2,393 research outputs found
Local-Ansatz Approach with Momentum Dependent Variational Parameters to Correlated Electron Systems
A new wavefunction which improves the Gutzwiller-type local ansatz method has
been proposed to describe the correlated electron system. The ground-state
energy, double occupation number, momentum distribution function, and
quasiparticle weight have been calculated for the half-filled band Hubbard
model in infinite dimensions. It is shown that the new wavefunction improves
the local-ansatz approach (LA) proposed by Stollhoff and Fulde. Especially,
calculated momentum distribution functions show a reasonable momentum
dependence. The result qualitatively differs from those obtained by the LA and
the Gutzwiller wavefunction. Furthermore, the present approach combined with
the projection operator method CPA is shown to describe quantitatively the
excitation spectra in the insulator regime as well as the critical Coulomb
interactions for a gap formation in infinite dimensions.Comment: To be published in Phys. Soc. Jpn. 77 No.11 (2008
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
Density of states near the Mott-Hubbard transition in the limit of large dimensions
The zero temperature Mott-Hubbard transition as a function of the Coulomb
repulsion U is investigated in the limit of large dimensions. The behavior of
the density of states near the transition at U=U_c is analyzed in all orders of
the skeleton expansion. It is shown that only two transition scenarios are
consistent with the skeleton expansion for U<U_c: (i) The Mott-Hubbard
transition is "discontinuous" in the sense that in the density of states finite
spectral weight is redistributed at U_c. (ii) The transition occurs via a point
at U=U_c where the system is neither a Fermi liquid nor an insulator.Comment: 4 pages, 1 figure; revised version accepted for publication in Phys.
Rev. Let
Mott transition at large orbital degeneracy: dynamical mean-field theory
We study analytically the Mott transition of the N-orbital Hubbard model
using dynamical mean-field theory and a low-energy projection onto an effective
Kondo model. It is demonstrated that the critical interaction at which the
insulator appears (Uc1) and the one at which the metal becomes unstable (Uc2)
have different dependence on the number of orbitals as the latter becomes
large: Uc1 ~ \sqrt{N} while Uc2 ~ N. An exact analytical determination of the
critical coupling Uc2/N is obtained in the large-N limit. The metallic solution
close to this critical coupling has many similarities at low-energy with the
results of slave boson approximations, to which a comparison is made. We also
discuss how the critical temperature associated with the Mott critical endpoint
depends on the number of orbitals.Comment: 13 pages. Minor changes in V
Landau Theory of the Finite Temperature Mott Transition
In the context of the dynamical mean-field theory of the Hubbard model, we
identify microscopically an order parameter for the finite temperature Mott
endpoint. We derive a Landau functional of the order parameter. We then use the
order parameter theory to elucidate the singular behavior of various physical
quantities which are experimentally accessible.Comment: 4 pages, 2 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
Suppressed antinodal coherence with a single d-wave superconducting gap leads to two energy scales in underdoped cuprates
Conventional superconductors are characterized by a single energy scale, the
superconducting gap, which is proportional to the critical temperature Tc . In
hole-doped high-Tc copper oxide superconductors, previous experiments have
established the existence of two distinct energy scales for doping levels below
the optimal one. The origin and significance of these two scales are largely
unexplained, although they have often been viewed as evidence for two gaps,
possibly of distinct physical origins. By measuring the temperature dependence
of the electronic Raman response of Bi2Sr2CaCu2O8+d (Bi-2212) and HgBa2CuO4+d
(Hg-1201) crystals with different doping levels, we establish that these two
scales are associated with coherent excitations of the superconducting state
which disappears at Tc. Using a simple model, we show that these two scales do
not require the existence of two gaps. Rather, a single d-wave superconducting
gap with a loss of Bogoliubov quasiparticle spectral weight in the antinodal
region is shown to reconcile spectroscopic and transport measurements.Comment: 3 figure
Semiclassical Analysis of Extended Dynamical Mean Field Equations
The extended Dynamical Mean Field Equations (EDMFT) are analyzed using
semiclassical methods for a model describing an interacting fermi-bose system.
We compare the semiclassical approach with the exact QMC (Quantum Montecarlo)
method. We found the transition to an ordered state to be of the first order
for any dimension below four.Comment: RevTex, 39 pages, 16 figures; Appendix C added, typos correcte
Thermoelectric Response Near the Density Driven Mott Transition
We investigate the thermoelectric response of correlated electron systems
near the density driven Mott transition using the dynamical mean field theory.Comment: 4 pages, 2 embedded figure
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