Metallic to tunneling transition in Cu-Nb point contacts

Abstract

In a recent paper we proposed a detailed theory for the $I-V$ curves of a normal-superconductor microconstriction, predicting a smooth crossover from metallic to tunnel-junction behavior. This paper describes experiments on Cu-Nb point contacts which span the crossover regime. We find excellent quantitative agreement between theory and experiment over a substantial range of contact resistances.