Heat-capacity measurements of the critical coupling between aluminum grains

Abstract

We have measured the heat capacity of granular aluminum specimens with normal-state resistivities N between 0.6×10-3 and 40 × 10-3 cm. The specimens become superconducting with a heat-capacity transition which is BCS-like for the lowest N, and then diminishes until it is no longer observable for the highest N. We conclude that the grains become decoupled such that, because of their small size, they do not exhibit bulk superconductivity when they are isolated. © 1978 The American Physical Society.