The intermediate type-I superconductors in the mesoscopic scale

Abstract

M. Tinkham and P. G. de Gennes, described in their books [1,2] the existence of an intermediate type-I superconductor as a consequence of an external surface that affects the well known classification of superconductors into type-I and II. Here we consider the mesoscopic superconductor where the ratio volume to area is small and the effects of the external surface are enhanced. By means of the standard Ginzburg-Landau theory the Tinkham-de Gennes scenario is extended to the mesoscopic type-I superconductor. We find new features of the transition at the passage from the genuine to the intermediate type-I. The latter has two distinct transitions, namely, from a paramagnetic to diamagnetic response in descending field and a quasi type-II behavior as the critical coupling 1/ √ 2 is approached in ascending field. The intermediate type-I phase proposed here, and its corresponding transitions, reflect intrinsic features of the superconductor and not its geometrical properties.