Phase transitions and steady-state microstructures in a two-temperature lattice-gas model with mobile active impurities

The nonequilibrium, steady-state phase transitions and the structure of the different phases of a two-dimensional system with two thermodynamic temper atures are studied via a simple lattice-gas model with mobile active impuri ties ("hot/cold spots'') whose activity is controlled by an external drive. The properties of the model are calculated by Monte Carlo computer-simulat ion techniques. The two temperatures and the external drive on the system l ead to a rich phase diagram including regions of microstructured phases in addition to macroscopically ordered (phase-separated) and disordered phases . Depending on the temperatures, microstructured phases of both lamellar an d droplet symmetry arise, described by a length scale that is determined by the characteristic temperature controlling the diffusive motion of the act ive impurities.