Superconductivity of vacuum-deposited bismuth films

Abstract

The superconducting transition in conjunction with structural changes of amorphous bismuth thin films is investigated by way of electrical resistance measurements and low-temperature electron diffraction. In the process of annealing, bismuth films show two distinct stages of superconducting transition. One, at higher temperature, is associated with a sharp drop in the film resistance and its critical temperature gradually decreases by annealing to higher temperatures. The other, at lower temperature, exhibits a gradual decrease in resistance due to a widespread transition over a few degrees. Using low-temperature electron diffraction, a mixture of the amorphous phase and the crystalline phase with the normal rhombohedral structure is observed and no intermediate phase is observed during the crystallisation process. The two-step superconducting transition is interpreted by the size distribution of residual amorphous regions in the film.