Superconductivity in Lightly Doped Crystalline Bismuth

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Abstract
Using a sensitive SQUID (superconducting quantum interference device) detector and well-shielded dilution refrigerator, we have observed a broad resistance transition below about 1 K on samples of crystalline Bi lightly doped with either tin (0.02-0.23 at.% Sn) or tellurium (0.1 at.% Te). Between 30 mK, which is the lowest temperature available to us, and 60 mK, the resistance of samples containing 0.08-, 0.12-, and 0.16-at.% Sn actually disappears and the transition temperature increases with increasing amounts of Sn.