Upper critical fields of amorphous transition metal based alloys

Abstract

The upper critical fields [ H c2 ( T)] for several superconducting amorphous transition metal alloys have been measured. At low temperatures and high fields, the behavior of the critical field cannot be described by existing theory. Corrections to the theory for electron spin and spin-orbit scattering effects, strong-coupling, purity, and anisotropy effects are not adequate to bring the theory into agreement with experiment even when an unphysical choice of correction parameters is assumed. Using the present and all other available H c2 ( T) data on three dimensional amorphous superconductors, we show that the magnitude of the deviation from theory is systematically related to the normal state electrical resistivity of the samples. We therefore argue that the breakdown of the theory is due to its failure to account for strong electron scattering effects. Such effects are associated with the disorder induced tendency toward Anderson localization.