Phase transitions at the early stages of surface melting

We show that the early stage of surface melting can be associated with a well defined phase transition, of the pre-roughening type. The problem is modeled by simulating the surface as an interface in the three-dimensional large N-state lattice Potts model, which is shown to exhibit pre-roughening, roughening, and a lattice version of surface melting. The lowest transition is pre-roughening, but it is in fact linked to the appearance of liquid-like signatures in the first surface layer, and thus represents the phase transition where surface melting starts. We suggest that this physics is realized on rare-gas-solid (111) surfaces and possibly also on other semiconductor and metal surfaces.