25 research outputs found
Glassy dynamics in thin films of polystyrene
Glassy dynamics was investigated for thin films of atactic polystyrene by
complex electric capacitance measurements using dielectric relaxation
spectroscopy. During the isothermal aging process the real part of the electric
capacitance increased with time, whereas the imaginary part decreased with
time. It follows that the aging time dependences of real and imaginary parts of
the electric capacitance were primarily associated with change in volume (film
thickness) and dielectric permittivity, respectively. Further, dielectric
permittivity showed memory and rejuvenation effects in a similar manner to
those observed for poly(methyl methacrylate) thin films. On the other hand,
volume did not show a strong rejuvenation effect.Comment: 7 pages, 7 figures. Phys. Rev. E (in press
A microscopic description of the aging dynamics: fluctuation-dissipation relations, effective temperature and heterogeneities
We consider the dynamics of a diluted mean-field spin glass model in the
aging regime. The model presents a particularly rich heterogeneous behavior. In
order to catch this behavior, we perform a **spin-by-spin analysis** for a
**given disorder realization**. The results compare well with the outcome of a
static calculation which uses the ``survey propagation'' algorithm of Mezard,
Parisi, and Zecchina [Sciencexpress 10.1126/science.1073287 (2002)]. We thus
confirm the connection between statics and dynamics at the level of single
degrees of freedom. Moreover, working with single-site quantities, we can
introduce a new response-vs-correlation plot, which clearly shows how
heterogeneous degrees of freedom undergo coherent structural rearrangements.
Finally we discuss the general scenario which emerges from our work and
(possibly) applies to more realistic glassy models. Interestingly enough, some
features of this scenario can be understood recurring to thermometric
considerations.Comment: 4 pages, 5 figures (7 eps files
Fluctuation-Dissipation-Theorem violation during the formation of a colloidal-glass
The relationship between the conductivity and the polarization noise is
measured in a gel as a function of frequency in the range . It is
found that at the beginning of the transition from a fluid like sol to a solid
like gel the fluctuation dissipation theorem is strongly violated. The
amplitude and the persistence time of this violation are decreasing functions
of frequency. At the lowest frequencies of the measuring range it persists for
times which are about 5% of the time needed to form the gel. This phenomenology
is quite close to the recent theoretical predictions done for the violation of
the fluctuation dissipation theorem in glassy systems.Comment: 6 pages + 4 figure
Coarsening of Disordered Quantum Rotors under a Bias Voltage
We solve the dynamics of an ensemble of interacting rotors coupled to two
leads at different chemical potential letting a current flow through the system
and driving it out of equilibrium. We show that at low temperature the
coarsening phase persists under the voltage drop up to a critical value of the
applied potential that depends on the characteristics of the electron
reservoirs. We discuss the properties of the critical surface in the
temperature, voltage, strength of quantum fluctuations and coupling to the bath
phase diagram. We analyze the coarsening regime finding, in particular, which
features are essentially quantum mechanical and which are basically classical
in nature. We demonstrate that the system evolves via the growth of a coherence
length with the same time-dependence as in the classical limit, -- the scalar curvature driven universality class. We obtain the
scaling function of the correlation function at late epochs in the coarsening
regime and we prove that it coincides with the classical one once a prefactor
that encodes the dependence on all the parameters is factorized. We derive a
generic formula for the current flowing through the system and we show that,
for this model, it rapidly approaches a constant that we compute.Comment: 53 pages, 12 figure
Correlation function and generalized master equation of arbitrary age
We study a two-state statistical process with a non-Poisson distribution of
sojourn times. In accordance with earlier work, we find that this process is
characterized by aging and we study three different ways to define the
correlation function of arbitrary age of the corresponding dichotomous
fluctuation based respectively on the Generalized Master Equation formalism, on
a Liouville-like approach and on a trajectory perspective.Comment: 11 pages, 1figur
Aging, memory and rejuvenation: some lessons from simple models
Many recent experiments probed the off equilibrium dynamics of spin glasses
and other glassy systems through temperature cycling protocols and observed
memory and rejuvenation phenomena. Here we show through numerical simulations,
using powerful algorithms, that such features can already be observed to some
extent in simple models such as two dimensional ferromagnets. We critically
discuss these results and review some aspects of the literature in the light of
our findings.Comment: 10 pages, 8 figures. Contribution to the Proceedings of the
Summerschool "Ageing and the glass transition", Luxembourg 14-25 Sept. 200
Multiple scaling regimes in simple aging models
We investigate aging in glassy systems based on a simple model, where a point
in configuration space performs thermally activated jumps between the minima of
a random energy landscape. The model allows us to show explicitly a subaging
behavior and multiple scaling regimes for the correlation function. Both the
exponents characterizing the scaling of the different relaxation times with the
waiting time and those characterizing the asymptotic decay of the scaling
functions are obtained analytically by invoking a `partial equilibrium'
concept.Comment: 4 pages, 3 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
Growing correlations and aging of an elastic line in a random potential
We study the thermally assisted relaxation of a directed elastic line in a
two dimensional quenched random potential by solving numerically the
Edwards-Wilkinson equation and the Monte Carlo dynamics of a solid-on-solid
lattice model. We show that the aging dynamics is governed by a growing
correlation length displaying two regimes: an initial thermally dominated
power-law growth which crosses over, at a static temperature-dependent
correlation length , to a logarithmic growth consistent with an
algebraic growth of barriers. We present a scaling arguments to deal with the
crossover-induced geometrical and dynamical effects. This analysis allows to
explain why the results of most numerical studies so far have been described
with effective power-laws and also permits to determine the observed anomalous
temperature-dependence of the characteristic growth exponents. We argue that a
similar mechanism should be at work in other disordered systems. We generalize
the Family-Vicsek stationary scaling law to describe the roughness by
incorporating the waiting-time dependence or age of the initial configuration.
The analysis of the two-time linear response and correlation functions shows
that a well-defined effective temperature exists in the power-law regime.
Finally, we discuss the relevance of our results for the slow dynamics of
vortex glasses in High-Tc superconductors.Comment: 18 pages, 15 figures, submitted for publicatio
Driven quantum coarsening
We study the driven dynamics of quantum coarsening. We analyze models of
M-component rotors coupled to two electronic reservoirs at different chemical
potentials that generate a current threading through the system. In the large M
limit we derive the dynamical phase diagram as a function of temperature,
strength of quantum fluctuations, voltage and coupling to the leads. We show
that the slow relaxation in the ordering phase is universal. On large time and
length scales the dynamics are analogous to stochastic classical ones, even for
the quantum system driven out of equilibrium at zero temperature. We argue that
our results apply to generic driven quantum coarsening.Comment: 4 pages, 3 figure