共查询到20条相似文献,搜索用时 15 毫秒
1.
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
2.
S. Fratini P. Quémerais 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,29(1):41-49
We consider a three dimensional Wigner crystal of electrons lying in a host ionic dielectric. Owing to their interaction with
the lattice polarization, each localized electron forms a polaron. We study the collective excitations of such a polaronic
Wigner crystal at zero temperature, taking into account the quantum fluctuations of the polarization within the Feynman harmonic
approximation. We show that, contrary to the ordinary electron crystal, the system undergoes a polarization catastrophe when
the density is increased. An optical signature of this instability is derived, whose trend agrees with the experiments carried
out in Nd-based cuprates.
Received 4 July 2002 Published online 17 September 2002 相似文献
3.
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
4.
U. Fasol E. Dormann 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,26(4):455-465
The electron-spin resonance (ESR) line of delocalised electrons shifts upon saturation due to the hyperfine interaction with
the dynamically polarized nuclear spins. The
29
Si part of the Overhauser shift of the ESR line of phosphorus doped silicon (Si:P) is separated in the concentration range 2.7
... 7.3×10
18
/
cm
3
covering the metal-insulator transition. The Overhauser shift profiles, recorded versus
29
Si nuclear magnetic resonance (NMR) frequency, are asymmetric. Their dependence on temperature and ESR saturation compares reasonably
with simulations. Time and NMR frequency dependence of the dynamic nuclear polarization is studied in detail. No pronounced
variation of the
29
Si Overhauser shift profiles with P concentration is observed, but the maximum value of the shift profile decreases with increasing
P concentration. In contrast to standard
29
Si NMR results, these measurements reveal the behaviour of the
29
Si nuclei close to the P doping sites.
Received 8 November 2001 相似文献
5.
F. Fauth E. Suard V. Caignaert B. Domengès I. Mirebeau L. Keller 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,21(2):163-174
The oxygen deficient cobaltites LnBaCo2O5 (Ln = Tb, Dy, Ho) exhibit two successive crystallographic transitions at T
N
∼340 K and at T
CO
∼210 K. Whereas the first transition (P4/mmm to Pmmm) is related to the long-range antiferromagnetic ordering of the Co ions
(spin ordering), the second transition (Pmmm to Pmmb) corresponds to the long-range ordering of the Co2+ and Co3+ species (charge ordering) occurring in 1:1 ratio in the structure. The charge ordered (CO) state was directly evidenced by
the observation of additional superstructure peaks using neutron and electron diffraction techniques. The CO state was also
confirmed indirectly from refinement of high resolution neutron diffraction data as well as from resistivity and DSC measurements.
From the refined saturated magnetic moment values only, ∼3.7
and ∼2.7
, the electronic configuration of the Co ions in LnBaCo2O5 remains conjectural. Two pictures, with Co3+ ions either in intermediate spin state ( t
5
2g
e
1
g
) or in high spin state ( t
4
2g
e
2
g
), describe equally well our experimental data. In both cases, the observed magnetic structure can be explained using the
qualitative Goodenough-Kanamori rules for superexchange. Finally, in contrast to the parent Ln = Y compound [Vogt et al. , Phys. Rev. Lett. 84, 2969 (2000)], we do not report any spin transition in LnBaCo2O5 (Ln = Tb, Dy, Ho).
Received 13 December 2000 相似文献
6.
T. Döppner Th. Diederich J. Tiggesbäumker K.-H. Meiwes-Broer 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,16(1):13-16
Magnesium clusters grown in helium droplets and ionized with femtosecond laser pulses have been studied by high resolution
mass spectrometry. For moderate laser intensities the abundance spectra show characteristic features indicating electronic
shell effects. Compared to clusters of s1-electron metals additional shell closures appear resulting from an electron rearrangement. Irradiation with higher laser
intensities leads to a decomposition of the magnesium clusters into atomic ions. Due to charge exchange with the surrounding
helium matrix mainly singly and doubly charged magnesium ions remain. In addition, the occurrence of MgHeN
+-complexes is observed. Their abundance depends on the shape of the laser field, i.e. the laser width and the optical delay when applying the pump-probe technique.
Received 2 January 2001 相似文献
7.
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
8.
R. Zitzler Th. Pruschke R. Bulla 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,27(4):473-481
We discuss the ground state magnetic phase diagram of the Hubbard model off half filling within the dynamical mean-field theory.
The effective single-impurity Anderson model is solved by Wilson's numerical renormalization group calculations, adapted to
symmetry broken phases. We find a phase separated, antiferromagnetic state up to a critical doping for small and intermediate
values of U, but could not stabilize a Néel state for large U and finite doping. At very large U, the phase diagram exhibits an island with a ferromagnetic ground state. Spectral properties in the ordered phases are discussed.
Received 9 January 2002 Published online 25 June 2002 相似文献
9.
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
10.
Y. Ōno R. Bulla A.C. Hewson 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,19(3):375-384
The Mott metal-insulator transition in the two-band Hubbard model in infinite dimensions is studied by using the linearized
dynamical mean-field theory recently developed by Bulla and Potthoff. The phase boundary of the metal-insulator transition
is obtained analytically as a function of the on-site Coulomb interaction at the d-orbital, the charge-transfer energy between the d- and p-orbitals and the hopping integrals between p-d, d-d and p-p orbitals. The result is in good agreement with the numerical results obtained from the exact diagonalization method.
Received 5 October 2000 and Received in final form 8 December 2000 相似文献
11.
X. Waintal J.-L. Pichard 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,1(1):117-121
For N interacting particles in a one dimensional random potential, we study the structure of the corresponding network in Hilbert
space. The states without interaction play the role of the “sites”. The hopping terms are induced by the interaction. When
the one body states are localized, we numerically find that the set of directly connected “sites” is multifractal. For the
case of two interacting particles, the fractal dimension associated to the second moment of the hopping term is shown to characterize
the Golden rule decay of the non interacting states and the enhancement factor of the localization length.
Received: 17 April 1998 / Accepted: 14 May 1998 相似文献
12.
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
13.
14.
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
15.
A. Perali M. Sindel G. Kotliar 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,24(4):487-503
A number of normal state transport properties of cuprate superconductors are analyzed in detail using the Boltzmann equation.
The momentum dependence of the electronic structure and the strong momentum anisotropy of the electronic scattering are included
in a phenomenological way via a multi-patch model. The Brillouin zone and the Fermi surface are divided in regions where scattering between the electrons
is strong and the Fermi velocity is low (hot patches) and in regions where the scattering is weak and the Fermi velocity is
large (cold patches). We present several motivations for this phenomenology starting from various microscopic approaches.
A solution of the Boltzmann equation in the case of N patches is obtained and an expression for the distribution function away from equilibrium is given. Within this framework,
and limiting our analysis to the two patches case, the temperature dependence of resistivity, thermoelectric power, Hall angle,
magnetoresistance and thermal Hall conductivity are studied in a systematic way analyzing the role of the patch geometry and
the temperature dependence of the scattering rates. In the case of Bi-based cuprates, using ARPES data for the electronic
structure, and assuming an inter-patch scattering between hot and cold states with a linear temperature dependence, a reasonable
agreement with the available experiments is obtained.
Received 3 August 2001 and Received in final form 1st November 2001 相似文献
16.
X. Waintal D. Weinmann J.-L. Pichard 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,7(3):451-456
For two particles in a disordered chain of length L with on-site interaction U, a duality transformation maps the behavior at weak interaction onto the behavior at strong interaction. Around the fixed
point of this transformation, the interaction yields a maximum mixing of the one body states. When (the one particle localization length), this mixing results in weak chaos accompanied by multifractal wave functions and
critical spectral statistics, as in the one particle problem at the mobility edge or in certain pseudo-integrable billiards.
In one dimension, a local interaction can only yield this weak chaos but can never drive the two particle system to full chaos
with Wigner-Dyson statistics.
Received: 22 May 1998 / Received in final form: 24 August 1998 / Accepted: 4 September 1998 相似文献
17.
S. De Toro Arias X. Waintal J.-L. Pichard 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,10(1):149-158
The interplay between the quantum interferences responsible for one particle localization over a length L1, and the partial dephasing induced by a local interaction of strength U with another particle leading to partial delocalization over a length L
2
> L
1
, is illustrated by a study of the motion of two particles put close to each other at the initial time. Localization is reached
in two steps. First, before the time t1 necessary to propagate over L1, the interaction slows down the ballistic motion. On the contrary, after t1 the interaction favors a very slow delocalization, characterized by a spreading of the center of mass, until L2 is reached. This slow motion is related to the absence of quantum chaos in this one dimensional model, the interaction being
only able to induce weaker chaos with critical spectral statistics. Under appropriate initial conditions, the motion remains
invariant under the duality transformation mapping the behavior at small U onto the behavior at large U.
Received 24 August 1998 相似文献
18.
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
19.
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
20.
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