88 research outputs found

### Domain growth within the backbone of the three-dimensional $\pm J$ 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 $\pm J$
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

### 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

### Effective Edwards-Wilkinson equation for single-file diffusion

In this work, we present an effective discrete Edwards-Wilkinson equation
aimed to describe the single-file diffusion process. The key physical
properties of the system are captured defining an effective elasticity, which
is proportional to the single particle diffusion coefficient and to the inverse
squared mean separation between particles. The effective equation gives a
description of single-file diffusion using the global roughness of the system
of particles, which presents three characteristic regimes, namely normal
diffusion, subdiffusion and saturation, separated by two crossover times. We
show how these regimes scale with the parameters of the original system.
Additional repulsive interaction terms are also considered and we analyze how
the crossover times depend on the intensity of the additional terms. Finally,
we show that the roughness distribution can be well characterized by the
Edwards-Wilkinson universal form for the different single-file diffusion
processes studied here.Comment: 9 pages, 9 figure

### Random-Manifold to Random-Periodic Depinning of an Elastic Interface

We study numerically the depinning transition of driven elastic interfaces in
a random-periodic medium with localized periodic-correlation peaks in the
direction of motion. The analysis of the moving interface geometry reveals the
existence of several characteristic lengths separating different length-scale
regimes of roughness. We determine the scaling behavior of these lengths as a
function of the velocity, temperature, driving force, and transverse
periodicity. A dynamical roughness diagram is thus obtained which contains, at
small length scales, the critical and fast-flow regimes typical of the
random-manifold (or domain wall) depinning, and at large length-scales, the
critical and fast-flow regimes typical of the random-periodic (or
charge-density wave) depinning. From the study of the equilibrium geometry we
are also able to infer the roughness diagram in the creep regime, extending the
depinning roughness diagram below threshold. Our results are relevant for
understanding the geometry at depinning of arrays of elastically coupled thin
manifolds in a disordered medium such as driven particle chains or vortex-line
planar arrays. They also allow to properly control the effect of transverse
periodic boundary conditions in large-scale simulations of driven disordered
interfaces.Comment: 19 pages, 10 figure

### Uniqueness of the thermodynamic limit for driven disordered elastic interfaces

We study the finite size fluctuations at the depinning transition for a
one-dimensional elastic interface of size $L$ displacing in a disordered medium
of transverse size $M=k L^\zeta$ with periodic boundary conditions, where
$\zeta$ is the depinning roughness exponent and $k$ is a finite aspect ratio
parameter. We focus on the crossover from the infinitely narrow ($k\to 0$) to
the infinitely wide ($k\to \infty$) medium. We find that at the thermodynamic
limit both the value of the critical force and the precise behavior of the
velocity-force characteristics are {\it unique} and $k$-independent. We also
show that the finite size fluctuations of the critical force (bias and
variance) as well as the global width of the interface cross over from a
power-law to a logarithm as a function of $k$. Our results are relevant for
understanding anisotropic size-effects in force-driven and velocity-driven
interfaces.Comment: 10 pages, 12 figure

### Anisotropy-based mechanism for zigzag striped patterns in magnetic thin films

In this work we studied a two dimensional ferromagnetic system using Monte
Carlo simulations. Our model includes exchange and dipolar interactions, a
cubic anisotropy term, and uniaxial out-of-plane and in-plane ones. According
to the set of parameters chosen, the model including uniaxial out-of-plane
anisotropy has a ground-state which consists of a canted state with stripes of
opposite out-of-plane magnetization. When the cubic anisotropy is introduced
zigzag patterns appear in the stripes at fields close to the remanence. An
analysis of the anisotropy terms of the model shows that this configuration is
related to specific values of the ratio between the cubic and the effective
uniaxial anisotropy. The mechanism behind this effect is related to particular
features of the anisotropy's energy landscape, since a global minima transition
as a function of the applied field is required in the anisotropy terms. This
new mechanism for zigzags formation could be present in monocrystal
ferromagnetic thin films in a given range of thicknesses.Comment: 910 pages, 10 figure

### Thermal rounding of the depinning transition

We study thermal effects at the depinning transition by numerical simulations
of driven one-dimensional elastic interfaces in a disordered medium. We find
that the velocity of the interface, evaluated at the critical depinning force,
can be correctly described with the power law $v\sim T^\psi$, where $\psi$ is
the thermal exponent. Using the sample-dependent value of the critical force,
we precisely evaluate the value of $\psi$ directly from the temperature
dependence of the velocity, obtaining the value $\psi = 0.15 \pm 0.01$. By
measuring the structure factor of the interface we show that both the
thermally-rounded and the T=0 depinning, display the same large-scale geometry,
described by an identical divergence of a characteristic length with the
velocity $\xi \propto v^{-\nu/\beta}$, where $\nu$ and $\beta$ are respectively
the T=0 correlation and depinning exponents. We discuss the comparison of our
results with previous estimates of the thermal exponent and the direct
consequences for recent experiments on magnetic domain wall motion in
ferromagnetic thin films.Comment: 6 pages, 3 figure

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