INSTABILITY OF SUPERCONDUCTING STATE IN JOSEPHSON TUNNEL JUNCTIONS.

Experiments on low-resistance Josephson Sn-I-Sn tunnel junctions have shown the superconductor to exhibit an instability that manifests itself on the current-voltage characteristic (IVC) in the form of a jumplike decrease of the voltage when it reaches a value 2 DELTA /e. When a weak magnetic field H is applied parallel to the junction plane and suppresses the nonstationary Josephson effect, the negative-slope IVC section vanishes. The H-dependent instability-current component, as well as the dc component of the Josephson current near 2 DELTA /e, can be approximated by a function of H** minus **2. The singularity observed is attributed to the presence of a maximum of the superconducting component, due to the Riedel singularity, at V equals 2 DELTA /e.