Stability of supercurrents in flat films of tin

Abstract

Using pulsed, 80-nsec-currents the stability of supercurrents in flat films of tin with compensating current return has been investigated. It is found that the voltage along the film rises with timet approximately asV=b+a[t′/2(t−c))1/2], whereb represents the (almost instantaneous) flux-flow voltage in a perpendicular field and the time constantt′ is an exponentially decreasing function ofJ(1+420/d)/[1−(T/Tc4][1−H⊥/Hc⊥]. HereJ is the current density in the film of thicknessd in A,T/Tc is the reduced temperature, andH⊥/Hc⊥ is the reduced magnetic field. It is suggested that this instability is of the type investigated by Kramer and by Fink and Presson for currents in a superconducting surface sheath. At lower temperatures a second instability is found which is distinctly different from the one dominant at the higher temperatures.