  We investigate properties of the diffusive motion of an interface in the
two-dimensional Ising model in equilibrium or nonequilibrium situations. We
focused on the relation between the power spectrum of a time sequence of spins
and diffusive motion of an interface which was already clarified in one-
dimensional systems with a nonequilibrium phase transition like the asymmetric
simple exclusion process. It is clarified that the interface motion is a
diffusion process with a drift force toward the higher-temperature side when
the system is in contact with heat reservoirs at different temperatures and
heat transfers through the system. Effects of the width of the interface are
also discussed.
