244 research outputs found
Critical behavior and out-of-equilibrium dynamics of a two-dimensional Ising model with dynamic couplings
We study the critical behavior and the out-of-equilibrium dynamics of a
two-dimensional Ising model with non-static interactions. In our model, bonds
are dynamically changing according to a majority rule depending on the set of
closest neighbors of each spin pair, which prevents the system from ordering in
a full ferromagnetic or antiferromagnetic state. Using a parallel-tempering
Monte Carlo algorithm, we find that the model undergoes a continuous phase
transition at finite temperature, which belongs to the Ising universality
class. The properties of the bond structure and the ground-state entropy are
also studied. Finally, we analyze the out-of-equilibrium dynamics which
displays typical glassy characteristics at a temperature well below the
critical one.Comment: 10 pages with 12 figure
Anisotropic finite-size scaling of an elastic string at the depinning threshold in a random-periodic medium
We numerically study the geometry of a driven elastic string at its
sample-dependent depinning threshold in random-periodic media. We find that the
anisotropic finite-size scaling of the average square width and of
its associated probability distribution are both controlled by the ratio
, where is the
random-manifold depinning roughness exponent, is the longitudinal size of
the string and the transverse periodicity of the random medium. The
rescaled average square width displays a
non-trivial single minimum for a finite value of . We show that the initial
decrease for small reflects the crossover at from the
random-periodic to the random-manifold roughness. The increase for very large
implies that the increasingly rare critical configurations, accompanying
the crossover to Gumbel critical-force statistics, display anomalous roughness
properties: a transverse-periodicity scaling in spite that ,
and subleading corrections to the standard random-manifold longitudinal-size
scaling. Our results are relevant to understanding the dimensional crossover
from interface to particle depinning.Comment: 11 pages, 7 figures, Commentary from the reviewer available in Papers
in Physic
Domain growth within the backbone of the three-dimensional Edwards-Anderson spin glass
The goal of this work is to show that a ferromagnetic-like domain growth
process takes place within the backbone of the three-dimensional
Edwards-Anderson (EA) spin glass model. To sustain this affirmation we study
the heterogeneities displayed in the out-of-equilibrium dynamics of the model.
We show that both correlation function and mean flipping time distribution
present features that have a direct relation with spatial heterogeneities, and
that they can be characterized by the backbone structure. In order to gain
intuition we analyze the pure ferromagnetic Ising model, where we show the
presence of dynamical heterogeneities in the mean flipping time distribution
that are directly associated to ferromagnetic growing domains. We extend a
method devised to detect domain walls in the Ising model to carry out a similar
analysis in the three-dimensional EA spin glass model. This allows us to show
that there exists a domain growth process within the backbone of this model.Comment: 10 pages, 10 figure
Non-steady relaxation and critical exponents at the depinning transition
We study the non-steady relaxation of a driven one-dimensional elastic
interface at the depinning transition by extensive numerical simulations
concurrently implemented on graphics processing units (GPUs). We compute the
time-dependent velocity and roughness as the interface relaxes from a flat
initial configuration at the thermodynamic random-manifold critical force.
Above a first, non-universal microscopic time-regime, we find a non-trivial
long crossover towards the non-steady macroscopic critical regime. This
"mesoscopic" time-regime is robust under changes of the microscopic disorder
including its random-bond or random-field character, and can be fairly
described as power-law corrections to the asymptotic scaling forms yielding the
true critical exponents. In order to avoid fitting effective exponents with a
systematic bias we implement a practical criterion of consistency and perform
large-scale (L~2^{25}) simulations for the non-steady dynamics of the continuum
displacement quenched Edwards Wilkinson equation, getting accurate and
consistent depinning exponents for this class: \beta = 0.245 \pm 0.006, z =
1.433 \pm 0.007, \zeta=1.250 \pm 0.005 and \nu=1.333 \pm 0.007. Our study may
explain numerical discrepancies (as large as 30% for the velocity exponent
\beta) found in the literature. It might also be relevant for the analysis of
experimental protocols with driven interfaces keeping a long-term memory of the
initial condition.Comment: Published version (including erratum). Codes and Supplemental
Material available at https://bitbucket.org/ezeferrero/qe
Nonequilibrium dynamics of the three-dimensional Edwards-Anderson spin-glass model with Gaussian couplings: Strong heterogeneities and the backbone picture
We numerically study the three-dimensional Edwards-Anderson model with
Gaussian couplings, focusing on the heterogeneities arising in its
nonequilibrium dynamics. Results are analyzed in terms of the backbone picture,
which links strong dynamical heterogeneities to spatial heterogeneities
emerging from the correlation of local rigidity of the bond network. Different
two-times quantities as the flipping time distribution and the correlation and
response functions, are evaluated over the full system and over high- and
low-rigidity regions. We find that the nonequilibrium dynamics of the model is
highly correlated to spatial heterogeneities. Also, we observe a similar
physical behavior to that previously found in the Edwards-Anderson model with a
bimodal (discrete) bond distribution. Namely, the backbone behaves as the main
structure that supports the spin-glass phase, within which a sort of
domain-growth process develops, while the complement remains in a paramagnetic
phase, even below the critical temperature
Kinetic roughening, global quantities, and fluctuation-dissipation relations
Growth processes and interface fluctuations can be studied through the
properties of global quantities. We here discuss a global quantity that not
only captures better the roughness of an interface than the widely studied
surface width, but that is also directly conjugate to an experimentally
accessible parameter, thereby allowing us to study in a consistent way the
global response of the system to a global change of external conditions.
Exploiting the full analyticity of the linear Edwards-Wilkinson and
Mullins-Herring equations, we study in detail various two-time functions
related to that quantity. This quantity fulfills the fluctuation-dissipation
theorem when considering steady-state equilibrium fluctuations.Comment: 13 pages, 5 figure
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