547 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
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
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
Evidence of aging in mean-field spin glass models
We study numerically the out of equilibrium dynamics of the hypercubic cell
spin glass in high dimensionalities. We obtain evidence of aging effects
qualitatively similar both to experiments and to simulations of low dimensional
models. This suggests that the Sherrington-Kirkpatrick model as well as other
mean-field finite connectivity lattices can be used to study these effects
analytically.Comment: 13 pages + 5 figures (upon request
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
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
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