Effective forces between interfaces in type-I superconductors

Semi-infinite type-I superconductors with surface enhancement at the wall show interface delocalization transitions analogous to wetting transitions in classical liquids. Within Ginzburg-Landau theory the effective forces between the wall and the SC/N-interface decay exponentially (''short-range forces''). Going beyond GL-theory we show that in general planar interfaces of a type-I superconductor with vacuum, normal conductors or other superconductors interact via long-ranged (algebraic) dispersion forces. Invoking BCS-results for the dielectric function of a superconductor an algebraic correction to the effective interface potential of the unusual form V(l) ∝ l-5 is found, where l is the thickness of the surface superconducting sheath. This in contrast to classical fluids, where the retarded contribution is V(l) ∝ l-3. The effective force can be either attractive or repulsive depending on the superconductor used for surface enhancement. Consequences for the interface displacement transition scenario are outlined. (orig.)