Determining accurate superconducting tunneling energy gaps: Anisotropy in single-crystal Nb

Superconducting tunneling experiments on niobium single crystals with indium and lead-bismuth counterelectrodes show an isotropic energy-gap value of 3.12±0.05 meV, or 3.93kTc, for 26 junction orientations. Self-consistent analysis criteria have been developed for the determination of gap values. These criteria are not met in the existing literature on transition-metal tunneling.