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1.
Y. Asada A. Freyn J.-L. Pichard 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,53(1):109-120
A nano-system in which electrons interact and in contact with
Fermi leads gives rise to an effective one-body scattering which
depends on the presence of other scatterers in the attached leads.
This non local effect is a pure many-body effect that one neglects
when one takes non interacting models for describing quantum transport.
This enhances the non-local character of the quantum conductance by
exchange interactions of a type similar to the RKKY-interaction between
local magnetic moments. A theoretical study of this effect is given
assuming the Hartree-Fock approximation for spinless fermions of Fermi
momentum kF in an infinite chain embedding two scatterers
separated by a segment of length Lc. The fermions interact only inside
the two scatterers. The dependence of one scatterer onto the other exhibits
oscillations of period π/kF which decay as 1/Lc and
which are suppressed when Lc exceeds the thermal length
LT. The analytical results given by the Hartree-Fock
approximation are compared with exact numerical results obtained with
the embedding method and the DMRG algorithm. 相似文献
2.
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
3.
B. Kim M.-H. Chung 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,60(1):67-73
We consider the symmetry group inherent in
two-dimensional triangle and honeycomb lattice systems. We find
analytically and numerically the character of the reducible
representation for the corresponding Fock space. Using the
irreducible characters and the reducible character of the
representation, we decompose the Fock space explicitly. For example,
we calculate the multiplicity of each irreducible representation
contained in the Fock space. 相似文献
4.
R. Calemczuk J. Riera D. Poilblanc J.-P. Boucher G. Chaboussant L. Lévy O. Piovesana 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,7(2):171-174
Specific heat (CV) measurements in the spin-1/2 Cu2(C2H12N2)2Cl4 system under a magnetic field up to H
=8.25 T are reported and compared to the results of numerical calculations based on the 2-leg antiferromagnetic Heisenberg ladder.
While the temperature dependences of both the susceptibility and the low-field specific heat are accurately reproduced by
this model, deviations are observed above the critical field HC1 at which the spin gap closes. In this Quantum High Field phase, the contribution of the low-energy quantum fluctuations are
stronger than in the Heisenberg ladder model. We argue that this enhancement can be attributed to dynamical lattice fluctuations.
Finally, we show that such a Heisenberg ladder, for H
>
H
C1, is unstable, when coupled to the 3D lattice, against a lattice distortion. These results provide an alternative explanation
for the observed low temperature ( K-0.8 K) phase (previously interpreted as a 3D magnetic ordering) as a new type of incommensurate gapped state.
Received: 23 July 1998 / Accepted: 24 August 1998 相似文献
5.
R. Baltin Y. Gefen G. Hackenbroich H.A. Weidenmüller 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,10(1):119-129
We investigate the Coulomb blockade resonances and the phase of the transmission amplitude of a deformed ballistic quantum
dot weakly coupled to leads. We show that preferred single-particle levels exist which stay close to the Fermi energy for
a wide range of values of the gate voltage. These states give rise to sequences of Coulomb blockade resonances with correlated
peak heights and transmission phases. The correlation of the peak heights becomes stronger with increasing temperature. The
phase of the transmission amplitude shows lapses by between the resonances. Implications for recent experiments on ballistic quantum dots are discussed.
Received 17 July 1998 相似文献
6.
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
7.
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
8.
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
9.
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
10.
A. Eilmes R.A. Römer M. Schreiber 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,23(2):229-234
We study the influence of many-particle interactions on a metal-insulator transition. We consider the two-interacting-particle
problem for onsite interacting particles on a one-dimensional quasiperiodic chain, the so-called Aubry-André model. We show
numerically by the decimation method and finite-size scaling that the interaction does not modify the critical parameters
such as the transition point and the localization-length exponent. We compare our results to the case of finite density systems
studied by means of the density-matrix renormalization scheme.
Received 28 June 2001 相似文献
11.
A. V. Lukoyanov V. V. Mazurenko V. I. Anisimov M. Sigrist T. M. Rice 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,53(2):205-207
We propose FeSb2 to be a nearly ferromagnetic small gap semiconductor, hence a direct analog
of FeSi. We find that despite different compositions and crystal structures,
in the local density approximation with on-site Coulomb repulsion correction (LDA+U) method
magnetic and semiconducting solutions for U=2.6 eV are energetically degenerate
similar to the case of FeSi. For both FeSb2 and FeSi (FeSi1-xGex alloys)
the underlying transition mechanism allows one to switch from a small gap semiconductor
to a ferromagnetic metal with magnetic moment ≈1 μB per Fe ion with external magnetic field. 相似文献
12.
A. Liebsch H. Ishida 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,61(4):405-411
There exists presently considerable debate over the question whether
local Coulomb interactions can explain the absence of the small e′
g
Fermi surface hole pockets in photoemission studies of Na0.3CoO2.
By comparing dynamical mean field results for different single particle
Hamiltonians and exact diagonalization as well as quantum Monte Carlo
treatments, we show that, for realistic values of the Coulomb energy U
and Hund exchange J, the e′
g pockets can be slightly enhanced or
reduced compared to band structure predictions, but they do not disappear. 相似文献
13.
I.A. Nekrasov K. Held N. Blümer A.I. Poteryaev V.I. Anisimov D. Vollhardt 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,18(1):55-61
The spectral properties of La1–xSrxTiO3, a doped Mott insulator with strong Coulomb correlations, are calculated with the ab initio computational scheme LDA+DMFT(QMC). It starts from the non-interacting electronic band structure as calculated by the local
density approximation (LDA), and introduces the missing correlations by the dynamical mean-field theory (DMFT), using numerically
exact quantum Monte-Carlo (QMC) techniques to solve the resulting self-consistent multi-band single-impurity problem. The
results of the LDA+DMFT(QMC) approach for the photoemission spectra of La1–xSrxTiO3 are in good agreement with experiment and represent a considerable qualitative and quantitative improvement on standard LDA
calculations.
Received 20 May 2000 and Received in final form 27 July 2000 相似文献
14.
P. Bonville M. Rams K. Królas J.-P. Sanchez P. C. Canfield O. Trovarelli C. Geibel 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,55(1):77-84
We have examined the magnetic properties of the heavy electron compounds
YbAgGe and YbPtIn by 170Yb M?ssbauer spectroscopy down to 0.1 K, and
the crystal field properties of YbAgGe by Perturbed Angular Correlations
(PAC) measurements up to 900 K. In YbAgGe, we show that each of the two
magnetically ordered phases below 0.8 K involves a specific incommensurate
modulation of the Yb moment. An analysis of existing low temperature specific
heat data suggests the
persistence of fluctuations of the correlated Yb spins down to 0.1 K.
The PAC data allow to discriminate among proposed Yb3+ crystal field
level schemes. In YbPtIn, we show that the low temperature magnetic order
phase has an antiferro-para structure, where zero moment Yb ions coexist with
large moment ones, and that a 90° moment reorientation occurs at
1.4 K. 相似文献
15.
16.
A. K. Zhuravlev V. Yu. Irkhin M. I. Katsnelson 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,55(4):377-382
Using the numerical renormalization group method, the dependences on
temperature of the magnetic susceptibility χ(T) and specific heat C(T)
are obtained for the single-impurity Anderson model with inclusion of
d-f the Coulomb interaction. It is shown that the exciton effects
caused by this effect (charge fluctuations) can significantly change the
behaviour of C(T) in comparison with the standard Anderson model at
moderately low temperatures, whereas the behaviour of χ(T) remains nearly
universal. The ground-state and temperature-dependent renormalizations of the
effective hybridization parameter and f-level position caused by the
d-f interaction are calculated, and satisfactory agreement with the
Hartree-Fock approximation is derived. 相似文献
17.
J. M.P. Carmelo K. Penc 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,51(4):477-499
We introduce a method that allows the evaluation of general expressions for the spectral
functions of the one-dimensional Hubbard model for all values of the on-site
electronic repulsion U. The spectral weights are expressed in terms of pseudofermion
operators such that the spectral functions can be written as a convolution of
pseudofermion dynamical correlation functions. Our results are valid for all finite
energy and momentum values and are used elsewhere in the study of the unusual
finite-energy properties of quasi-one-dimensional compounds and the new quantum systems
of ultra-cold fermionic atoms on an optical lattice. 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.
A. Liebsch T. A. Costi 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,51(4):523-536
The two-band Hubbard model involving subbands of different widths is
investigated via finite-temperature exact diagonalization (ED) and
dynamical mean field theory (DMFT). In contrast to the quantum Monte Carlo
(QMC) method which at low temperatures includes only Ising-like exchange
interactions to avoid sign problems, ED permits a treatment of Hund's
exchange and other onsite Coulomb interactions on the same footing.
The role of finite-size effects caused by the limited number of bath
levels in this scheme is studied by analyzing the low-frequency behavior
of the subband self-energies as a function of temperature, and by
comparing with numerical renormalization group (NRG) results for a
simplified effective model.
For half-filled, non-hybridizing bands, the metallic and insulating
phases are separated by an intermediate mixed phase with an insulating
narrow and a bad-metallic wide subband. The wide band in this phase
exhibits different degrees of non-Fermi-liquid behavior, depending on
the treatment of exchange interactions. Whereas for complete Hund's
coupling, infinite lifetime is found at the Fermi level, in the
absence of spin-flip and pair-exchange, this lifetime becomes finite.
Excellent agreement is obtained both with new NRG and previous
QMC/DMFT calculations. These results suggest that-finite temperature
ED/DMFT might be a useful scheme for realistic multi-band materials. 相似文献
20.
I. Titvinidze G.I. Japaridze 《The European Physical Journal B - Condensed Matter and Complex Systems》2003,32(3):383-393
The quantum phase transition in the ground state of the extended spin S
= 1/2 XY model has been studied in detail. Using the exact solution of the model the low temperature thermodynamics, as well as the
ground state phase diagram of the model in the presence of applied uniform and/or staggered magnetic field are discussed.
Received 29 November 2002 / Received in final form 24 February 2003 Published online 11 April 2003
RID="a"
ID="a"e-mail: japa@iph.hepi.edu.ge 相似文献