Metallic to tunneling transition in Cu-Nb point contacts

In a recent paper we proposed a detailed theory for the $I\ensuremath{-}V$ 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.

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