Fluctuation current in superconducting loops

Abstract

A superconducting loop that encloses noninteger flux holds a permanent current. On the average, this current is also present above Tc, and has been measured in recent years. We are able to evaluate the permanent current within the TDGL or the Kramer-Watts-Tobin models for loops of general configuration, i.e., we don't require uniform cross section, material or temperature. We can also consider situations in which the width is not negligible in comparison to the radius. Our results agree with experiments. The situations with which we deal at present include fluctuation superconductivity in two-band superconductors, equilibrium thermal fluctuations of supercurrent along a weak link, and ratchet effects. © Published under licence by IOP Publishing Ltd.