Tunneling into Superconducting Films in a Magnetic Field

Abstract

Tunneling experiments were performed on thin superconducting films in the presence of a magnetic field. The experiments were done at ${\mathrm{He}}^3$ temperatures on tin and tin-indium alloy films with thicknesses between 600 and 2000 Å. As expected theoretically, the effect of the field on the density of states is, for dirty films, similar to the effect of paramagnetic impurities with the square of the magnetic field playing a role analogous to the paramagnetic impurity concentration. The data are compared with the theoretical results of Maki for the limit of zero mean free path, and agreement is fair. The difference between these results and those of this experiment is attributed to the finite mean free path. Strässler and Wyder have calculated the field dependence of the density of states for small particles with arbitrary mean free path. We find that their calculations are in good agreement with experiment.