Onset of superconductivity in 2D granular films composed of Bi clusters

TL;DR

This paper investigates how the superconducting transition in 2D Bi cluster films depends on cluster size and matrix effects, revealing quantum size effects and surface superconductivity phenomena.

Contribution

It demonstrates the influence of cluster size and matrix on superconductivity in 2D Bi films, highlighting quantum size effects and surface superconductivity.

Findings

Superconducting transition temperature varies with cluster size.

Quantum size effects are observed with changing deposition temperature.

Superconductivity likely occurs at the surface of Bi clusters.

Abstract

Two dimensional films comprising of Bi clusters ranging in size from 25 to 100 $\mathrm{\AA}$ show an influence of the underlying matrix on normal state resistivity and the superconducting transition temperature $T_\mathrm{c}$. This is in contrast to crystalline Bi. Quantum size effects are observed by changing the deposition temperature, which determines cluster size. These observations can be attributed to superconductivity at the surface. Implications for the requirement of a critical number of superconducting clusters before the establishment of global phase coherence are briefly discussed.