Current-induced breakdown of superconductivity in constricted type I superconducting films

Abstract

In simultaneous magneto-optical and electrical measurements on constricted type I superconducting films we have correlated step structure in the currentvoltage characteristic with the nucleation of individual flux-tube trains. A central feature of this experiment is the development of a sample geometry with which we can restrict the breakdown behavior to a single, localized flux-tube train running perpendicular to the transport current. Apparently, the step structure in the I–V characteristic results from a Gibbs free-energy barrier against the nucleation of flux-tube trains. The experiments are performed with films of lead and indium. From the I–V characteristics of the indium constrictions we conclude that the flux-tube nucleation rate can vary substantially with applied current beyond a voltage step at temperatures near Tc.