1 3 Fe b 20 02 Phase diagram of a driven interacting three - state lattice gas

We present Monte Carlo simulations of a three-state lattice gas, half-filled with two types of particles which attract one another, irrespective of their identities. A bias drives the two particle species in opposite directions, establishing and maintaining a non-equilibrium steady state. We map out the phase diagram at fixed bias, as a function of temperature and fraction of the second species. As the temperature is lowered, a continuous transition occurs, from a disordered homogeneous into two distinct strip-like ordered phases. Which of the latter is selected depends on the admixture of the second species. A first order line separates the two ordered states at lower temperatures, emerging from the continuous line at a non-equilibrium bicritical point. For intermediate fraction of the second species, all three phases can be observed. Introduction. For systems in thermal equilibrium, the theoretical framework is firmly laid, resting on the work of Boltzmann and Gibbs over a hundred years ago. In particular, the study of simple equilibrium models has a long and illustrious history, as reduction in complexity facilitates the development of theoretical techniques and intuition. In contrast, for systems far from equilibrium there exists no general theoretical framework, and the field remains in an undeveloped state. The strategy of investigating simple models motivates our Monte Carlo study of a driven diffusive system far from equilibrium. A modification of the Ising model, our system departs from well-travelled ground in equilibrium statistical mechanics. Our goal is to develop some intuition about systems far from equilibrium while extending earlier work in the field [1]. Almost twenty years ago, Katz, Lebowitz, and Spohn (KLS) [2] introduced a generalization of the Ising lattice gas [3], motivated by the physics of fast ionic conductors [4]: A bias E is applied along a specified lattice axis, driving the particles much like an electric field would drive positive charges. With conserved density and periodic boundary conditions, the system settles into a non-equilibrium steady state, characterized by a uniform particle current. Similar to the equilibrium Ising model, the KLS phase space consists of a high temperature disordered phase and a low temperature phase-separated phase, characterized by a particle-rich strip parallel to the field direction. At half-filling, the transition remains continuous, but shifts to a higher temperature T c (E). Remarkably, the transition belongs to a novel universality class [5, 6, 7], distinct from the Ising class. One of its key signals is strong anisotropy: …