  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.
