2,126 research outputs found
Symmetrical Temperature-Chaos Effect with Positive and Negative Temperature Shifts in a Spin Glass
The aging in a Heisenberg-like spin glass Ag(11 at% Mn) is investigated by
measurements of the zero field cooled magnetic relaxation at a constant
temperature after small temperature shifts . A
crossover from fully accumulative to non-accumulative aging is observed, and by
converting time scales to length scales using the logarithmic growth law of the
droplet model, we find a quantitative evidence that positive and negative
temperature shifts cause an equivalent restart of aging (rejuvenation) in terms
of dynamical length scales. This result supports the existence of a unique
overlap length between a pair of equilibrium states in the spin glass system.Comment: 4 page
Time and length scales in spin glasses
We discuss the slow, nonequilibrium, dynamics of spin glasses in their glassy
phase. We briefly review the present theoretical understanding of the
spectacular phenomena observed in experiments and describe new numerical
results obtained in the first large-scale simulation of the nonequilibrium
dynamics of the three dimensional Heisenberg spin glass.Comment: Paper presented at "Highly Frustrated Magnetism 2003", Grenoble,
August 200
Interference Commensurate Oscillations in Q1D Conductors
We suggest an analytical theory to describe angular magnetic oscillations
recently discovered in quasi-one-dimensional conductor (TMTSF)2PF6 [see Phys.
Rev. B, 57, 7423 (1998)] and define the positions of the oscillation minima.
The origin of these oscillations is related to interference effects resulting
from an interplay of quasi-periodic and periodic ("commensurate") electron
trajectories in an inclined magnetic field. We reproduce via calculations
existing experimental data and predict some novel effects.Comment: 10 pages, 2 figure
Step-wise responses in mesoscopic glassy systems: a mean field approach
We study statistical properties of peculiar responses in glassy systems at
mesoscopic scales based on a class of mean-field spin-glass models which
exhibit 1 step replica symmetry breaking. Under variation of a generic external
field, a finite-sized sample of such a system exhibits a series of step wise
responses which can be regarded as a finger print of the sample. We study in
detail the statistical properties of the step structures based on a low
temperature expansion approach and a replica approach. The spacings between the
steps vanish in the thermodynamic limit so that arbitrary small but finite
variation of the field induce infinitely many level crossings in the
thermodynamic limit leading to a static chaos effect which yields a
self-averaging, smooth macroscopic response. We also note that there is a
strong analogy between the problem of step-wise responses in glassy systems at
mesoscopic scales and intermittency in turbulent flows due to shocks.Comment: 50 pages, 18 figures, revised versio
Memory and chaos in an Ising spin glass
The non-equilibrium dynamics of the model 3d-Ising spin glass
- FeMnTiO - has been investigated from the temperature
and time dependence of the zero field cooled magnetization recorded under
certain thermal protocols. The results manifest chaos, rejuvenation and memory
features of the equilibrating spin configuration that are very similar to those
observed in corresponding studies of the archetypal RKKY spin glass Ag(Mn). The
sample is rapidly cooled in zero magnetic field, and the magnetization recorded
on re-heating. When a stop at constant temperature is made during the
cooling, the system evolves toward its equilibrium state at this temperature.
The equilibrated state established during the stop becomes frozen in on further
cooling and is retrieved on re-heating. The memory of the aging at is not
affected by a second stop at a lower temperature
. Reciprocally, the first equilibration at has no influence on
the relaxation at , as expected within the droplet model for domain
growth in a chaotic landscape.Comment: REVTeX style; 4 pages, 4 figure
Energy landscapes in random systems, driven interfaces and wetting
We discuss the zero-temperature susceptibility of elastic manifolds with
quenched randomness. It diverges with system size due to low-lying local
minima. The distribution of energy gaps is deduced to be constant in the limit
of vanishing gaps by comparing numerics with a probabilistic argument. The
typical manifold response arises from a level-crossing phenomenon and implies
that wetting in random systems begins with a discrete transition. The
associated ``jump field'' scales as and for
(1+1) and (2+1) dimensional manifolds with random bond disorder.Comment: Accepted for publication in Phys. Rev. Let
Rejuvenation in the Random Energy Model
We show that the Random Energy Model has interesting rejuvenation properties
in its frozen phase. Different `susceptibilities' to temperature changes, for
the free-energy and for other (`magnetic') observables, can be computed
exactly. These susceptibilities diverge at the transition temperature, as
(1-T/T_c)^-3 for the free-energy.Comment: 9 pages, 1 eps figur
Generalized susceptibility of quasi-one dimensional system with periodic potential: model for the organic superconductor (TMTSF)ClO
The nesting vector and the magnetic susceptibility of the
quasi-one-dimensional system having imperfectly nested Fermi surface are
studied analytically and numerically. The magnetic susceptibility has the
plateau-like maximum in ``\textit{sweptback}'' region in the momentum space,
which is surrounded by ( is the
Fermi wave number, , and , and
are given in this paper). The best nesting vector, at which
the susceptibility has the absolute maximum at T=0, is
obtained near but not at the inflection point, . The effect of the periodic potential on the
susceptibility is studied, which is important for the successive transitions of
the field-induced spin density wave in (TMTSF)ClO. We obtain that the
sweptback region (surrounded by , and
when ) becomes small as increases and it shrinks to
for , where gives the degree of imperfect
nesting of the Fermi surface, i.e. the second harmonics of the warping in the
Fermi surface. The occurrence of the sign reversal of the Hall coefficient in
the field-induced spin density wave states is discussed to be possible only
when , where is the amplitude of the fourth harmonics of
the warping in the Fermi surface. This gives the novel limitation for the
magnitude of
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