Character of the Phase Transition in Thin Ising Films with Competing Walls

By extensive Monte Carlo simulations of a lattice gas model we have studied the controversial nature of the gas-liquid transition of a fluid confined between two parallel plates that exert competing surface fields. We find that the transition is shifted to a temperature just below the wetting transition of a semi-infinite fluid but belongs to the two-dimensional Ising universality class. In between this new type of critical point and bulk criticality, a response function xₙₙᵐᵃˣ varying exponentially with D is observed, 2 lnχₙₙᵐᵃˣD=^-1, where is a new length characterizing interfaces.