arXiv subjects

Ezequiel V. Albano

Publications and source records attributed to Ezequiel V. Albano.

At least 37 records · Page 2Linked to original sources

arXiv2007

Dynamic response of Ag monolayers adsorbed on Au(100) upon an oscillatory variation of the chemical potential: A Monte Carlo simulation study

Based on the fact that the underpotential electrochemical deposition of Ag atoms on the $Au(100)$ surface exhibits sharp first-order phase transitions at well-defined values of the (coexistence) chemical potential ($μ_{coex}$), we performed extensive simulations aimed at investigating the hysteretic dynamic behavior of the system close to coexistence upon the application of a periodic signal of the form $μ(t) = μ_{coex} + μ_{o}sin(2Πt/τ) $, where $μ_{o}$ and $τ$ are the amplitude and the period of the sweep, respectively. For relatively short periods and small enough amplitudes the system becomes trapped either at low or high Ag coverage states, as evidenced by recording hysteresis loops. This scenario is identified as dynamically ordered states (DOS), such that the relaxation time $(τ_{relax})$ of the corresponding metastable state obeys $τ_{relax} > τ$. On the other hand, by properly increasing $μ_{o}$ or/and $τ$, one finds that the $Ag$ coverage gently follows the external drive (here $τ_{relax} < τ$) and the system is said to enter into dynamically disordered states (DDS), where hysteresis loops show almost symmetric limiting cycles. This symmetry breaking between limiting cycles driven by an external signal is discussed in terms of the concept of (out-of-equilibrium) Dynamic Phase Transitions between DOS and DDS, similar to those encountered when a magnetic system is placed in the presence of a variable external magnetic field. However, a careful finite-size scaling study reveals that, at least at $T = 300K$, the $Ag/Au(100)$ system does not exhibit true second-order phase transitions but rather a crossover behavior between states. A diagram showing the location of the ordered and disordered states in the $μ$ versus $τ$ plane is obtained and discussed.

cond-mat.stat-mech↗

arXiv2007

A Model for Damage Spreading with Damage Healing: Monte Carlo Study of the two Dimensional Ising Ferromagnet

An Ising model for damage spreading with a probability of damage healing ($q = 1 - p$) is proposed and studied by means of Monte Carlo simulations. In the limit $p \to 1$ the new model is mapped to the standard Ising model. It is found that, for temperatures above the Onsager critical temperature ($T_{C}$), there exist a no trivial finite value of $p$ that sets the critical point ($p_{c}$) for the onset of damage spreading. It is found that $p_{c}$ depends on $T$, defining a critical curve at the border between damage spreading and damage healing. Transitions along such curve are found to belong to the universality class of directed percolation. The phase diagram of the model is also evaluated showing that for large $T$ one has $p_{c} \propto (T- T_{C})^α$, with $α= 1$. Within the phase where the damage remains active, the stationary value of the damage depends lineally on both $p - p_{c}$ and $T - T_{C} $.

cond-mat.stat-mech↗

arXiv2007

Study of Damage Propagation at the Interface Localization-Delocalization Transition of the Confined Ising Model

The propagation of damage in a confined magnetic Ising film, with short range competing magnetic fields ($h$) acting at opposite walls, is studied by means of Monte Carlo simulations. Due to the presence of the fields, the film undergoes a wetting transition at a well defined critical temperature $T_w(h)$. In fact, the competing fields causes the occurrence of an interface between magnetic domains of different orientation. For $T < T_w(h)$ ($T > T_w(h)$) such interface is bounded (unbounded) to the walls, while right at $T_w(h)$ the interface is essentially located at the center of the film. It is found that the spatio-temporal spreading of the damage becomes considerably enhanced by the presence of the interface, which act as a ''catalyst'' of the damage causing an enhancement of the total damaged area. The critical points for damage spreading are evaluated by extrapolation to the thermodynamic limit using a finite-size scaling approach. Furthermore, the wetting transition effectively shifts the location of the damage spreading critical points, as compared with the well known critical temperature of the order-disorder transition characteristic of the Ising model. Such a critical points are found to be placed within the non-wet phase.

cond-mat.stat-mech↗

arXiv2006

Damage Spreading at the Corner Filling Transition in the two-dimensional Ising Model

The propagation of damage on the square Ising lattice with a corner geometry is studied by means of Monte Carlo simulations. It is found that, just at $T=T_f (h)$ (critical temperature of the filling transition) the damage initially propagates along the interface of the competing domains, according to a power law given by $D(t) \propto t^η$. The value obtained for the dynamic exponent ($η^{*} = 0.89(1)$) is in agreement with that corresponding to the wetting transition in the slit geometry (Abraham Model) given by $η^{WT} = 0.91(1)$. However, for later times the propagation crosses to a new regime such as $η^{**} = 0.40 \pm 0.02$, which is due to the propagation of the damage into the bulk of the magnetic domains. This result can be understood due to the constraints imposed to the propagation of damage by the corner geometry of the system that cause healing at the corners where the interface is attached.

cond-mat.stat-mech↗

arXiv2006

Short time relaxation of a driven elastic string in a random medium

We study numerically the relaxation of a driven elastic string in a two dimensional pinning landscape. The relaxation of the string, initially flat, is governed by a growing length $L(t)$ separating the short steady-state equilibrated lengthscales, from the large lengthscales that keep memory of the initial condition. We find a macroscopic short time regime where relaxation is universal, both above and below the depinning threshold, different from the one expected for standard critical phenomena. Below the threshold, the zero temperature relaxation towards the first pinned configuration provides a novel, experimentally convenient way to access all the critical exponents of the depinning transition independently.

cond-mat.dis-nn↗

arXiv2006

Monte Carlo simulation of the irreversible growth of magnetic thin films

The growth of magnetic films with ferromagnetic interactions between nearest-neighbor spins is studied in $(d+1)-$dimensional rectangular geometries for $d = 1,2$. Magnetic films are grown irreversibly by adding spins at the boundaries of the growing interface. The orientation of the added spins depends on both the energetic interaction with already deposited spins and the temperature, through a Boltzmann factor. At low temperatures thin films, of thickness $L$, are constituted by a sequence of well ordered magnetic domains. Spins belonging to each domain, of average length $l_{D} \gg L$, have mostly the same orientation, but consecutive domains have opposite magnetization. Such kind of ``spontaneous magnetization reversal'' during the growth process has a short characteristic length $l_{R}$, such that $l_{D} \gg l_{R} \sim L$. At higher temperatures, a transition between ordered and disordered states is also observed. The emerging behavior is compared to that of the equilibrium Ising model.

cond-mat.stat-mech↗

arXiv2006

Dynamic properties in a family of competitive growing models

The properties of a wide variety of growing models, generically called $X/RD$, are studied by means of numerical simulations and analytic developments. The study comprises the following $X$ models: Ballistic Deposition, Random Deposition with Surface Relaxation, Das Sarma-Tamboronea, Kim-Kosterlitz, Lai-Das Sarma, Wolf-Villain, Large Curvature, and three additional models that are variants of the Ballistic Deposition model. It is shown that after a growing regime, the interface width becomes saturated at a crossover time ($t_{x2}$) that, by fixing the sample size, scales with $p$ according to $t_{x2}(p)\propto p^{-y}, \qquad (p > 0)$, where $y$ is an exponent. Also, the interface width at saturation ($W_{sat}$) scales as $W_{sat}(p)\propto p^{-δ}, \qquad (p > 0)$, where $δ$ is another exponent. It is proved that, in any dimension, the exponents $δ$ and $y$ obey the following relationship: $δ= y β_{RD}$, where $β_{RD} = 1/2$ is the growing exponent for $RD$. Furthermore, both exponents exhibit universality in the $p \to 0$ limit. By mapping the behaviour of the average height difference of two neighbouring sites in discrete models of type $X/RD$ and two kinds of random walks, we have determined the exact value of the exponent $δ$. Finally, by linking four well-established universality classes (namely Edwards-Wilkinson, Kardar-Parisi-Zhang, Linear-MBE and Non-linear-MBE) with the properties of both random walks, eight different stochastic equations for all the competitive models studied are derived.

cond-mat.stat-mech↗

arXiv2005

Dynamic Critical approach to Self-Organized Criticality

A dynamic scaling Ansatz for the approach to the Self-Organized Critical (SOC) regime is proposed and tested by means of extensive simulations applied to the Bak-Sneppen model (BS), which exhibits robust SOC behavior. Considering the short-time scaling behavior of the density of sites ($ρ(t)$) below the critical value, it is shown that i) starting the dynamics with configurations such that $ρ(t=0) \to 0$ one observes an {\it initial increase} of the density with exponent $θ= 0.12(2)$; ii) using initial configurations with $ρ(t=0) \to 1$, the density decays with exponent $δ= 0.47(2)$. It is also shown that he temporal autocorrelation decays with exponent $C_a = 0.35(2)$. Using these, dynamically determined, critical exponents and suitable scaling relationships, all known exponents of the BS model can be obtained, e.g. the dynamical exponent $z = 2.10(5)$, the mass dimension exponent $D = 2.42(5)$, and the exponent of all returns of the activity $τ_{ALL} = 0.39(2)$, in excellent agreement with values already accepted and obtained within the SOC regime.

nlin.AO↗

arXiv2005

Comparative study of an Eden model for the irreversible growth of spins and the equilibrium Ising model

The Magnetic Eden Model (MEM) with ferromagnetic interactions between nearest-neighbor spins is studied in $(d+1)-$dimensional rectangular geometries for $d = 1,2$. In the MEM, magnetic clusters are grown by adding spins at the boundaries of the clusters. The orientation of the added spins depends on both the energetic interaction with already deposited spins and the temperature, through a Boltzmann factor. A numerical Monte Carlo investigation of the MEM has been performed and the results of the simulations have been analyzed using finite-size scaling arguments. As in the case of the Ising model, the MEM in $d = 1 $ is non-critical (only exhibits an ordered phase at $T= 0$). In $d = 2$ the MEM exhibits an order-disorder transition of second-order at a finite temperature. Such transition has been characterized in detail and the relevant critical exponents have been determined. These exponents are in agreement (within error bars) with those of the Ising model in 2 dimensions. Further similarities between both models have been found by evaluating the probability distribution of the order parameter, the magnetization and the susceptibility. Results obtained by means of extensive computer simulations allow us to put forward a conjecture which establishes a nontrivial correspondence between the MEM for the irreversible growth of spins and the equilibrium Ising model. This conjecture is certainly a theoretical challenge and its confirmation will contribute to the development of a framework for the study of irreversible growth processes.

cond-mat.stat-mech↗

arXiv2005

Irreversible growth of a binary mixture confined in a thin film geometry with competing walls

The irreversible growth of a binary mixture under far-from-equilibrium conditions is studied in three-dimensional confined geometries of size $L_x \times L_y \times L_z$, where $L_z \gg L_x = L_y$ is the growing direction. A competing situation where two opposite surfaces prefer different species of the mixture is analyzed. Due to this antisymmetric condition an interface between the different species develops along the growing direction. Such interface undergoes a localization-delocalization transition that is the precursor of a wetting transition in the thermodynamic limit. Furthermore, the growing interface also undergoes a concave-convex transition in the growth mode. So, the system exhibits a multicritical wetting point where the growing interface is almost flat and the interface between species is essentially localized at the center of the film.

cond-mat.stat-mech↗

arXiv2005

Quasi-wetting and morphological phase transitions in confined far-from-equilibrium magnetic thin films

The growth of confined magnetic films with ferromagnetic interactions between nearest-neighbor spins is studied in a stripped $(1+1)-$dimensional rectangular geometry. Magnetic films are grown irreversibly by adding spins at the boundaries of the growing interface. A competing situation with two opposite short range surface magnetic fields of the same magnitude is analyzed. Due to the antisymmetric condition considered, an interface between domains with spins having opposite orientations develops along the growing direction. Such interface undergoes a localization-delocalization transition that is identified as a quasi-wetting transition, in qualitative agreement with observations performed under equilibrium conditions. In addition, the film also exhibits a growing interface that undergoes morphological transitions in the growth mode. It is shown that, as a consequence of the nonequilibrium nature of the investigated model, the subtle interplay between finite-size effects, wetting, and interface growth mechanisms leads to more rich and complex physical features than in the equilibrium counterpart. Indeed, a phase diagram that exhibits eight distinct regions is evaluated and discussed. In the thermodynamic limit, the whole ordered phase (which contains the quasi-wetting transition) collapses, while within the disordered phase, standard extrapolation procedures show that only two regions are present in the phase diagram of the infinite system.

cond-mat.stat-mech↗

arXiv2005

Non-equilibrium wetting transition in a magnetic Eden model

Magnetic Eden clusters with ferromagnetic interaction between nearest-neighbor spins are grown in a confined 2d-geometry with short range magnetic fields acting on the surfaces. The change of the growing interface curvature driven by the field and the temperature is identified as a non-equilibrium wetting transition and the corresponding phase diagram is evaluated.

cond-mat.stat-mech↗

arXiv2005

Corner wetting in a far-from-equilibrium magnetic growth model

The irreversible growth of magnetic films is studied in three-dimensional confined geometries of size $L\times L\times M$, where $M\gg L$ is the growing direction. Competing surface magnetic fields, applied to opposite corners of the growing system, lead to the observation of a localization-delocalization (weakly rounded) transition of the interface between domains of up and down spins on the planes transverse to the growing direction. This effective transition is the precursor of a true far-from-equilibrium corner wetting transition that takes place in the thermodynamic limit. The phenomenon is characterized quantitatively by drawing a magnetic field-temperature phase diagram, firstly for a confined sample of finite size, and then by extrapolating results, obtained with samples of different size, to the thermodynamic limit. The results of this work are a nonequilibrium realization of analogous phenomena recently investigated in equilibrium systems, such as corner wetting transitions in the Ising model.

cond-mat.stat-mech↗

arXiv2003

On the fluctuations of jamming coverage upon random sequential adsorption on homogeneous and heterogeneous media

The fluctuations of the jamming coverage upon Random Sequential Adsorption (RSA) are studied using both analytical and numerical techniques. Our main result shows that these fluctuations (characterized by $σ_{θ_J}$) decay with the lattice size according to the power-law $σ_{θ_J} \propto L^{-1/ ν}$. The exponent $ν$ depends on the dimensionality $D$ of the substrate and the fractal dimension of the set where the RSA process actually takes place ($d_f$) according to $ν= 2 / (2D - d_f)$.This theoretical result is confirmed by means of extensive numerical simulations applied to the RSA of dimers on homogeneous and stochastic fractal substrates. Furthermore, our predictions are in excellent agreement with different previous numerical results. It is also shown that, studying correlated stochastic processes, one can define various fluctuating quantities designed to capture either the underlying physics of individual processes or that of the whole system. So, subtle differences in the definitions may lead to dramatically different physical interpretations of the results. Here, this statement is demonstrated for the case of RSA of dimers on binary alloys.

cond-mat.stat-mech↗

arXiv2003

Scaling behavior of jamming fluctuations upon random sequential adsorption

It is shown that the fluctuations of the jamming coverage upon Random Sequential Adsorption ($σ_{θ_J}$), decay with the lattice size according to the power-law $σ_{θ_J} \propto L^{-1 / ν_J}$, with $ν_{J} = 2 / (2D - d_f)$, where $D$ is the dimension of the substrate and $d_{\rm f}$ is the fractal dimension of the set of sites belonging to the substrate where the RSA process actually takes place. This result is in excellent agreement with the figure recently reported by Vandewalle {\it et al} ({\it Eur. Phys. J.} B. {\bf 14}, 407 (2000)), namely $ν_J = 1.0 (1)$ for the RSA of needles with $D = 2$ and $d_f = 2$, that gives $ν_J = 1$. Furthermore, our prediction is in excellent agreement with different previous numerical results. The derived relationships are also confirmed by means of extensive numerical simulations applied to the RSA of dimers on both stochastic and deterministic fractal substrates.

cond-mat.stat-mech↗

arXiv2002

Numerical study of a first-order irreversible phase transition in a CO+NO catalyzed reaction model

The first-order irreversible phase transitions (IPT) of the Yaldran-Khan model (Yaldran-Khan, J. Catal. 131, 369, 1991) for the CO+NO reaction is studied using the constant coverage (CC) ensemble and performing epidemic simulations. The CC method allows the study of hysteretic effects close to coexistence as well as the location of both the upper spinodal point and the coexistence point. Epidemic studies show that at coexistence the number of active sites decreases according to a (short-time) power law followed by a (long-time) exponential decay. It is concluded that first-order IPT's share many characteristic of their reversible counterparts, such as the development of short ranged correlations, hysteretic effects, metastabilities, etc.

cond-mat.stat-mech↗

arXiv2002

A numerical study of the development of bulk scale-free structures upon growth of self-affine aggregates

During the last decade, self-affine geometrical properties of many growing aggregates, originated in a wide variety of processes, have been well characterized. However, little progress has been achieved in the search of a unified description of the underlying dynamics. Extensive numerical evidence has been given showing that the bulk of aggregates formed upon ballistic aggregation and random deposition with surface relaxation processes can be broken down into a set of infinite scale invariant structures called "trees". These two types of aggregates have been selected because it has been established that they belong to different universality classes: those of Kardar-Parisi-Zhang and Edward-Wilkinson, respectively. Exponents describing the spatial and temporal scale invariance of the trees can be related to the classical exponents describing the self-affine nature of the growing interface. Furthermore, those exponents allows us to distinguish either the compact or non-compact nature of the growing trees. Therefore, the measurement of the statistic of the process of growing trees may become a useful experimental technique for the evaluation of the self-affine properties of some aggregates.

cond-mat.stat-mech↗

arXiv2002

Dynamic behavior of anisotropic non-equilibrium driving lattice gases

It is shown that intrinsically anisotropic non-equilibrium systems relaxing by a dynamic process exhibit universal critical behavior during their evolution toward non-equilibrium stationary states. An anisotropic scaling anzats for the dynamics is proposed and tested numerically. Relevant critical exponents can be evaluated self-consistently using both the short- and long-time dynamics frameworks. The obtained results allow us to clarify a long-standing controversy about the theoretical description, the universality and the origin of the anisotropy of driven diffusive systems, showing that the standard field theory does not hold and supporting a recently proposed alternative theory.

cond-mat.stat-mech↗