Analysis of the proximity-induced Josephson effect in superconducting-normal contacts

Several investigators have observed microwave-induced steps and other Josephson-like features in the I-V characteristics of point contacts between a conventional superconductor (S) and a normal metal (N). Recently, S. Han et al. have interpreted these results in terms of a model of a proximity-induced Josephson effect (PIJE) in an SN contact and have used this model to infer the existence of p-wave pairing in superconducting ${\mathrm{UBe}}_{13}$. We show that their model is incorrect on fundamental grounds, and that their PIJE analysis is in direct conflict with long-standing theoretical and experimental studies of the pair-field susceptibility in SN tunnel junctions. In addition, we outline a possible alternative explanation for the experimental observations of Han et al. based on a model of a phase-slip center near the tip of the S point in an SN contact.