EXISTENCE OF LONG-RANGE ORDER IN THE STEADY-STATE OF A 2-DIMENSIONAL, 2-TEMPERATURE XY MODEL

Monte Carlo simulations are used to show that the steady state of the d = 2, two-temperature, diffusive XY model displays a continuous phase transition from a homogeneous disordered phase to a phase with long-range order. The long-range order exists although both the dynamics and the interactions are local, thus indicating the failure of a naive extension of the Mermin-Wagner theorem to nonequilibrium steady states. It is argued that the ordering is due to effective dipole interactions generated by the nonequilibrium dynamics.