WETTING PHASE TRANSITIONS AND SUPERCONDUCTIVITY The Role of Surface Enhancement of the Order Parameter in the GL Theory

摘要

The principal subject of these lectures is the precise analogy between a wetting phase transition in an adsorbed fluid and the interface delocalization transition in a type-I superconductor. Although there is up to now very sparse experimental evidence of this phenomenon in superconductors, the Ginzburg-Landau (GL) theory gives a detailed prediction of the "wetting" phase diagram for type-Ⅰ materials that can in principle be verified directly by magnetization or resistivity measurements. In addition, the mechanism responsible for the transition can occur equally well in type-Ⅱ superconductors, for which it leads to interesting modifications of the phase diagram of critical field versus temperature, including an increase of T_c in zero field. A microscopic identification and derivation of the mechanism is still lacking, but at the phenomenological level of the GL theory the mechanism is the enhancement of the superconducting order parameter at the surface.