Discontinuous Interface Depinning from a Rough Wall

Abstract

Depinning of an interface from a random self--affine substrate with roughness exponent $ζ_S$ is studied in systems with short--range interactions. In 2$D$ transfer matrix results show that for $ζ_S<1/2$ depinning falls in the universality class of the flat case. When $ζ_S$ exceeds the roughness ($ζ_0=1/2$) of the interface in the bulk, geometrical disorder becomes relevant and, moreover, depinning becomes \underline{discontinuous}. The same unexpected scenario, and a precise location of the associated tricritical point, are obtained for a simplified hierarchical model. It is inferred that, in 3$D$, with $ζ_0=0$, depinning turns first--order already for $ζ_S>0$. Thus critical wetting may be impossible to observe on rough substrates.