4,178 research outputs found
Coexistence of solutions in dynamical mean-field theory of the Mott transition
In this paper, I discuss the finite-temperature metal-insulator transition of
the paramagnetic Hubbard model within dynamical mean-field theory. I show that
coexisting solutions, the hallmark of such a transition, can be obtained in a
consistent way both from Quantum Monte Carlo (QMC) simulations and from the
Exact Diagonalization method. I pay special attention to discretization errors
within QMC. These errors explain why it is difficult to obtain the solutions by
QMC close to the boundaries of the coexistence region.Comment: 3 pages, 2 figures, RevTe
Orbital selective Mott transition in multi-band systems: slave-spin representation and dynamical mean-field theory
We examine whether the Mott transition of a half-filled, two-orbital Hubbard
model with unequal bandwidths occurs simultaneously for both bands or whether
it is a two-stage process in which the orbital with narrower bandwith localizes
first (giving rise to an intermediate `orbital-selective' Mott phase). This
question is addressed using both dynamical mean-field theory, and a
representation of fermion operators in terms of slave quantum spins, followed
by a mean-field approximation (similar in spirit to a Gutzwiller
approximation). In the latter approach, the Mott transition is found to be
orbital-selective for all values of the Coulomb exchange (Hund) coupling J when
the bandwidth ratio is small, and only beyond a critical value of J when the
bandwidth ratio is larger. Dynamical mean-field theory partially confirms these
findings, but the intermediate phase at J=0 is found to differ from a
conventional Mott insulator, with spectral weight extending down to arbitrary
low energy. Finally, the orbital-selective Mott phase is found, at
zero-temperature, to be unstable with respect to an inter-orbital
hybridization, and replaced by a state with a large effective mass (and a low
quasiparticle coherence scale) for the narrower band.Comment: Discussion on the effect of hybridization on the OSMT has been
extende
The Finite Temperature Mott Transition in the Hubbard Model in Infinite Dimensions
We study the second order finite temperature Mott transition point in the
fully frustrated Hubbard model at half filling, within Dynamical Mean Field
Theory. Using quantum Monte Carlo simulations we show the existence of a finite
temperature second order critical point by explicitly demonstrating the
existence of a divergent susceptibility as well as by finding coexistence in
the low temperature phase. We determine the location of the finite temperature
Mott critical point in the (U,T) plane. Our study verifies and quantifies a
scenario for the Mott transition proposed in earlier studies (Reviews of Modern
Physics 68, 13, 1996) of this problem.Comment: 4 RevTex pages, uses epsf, 2 figure
Non Fermi Liquid Behaviour near a spin-glass transition
In this paper we study the competition between the Kondo effect and RKKY
interactions near the zero-temperature quantum critical point of an Ising-like
metallic spin-glass. We consider the mean-field behaviour of various physical
quantities. In the `quantum- critical regime' non-analytic corrections to the
Fermi liquid behaviour are found for the specific heat and uniform static
susceptibility, while the resistivity and NMR relaxation rate have a non-Fermi
liquid dependence on temperature.Comment: 15 pages, RevTex 3.0, 1 uuencoded ps. figure at the en
Self-consistency over the charge-density in dynamical mean-field theory: a linear muffin-tin implementation and some physical implications
We present a simple implementation of the dynamical mean-field theory
approach to the electronic structure of strongly correlated materials. This
implementation achieves full self-consistency over the charge density, taking
into account correlation-induced changes to the total charge density and
effective Kohn-Sham Hamiltonian. A linear muffin-tin orbital basis-set is used,
and the charge density is computed from moments of the many body
momentum-distribution matrix. The calculation of the total energy is also
considered, with a proper treatment of high-frequency tails of the Green's
function and self-energy. The method is illustrated on two materials with
well-localized 4f electrons, insulating cerium sesquioxide Ce2O3 and the
gamma-phase of metallic cerium, using the Hubbard-I approximation to the
dynamical mean-field self-energy. The momentum-integrated spectral function and
momentum-resolved dispersion of the Hubbard bands are calculated, as well as
the volume-dependence of the total energy. We show that full self-consistency
over the charge density, taking into account its modification by strong
correlations, can be important for the computation of both thermodynamical and
spectral properties, particularly in the case of the oxide material.Comment: 20 pages, 6 figures (submitted in The Physical Review B
Frequency-dependent local interactions and low-energy effective models from electronic structure calculations
We propose a systematic procedure for constructing effective models of
strongly correlated materials. The parameters, in particular the on-site
screened Coulomb interaction U, are calculated from first principles, using the
GW approximation. We derive an expression for the frequency-dependent U and
show that its high frequency part has significant influence on the spectral
functions. We propose a scheme for taking into account the energy dependence of
U, so that a model with an energy-independent local interaction can still be
used for low-energy properties.Comment: 16 pages, 5 figure
Transport Properties of the Infinite Dimensional Hubbard Model
Results for the optical conductivity and resistivity of the Hubbard model in
infinite spatial dimensions are presented. At half filling we observe a gradual
crossover from a normal Fermi-liquid with a Drude peak at in the
optical conductivity to an insulator as a function of for temperatures
above the antiferromagnetic phase transition. When doped, the ``insulator''
becomes a Fermi-liquid with a corresponding temperature dependence of the
optical conductivity and resistivity. We find a -coefficient in the low
temperature resistivity which suggests that the carriers in the system acquire
a considerable mass-enhancement due to the strong local correlations. At high
temperatures, a crossover into a semi-metallic regime takes place.Comment: 14 page
The infinite-range quantum random Heisenberg magnet
We study with exact diagonalization techniques the Heisenberg model for a
system of SU(2) spins with S=1/2 and random infinite-range exchange
interactions. We calculate the critical temperature T_g for the spin-glass to
paramagnetic transition. We obtain T_g ~ 0.13, in good agreement with previous
quantum Monte Carlo and analytical estimates. We provide a detailed picture for
the different kind of excitations which intervene in the dynamical response
chi''(w,T) at T=0 and analyze their evolution as T increases. We also calculate
the specific heat Cv(T). We find that it displays a smooth maximum at TM ~
0.25, in good qualitative agreement with experiments. We argue that the fact
that TM>Tg is due to a quantum disorder effect.Comment: 17 pages, 14 figure
k-dependent spectrum and optical conductivity near metal-insulator transition in multi-orbital Hubbard bands
We apply the dynamical mean field theory (DMFT) in the iterative perturbation
theory(IPT) to doubly degenerate eg bands and triply degenerate tg bands on a
simple cubic lattice and calculate the spectrum and optical conductivity in
arbitrary electron occupation. The spectrum simultaneously shows the effects of
multiplet structure and DMFT together with the electron ionization and affinity
levels of different electron occupations, coherent peaks at the Fermi energy in
the metallic phase and a gap at an integer filling of electrons for
sufficiently large Coulomb U. We also calculate the critical value of the
Coulomb U for degenerate orbitals.Comment: 8 pages, 6 figure
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