共查询到20条相似文献,搜索用时 10 毫秒
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M.-B. Lepetit M. Cousy G.M. Pastor 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,13(3):421-427
The half-filled Hubbard model on the Bethe lattice with coordination number z=3 is studied using the density-matrix renormalization group (DMRG) method. Ground-state properties such as the energy per
site E, average local magnetization , its fluctuations and various spin correlation functions are determined as a function of the Coulomb interaction strength U/t. The local magnetic moments increase monotonically with increasing Coulomb repulsion U/t showing antiferromagnetic order between nearest neighbors []. At large U/t, is strongly reduced with respect to the saturation value 1/2 due to exchange fluctuations between nearest neighbors (NN)
spins [ for ]. shows a maximum for U/t=2.4-2.9 that results from the interplay between the usual increase of with increasing U/t and the formation of important permanent moments at large U/t. While NN sites show antiferromagnetic spin correlations that increase with increasing Coulomb repulsion, the next NN sites
are very weakly correlated over the whole range of U/t. The DMRG results are discussed and compared with tight-binding calculations for U=0, independent DMRG studies for the Heisenberg model and simple first-order perturbation estimates.
Received 8 February 1999 and Received in final form 14 June 1999 相似文献
4.
B. M. Letfulov 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,11(3):423-428
Phase separation in the strongly correlated Falicov-Kimball model in infinite dimensions is examined. We show that the phase
separation can occur for any values of the interaction constant J* when the site energy of the localized electrons is equal to zero. Electron-poor regions always have homogeneous state and electron-rich regions
have chessboard state for , chessboard state or homogeneous state in dependence upon temperature for 0<J
*
<0.03 and homogeneous state for J
*
=0. For J
*
=0 and T=0, phase separation (segregation) occurs at .The obtained results are exact for the Bethe lattice with infinite number of the nearest neighbours.
Received 1 December 1998 and Received in final form 12 April 1999 相似文献
5.
M.P.H. Stumpf D.E. Logan 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,8(3):377-387
The dynamics of a single hole in the t
-
J model is solved exactly for all temperature, T, in the limit of large spatial dimensions, , using the Feenberg renormalized perturbation series. We focus in particular on single-particle spectra, together with optical
and static hole conductivities. Explicit results are illustrated for a Bethe lattice, and exemplify the continuous thermal
evolution of the underlying string picture from the T
=0 string-pinned limit through to the paramagnetic phase. Quenched site-disorder is also readily incorporated, exact results
thereby being obtained for the interplay between disorder and thermally-induced hole dynamics.
Received 16 September 1998 相似文献
6.
B.M. Letfulov 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,14(1):19-28
Simplified double-exchange model including transfer of the itinerant electrons with spin parallel to the localized spin in
the same site and the indirect interaction J of kinetic type between localized spins is comprihensively investigated. The model is exactly solved in infinite dimensions.
The exact equations describing the main ordered phases (ferromagnetic and antiferromagnetic) are obtained for the Bethe lattice
with (z is the coordination number) in analytical form. The exact expression for the generalized paramagnetic susceptibility of the
localized-spin subsystem is also obtained in analytical form. It is shown that temperature dependence of the uniform and the
staggered susceptibilities has deviation from Curie-Weiss law. Dependence of Curie and Néel temperatures on itinerant-electron
concentration is discussed to study instability conditions of the paramagnetic phase. Anomalous temperature behaviour of the
chemical potential, the thermopower and the specific heat is investigated near the Curie point. It is found for J=0 that the system is unstable towards temperature phase separation between ferromagnetic and paramagnetic states. A phase
separation connected with antiferromagnetic and the paramagnetic phases can occur only at . Zero-temperature phase diagram including the phase separation between ferromagnetic and antiferromagnetic states is given.
Received 28 May 1999 and Received in final form 14 July 1999 相似文献
7.
W. Hanke O. Schmitt H. Endres R. Kleiner P. Müller 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,5(3):465-471
A quantitative analysis of a microscopic model for the intrinsic Josephson effect in high-temperature superconductors based
on interlayer tunneling is presented both within a mean-field BCS evaluation and a numerically essentially exact Quantum Monte-Carlo
study. The pairing correlations in the CuO2-planes are modelled by a 2D Hubbard model with attractive interaction, a model which accounts well for some of the observed
features such as the short planar coherence length. The stack of Hubbard planes is arranged on a torus, which is threaded
by a magnetic flux. The current perpendicular to the planes is calculated as a function of applied flux (i.e. the phase), and - after careful elimination of finite-size effects due to single-particle tunneling - found to display a
sinusoidal field dependence in accordance with interlayer Josephson tunneling. Studies of the temperature dependence of the
supercurrent reveal at best a mild elevation of the Josephson transition temperature compared to the planar Kosterlitz-Thouless
temperature. These and other results on the dependence of the model parameters are compared with a standard BCS evaluation.
Received: 24 February 1998 / Revised: 28 April 1998 / Accepted: 23 June 1998 相似文献
8.
F.F. Assaad M. Imada 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,10(4):595-598
The dispersion relation of a doped hole in the half-filled 2D Hubbard model is shown to follow a law around the and points in the Brillouin zone. Upon addition of pair-hopping processes this dispersion relation is unstable towards a law. The above follows from T=0 Quantum Monte-Carlo calculations of the single particle spectral function on lattices. We discuss finite dopings and argue that the added term restores coherence to charge dynamics and drives the system
towards a d
x2 - y2
superconductor.
Received 22 March 1999 相似文献
9.
V. Hankevych F. Wegner 《The European Physical Journal B - Condensed Matter and Complex Systems》2003,31(3):333-342
We present a stability analysis of the 2D t
-
t' Hubbard model on a square lattice for various values of the next-nearest-neighbor hopping t' and electron concentration. Using the free energy expression, derived by means of the flow equations method, we have performed
numerical calculation for the various representations under the point group C
4ν
in order to determine at which temperature symmetry broken phases become more favorable than the symmetric phase. A surprisingly
large number of phases has been observed. Some of them have an order parameter with many nodes in -space. Commonly discussed types of order found by us are antiferromagnetism, d
x2 - y2
-wave singlet superconductivity, d-wave Pomeranchuk instability and flux phase. A few instabilities newly observed are a triplet analog of the flux phase, a
particle-hole instability of p-type symmetry in the triplet channel which gives rise to a phase of magnetic currents, an s*-magnetic phase, a g-wave Pomeranchuk instability and the band splitting phase with p-wave character. Other weaker instabilities are found also. A comparison with experiments is made.
Received 25 July 2002 / Received in final form 28 November 2002 Published online 14 February 2003
RID="a"
ID="a"Current address: Département de physique and Centre de recherche sur les propriétés électroniques de matériaux avancés, Université de Sherbrooke,
Sherbrooke, Québec, Canada J1K 2R1 e-mail: vaha@physique.usherb.ca 相似文献
10.
C. Honerkamp M. Salmhofer T.M. Rice 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,27(1):127-134
We extend the analysis of the renormalization group flow in the two-dimensional Hubbard model close to half-filling using
the recently developed temperature flow formalism. We investigate the interplay of d-density wave and Fermi surface deformation tendencies with those towards d-wave pairing and antiferromagnetism. For a ratio of next nearest to nearest neighbor hoppings, t'/t = - 0.25, and band fillings where the Fermi surface is inside the Umklapp surface, only the d-pairing susceptibility diverges at low temperatures. When the Fermi surface intersects the Umklapp surface close to the saddle
points, d-wave pairing, d-density wave, antiferromagnetic and, to a weaker extent, d-wave Fermi surface deformation susceptibilities grow together when the interactions flow to strong coupling. We interpret
these findings as indications for a non-trivial strongly coupled phase with short-ranged superconducting and antiferromagnetic
correlations, in close analogy with the spin liquid ground state in the well-understood two-leg Hubbard ladder.
Received 23 January 2002 相似文献
11.
C. Honerkamp 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,21(1):81-91
We compare the one-loop renormalization group flow to strong coupling of the electronic interactions in the two-dimensional
t-t'-Hubbard model with t' = - 0.3t for band fillings smaller and larger than half-filling. Using a numerical N-patch scheme ( N = 32, ..., 96) we show that in the electron-doped case with decreasing electron density there is a rapid transition from
a d
x2 - y2-wave superconducting regime with small characteristic energy scale to an approximate nesting regime with strong antiferromagnetic
tendencies and higher energy scales. This contrasts with the hole-doped side discussed recently which exhibits a broad parameter
region where the renormalization group flow suggests a truncation of the Fermi surface at the saddle points. We compare the
quasiparticle scattering rates obtained from the renormalization group calculation which further emphasize the differences
between the two cases.
Received 19 December 2000 and Received in final form 28 February 2001 相似文献
12.
R. Lacaze A. Morel B. Petersson J. Schröper 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,2(4):509-523
We present an investigation of the 2D attractive Hubbard model, considered as an effective model relevant to superconductivity
in strongly interacting electron systems. We use both hybrid Monte-Carlo simulations and existing hopping parameter expansions
to explore the low temperature domain. The increase of the static S-wave pair correlation with decreasing temperature, which depends weakly on the band filling in the explored temperature range,
is analyzed in terms of an expected Kosterlitz-Thouless superconducting transition. Using both our data and previously published
results, we show that the evidence for this transition is weak: If it exists, its temperature is very low. The number of unpaired
electrons remains nearly constant with temperature at fixed attractive potential strength. In contrast, the static magnetic
susceptibility decreases fast with temperature, and cannot be related only to pair formation. We introduce a method by which
the Padé approximants of the existing series for the susceptibility give sensible results down to rather low temperature region,
as shown by comparison with our numerical data.
Received: 30 October 1996 / Revised: 23 October 1997 / Accepted: 29 January 1998 相似文献
13.
J.E. Espinosa O. Navarro M. Avignon 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,18(1):9-16
A real-space method has been introduced to study the pairing problem within the generalized Hubbard Hamiltonian. This method
includes the bond-charge interaction term as an extension of the previously proposed mapping method [1] for the Hubbard model.
The generalization of the method is based on mapping the correlated many-body problem onto an equivalent site- and bond-impurity
tight-binding one in a higher dimensional space, where the problem can be solved exactly. In a one-dimensional lattice, we
analyzed the three particle correlation by calculating the binding energy at the ground state, using different values of the
bond-charge, the on-site (U) and the nearest-neighbor (V) interactions. A pairing asymmetry is found between electrons and holes for the generalized hopping amplitude, where the
hole pairing is not always easier than the electron case. For some special values of the hopping parameters and for all kinds
of interactions in the Hubbard Hamiltonian, an analytical solution is obtained.
Received 21 January 2000 and Received in final form 18 July 2000 相似文献
14.
S. Pairault D. Sénéchal A.-M.S. Tremblay 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,16(1):85-105
The strong-coupling perturbation theory of the Hubbard model is presented and carried out to order (t/U)5 for the one-particle Green function in arbitrary dimension. The spectral weight is expressed as a Jacobi continued fraction and compared with new Monte-Carlo data of the one-dimensional, half-filled Hubbard
model. Different regimes (insulator, conductor and short-range antiferromagnet) are identified in the temperature-hopping
integral (T,t) plane. This work completes a first paper on the subject (Phys. Rev. Lett. 80, 5389 (1998)) by providing details on diagrammatic rules and higher-order results. In addition, the non half-filled case,
infinite resummations of diagrams and the double occupancy are discussed. Various tests of the method are also presented.
Received 25 October 1999 相似文献
15.
F. Mancini F. P. Mancini A. Naddeo 《The European Physical Journal B - Condensed Matter and Complex Systems》2009,68(3):309-315
We consider the extended Hubbard model in the atomic limit on a Bethe lattice with coordination number z. By using the equations
of motion formalism, the model is exactly solved for both attractive and repulsive intersite potential V. By focusing on the
case of negative V, i.e., attractive intersite interaction, we study the phase diagram at finite temperature and find, for
various values of the filling and of the on-site coupling U, a phase transition towards a state with phase separation. We
determine the critical temperature as a function of the relevant parameters, U/|V|, n and z and we find a reentrant behavior
in the plane (U/|V|, T). Finally, several thermodynamic properties are investigated near criticality. 相似文献
16.
M. Brunner F.F. Assaad A. Muramatsu 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,16(2):209-212
We present a new finite-temperature quantum Monte Carlo algorithm to compute imaginary-time Green functions for a single hole
in the t-J model on non-frustrated lattices. Spectral functions are obtained with the Maximum Entropy method. Simulations of the one-dimensional
case show that a simple charge-spin separation Ansatz is able to describe the overall features of the spectral function such as the bandwidth and the compact support of the spectral function, over the whole energy range for values of J
/
t from 1/3 to 4. This is contrasted with the two-dimensional case. The quasiparticle weight Zk is computed on lattices up to L
=128 sites in one dimension, and scales as .
Received 15 February 2000 相似文献
17.
F. Selva D. Weinmann 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,18(1):137-148
A Wigner crystal structure of the electronic ground state is induced by strong Coulomb interactions at low temperature in
clean or disordered two-dimensional (2d) samples. For fermions on a mesoscopic disordered 2d lattice, being closed to a torus,
we study the persistent current in the regime of strong interaction at zero temperature. We perform a perturbation expansion
starting from the Wigner crystal limit which yields power laws for the dependence of the persistent current on the interaction
strength. The sign of the persistent current in the strong interaction limit is independent of the disorder realization and
strength. It depends only on the electro-statically determined configuration of the particles in the Wigner crystal.
Received 14 March 2000 相似文献
18.
J. Bauer A. C. Hewson 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,57(3):235-249
We analyze the properties of the quasiparticle excitations of metallic
antiferromagnetic states in a strongly correlated electron system. The study is based on
dynamical mean field theory (DMFT) for the infinite dimensional Hubbard model with
antiferromagnetic symmetry breaking. Self-consistent solutions of the DMFT
equations are calculated using the numerical renormalization group (NRG). The
low energy behavior in these results is then analyzed in terms
of renormalized quasiparticles. The parameters for these quasiparticles are
calculated directly from the NRG derived self-energy, and also from the low
energy fixed point of the effective impurity model. From these the quasiparticle
weight and the effective mass are deduced. We show that
the main low energy features of the k-resolved spectral density can be understood in
terms of the quasiparticle picture. We also find that Luttinger's theorem
is satisfied for the total electron number in the doped antiferromagnetic
state. 相似文献
19.
Ph. Brune A.P. Kampf 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,18(2):241-245
We apply a diagrammatic expansion method around the atomic limit () for the U-t-t
' Hubbard model at half filling and finite temperature by means of a continued fraction representation of the one-particle
Green's function. From the analysis of the spectral function we find an energy dispersion relation with a modulation of the energy gap in the insulating phase. This anisotropy is compared with experimental ARPES results on insulating
cuprates.
Received 18 May 2000 and Received in final form 9 August 2000 相似文献
20.
T. Saikawa A. Ferraz 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,20(1):65-74
A precursor effect on the Fermi surface in the two-dimensional Hubbard model at finite temperatures near the antiferromagnetic
instability is studied using three different itinerant approaches: the second order perturbation theory, the paramagnon theory
(PT), and the two-particle self-consistent (TPSC) approach. In general, at finite temperature, the Fermi surface of the interacting
electron systems is not sharply defined due to the broadening effects of the self-energy. In order to take account of those
effects we consider the single-particle spectral function A(, 0) at the Fermi level, to describe the counterpart of the Fermi surface at T = 0. We find that the Fermi surface is destroyed close to the pseudogap regime due to the spin-fluctuation effects in both
PT and TPSC approaches. Moreover, the top of the effective valence band is located around = (π/2,π/2) in agreement with earlier investigations on the single-hole motion in the antiferromagnetic background. A crossover
behavior from the Fermi-liquid regime to the pseudogap regime is observed in the electron concentration dependence of the
spectral function and the self-energy.
Received 8 September 2000 and Received in final form 20 December 2000 相似文献