Bulk Tunneling Measurements of the Superconducting Energy Gaps of Gallium, Indium, and Aluminum
Since Giaever1 first reported superconductive tunneling into thin films attempts have been made to obtain tunneling data on single-crystal materials. Such data should yield a tremendous amount of information about the anisotropy of the pairing interaction, the Fermi surface, and the phonon spectrum. In other words, almost all of the real, anisotropic electronic properties and the lattice dynamics should be measureable with bulk tunneling. Early progress in performing such experiments was slow, but since the report by Zavaritskii of tunneling into single-crystal tin,2 bulk tunneling has been achieved into single crystals of most elemental superconductors.3 Still the problem remains of obtaining large amounts of data on samples of a desired orientation. In addition, problems of interpretation of the data are now being discussed. The selection rules that determine the portions of the Fermi surface participating in the tunneling process, as well as the role of the barrier in selecting the tunneling direction relative to the sample surface, are not quite clear.4 In this paper we report our progress in making large numbers of acceptable samples, with controlled orientation, and interpreting the tunneling data obtained from them for three superconductors: indium, aluminum, and gallium.
KeywordsFermi Surface Versus Curve Tunnel Junction Tunneling Direction Sharp Cusp
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