetic susceptibility, χ, 1 H- and 13 C-NMR measurements.
TL;DR: The metal-insulator transition in one-dimensional fermionic systems with long-range interaction is investigated in this article, where the gap opening transition from the Tomonaga-Luttinger liquid to the Mott insulator is associated with a discrete symmetry breaking by changing the interaction strength.
Abstract: The metal-insulator transition in one-dimensional fermionic systems with long-range interaction is investigated. We have focused on an excitation spectrum by the exact diagonalization technique in sectors with different momentum quantum numbers. At rational fillings, we have demonstrated gap opening transitions from the Tomonaga-Luttinger liquid to the Mott insulator associated with a discrete symmetry breaking by changing the interaction strength. Finite interaction range is crucial to have the Mott transition at a rational filling away from the half filling. It is consistent with the strong coupling picture where the Mott gap exists at any rational fillings with sufficiently strong interaction. The critical regions as a quantum phase transition are also investigated numerically. Nonanalytic behavior of the Mott gap is the characteristic in the weak coupling. It is of the order of the interaction in the strong coupling. It implies that the metal-insulator transition of the model is of the infinite order as a quantum phase transition at zero temperature. The fractal nature of the ground-state phase diagram is also revealed.
TL;DR: In this paper, the authors investigated the Bose glass phase and the insulator-to-superfluid transition in the two-dimensional disordered Boson Hubbard model in the Villain representation via Monte Carlo simulations.
Abstract: We investigate the Bose glass phase and the insulator-to-superfluid transition in the two-dimensional disordered Boson Hubbard model in the Villain representation via Monte Carlo simulations. In the Bose glass phase the probability distribution of the local susceptibility is found to have a 1 χ 2 tail and the imaginary time Green's function decays algebraically C(τ) ≈ τ−1 giving rise to a divergent global susceptibility. By considering the participation ratio it is shown that the excitations in the Bose glass phase are fully localized and a scaling law is established. For commensurate Boson densities we find direct Mott insulator to superfluid transition without an intervening Bose glass phase for weak disorder. For this transition we obtain the critical exponents z = 1, v = 0.7 ± 0.1 and η = 0.1 ± 0.1, which agree with those for the classical three-dimensional XY model without disorder. This indicates that disorder is irrelevant at the tip of the Mott-lobes and that here the inequality v⩾2 d is violated.
TL;DR: In this paper, the theoretical understanding of high Tc cuprates is given based on the slave-boson mean-field theory of the extended t-J model, and a special emphasis is placed on the spin-gap phenomena.
Abstract: Key experimental facts of high Tc cuprates have been summarized and theoretical understanding of these systems viewed as doped Mott insulators is given based on the slave-boson mean-field theory of the extended t-J model. A special emphasis is placed on the spin-gap phenomena. Effects of fluctuations around this mean field theory treated as a gauge field are also briefly discussed.
TL;DR: In this article, the results of the molecular field theory by Pincus with easy-plane type anisotropy including the Dzyaloshinsky-Moriya interaction were analyzed by this model.
TL;DR: In this paper, two distinct layered ruthenates of Ca2RuO4 were synthesized, which are related to the layered perovskite superconductor (Tc ≈ 1K) without copper.
Abstract: We have newly synthesized two distinct layered ruthenates of Ca2RuO4. They are both related to Sr2RuO4, the layered perovskite superconductor (Tc ≈ 1K) without copper. In contrast with the highly correlated metal Sr2RuO4, both phases of Ca2RuO4 are Mott insulators.
TL;DR: In this article, the authors investigate the transport of interacting electrons through single-mode quantum wires whose parameters are periodically modulated on the scale of the electronic Fermi wave length, and analyze the precursors of the Mott transition.
Abstract: We investigate the transport of interacting electrons through single-mode quantum wires whose parameters are periodically modulated on the scale of the electronic Fermi wave length. The Umklapp and backscattering of electrons can be described in terms of non-uniform quantum sine-Gordon-like models which also incorporate the effects of electronic reservoirs (electrodes) adiabatically coupled to the wire. We concentrate on weak Umklapp scattering and analyze the precursors of the Mott transition. At half-filling the temperature dependence of the extra resistance $\Delta R = R - \pi \hbar/e^2$ of a modulated quantum wire of length $L$ changes from the interaction-dependent "bulk" power-law $\Delta R \propto T^{4K_\rho-3}$ at high temperatures, $T \gg v_\rho/L$, to the universal $\Delta R \propto T^2$ behavior at low temperatures, $T \ll v_\rho/L$. Away from half-filling the "bulk" results are qualitatively incorrect even at high temperatures $v_\rho/L \ll T \ll T^{*}$ despite the electron coherence in the wire is absent in this regime.
TL;DR: In this paper, a multiband one-dimensional Jahn-teller model with strong electron correlations using the Lieb-Wu Bethe ansatz equations was solved and two JT distorted phases were found.
Abstract: We solve exactly a multiband one-dimensional Jahn-Teller (JT) model with strong electron correlations using the Lieb-Wu Bethe ansatz equations. As well as the metallic undistorted phase, we find two JT distorted phases. The first is a conducting phase, in which most carriers sit on one chain with the remaining carriers distributed equally among the other chains. We suggest that this phase is what is observed at low temperatures in Yb{sub 4}As{sub 3}. In the second phase all the carriers sit on one chain. This phase becomes a Mott insulator when the chain is half filled. We also show that a mean-field treatment of the model is misleading and that an exact treatment of interactions is essential. {copyright} {ital 1997} {ital The American Physical Society}
TL;DR: In this article, a modification of the quantized conductance of a one-dimensional doped Mott insulator, where the Umklapp scattering plays an important role, is studied based on the method by Maslov, Stone and Ponomarenko.
Abstract: Possible modification of the quantized conductance of a one-dimensional doped Mott insulator, where the Umklapp scattering plays an important role, is studied based on the method by Maslov, Stone and Ponomarenko. At T =0 and away from half-filling, the conductance is quantized as g =2 e 2 / h and there is no renormalization by the Umklapp scattering process. At finite temperatures, however, the quantization is influenced by the gate voltage and temperature.
TL;DR: In this article, the angular dependence of the order parameter and tunneling amplitude in a model exhibiting topological superconductivity and sketch its derivation as a model of a doped Mott insulator was derived.
Abstract: We compute the angular dependence of the order parameter and tunneling amplitude in a model exhibiting topological superconductivity and sketch its derivation as a model of a doped Mott insulator. We show that ground states differing by an odd number of particles are orthogonal and the order parameter is in the {ital d} representation, although the gap in the electronic spectrum has no nodes. We also develop an operator algebra that allows one to compute off-diagonal correlation functions. {copyright} {ital 1997} {ital The American Physical Society}
01 Jan 1997
TL;DR: In this article, the authors defined an insulator as a substance with a vanishing electrical conductivity in a (weak) static electrical field at zero temperature, where the transport of electrical charge in the solid state is provided by electrons that are subjected to the Coulomb interaction with the ions and the other electrons.
Abstract: In the first section we specify an insulator as a substance with a vanishing electrical conductivity in a (weak) static electrical field at zero temperature. The transport of electrical charge in the solid state is provided by electrons that are subjected to the Coulomb interaction with the ions and the other electrons. Correspondingly, in the first category of insulators we find band, Peierls, and Anderson insulators, which can be understood in terms of single electrons that interact with the electrostatic field of the ions. Mott insulators constitute the second category, where the insulating behavior is understood as a cooperative many-electron phenomenon. In the absence of electron pairing an insulator may be characterized by a gap for charge excitations into states in which the wave functions of the excitations spatially extend over the whole specimen (gap criterion). This zero-temperature gap sets an energy scale that allows us to distinguish in practical terms between good conductors (“metals”) and bad conductors (“insulators”) at finite temperature.
TL;DR: For κ-ET 2 X salts as strongly correlated electron systems, the electronic structure and the insulator-metal transition of the Mott-Hubbard kind were derived in this paper.
Abstract: For κ-ET 2 X salts as strongly correlated electron systems the electronic structure and the insulator-metal transition of the Mott-Hubbard kind are derived.
TL;DR: In this article, the effect of carrier doping on electronic correlations in La 1−x Sr x TiO 3 has been investigated by 47/49 Ti and 139 La NMR, and no evidences for a prominent increase of antiferromagnetic spin fluctuations at q≈Q near the Mott transition boundary, which is sharply contrast to the case of high- T c cuprates.
Abstract: Carrier doping effects on electronic correlations in La 1−x Sr x TiO 3 have been investigated by 47/49 Ti and 139 La NMR. The increases of nuclear spin-lattice relaxation rates, (T 1 T) −1 , of both La and Ti provide the critical enhancements of effective carrier mass on approaching the Mott transition phase boundary from the metallic side. We have no evidences for a prominent increase of antiferromagnetic spin fluctuations at q≈Q near the Mott-transition boundary, which is sharply contrast to the case of high- T c cuprates.
TL;DR: In this paper, the phonon-assisted absorption in the quantum spin chain model of one-dimensional Mott insulators including CuO chains is studied theoretically. And the mid-infrared absorption spectrum has an asymmetric cusp-like singularity.
Abstract: Optical spectra of one-dimensional Mott insulators including CuO chains are studied theoretically. The midinfrared absorption spectrum has an asymmetric cusp-like singularity. We analyze this spectrum in terms of the phonon-assisted absorption in the quantum spin chain model. A good agreement between theory and experiments is obtained, and the singularity is identified with the van Hove singularity of the des Cloizeaux-Pearson modes.