Phenomenological theory of the surface nucleation field in anisotropic superconductors

Abstract

Abstract The surface nucleation field for anisotropic (conventional) superconductors is calculated for an arbitrary modification of the superconducting transition temperature near the surface. We use, as a phenomenological description, anisotropic Ginzburg‐Landau theory including appropriate surface terms. A uniaxial situation, as in layered high‐ T c compounds, is considered, with the external magnetic field oriented along one of the main crystallographic axes. The resulting nucleation fields are all determined by a single universal curve (and appropriate direction‐dependent scaling factors). Depending on the surface state, both an enhancement and a suppression of the usual third critical field 1.7 H c2 may occur. The results are relevant for layered compounds, in particular for high‐ T c materials, where the surface conditions depend sensitively on the nature of the first layer on top of the surface.