PHASE-TRANSITIONS IN DRIVEN LATTICE GASES

We have studied nonequilibrium lattice gases whose particles are drive n by a field. The lattice is either a half-occupied square lattice or else the union of two energetically uncoupled ones. Monte Carlo simula tions of the latter, which is always crossed by a dissipative particle current, show a tricritical point and a continuum of Ising-like criti cal points as the field is decreased, in addition to non-Ising, anisot ropic critical behavior at higher temperatures for saturating fields. A comparison of the various phase transitions involved, and a detailed study of scaling of correlations with system size, indicate the relev ance of the anisotropic liquid-vapor interface (rather than the drivin g field) for inducing non-Ising behavior in a class of systems, It is likely that some of the properties reported here are experimentally ob servable.