MAGNETIC EFFECTS AND CURRENT SENSITIVITY OF SUPERCONDUCTING FILMS

Abstract

The work described in this paper is a continuation of the investigation of the anomalous behavior of superconducting metals in the form of thin films (12.2–0.3 μ). The manner in which an external magnetic field will penetrate when applied to superconducting films of various thicknesses at a variety of temperatures below their transition points has been studied. It is found that there is a critical field that will penetrate the film, and that this field is less than the threshold field required to restore the resistance of the film at the same temperature. Even for fields much larger than the threshold field, the films act as partial magnetic shields and diminish the field strength by an almost constant amount.By measuring the current required to restore the resistance of films formed on cylindrical supports of different diameters, it is shown that their current sensitivity is due to a surface density of current. The critical magnetic field associated with this threshold current is less than either the threshold field (external) or the critical field for penetration. The similarity between these effects and those found for certain superconducting alloys is discussed.