DISCONTINUOUS INTERFACE DEPINNING FROM A ROUGH WALL

Depinning of an interface from a random self-affine substrate with rou ghness exponent zeta(S) is studied in systems with short-range interac tions. In two dimensions transfer matrix results show that for zeta(S) < 1/2 depinning falls in the universality class of the flat case. Whe n zeta(S) exceeds the roughness (zeta(0) = 1/2) of the interface in th e bulk, geometrical disorder becomes relevant and, moreover, depinning becomes discontinuous. The same unexpected scenario, and a precise lo cation of the associated tricritical point, are obtained for a simplif ied hierarchical model. It is inferred that, in three dimensions, with zeta(S) = 0, depinning turns first order already for zeta(S) > 0. Thu s critical wetting may be impossible to observe on rough substrates.