Phase slip centers in long superconducting aluminum microbridges

Abstract

Phase slip center (PSC) measurements in long superconducting aluminum microbridges are reported. The usual divergence of the effective size 2Λ of a PSC, as indicated by its differential resistance, occurs only at temperatures extremely close to the critical temperatureT c . At lower temperatures Λ is observed to be essentially constant; this is attributed to the onset of intermediate regions separating the core from the usual diverging regions of exponential electric field penetration (wings). In the low-temperature regime the equivalent decay time Λ2/D is found to be much larger (50 nsec) than the inelastic scattering time obtained from homogeneous charge imbalance experiments (12 nsec). In contrast, an analysis of the divergence gives the same order of magnitude (7 nsec). Furthermore, the onset of the intermediate regions is correlated with departure from local equilibrium close to the core. The effect of pair breaking on the local equilibrium condition is also discussed and compared with results from different experiments. Special emphasis is given to the interpretation of data from inhomogeneous samples where a spatially localized pair-breaking contribution is expected. Detailed analysis of the inhomogeneity itself provides complementary information as well as additional physical insight.