Investigation of the Superconducting-Energy-Gap Behavior of Single-Crystal Rhenium by Tunneling

A 15.7% anisotropy in the superconducting energy gap has been measured by electron tunneling into single crystals of rhenium, using thin carbon films as the tunneling barrier to form Re-C-In sandwiches. The energy-gap behavior vs temperature is BCS-like. The anisotropy agrees with ultrasonic measurements of other hcp metals and suggests that phonon dispersion plays a dominating role in the gap behavior. However, gap values determined from multiparticle tunneling data exhibited reduced gap magnitudes and a dissimilar crystallographic behavior.