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1.
G. De Smedt C. Godrèche J.M. Luck 《The European Physical Journal B - Condensed Matter and Complex Systems》2003,32(2):215-225
We consider a ferromagnetic Ising chain evolving under Kawasaki dynamics at zero temperature. We investigate the statistics
of the blocking time, as well as various characteristics of the metastable configurations reached by the system, including
the statistics of the final energy, the spin correlations, and the distribution of domain sizes. Results of extensive numerical
simulations are compared with analytical predictions made for the a priori ensemble of all blocked configurations with equal weights. Qualitative differences are found, e.g. in the domain sizes, which are found to be neither statistically independent nor exponentially distributed.
Received 24 October 2002 / Received in final form 13 January 2003 Published online 1st April 2003
RID="a"
ID="a"e-mail: luck@spht.saclay.cea.fr
RID="b"
ID="b"URA 2306 of CNRS 相似文献
2.
L. Berthier 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,17(4):689-692
We study analytically the aging dynamics of the O(n) model in the limit of , with conserved and with non-conserved order parameter. While in the non-conserved dynamics, the autocorrelation function
scales in the usual way , in the case of a conserved order parameter, `multiscaling' manifests itself in the form , with a relaxation time growing more slowly than the age of the system (sub-aging), and h(t) a function growing faster than any length scale of the problem. In both cases, the effective temperature associated to the
violation of the fluctuation theorem tends to infinity in the asymptotic limit of large waiting times.
Received 15 May 2000 and Received in final form 5 July 2000 相似文献
3.
M. Picco F. Ricci-Tersenghi F. Ritort 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,21(2):211-217
We present a detailed study of the scaling behavior of correlations functions and AC susceptibility relaxations in the aging
regime in three-dimensional spin glasses. The agreement between simulations and experiments is excellent confirming the validity
of the full aging scenario with weak sub-aging effects.
Received 21 December 2000 and Received in final form 22 February 2001 相似文献
4.
D. Karevski Y-C. Lin H. Rieger N. Kawashima F. Iglói 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,20(2):267-276
We study the critical behavior of Ising quantum magnets with broadly distributed random couplings (J), such that P(ln J) ∼ | ln J|-1 - α, α > 1, for large | ln J| (Lévy flight statistics). For sufficiently broad distributions, α < , the critical behavior is controlled by a line of fixed points, where the critical exponents vary with the Lévy index, α.
In one dimension, with = 2, we obtained several exact results through a mapping to surviving Riemann walks. In two dimensions the varying critical
exponents have been calculated by a numerical implementation of the Ma-Dasgupta-Hu renormalization group method leading to
≈ 4.5. Thus in the region 2 < α < , where the central limit theorem holds for | ln J| the broadness of the distribution is relevant for the 2d quantum Ising model.
Received 6 December 2000 and Received in final form 22 January 2001 相似文献
5.
H. Maury P. Jonnard K. Le Guen J. -M. André Z. Wang J. Zhu J. Dong Z. Zhang F. Bridou F. Delmotte C. Hecquet N. Mahne A. Giglia S. Nannarone 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,61(2):193-199
The interplay between optical performance and the thermally activated interface chemistry of periodic Mg/SiC multilayers designed for application at 30.4 nm are investigated by optical (hard X-ray, soft X-ray and ultraviolet ranges, i.e. from 0.154 to 30.4 nm) reflectivity and X-ray emission spectroscopy. The multilayers are prepared by magnetron sputtering and then annealed up to a temperature of 500 °C. Two clear changes take place in the multilayer upon annealing. At first, between 200 and 300 °C a strong decrease of the reflectivity is observed, due to the development of interfacial roughness following the crystallization of the Mg layers. No interfacial compound is detected. Then, between 350 and 400 °C there is formation of the Mg2Si magnesium silicide at the interfaces following the reaction between the Mg and SiC layers. This also leads to the almost total loss of reflectivity of the multilayer. Thus, this kind of multilayer is thermally stable only for application requiring no heating above 200 °C. 相似文献
6.
R. Mélin K. Biljaković J.C. Lasjaunias P. Monceau 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,26(4):417-430
We show that the dynamics of disordered charge density waves (CDWs) and spin density waves (SDWs) is a collective phenomenon.
The very low temperature specific heat relaxation experiments are characterized by: (i) “interrupted” ageing (meaning that
there is a maximal relaxation time); and (ii) a broad power-law spectrum of relaxation times which is the signature of a collective
phenomenon. We propose a random energy model that can reproduce these two observations and from which it is possible to obtain
an estimate of the glass cross-over temperature (typically T
g≃ 100-200 mK). The broad relaxation time spectrum can also be obtained from the solutions of two microscopic models involving
randomly distributed solitons. The collective behavior is similar to domain growth dynamics in the presence of disorder and
can be described by the dynamical renormalization group that was proposed recently for the one dimensional random field Ising
model [D.S. Fisher, P. Le Doussal, C. Monthus, Phys. Rev. Lett. 80, 3539 (1998)]. The typical relaxation time scales like ∼τexp(T
g/T). The glass cross-over temperature Tg related to correlations among solitons is equal to the average energy barrier and scales like T
g∼ 2xξΔ. x is the concentration of defects, ξ the correlation length of the CDW or SDW and Δ the charge or spin gap.
Received 12 December 2001 相似文献
7.
M. Picco F. Ritort M. Sales 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,19(4):565-582
The use of parameters measuring order-parameter fluctuations (OPF) has been encouraged by the recent results reported in referenece
[2,3] which show that two of these parameters, G and G
c, take universal values in the . In this paper we present a detailed study of parameters measuring OPF for two mean-field models with and without time-reversal
symmetry which exhibit different patterns of replica symmetry breaking below the transition: the Sherrington-Kirkpatrick model
with and without a field and the Ising p-spin glass (p = 3). We give numerical results and analyze the consequences which replica equivalence imposes on these models in the infinite
volume limit. We give evidence for the transition in each system and discuss the character of finite-size effects. Furthermore,
a comparative study between this new family of parameters and the usual Binder cumulant analysis shows what kind of new information
can be extracted from the finite T behavior of these quantities. The two main outcomes of this work are: 1) Parameters measuring OPF give better estimates than
the Binder cumulant for T
c and even for very small systems they give evidence for the transition. 2) For systems with no time-reversal symmetry, parameters
defined in terms of connected quantities are the proper ones to look at.
Received 20 September 2000 and Received in final form 10 January 2001 相似文献
8.
P. Podio-Guidugli G. Tomassetti 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,26(2):191-198
A new derivation is presented of Walker's exact solution to Gilbert equation, a solution which mimicks the travelling-wave
motion of a flat domain wall at 180°. It is shown that a process during which the working of the applied magnetic field exactly compensates dissipation (the Walker
condition) exists both under the constitutive circumstances considered in the standard Gilbert equation and when either the
internal free-energy or the dissipation, or both, are generalized by the introduction of higher-gradient terms; but that such
a process cannot solve the generalized Gilbert equation. It is also shown that, when dry-friction dissipation is considered
and a suitable magnetic field is applied, the associated Gilbert equation has a Walker-type solution mimicking a flat wall,
at 90° this time, which however does not satisfy the Walker condition.
Received 16 November 2001 相似文献
9.
10.
T.J. Smith H. Capellmann R.K. Kremer K-U. Neumann K.R.A. Ziebeck 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,21(3):341-347
A polarised neutron scattering investigation has been carried out on a powder sample of CuGeO3 within the temperature range of 1.5 K to 600 K. The magnetic scattering has been separated from all other contributions by
using polarised neutrons and polarisation analysis and placed onto an absolute scale. At low temperatures the long wavelength
components of the paramagnetic response are suppressed consistent with the formation of Cu dimers in which the magnetic moments
are correlated antiferromagnetically. This form of the scattering persists to temperatures well above the dimerisation temperature
T
sp
∼ 14 K. However as the temperature is raised the intensity of the long wavelength spin fluctuations increases and above ∼150 K they are the dominant feature in the wave vector dependence of the response. At all temperatures the observed scattering
extrapolates smoothly to the Q
= 0 value given by the uniform susceptibility. Consequently the thermal variation of the uniform susceptibility arises from the
evolution of the long wavelength magnetic fluctuations. At large wave vectors the energy dependence of the scattering revealed
that the response occurs below 16 meV in agreement with the reported maximum magnetic excitation energy at the zone boundary
in the ground state. However the total magnetic scattering is significantly less than that expected for a local moment system
suggesting that the spectrum of thermal and quantum fluctuations overlap.
Received 30 May 2000 and Received in final form 22 March 2001 相似文献
11.
J. Gemmer G. Mahler 《The European Physical Journal B - Condensed Matter and Complex Systems》2003,31(2):249-257
For a closed bi-partite quantum system partitioned into system proper and environment we interpret the microcanonical and
the canonical condition as constraints for the interaction between those two subsystems. In both cases the possible pure-state
trajectories are confined to certain regions in Hilbert space. We show that in a properly defined thermodynamical limit almost
all states within those accessible regions represent states of some maximum local entropy. For the microcanonical condition
this dominant state still depends on the initial state; for the canonical condition it coincides with that defined by Jaynes'
principle. It is these states which thermodynamical systems should generically evolve into.
Received 13 June 2002 / Received in final form 14 November 2002 Published online 4 February 2003
RID="a"
ID="a"e-mail: jochen@theol.physik.uni-stuttgart.de 相似文献
12.
C. Djurberg K. Jonason P. Nordblad 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,10(1):15-21
Experiments on the temperature and time dependence of the response function and the field cooled magnetisation of a Cu(Mn)
spin glass at temperatures below the zero field spin glass temperature are used to explore the non-equilibrium nature of the
underlying spin configuration. The results imply that a certain spin configuration is imprinted on the system as the temperature
is decreased at a constant cooling rate. The cooling rate governs the magnitude of the FC magnetisation ((H,T)). Any intermittent halt at a constant temperature, , imprints an extended spin configuration, a process that is reflected e.g. in a downward relaxation of . On continued cooling at the same rate, the magnitude of (T) remains at a lower level than that of a continuous cooling curve. These results are put into the context of the corresponding
behaviour of the response function as observed in measurements of the relaxation of the zero field cooled magnetisation.
Received 27 October 1998 and Received in final form 30 November 1998 相似文献
13.
I.I. Satija 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,29(2):345-348
Disordered systems exhibiting exponential localization are mapped to anisotropic spin chains with localization length being
related to the anisotropy of the spin model. This relates localization phenomenon in fermions to the rotational symmetry breaking
in the critical spin chains. One of the intriguing consequence is that the statement of Onsager universality in spin chains
implies universality of the localized fermions where the fluctuations in localized wave functions are universal. We further
show that the fluctuations about localized nonrelativistic fermions describe relativistic fermions. This provides a new approach
to understand the absence of localization in disordered Dirac fermions. We investigate how disorder affects well known universality
of the spin chains by examining the multifractal exponents. Finally, we examine the effects of correlations on the localization
characteristics of relativistic fermions.
Received 28 September 2001 / Received in final form 30 November 2001 Published online 2 October 2002
RID="a"
ID="a"e-mail: isatija@nickel.nist.gov 相似文献
14.
P. Podio-Guidugli 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,19(3):417-424
Within the framework of a dynamic version of micromagnetics [1,2], the space-time evolution of magnetization in a rigid, saturated ferromagnet is governed by the following equation: γ-1
= ×( + + div
), where the interaction couple × and the couple stress are to be constitutively specified. Under constitutive assumptions for , , and the free energy ψ, that allow for equilibrium response and viscosity out of equilibrium and agree with the dissipation
principle -
.
+
. ∇ - ≥ 0, the above evolution equation yields a broad generalization of the standard Gilbert equation. In particular, while the
standard Gilbert equation only incorporates relativistic dissipation, it is shown that the dissipation mechanisms compatible
with the generalized Gilbert equation include exchange dissipation [2], dry-friction dissipation [3], and others. It is also
shown that the additional term proposed in [4] to account for exchange dissipation, rather than having a genuine dissipative
nature, modifies instead the nature of possible equilibria; and that such a modification is an automatic side effect when
dry-friction dissipation is incorporated in the manner of [3].
Received 31 October 2000 相似文献
15.
T. Saikawa A. Ferraz 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,3(1):17-22
Dynamical properties of the spin and charge response functions in the doped two-dimensional Hubbard model are calculated by
taking into account the drastic separation of the single-particle spectral function into the low-energy coherent and high-energy
incoherent parts due to the strong Coulomb interaction. We show that this evolution of the electronic states is the origin
of the broad and structureless feature in the charge response function. In the weak coupling regime the low-energy enhancement
of the spin excitation is produced which can be explained within the random phase approximation. However, for the larger interaction
close to the antiferromagnetic Stoner condition, the low-energy intensity of the spin excitation is suppressed.
Received: 25 September 1997 / Revised: 19 December 1997 / Accepted: 9 January 1998 相似文献
16.
A. Furrer H.-U. Güdel 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,16(1):81-84
The inelastic neutron scattering technique was employed to study the magnetic excitation spectra in the diluted one-dimensional
Heisenberg antiferromagnet CsMn1-xMgxBr3 (x
=0, 0.05, 0.10, 0.25, 0.50). The spectral response is interpreted in terms of spin-wave excitations in finite chain segments
of Mn2+ ions, which are found to exist as long as the chain length exceeds twice the wavelength of the spin excitation. This limit
determines the crossover into the mesoscopic regime.
Received 31 December 1999 相似文献
17.
18.
J. Gemmer M. Michel 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,53(4):517-528
We consider discrete quantum systems coupled to finite environments which may possibly consist of only one particle in contrast
to the standard baths which usually consist of continua of oscillators, spins, etc.
We find that such finite environments may, nevertheless, act as thermostats, i.e., equilibrate the system though not necessarily
in the way predicted by standard open system techniques.
Thus, we apply a novel technique called the Hilbert space Average Method (HAM) and verify its results numerically. 相似文献
19.
M.N. Kiselev H. Feldmann R. Oppermann 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,22(1):53-63
We represent the generators of the SU(N) algebra as bilinear combinations of Fermi operators with imaginary chemical potential. The distribution function, consisting
of a minimal set of discrete imaginary chemical potentials, is introduced to satisfy the local constraints. This representation
leads to the conventional temperature diagram technique with standard Feynman codex, except that the Matsubara frequencies
are determined by neither integer nor half-integer numbers. The real-time Schwinger-Keldysh formalism is formulated in the
framework of complex equilibrium distribution functions for auxiliary semi-fermionic fields. We discuss the continuous large
N and SU(2) large spin limits. We illustrate the application of this technique for magnetic and spin-liquid states of the Heisenberg
model.
Received 26 February 2001 and Received in final form 25 April 2001 相似文献
20.
A new and rather trivial model is suggested with mechanism that implies simultaneous violation of the zeroth and the second
laws of thermodynamics. Mathematically rigorous quantum theory reduces to a trivial application of the Golden rule formula.
It yields exciton on-energy-shell diffusion caused by bath-nonassisted excitation hopping between tails of different exciton
site levels ε1 < ε2 broadened by bath-assisted finite life-time effects. The elastic character of the hopping implies 1 ↔ 2-symmetric transfer
rate W. Thus the net diffusion exciton flow W(P
1 - P
2) and also, as argued, the net energy flow are possible due to different near-to-equilibrium exciton populations P
1 > P
2. As the sites are provided with two different baths, the population imbalance and the flows survive even for slightly different
local bath temperatures T
1 < T
2 < T
1ε2/ε1. Thus spontaneous exciton and also energy flows against temperature step become possible, in contradiction with the Clausius
form of the second law. Violations of both the laws disappear in the high-temperature, i.e. classical limit
Received 16 May 2001 and Received in final form 20 September 2001 相似文献