Wetting-like phase transitions in a surface-enhanced type-I superconductor*

Superconductivity in single crystal Sn samples with surface enhanced order parameter was studied experimentally. Controllable surface enhancement was achieved by mechanical polishing or by ion irradiation. A first-order surface superconductivity transition was found in parallel magnetic fields close to the bulk critical field Hc(T) and for temperatures above 0.8Tc up till a surface critical temperature Tcs higher than Tc, where Tc is the bulk critical temperature. The resulting phase diagram agrees with that predicted for interface delocalization or wetting transitions in type-I superconductors, based on the Ginzburg--Landau theory.