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1.
P. Pirooznia P. Kopietz 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,58(3):291-296
We calculate the damping γq of collective density oscillations
(zero sound) in a
one-dimensional Fermi gas
with dimensionless forward scattering interaction
F and quadratic energy dispersion
k2 / 2 m at zero temperature.
Using standard many-body perturbation theory,
we obtain γq from the expansion
of the
inverse irreducible polarization to first order
in the effective screened (RPA) interaction.
For wave-vectors | q| /kF ≪F (where kF = m vF is the Fermi wave-vector)
we find to leading order γq ∝| q |3 /(vF m2).
On the other hand, for F ≪| q| /kF most of the spectral weight
is carried by the particle-hole continuum, which is
distributed over a frequency interval of the order of q2/m.
We also show that zero sound damping
leads to a finite maximum proportional to
|k - kF | -2 + 2 η
of the charge peak in the single-particle
spectral function, where η is the anomalous
dimension. Our prediction agrees with photoemission data for
the blue bronze K0.3MoO3.
We comment on other recent calculations of γq. 相似文献
2.
We investigate the phase diagram of a quarter filled
Hubbard ladder with nearest-neighbor Coulomb repulsion using
bosonization and renormalization group approach. Focusing on the
strong-repulsion regime, we discuss the effect of an interchain
exchange interaction J
and interchain repulsion
V
on the possible ground states of the
system and charge order configurations. Since the spin
excitations always possess a gap, we find competing bond-order
wave and charge density wave phases as possible ground states of
the ladder model. We discuss the elementary excitations in these
various phases and point an analogy between the excitations on
some of these phases and those of a Kondo-Heisenberg insulator.
We also study the order of the quantum phase transitions between
the different ground states of the system. We obtain second
order transitions in the Ising or SU(2)2
universality class or first order transitions. We map the
complete phase diagram in the J
–V
plane by integrating perturbative
renormalization-group equations. Finally, we discuss the effect
of doping away from half-filling and the effect of an applied
magnetic field. 相似文献
3.
Gun Sang Jeon Chia-Chen Chang Jainendra K. Jain 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,55(3):271-282
We review and extend the composite fermion theory for semiconductor quantum dots in high magnetic fields. The mean-field model
of composite fermions is unsatisfactory for the qualitative physics at high angular momenta.
Extensive numerical calculations demonstrate that the microscopic CF theory,
which incorporates interactions between composite fermions, provides an excellent qualitative and quantitative account
of the quantum dot ground state down to the largest angular momenta studied,
and allows systematic improvements by inclusion of mixing between composite
fermion Landau levels (called Λ levels). 相似文献
4.
G. Roux S. Capponi P. Lecheminant P. Azaria 《The European Physical Journal B - Condensed Matter and Complex Systems》2009,68(3):293-308
We study spin 3/2 fermionic cold atoms with attractive interactions confined in a one-dimensional optical lattice. Using numerical
techniques, we determine the phase diagram for a generic density. For the chosen parameters, one-particle excitations are
gapped and the phase diagram is separated into two regions: one where the two-particle excitation gap is zero, and one where
it is finite. In the first region, the two-body pairing fluctuations (BCS) compete with the density ones. In the other one,
a molecular superfluid (MS) phase, in which bound-states of four particles form, competes with the density fluctuations. The
properties of the transition line between these two regions is studied through the behavior of the entanglement entropy. The
physical features of the various phases, comprising leading correlations, Friedel oscillations, and excitation spectra, are
presented. To make the connection with experiments, the effect of a harmonic trap is taken into account. In particular, we
emphasize the conditions under which the appealing MS phase can be realized, and how the phases could be probed by using the
density profiles and the associated structure factor. Lastly, the consequences on the flux quantization of the different nature
of the pairing in the BCS and MS phases are studied in a situation where the condensate is in a ring geometry. 相似文献
5.
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
6.
S. Sykora A. Hübsch K. W. Becker 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,51(2):181-187
We study the one-dimensional Holstein model of spinless fermions interacting
with dispersion-less phonons by using a recently developed projector-based
renormalization method (PRM). At half-filling the system shows a
metal-insulator transition to a Peierls distorted
state at a critical electron-phonon coupling where both phases
are described within the same theoretical framework.
The transition is accompanied by a phonon softening
at the Brillouin zone boundary and a gap in the electronic spectrum.
For different filling, the phonon softening appears away from the Brillouin
zone boundary and thus reflects a different type of broken symmetry state. 相似文献
7.
P. M.R. Brydon M. Gulácsi A. Bussmann-Holder 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,54(1):73-81
We present a non-perturbative study of an extended Falicov-Kimball model in
one
dimension. Working within the binary alloy interpretation, we include the
spin of the itinerant electrons and a Hubbard interaction to model the
inter-electron correlations. We derive an effective Ising model for the atomic
configuration in order to show how the Hubbard term affects the stability
of the phase separated states. Furthermore, we investigate the competition
between the Mott insulator state of the itinerant electrons and the
checkerboard phase of the spinless Falicov-Kimball model. 相似文献
8.
9.
L. Mayrhofer M. Grifoni 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,56(2):107-125
We present a low energy-theory for non-linear transport in finite-size
interacting single-wall carbon nanotubes. It is based on a microscopic
model for the interacting pz electrons and successive bosonization.
We consider weak coupling to the leads and derive equations of motion
for the reduced density matrix. We focus on the case of large-diameter nanotubes where exchange effects can be neglected.
In this situation the energy spectrum is highly degenerate. Due to the multiple degeneracy, diagonal as well as off-diagonal
(coherences)
elements of the density matrix contribute to the nonlinear transport.
At low bias, a four-electron periodicity with a characteristic ratio
between adjacent peaks is predicted. Our results are in quantitative
agreement with recent experiments. 相似文献
10.
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
11.
An analysis of Luttinger's theorem shows that – contrary to recent
claims – it is not valid for a generic Mott insulator. For a
two-orbital Hubbard model with two electrons per site the crossover
from a non-magnetic correlated insulating phase (Mott or Kondo
insulator) to a band insulator is investigated. Mott insulating
phases are characterized by poles of the self-energy and
corresponding zeros in the Greens functions defining a “Luttinger
surface” which is absent for band insulators. Nevertheless, the
ground states of such insulators with two electrons per unit cell
are adiabatically connected. 相似文献
12.
We consider one-dimensional (1D) interacting spinless fermions with a non-linear spectrum in a clean quantum wire (non-linear
bosonization). We compute diagrammatically the 1D dynamical structure factor, S(ω,q), beyond the Tomonaga approximation focusing
on it's tails, |ω| ≫vq,
i.e. the 2-pair excitation continuum due to forward scattering. Our methodology reveals three classes of diagrams: two “chiral”
classes which bring divergent contributions in the limits ω→±vq, i.e. near the single-pair excitation continuum, and a “mixed”
class (so-called Aslamasov-Larkin or Altshuler-Shklovskii type diagrams) which is crucial for the f-sum rule to be satisfied.
We relate our approach to the T=0 ones present in the literature. We also consider the
case and show that the 2-pair excitation continuum dominates the single-pair one in the range: |q|T/kF ≪ω±vq ≪T (substantial for q ≪kF). As applications we first derive the small-momentum optical conductivity due to forward scattering: σ∼1/ω for T ≪ω and σ∼T/ω2 for T ≫ω. Next, within the 2-pair excitation continuum, we show that the attenuation rate of a coherent mode of dispersion
Ωq crosses over from
, e.g. γq ∼|q|3 for an acoustic mode, to
, independent of Ωq, as temperature increases. Finally, we show that the 2-pair excitation continuum yields subleading curvature corrections
to the electron-electron scattering rate:
, where V is the dimensionless strength of the interaction. 相似文献
13.
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
14.
T. Gottwald P. G.J. van Dongen 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,61(3):277-285
In order to describe unbalanced ultracold fermionic quantum gases on optical lattices in a harmonic trap, we investigate an
attractive (U < 0) asymmetric (t↑≠t↓) Hubbard model with a Zeeman-like magnetic field. In view of the model's spatial inhomogeneity, we focus in this paper on
the solution at Hartree-Fock level. The Hartree-Fock Hamiltonian is diagonalized with particular emphasis on superfluid phases.
For the special case of spin-independent hopping we analytically determine the number of solutions of the resulting self-consistency
equations and the nature of the possible ground states at weak coupling. We present the phase diagram of the homogeneous system
and numerical results for unbalanced Fermi-mixtures obtained within the local density approximation. In particular, we find
a fascinating shell structure, involving normal and superfluid phases. For the general case of spin-dependent hopping we calculate
the density of states and the possible superfluid phases in the ground state. In particular, we find a new magnetized superfluid
phase. 相似文献
15.
A. Agliolo Gallitto G. Bonsignore G. Giunchi M. Li Vigni 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,51(4):537-542
We discuss the microwave second-harmonic generation in
high-density bulk MgB2, prepared by the reactive liquid Mg
infiltration technology. The intensity of the harmonic signal has
been investigated as a function of temperature and amplitudes of
the DC and microwave magnetic fields. The results are discussed in
the framework of a phenomenological theory, based on the two-fluid
model, which assumes that both the microwave and static magnetic
fields, penetrating in the surface layers of the sample, weakly
perturb the partial concentrations of the normal and
superconducting fluids. We show that, in order to account for the
experimental results, it is essential to suppose that in MgB2
the densities of the normal and condensed fluids linearly depend
on the temperature. 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.
R.J. Komlos 《Physics letters. A》2008,372(44):6670-6676
The model presented here applies a self-consistent method to electrons in crystals, thus enabling the calculation of the effective inner potential field. For this purpose, a Thomas-Fermi (TF) type model was developed, using a “qausi” one-dimensional finite crystal—a set of equidistant infinite thin plates representing the ionic planes, spread perpendicularly to a length axis. The model is applied to a finite crystal with no external fields. This application of a “multi-centered” TF model to an entire crystal is carried out for the first time in this work; the TF model was widely used in the past for atomic and molecular calculations, but in crystals it was limited to local use such as impurities. Poisson's (non-linear) differential equation describing the problem is solved using the highly efficient Relaxation Method. A pattern of almost periodical peaks (except near the boundaries) residing at the ionic sites is obtained for the potential, as well as for the electronic local density (indicating the electrons' tendency to pack mainly near the ions). 相似文献
18.
S. H. Abedinpour M. Polini G. Xianlong M. P. Tosi 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,56(2):127-134
Motivated by current interest in strongly correlated quasi-one-dimensional (1D) Luttinger liquids subject to axial confinement,
we present a novel density-functional study of few-electron systems confined by power-low external potentials inside a short
portion of a thin quantum wire. The theory employs the
1D homogeneous Coulomb liquid as the reference system for a Kohn-Sham treatment and transfers the Luttinger ground-state correlations
to the inhomogeneous electron system by means of a suitable local-density approximation (LDA) to the exchange-correlation
energy functional. We show that such 1D-adapted LDA is appropriate for fluid-like states at weak coupling, but fails to account
for the transition to a “Wigner molecules” regime of electron localization as observed in thin quantum wires at very strong
coupling. A detailed analyzes is given for the two-electron problem under axial harmonic confinement. 相似文献
19.
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
20.
A. Hübsch K. W. Becker 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,52(3):345-353
A very rich phase diagram has recently been found in CeCu2Si2 from
high pressure experiments where, in particular, a transition between an
intermediate valence configuration and an integral valent heavy fermion
state has been observed. We show that such a valence transition can be
understood in the framework of the periodic Anderson model. In particular,
our results show a breakdown of a mixed-valence state which is accompanied
by a drastic change in the f occupation in agreement with
experiment. This valence transition can possibly be interpreted as a
collapse of the large Fermi surface of the heavy fermion state which
incorporates not only the conduction electrons but also the localized
f electrons. The theoretical approach used in this paper
is based on the novel projector-based renormalization method (PRM). With
respect to the periodic Anderson model, the method was before only employed
in combination with the basic approximations of the well-known slave-boson
mean-field theory. In this paper, the PRM treatment is performed in a more
sophisticated manner where both mixed as well as integral valent solutions
have been obtained. Furthermore, we argue that the presented PRM approach
might be a promising starting point to study the competing interactions in
CeCu2Si2 and related compounds. 相似文献