SUPERCONDUCTIVITY AND DISSIPATION IN SMALL-DIAMETER PB-IN WIRES

Superconductivity in very small-diameter Pb-In wires has been studied through measurements of the resistance in the low-current limit, and the voltage-current characteristics. These properties were measured as functions of temperature and magnetic field, and in the presence of microwave radiation. The results are analyzed in terms of several different theoretical models. Predictions based on possible granularity and the Coulomb blockade, on the effects of mesoscopic fluctuations, and on the phenomena of thermal and quantum phase slip, are all considered. It appears that over most of the range which has been studied the behavior is best described by phase slip, and evidence for both thermally activated and quantum phase slip is found. The behavior during a phase-slip event is closely analogous to the motion of a particle in a multiwell potential. In this picture, thermally activated phase slip occurs when the particle is thermally activated over the potential barrier which separates adjacent wells, while quantum phase slip corresponds to tunneling of the particle between wells. We have also observed behavior which implies the existence of discrete energy levels of the particle within a well. While most of the results can be understood at least qualitatively with use of the phase-slip picture, certain aspects remain unexplained.