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1.
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
2.
Y. Ōno R. Bulla A.C. Hewson M. Potthoff 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,22(3):283-290
We have studied the critical behaviour of a doped Mott insulator near the metal-insulator transition for the infinite-dimensional
Hubbard model using a linearized form of dynamical mean-field theory. The discontinuity in the chemical potential in the change
from hole to electron doping, for U larger than a critical value U
c, has been calculated analytically and is found to be in good agreement with the results of numerical methods. We have also
derived analytic expressions for the compressibility, the quasiparticle weight, the double occupancy and the local spin susceptibility
near half-filling as functions of the on-site Coulomb interaction and the doping.
Received 15 March 2001 and Received in final form 22 May 2001 相似文献
3.
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
4.
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
5.
A. Wobst D. Weinmann 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,10(1):159-167
The curvatures of two-particle energy levels with respect to the enclosed magnetic flux in mesoscopic disordered rings are
investigated numerically. We find that the typical value of the curvatures is increased by interactions in the localised regime
and decreased in the metallic regime. This confirms a prediction by Akkermans and Pichard (Eur. Phys. J. B 1, 223 (1998)). The interaction-induced changes of the typical curvatures at different energies and disorder strengths exhibit
one-parameter scaling with a conductance-like single parameter. This suggests that interactions could influence the conductance
of mesoscopic systems similarly.
Received 24 August 1998 相似文献
6.
R. Bulla M. Potthoff 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,13(2):257-264
The Mott-Hubbard metal-insulator transition is studied within a simplified version of the Dynamical Mean-Field Theory (DMFT)
in which the coupling between the impurity level and the conduction band is approximated by a single pole at the Fermi energy.
In this approach, the DMFT equations are linearized, and the value for the critical Coulomb repulsion can be calculated analytically. For the symmetric single-band Hubbard model at zero temperature, the critical value is found
to be given by 6 times the square root of the second moment of the free (U=0) density of states. This result is in good agreement with the numerical value obtained from the Projective Selfconsistent
Method and recent Numerical Renormalization Group calculations for the Bethe and the hypercubic lattice in infinite dimensions.
The generalization to more complicated lattices is discussed. The “linearized DMFT” yields plausible results for the complete
geometry dependence of the critical interaction.
Received 6 May 1999 and Received in final form 2 July 1999 相似文献
7.
Fabian Wenger 《Zeitschrift für Physik B Condensed Matter》1995,98(2):171-185
We show that weak static random potentials have pronounced effects on the quasiparticle states of a 2Dd-wave superconductor close to a node. We prove that the vertex correction coming from the simplest crossed diagram is important even for a nonmagnetic potential. The leading frequency and momentum dependent logarithmic singularities in the self-energy are calculated exactly to second order in perturbation theory. The self-energy corrections lead to a modified low energy density of states which depends strongly on the type of random potential and which can be measured in experiments. There is an exceptional case for a potential with extremely local scatterers and opposite nodes separated by (, ) where an exact cancelation takes place eliminating the leading frequency dependent singularity in the simplest crossed diagram. A comparison of the perturbative results with a self-consistent CPA (coherent potential approximation) for the nonmagnetic disorder reveals qualitative differences in the self-energy at the smallest energies which are due to the neglectance of vertex corrections in CPA. 相似文献
8.
S. Fratini P. Quémerais 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,14(1):99-113
The melting of a Wigner Crystal of electrons placed into a host polar material is examined as a function of the density and
the temperature. When the coupling to the longitudinal optical modes of the host medium is turned on, the WC is progressively
transformed into a polaronic Wigner crystal. We estimate the critical density for crystal melting at zero temperature using
the Lindeman criterion. We show that above a certain critical value of the Fr?hlich electron-phonon coupling, the melting
towards a quantum liquid of polarons is not possible, and the insulator-to-metal transition is driven by the ionization of
the polarons (polaron dissociation). The phase diagram at finite temperature is obtained by making use of the same Lindeman
criterion. Results are also provided in the case of an anisotropic electron band mass, showing that the scenario of polaron
dissociation can be relevant in anisotropic compounds such as the superconducting cuprates at rather moderate e-ph couplings.
Received 13 August 1999 相似文献
9.
We investigate the influence of electron correlations on the temperature-dependence of the electronic structure of ferromagnetic bcc iron by use of a manybody evaluation of a generalized model of magnetism. The single-particle part of the model-Hamiltonian is taken from an LDA band structure calculation. The manybody interactions are described by only two parameters, an intraband Coulomb interactionU and an interband exchangeJ. WithU=1.8 eV andJ=0.2 eV the self-consistent model solution yields aT=0 moment of about 2.04 µB and a Curie-temperature of 1044K. Details of the magnetic behaviour of Fe can be traced back to a striking temperature variation of the quasiparticle density of states. A novel explanation for the experimentally-observed non-collapsing exchange splitting is demonstrated in terms of the temperature-dependent spectral density for wave-vectors near the -point. Typical differences in the magnetic behaviour of Fe and Ni are worked out. 相似文献
10.
The magnetic phase transitions and the magnetocaloric effects in MnNi1−xCoxGe (x=0.38 and 0.40) alloys were investigated. The substitution of Co for Ni in the MnNiGe antiferromagnet results in the metamagnetic transitions from antiferromagnetic to ferromagnetic state, which associates with very small thermal and magnetic hystereses. Positive and negative values of magnetic entropy changes are exhibited around the metamagnetic transition temperature and Curie temperature, respectively. The relatively large refrigerant capacity in low magnetic field along with the good reversibility suggest that MnNi1−xCoxGe (x=0.38 and 0.40) alloys are potential candidates for magnetic refrigeration. 相似文献
11.
A. Maignan C. Martin M. Hervieu B. Raveau 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,13(1):41-45
The substitution of manganese for cobalt in the perovskite La
0.8
Sr
0.2
CoO
3
has been studied. A significant increase of the magnetoresistance (MR) is obtained, reaching 60% at 5 K under 7 T for . This behavior originates from a spectacular increase of the resistivity correlated to a significant decrease of ferromagnetism
by Mn doping. This enhancement of magnetoresistance can be interpreted by the growth of ferromagnetic clusters in the insulating
matrix, by applying a magnetic field.
Received 7 May 1999 相似文献
12.
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
13.
R. Staudt M. Dzierzawa A. Muramatsu 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,17(3):411-415
We investigate the phase diagram of the three-dimensional Hubbard model at half filling using quantum Monte Carlo (QMC) simulations.
The antiferromagnetic Néel temperature is determined from the specific heat maximum in combination with finite-size scaling of the magnetic structure factor. Our
results interpolate smoothly between the asymptotic solutions for weak and strong coupling, respectively, in contrast to previous
QMC simulations. The location of the metal-insulator transition in the paramagnetic phase above is determined using the electronic compressibility as criterion.
Received 11 April 2000 and Revised in final form 29 June 2000 相似文献
14.
Z. Németh Z. Homonnay F. Árva Z. Klencsár E. Kuzmann A. Vértes J. Hakl S. Mészáros K. Vad P. F. de Châtel G. Gritzner Y. Aoki H. Konno J. M. Greneche 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,57(3):257-263
Emission and transmission M?ssbauer studies of
La0.8Sr0.2CoO3-δ perovskites doped with ∼0.02
stoichiometric units of oxygen vacancy or 2.5% iron corroborate the
occurrence of electronic phase separation in these systems. The effect of
the small perturbation of the CoO3 sublattice with either iron ions or
oxygen vacancies on the bulk magnetization as well as on the M?ssbauer
spectra is in good agreement with the double exchange based cluster model.
The magnetoresistance does not show any peak near the Curie temperature, but
reaches -84% in a field of 7.5 T at T = 8 K. Below TC ≈
180 K the M?ssbauer spectra distinctly include the contribution from
paramagnetic and ferromagnetic regions, providing direct evidence for phase
separation. No contribution to the spectra from Fe4+ ions can be
observed, which is an unambiguous evidence that at low concentration iron
(either directly doped or formed from 57Co by nuclear decay) is
accommodated in the cobaltate lattice as Fe3+ ion. 相似文献
15.
A. Mirone S. S. Dhesi G. van der Laan 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,53(1):23-28
Orbital ordering (OO) in La0.5Sr1.5MnO4 has been
studied using soft X-ray resonant diffraction (SXRD) at the Mn L2,3 edges
in combination with many-body cluster calculations. The SXRD intensity is modelled in second quantization using a
small planar cluster consisting of a central active Mn site with first-neighbour shells comprising O and Mn sites.
The effective Hamiltonian includes Slater-Koster parameters and charge transfer and electron correlation
energies obtained from previous measurements on manganites. The
energy dependence of the SXRD OO peak is calculated using
the Jahn-Teller distortions of the oxygen octahedra and in-plane spin correlations as adjustable parameters. These contributions
are clearly distinguished above the Néel temperature with a good spectroscopic agreement.
The results also suggest a significant charge separation between the Mn sites. 相似文献
16.
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
17.
L. Brossard R. Clerac C. Coulon M. Tokumoto T. Ziman D.K. Petrov V.N. Laukhin M.J. Naughton A. Audouard F. Goze A. Kobayashi H. Kobayashi P. Cassoux 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,1(4):439-452
In order to understand the magnetic field-induced restoration of a highly conductive state in , static (SQUID) and dynamic (ESR and AFR) magnetization measurements were performed on polycrystalline samples and single
crystals, respectively. In addition, cantilever and resistivity measurements under steady fields were performed. While the
metal-insulator transition curve of the () phase diagram exhibits a first order character, a “spin-flop” transition line divides the insulating state when the magnetic
field is applied along the easy axis of magnetization. The effects of a RKKY-type indirect exchange and of applied magnetic
field are described within the framework of a generalized Kondo lattice, namely two chains of localised spins coupled through the itinerant spins of the 2D sheets of BETS. The calculations, which can incorporate intramolecular
electron correlations within a mean field theory, are in qualitative agreement with the field induced transition from the
antiferromagnetic insulating ground state to a canted one, i.e. a not fully oriented paramagnetic, but metallic state.
Received: 6 August 1997 / Received: 5 November 1997 / Accepted: 10 November 1997 相似文献
18.
M. Stebelski M. Lisowski E. Zipper 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,1(2):215-222
Quantum coherence of electrons interacting via the magnetostatic coupling and confined to a mesoscopic cylinder is discussed. The electromagnetic response of a system is
studied. It is shown that the electromagnetic kernel has finite low frequency limit what implies infinite conductivity. It
means that part of the electrons is in a coherent state and the system can be in general described by a two-fluid model. The
coherent behavior is determined by the interplay between finite size effects and the correlations coming from the magnetostatic
interactions (the interaction is considered in the mean field approximation). The related persistent currents depend on the
geometry of the Fermi surface. If the Fermi surface has some flat portions the self-sustaining currents can be obtained. The
relation of the quantum coherent state in mesoscopic cylinders to other coherent phenomena is discussed.
Received: 9 July 1997 / Revised: 19 September 1997 / Accepted: 4 November 1997 相似文献
19.
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
20.
We consider dynamical correlation functions of short range interacting electrons in one dimension at finite temperature. Below a critical value of the chemical potential there is no Fermi surface anymore, and the system can no longer be described as a Luttinger liquid. Its low temperature thermodynamics is that of an ideal gas. We identify the impenetrable electron gas model as a universal model for the gas phase and present exact and explicit expressions for the asymptotics of correlation functions at small temperatures, in the presence of a magnetic field. 相似文献