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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.
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Bostock et al. (1973) studied this question.
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