Proximity effect in granular superconductor-normal metal structures

TL;DR

This study investigates how the proximity effect manifests in three-dimensional granular superconductor-normal metal structures, demonstrating that theoretical models can be adapted to describe random mixtures within the Cooper limit.

Contribution

It extends proximity effect theories from bilayers to granular mixtures, showing experimental validation in disordered Pb-Cu structures within the Cooper limit.

Findings

Proximity effect theories can be adapted for granular structures.

Experimental data fit well with de Gennes weak coupling limit theory.

The Cooper limit applies over a wide concentration range in granular systems.

Abstract

We fabricated three-dimensional disordered Pb-Cu granular structures, with various metal compositions. The typical grain size of both metals is smaller than the superconductor and normal metal coherence lengths, thus satisfying the Cooper limit. The critical temperature of the samples was measured and compared with the critical temperature of bilayers. We show how the proximity effect theories, developed for bilayers, can be modified for random mixtures and we demonstrate that our experimental data fit well the de Gennes weak coupling limit theory in the Cooper limit. Our results indicate that, in granular structures, the Cooper limit can be satisfied over a wide range of concentrations.