Origin of ’’capacitance’’ in superconducting microbridges

Abstract

The geometrical interelectrode capacitances of superconducting microbridges are too small to account for the observed hysteresis in their I-V characteristics. We propose a new model of microbridges in finite voltages, in which the relevant time constant is the supercurrent relaxation time τR. From an analysis of the experimental I-V curves it follows that τR can be identified with the pair relaxation time within a numerical factor. By equating τR/2π to the time constant C/G of the shunted Josephson junction model, we obtain values of C in reasonable agreement with those typically obtained from I-V characteristics.