Measurement of the superconducting energy gap anisotropy in single crystal gallium by superconductor-normal metal tunneling

Experiments are performed to answer some concerns regarding energy gap anisotropy. These experiments eliminate difficulties with (a) ac electronics, (b) negative resistance in S-S' junctions, (c) temperature extrapolation of 2Δ(T)/kT/sub c/ to T = 0, (d) noise pickup and, (e) sample preparation. The dc I-V curves of 15 N-S Ag(film)-Ga(crystal) tunnel junctions at 12 orientations in the Ga A-B plane (grown in a controlled environment room) were measured in a dilution refrigerator (T/T/sub c/ approximately 0.1) in a well shielded room. The data were digitized and fit to BCS-based theoretical I-V curves. The precision of 2Δ(O)/kT/sub c/ in the fits is 3-5 x 10-2 percent and the repeatability is 0.3 percent. 2Δ(O)/kT/sub c/ varies by 7 percent from the Ga A to B axis in good agreement with prior measurements