Tunable granularity of superconducting Pb films on substrates with different thermal conductivity

Abstract

Among various ways to tune the granularity in superconducting films, the effect of substrate thermal conductivity has rarely been considered. Here, as an effort to further study the effect of granularity on superconducting properties, superconducting Pb films with different granularity and morphology were grown on substrates with different thermal conductivity by using low temperature electron beam evaporation technique. Despite the similar lattice mismatch ratio, the granularity of Pb films changes monotonically with the substrate thermal conductivity. With decreasing the grain size, the upper critical field of Pb films increases, and Pb films tend to feature flux avalanche at low magnetic fields. Further analysis suggests that, the pinning mechanism gradually evolves from mixed δTc+δl to δl pinning. Our results further enrich the way to tune granularity of superconducting films, and open up a promising perspective for studying the pinning mechanism of granular superconductors and provide favorable conditions for potential applications of manipulative vortex pinning by adjusting the granularity of superconducting films.