619 research outputs found
Monte-Carlo simulations of the violation of the fluctuation-dissipation theorem in domain growth processes
Numerical simulations of various domain growth systems are reported, in order
to compute the parameter describing the violation of fluctuation dissipation
theorem (FDT) in aging phenomena. We compute two-times correlation and response
functions and find that, as expected from the exact solution of a certain
mean-field model (equivalent to the O(N) model in three dimensions, in the
limit of N going to infinity), this parameter is equal to one (no violation of
FDT) in the quasi-equilibrium regime (short separation of times), and zero in
the aging regime.Comment: 5 pages, 5 eps figure
Memory effects in classical and quantum mean-field disordered models
We apply the Kovacs experimental protocol to classical and quantum p-spin
models. We show that these models have memory effects as those observed
experimentally in super-cooled polymer melts. We discuss our results in
connection to other classical models that capture memory effects. We propose
that a similar protocol applied to quantum glassy systems might be useful to
understand their dynamics.Comment: 24 pages, 12 figure
Dynamical fluctuations in an exactly solvable model of spin glasses
In this work we calculate the dynamical fluctuations at O(1/N) in the low
temperature phase of the spherical spin glass model. We study the
large-times asymptotic regimes and we find, in a short time-differences regime,
a fluctuation dissipation relation for the four-point correlation functions.
This relation can be extended to the out of equilibrium regimes introducing a
function which, for large time , we find scales as as in
the case of the two-point functions.Comment: Latex, 8 page
Effective temperature of a dissipative driven mesoscopic system
We study the nonequilibrium dynamics of a mesoscopic metallic ring threaded
by a time-dependent magnetic field and coupled to an electronic reservoir. We
analyze the relation between the (non-stationary) real-time Keldysh and
retarded Green functions and we find that, in the linear response regime with
weak heat transfer to the environment, an effective temperature accounts for
the modification of the equilibrium fluctuation-dissipation relation. We
discuss possible extensions of this analysis.Comment: 4 pages, 4 figures, RevTe
Dissipative quantum disordered models
This article reviews recent studies of mean-field and one dimensional quantum
disordered spin systems coupled to different types of dissipative environments.
The main issues discussed are: (i) The real-time dynamics in the glassy phase
and how they compare to the behaviour of the same models in their classical
limit. (ii) The phase transition separating the ordered -- glassy -- phase from
the disordered phase that, for some long-range interactions, is of second order
at high temperatures and of first order close to the quantum critical point
(similarly to what has been observed in random dipolar magnets). (iii) The
static properties of the Griffiths phase in random Ising chains. (iv) The
dependence of all these properties on the environment. The analytic and numeric
techniques used to derive these results are briefly mentioned.Comment: Contribution to the 12th International Conference on Recent Progress
in Many-Body Theories, Santa Fe, New Mexico, USA, August 2004; 10 pages no
fig
Comment on "Fluctuation-dissipation relations in the nonequilibrium critical dynamics of Ising models"
Recently Mayer et al. [Phys. Rev. E {\bf 68}, 016116 (2003)] proposed a new
way to compute numerically the fluctuation-dissipation ratios in nonequilibrium
critical systems. Using well-known facts of nonequilibrium critical dynamics I
show that the leading contributions of the quantities they consider are in fact
one-time quantities which are independent of the waiting time. The ratio of
these one-time quantities determines the slope of the straight lines observed
in the fluctuation-dissipation plots of Mayer et al.Comment: 4 pages, 3 figures included, shortened versio
Out-of-equilibrium thermodynamic relations in systems with aging and slow relaxation
The experimental time scale dependence of thermodynamic relations in
out-of-equilibrium systems with aging phenomena is investigated theoretically
by using only aging properties of the two-time correlation functions and the
generalized fluctuation-dissipation theorem (FDT). We show that there are two
experimental time regimes characterized by different thermal properties. In the
first regime where the waiting time is much longer than the measurement time,
the principle of minimum work holds even though a system is out of equilibrium.
In the second regime where both the measurement time and the waiting time are
long, the thermal properties are completely different from properties in
equilibrium. For the single-correlation-scale systems such as -spin
spherical spin-glasses, contrary to a fundamental assumption of thermodynamics,
the work done in an infinitely slow operation depends on the path of change of
the external field even when the waiting time is infinite. On the other hand,
for the multi-correlation-scale systems such as Sherrington-Kirkpatrick model,
the work done in an infinitely slow operation is independent of the path. Our
results imply that in order to describe thermodynamic properties of systems
with aging it is essential to consider the experimental time scales and history
of a system as a state variable is necessary.Comment: 28 pages(REVTeX), 4 figure(EPS). To be published in Phys. Rev.
Off-Equilibrium Effective Temperature in Monatomic Lennard-Jones Glass
The off-equilibrium dynamics of a monatomic Lennard-Jones glass is
investigated after sudden isothermal density jumps (crunch) from well
equilibrated liquid configurations towards the glassy state. The generalized
fluctuation-dissipation relation has been studied and the temperature
dependence of the violation factor m is found in agreement with the one step
replica symmetry breaking scenario, i.e. at low temperature m(T) is found
proportional to T up to an off-equilibrium effective temperature T_eff, where
m(T_eff)=1. We report T_eff as a function of the density and compare it with
the glass transition temperatures T_g as determined by equilibrium
calculations.Comment: 4 pages,4 figure
Relaxation dynamics of the Ising -spin disordered model with finite number of variables
We study the dynamic and metastable properties of the fully connected Ising
-spin model with finite number of variables. We define trapping energies,
trapping times and self correlation functions and we analyse their statistical
properties in comparison to the predictions of trap models.Comment: 7 pages, 6 figures, final versio
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