共查询到20条相似文献,搜索用时 15 毫秒
1.
I. Paul G. Kotliar 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,51(2):189-193
Many-body Hamiltonians obtained from first principles
generally include all possible
non-local interactions. But in dynamical mean field theory the
non-local interactions are ignored,
and only the effects of the local interactions are taken into account.
The truncation of the non-local interactions is a basis dependent
approximation.
We propose a criterion to construct an appropriate
localized basis in which the truncation can be carried out.
This involves finding a
basis in which a functional given by the sum of the squares of
the local
interactions with appropriate weight factors is maximized under unitary
transformations of basis.
We argue that such a
localized basis is suitable for the application of dynamical mean field theory
for calculating material properties from first principles.
We propose an algorithm which can be used for constructing the
localized basis. We test our criterion on a toy model and find it
satisfactory. 相似文献
2.
V.?Derzhko J.?J?drzejewski T.?Krokhmalskii 《The European Physical Journal B - Condensed Matter and Complex Systems》2009,68(4):501-510
We discuss striped phases as a state of matter intermediate between
two extreme states: a crystalline state and a segregated state. We argue that
this state is very sensitive to weak interactions, compared to those
stabilizing a crystalline state, and to anisotropies.
Moreover, under suitable conditions a 2D system in a striped phase decouples
into (quasi) 1D chains. These observations are based on results of our studies
of an extension of a microscopic quantum model of crystallization, proposed originally
by Kennedy and Lieb. 相似文献
3.
F. Schönfeld G. Bouzerar G.S. Uhrig E. Müller-Hartmann 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,5(3):521-528
Using the density matrix renormalization group method (DMRG) we calculate the magnetization of frustrated S=1/2 Heisenberg chains for various modulation patterns of the nearest neighbour coupling: commensurate, incommensurate with
sinusoidal modulation and incommensurate with solitonic modulation. We focus on the order of the phase transition from the
commensurate dimerized phase (D) to the incommensurate phase (I). It is shown that the order of the phase transition depends
sensitively on the model. For the solitonic model in particular, a k-dependent elastic energy modifies the order of the transition. Furthermore, we calculate gaps in the incommensurate phase
in adiabatic approximation.
Received: 9 March 1998 / Accepted: 17 April 1998 相似文献
4.
J. Kokalj P. Prelovšek 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,63(4):431-435
The frequency-moment expansion method is developed to analyze the validity of the Luttinger sum rule within the Mott-Hubbard
insulator, as represented by the generalized Hubbard model at half filling and large U. For the particular case of the Hubbard model with nearest-neighbor hopping on a triangular lattice lacking the particle-hole
symmetry results reveal substantial violation of the sum rule. 相似文献
5.
A.V. Nikolaev K.H. Michel 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,17(1):15-32
We present a theoretical model of the “isostructural" - phase transition in Ce which is based on quadrupolar interactions due to coupled charge density fluctuations of 4f electrons and of conduction electrons. The latter are treated in tight-binding approximation. The - transition is described as an orientational ordering of quadrupolar electronic densities in a structure. The quadrupolar order of the conduction electron densities is complementary to the quadrupolar order of 4f electron densities. The inclusion of conduction electrons leads to an increase of the lattice contraction at the - transition in comparison to the sole effect of 4f electrons. We calculate the Bragg scattering law and suggest synchrotron radiation experiments in order to check the structure.
Received 21 September 1999 and Received in final form 2 May 2000 相似文献
6.
M.A. Garcia-Bach 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,14(3):439-448
For w-legged antiferromagnetic spin-1/2 Heisenberg ladders, a long-range spin pairing order can be identified which enables the
separation of the space spanned by finite-range (covalent) valence-bond configurations into w
+1 subspaces. Since every subspace has an equivalent counter subspace connected by translational symmetry, twofold degeneracy,
breaking translational symmetry is found except for the subspace where the ground state of w = even belongs to. In terms of energy ordering, (non)degeneracy and the discontinuities introduced in the long-range spin
pairing order by topological spin defects, the differences between even and odd ladders are explained in a general and systematic
way.
Received 19 July 1999 and Received in final form 8 October 1999 相似文献
7.
N. Grewe T. Jabben S. Schmitt 《The European Physical Journal B - Condensed Matter and Complex Systems》2009,68(1):23-32
The low energy region of certain transition metal compounds reveals dramatic correlation effects between electrons, which
can be studied by photoelectron spectroscopy. Theoretical investigations are often based on multi-orbital impurity models,
which exhibit modified versions of the Kondo effect. We present a systematic study of a multi-orbital Anderson-like model,
based on a new semi-analytical impurity solver which goes beyond simple modifications of the well known NCA. We discuss one-particle
excitation spectra and in particular the role of level positions and Coulomb-matrix elements. It is shown that the low-energy
region as well as the overall features of spectra critically depend on the model parameters and on the quality of the approximations
used. Recent photoelectron experiments and corresponding existing calculations are put into perspective. An interesting crossover
scenario between different regimes of ground states with characteristically different local correlations is uncovered. 相似文献
8.
R. Jursa S. Wermbter G. Czycholl 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,12(3):387-391
We study the influence of the short-ranged Hubbard correlation U between the conduction electrons on the Cooper pair formation in normal (s-wave) superconductors. The Coulomb correlation is considered within the standard second order perturbation theory, which
becomes exact in the weak coupling limit but goes beyond the simple Hartree-Fock treatment by yielding a finite lifetime of
the quasiparticles at finite temperature. An attractive pairing interaction V, which may be mediated by the standard electron-phonon mechanism, is considered between nearest neighbor sites. A critical
value for the attractive interaction is required to obtain a superconducting state. For finite temperature a gapless superconductivity is obtained due to the finite lifetime of the quasiparticles, i.e. the Coulomb correlation has a pair-breaking influence. The energy gap and depend very sensitively on U, V and band filling n and develop a maximum away from half filling as function of n. The ratio varies with n, being higher than the BCS value near half filling and reaching the BCS value for lower n.
Received 17 February 1999 相似文献
9.
F. Mancini F. P. Mancini 《The European Physical Journal B - Condensed Matter and Complex Systems》2009,68(3):341-351
Within the Green’s function and equations of motion formalism it is possible to exactly solve a large class of models useful
for the study of strongly correlated systems. Here, we present the exact solution of the one-dimensional extended Hubbard
model with on-site U and first nearest neighbor repulsive V interactions in the presence of an external magnetic field h,
in the narrow band limit. At zero temperature our results establish the existence of four phases in the three-dimensional
space (U, n, h) – n is the filling – with relative phase transitions, as well as different types of charge ordering. The magnetic
field may dramatically affect the behavior of thermodynamic quantities, inducing, for instance, magnetization plateaus in
the magnetization curves, and a change from a single to a double-peak tructure in the specific heat. According to the value
of the particle density, we find one or two critical fields, marking the beginning of full or partial polarization. A detailed
study of several thermodynamic quantities is also presented at finite temperature. 相似文献
10.
Y. Liu J. Dong D.Y. Xing 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,3(2):185-188
Minimizing total free energy by numerical calculations, we obtain the magnetic phase diagram of perovskite Mn oxides, such
as with , Ca, Sr, etc. in the whole doping region from x
=0 to x
=1 at temperature T
=0. It is discovered that a spiral state is stable in a low concentration of X ions while a canted state is stable in a high
concentration of X ions, and a ferromagnetic phase can exist in the intermediate concentrations when the antiferromagnetic
interaction is weak. The energy difference between spiral and canted states is found to be small when the Hund coupling is
large. Magnetic field induced spiral/canted phase transition is considered as a possible mechanism of the colossal magnetoresistance
(CMR) in the Mn oxides.
Received: 11 July 1996 / Revised: 7 December 1996 / Accepted: 24 July 1997 相似文献
11.
D. Weinmann R. A. Jalabert A. Freyn G.-L. Ingold J.-L. Pichard 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,66(2):239-244
We consider one-dimensional transport through an interacting region in
series with a point-like one-body scatterer. When the conductance of
the interacting region is perfect, independently of the interaction
strength, a nonlocal interaction effect yields a total conductance of
the composed system that depends on the interaction strength and is
lower than the transmission of the one-body scatterer. This qualitative
nonlocal effect allows to probe the dressing cloud of an interacting
system in ideal noninteracting leads. The conductance
correction increases with the strength of the interaction and the
reflection of the one-body scatterer (attaining relative changes >50%),
and decreases with the distance between the interacting region and the
one-body scatterer. Scaling laws are obtained and possible experimental
realizations are suggested. 相似文献
12.
A. Freyn J.-L. Pichard 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,58(3):279-290
We consider a nano-system connected to measurement probes via
non interacting leads. When the electrons interact inside the
nano-system, the coefficient |ts(EF)|2 describing its
effective transmission at the Fermi energy EF ceases to be
local. This effect of electron-electron interactions upon
|ts(EF)|2 is studied using a one dimensional model of spinless
fermions and the Hartree-Fock approximation. The non locality of
|ts(EF)|2 is due to the coupling between the Hartree and Fock
corrections inside the nano-system and the scatterers outside the
nano-system via long range Friedel oscillations. Using this phenomenon,
one can vary |ts(EF)|2 by an Aharonov-Bohm flux threading a ring
which is attached to one lead at a distance Lc from the nano-system.
For small distances Lc, the variation of the quantum conductance
induced by this non local effect can exceed 0.1 (e2/h). 相似文献
13.
A. Avella F. Mancini 《The European Physical Journal B - Condensed Matter and Complex Systems》2003,32(1):27-33
The magnetic properties of the La2CuO4 are analyzed by means of the paramagnetic solution of the Hubbard model within the composite operator method. The experimental
findings of the inelastic neutron magnetic scattering [R. Coldea et al., Phys. Rev. Lett. 86, 5377 (2001)] for the spin spectrum, the spin-wave intensity and the behavior of the dispersion at the zone boundary are
well described by our results although the difference in phase. The Hubbard model emerges has a minimal model capable to describe
the anomalous magnetic behavior of such a strongly correlated material.
Received 29 July 2002 / Received in final form 2 January 2003 Published online 14 March 2003 相似文献
14.
P. Bonville J. A. Hodges Z. Hossain R. Nagarajan S. K. Dhar L. C. Gupta E. Alleno C. Godart 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,11(3):377-383
We present magnetic properties of the three-band Hubbard model in the para- and antiferromagnetic phase on a hypercubic lattice
calculated with the Dynamical Mean-Field Theory (DMFT). To allow for solutions with broken spin-symmetry we extended the approach
to lattices with AB-like structure. Above a critical sublattice magnetization one can observe rich structures in the spectral-functions similar to the t-J model which can be related to the well known bound states for one hole in the Neél-background. In addition to the one-particle
properties we discuss the static spin-susceptibility in the paramagnetic state at the points and for different dopings . The -T-phase-diagram exhibits an enhanced stability of the antiferromagnetic state for electron-doped systems in comparison to hole-doped.
This asymmetry in the phase diagram is in qualitative agreement with experiments for high-Tc materials.
Received: 28 May 1998 / Revised and Accepted: 14 September 1998 相似文献
15.
M. Martínez J.-L. Pichard 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,30(1):93-100
The two dimensional crossover from independent particle towards collective motion is studied using 2 polarized electrons (spinless
fermions) interacting via a U/r Coulomb repulsion in a L×L square lattice with periodic boundary conditions and nearest neighbor hopping t. Three regimes characterize the ground state when U/t increases. Firstly, when the fluctuation Δr of the spacing r between the two particles is larger than the lattice spacing a, there is a scaling length L
0 = π2(t/U) such that the relative fluctuation Δr/〈r〉 is a universal function of the dimensionless ratio L/L
0, up to finite size corrections of order L-2. L < L
0 and L > L
0 are respectively the limits of the free particle Fermi motion and of the correlated motion of a Wigner molecule. Secondly,
when U/t exceeds a threshold U
*(L)/t, Δr becomes smaller than a, giving rise to a correlated lattice regime where the previous scaling breaks down and analytical expansions in powers of
t/U become valid. A weak random potential reduces the scaling length and favors the correlated motion.
Received 28 March 2002 Published online 19 November 2002 相似文献
16.
J. Links K. Hibberd M. Gould A. Foerster 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,5(3):309-312
A new model for correlated electrons is presented which is integrable in one-dimension. The symmetry algebra of the model
is the Lie superalgebra gl(2|1) which depends on a continuous free parameter. This symmetry algebra contains the pairing algebra as a subalgebra which is used to show that the model exhibits Off-Diagonal Long-Range Order in any number
of dimensions.
Received: 9 December 1997 / Revised: 12 February 1998 / Accepted: 17 March 1998 相似文献
17.
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
18.
S. Ejima F. Gebhard R. M. Noack 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,66(2):191-200
We use the Random Dispersion Approximation (RDA) to study the
Mott-Hubbard transition in the Hubbard model at half band filling.
The RDA becomes exact for the Hubbard model in infinite dimensions.
We implement the RDA on finite chains and employ the Lanczos exact
diagonalization method in real space to calculate the ground-state energy,
the average double occupancy, the charge gap, the momentum distribution,
and the quasi-particle weight. We find a satisfactory agreement with
perturbative results in the weak- and strong-coupling limits.
A straightforward extrapolation of the RDA data
for L ≤ 14 lattice results in a continuous Mott-Hubbard transition at
Uc≈W.
We discuss the significance of a possible signature
of a coexistence region between insulating and metallic
ground states in the RDA that would correspond to
the scenario of a discontinuous Mott-Hubbard transition
as found in numerical investigations
of the Dynamical Mean-Field Theory for the Hubbard model. 相似文献
19.
A.V. Nikolaev K.H. Michel 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,9(4):619-634
We have calculated the quantum quadrupolar interaction due to charge density fluctuations of localized 4f-electrons in Ce by taking into account the angular dependence, the degeneracy of the localized 4f
-orbitals and the spin-orbit coupling. The calculated crystal field of 4
f electronic states is in good agreement with neutron diffraction measurements. We show that orientational ordering of quantum
quadrupoles drives a phase transition at K which we assign with the transformation. In the phase the centers of mass of the Ce atoms still form a face centered cubic lattice. The theory accounts for the first order
character of the transition and for the cubic lattice contraction which accompanies the transition. The transition temperature
increases linearly with pressure. Our approach does not involve Kondo spin fluctuations as the significant process for the
phase transition.
Received 19 October 1998 相似文献
20.
A. Montorsi 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,5(3):419-422
We investigate under which circumstances extended Hubbard models, including bond-charge, exchange, and pair-hopping terms,
are invariant under gl
(2,1) superalgebra. This happens for a two-parameter Hamiltonian which includes as particular cases the t
-
J, the EKS and the one-parameter BGLZ Hamiltonians, all integrable in one dimension. We show that the two parameter Hamiltonian
can be recasted as the sum of the BGLZ Hamiltonian plus the graded permutation operator of electronic states on neighbouring
sites. The integrability of the corresponding one-dimensional model is discussed.
Received: 17 February 1998 / Received in final form: 6 March 1998 / Accepted: 17 April 1998 相似文献