Suppression of superconductivity in granular metals

TL;DR

This paper studies how Coulomb repulsion suppresses superconductivity in granular metals with high tunneling conductance, revealing conditions for insulating, superconducting, or metallic phases.

Contribution

It provides a theoretical analysis of the suppression of superconductivity in granular systems at large tunneling conductance, identifying different phase regimes based on system parameters.

Findings

Superconducting transition temperature is suppressed by Coulomb repulsion in granular metals.

Granular samples can be classified into two groups with distinct phase behaviors.

An intermediate metallic phase exists where superconductivity is suppressed but Coulomb blockade effects are weak.

Abstract

We investigate the suppression of the superconducting transition temperature due to Coulomb repulsion in granular metallic systems at large tunneling conductance between the grains, $g_{T}\gg 1$. We find the correction to the superconducting transition temperature for 3$D$ granular samples and films. We demonstrate that depending on the parameters of superconducting grains, the corresponding granular samples can be divided into two groups: (i) the granular samples that belong to the first group may have only insulating or superconducting states at zero temperature depending on the bare intergranular tunneling conductance $g_T$, while (ii) the granular samples that belong to the second group in addition have an intermediate metallic phase where superconductivity is suppressed while the effects of the Coulomb blockade are not yet strong.