Density of States of a Short-Mean-Free-Path Superconductor in a Magnetic Field by Electron Tunneling

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Abstract
Measurements of the density of states of a thin-film, short-mean-free-path superconductor in a magnetic field are reported. The measurements were made on indium-tin films by a conventional tunneling technique. Temperatures near 0.5°K were used, in order to minimize thermal smearing. The magnetic field was in the plane of the film, and the film thickness was such that the order parameter was expected to be substantially independent of position. The results are in excellent agreement with theoretical calculations of Maki, except very close to the critical field, where small discrepancies occur. Maki's calculations predict gapless superconductivity close to the critical field, but thermal smearing prevented a direct verification. An attempt to fit the data to a BCS density of states with a field-dependent energy gap was completely unsuccessful except at zero field, where the two theories agree.