Gustavo P. Saracco

Monte Carlo study of the phase transition in the critical behavior of the Ising model with shear

The critical behavior of the Ising model with nonconserved dynamics and an external driving field mimicking a shear profile is analyzed by studying its dynamical evolution in the short-time regime. Starting from high-temperature disordered configurations (fully disordered configurations, FDC), the critical temperature Tc is determined when the order parameter, defined as the absolute value of the transversal spin profile, exhibits a power-law behavior with an exponent that is a combination of some of the critical exponents of the transition. For each value of the shear field magnitude, labeled as gamma, Tc has been estimated and two stages have been found: (1) a growing stage at low values of gamma, where Tc approximately gammapsi and psi=0.52(3), and (2) a saturation regime at large gamma. The same values of Tc(gamma) were found studying the dynamical evolution from the ground-state configuration with all spins pointing in the same direction. By combining the exponents of the corresponding power laws obtained from each initial configuration, the set of critical exponents was calculated. These values, at large external field magnitude, define a critical behavior different from that of the Ising model and of other driven lattice gases.

Damage spreading in a driven lattice gas model

We studied damage spreading in a Driven Lattice Gas (DLG) model as a function of the temperature T, the magnitude of the external driving field E, and the lattice size. The DLG model undergoes an order–disorder second-order phase transition at the critical temperature Tc(E), such that the ordered phase is characterized by high-density strips running along the direction of the applied field; while in the disordered phase one has a lattice-gas-like behavior. It is found that the damage always spreads for all the investigated temperatures and reaches a saturation value Dsat that depends only on T. Dsat increases for TTc(E=∞) and is free of finite-size effects. This behavior can be explained as due to the existence of interfaces between the high-density strips and the lattice-gas-like phase whose roughness depends on T. Also, we investigated damage spreading for a range of finite fields as a function of T, finding a behavior similar to that of the case with E=∞.

Study of the Critical Behavior of Nonequilibrium Systems: Application to Driven Diffusive Lattice Gases

Due to the fact that there is not a standard theory for non‐equilibrium behavior, it is useful to gain insight on these systems studying some archetypical models, such as the non‐equilibrium lattice gas knew as the KLS model (Katz, Lebowitz and Spohn; Phys. Rev. B 28, 1665 (1983)). The KLS model assumes a lattice gas of particle density ρ0 with nearest‐neighbor attractive interactions. Furthermore, the particles also interact with an external driving field. The system is in contact with a reservoir at temperature T. In this work, the critical behavior of the KLS model is studied covering the region of the parameter space where the system undergoes both first‐ and second‐order phase transitions. First‐order phase transitions appear when ρ0 ≠ 0.5, while a second‐order phase transition is found exactly at ρ0 = 0.5. The critical exponents of the second‐order transition can be evaluated self consistently by means of a dynamical study of the order parameter. The magnitude or “strength” of the first‐order transi...