Critical Current and Electron Depairing in Superconducting Films

Abstract

By varying the magnetic flux enclosed by a cylindrical superconducting film, a supercurrent can be induced to flow in the film. A maximum in the current is reached at a certain value of flux, beyond which the current gradually decreases as a result of the breakup of electron pairs. The self-inductance of the cylinder prevents, however, the experimental study of the depairing situation. This difficulty can be overcome by filling the hollow cylinder with another superconductor whose Meissner effect reduces the flux linkage and the self-inductance of the film. This method of stabilizing the electron depairing should make possible the confirmation of both of the following effects of pair breakup: (a) almost normal tunneling current for voltages less than the gap voltage; (b) anisotropic-electromagnetic surface impedance of the supercurrent-carrying film.