Magnetic-Field-Induced Surface States in a Pure Type-I Superconductor

Abstract

We consider the problem of a bulk pure type-I superconductor in a static magnetic field ($H<\mathrm{}{H}_c$) applied parallel to the surface. We show that there may exist single-particle excitations of energy (relative to the Fermi energy) less than the zero-field energy gap, which are spatially bound to the surface region where the screening current flows. We then investigate the contribution of these localized states to the electromagnetic absorption of the superconductor at frequencies below the zero-field absorption edge ($2\Delta$). Order-of-magnitude estimates seem to be in agreement with the observations in aluminum by Budzinski and Garfunkel.