Superconductivity in the amorphous phase of topological insulator BixSb100-x alloys

In this work we investigated the electrical properties of rapidly quenched amorphous BixSb100-x alloys in the temperature range of 1.2 K to 345 K. The resistance reveals that for a broad range of different compositions, including that for the topological insulator (TI), a superconducting state in the amorphous phase is present. After crystallization and annealing at an intermediate temperature, we found that in pure Bi and BixSb100-x alloys with composition corresponding to the TI, the superconductivity persists, but the transition shifts to a lower temperature. The highest superconducting transition temperature T-C0 was found for pure Bi and those TI's, with a shift to low temperatures when the Sb content is increased. After annealing at a maximum temperature of T = 345 K, the samples are non-superconducting within the experimental range and the behavior changes from semiconducting-like for pure Bi, to metallic-like for pure Sb. Transition temperature T-C0 of the amorphous BixSb100-x alloys have been calculated in the BCS-Eliashberg-McMillan framework, modified for binary alloys. The results can explain the experimental results and show that amorphous BixSb100-x exhibits a strong to intermediate electron-phonon coupling.