Observation of superconductivity in granular bi nanowires fabricated by electrodeposition

Bulk rhombohedral Bi at ambient pressure is a well-known semimetal, and its transition to a superconductor has not been observed, at least down to 50 mK. We report that, unlike bulk rhombohedral Bi, granular Bi nanowires with well-defined rhombohedral grains of similar to 10 nm diameter, fabricated by electrochemically depositing Bi into porous polycarbonate membranes at ambient pressure, are superconducting with two transition temperatures, T-c, of 7.2 and 8.3 K. These T-c values coincide with T-c values of the high-pressure phases Bi-III and Bi-V, respectively. Analysis of our structural and transport data indicates that the superconductivity in granular Bi nanowires probably arises from grain boundary areas where there are structural reconstructions between the grains showing a preferred orientation within a small angular distribution.