Unequal Intra-layer Coupling in a Bilayer Driven Lattice Gas

TL;DR

This study explores how unequal intra-layer couplings affect the phase diagram and critical behavior of a driven bilayer lattice gas, revealing shifts in phase boundaries and potential deviations from Ising universality.

Contribution

It extends the phase diagram of a driven bilayer lattice gas by analyzing the effects of unequal intra-layer couplings and investigates the critical behavior of phase transitions.

Findings

Shift of the tri-critical point into the negative J_3 region with increased driving field.

Long-lived transient phases near the S-FE boundary.

Simulation suggests non-Ising critical behavior with gamma approximately 1.75.

Abstract

The system under study is a twin-layered square lattice gas at half-filling, being driven to non-equilibrium steady states by a large, finite `electric' field. By making intra-layer couplings unequal we were able to extend the phase diagram obtained by Hill, Zia and Schmittmann (1996) and found that the tri-critical point, which separates the phase regions of the stripped (S) phase (stable at positive interlayer interactions J_3), the filled-empty (FE) phase (stable at negative J_3) and disorder (D), is shifted even further into the negative J_3 region as the coupling traverse to the driving field increases. Many transient phases to the S phase at the S-FE boundary were found to be long-lived. We also attempted to test whether the universality class of D-FE transitions under a drive is still Ising. Simulation results suggest a value of 1.75 for the exponent gamma but a value close to 2.0 for the ratio gamma/nu. We speculate that the D-FE second order transition is different from Ising near criticality, where observed first-order-like transitions between FE and its "local minimum" cousin occur during each simulation run.