Evidence for superconductive microsegregations in tin-doped bismuth

Results on the resistivity drop around 3.7 K, observed in pulled tin-doped (0.004- to 0.3-at.% Sn) bismuth single crystals, are reported. The drop is ascribed to the superconductive transition of segregated metallic tin in the $p$-type bismuth matrix. This is confirmed by the behavior observed in a magnetic field. It is suggested that these segregations, which could not be detected by classical methods of analysis, should be taken into account in interpreting the electronic properties and the scattering mechanisms in tin-doped bismuth.