Universal Broadening of the Bardeen-Cooper-Schrieffer Coherence Peak of Disordered Superconducting Films

TL;DR

This paper investigates how mesoscopic fluctuations and Coulomb interactions universally broaden the BCS coherence peak in disordered superconducting films, especially near the quantum critical point.

Contribution

It reveals the universal mesoscopic effects on the BCS peak broadening and their enhancement by Coulomb repulsion in disordered superconductors.

Findings

Mesoscopic fluctuations cause universal broadening of the BCS peak.

Coulomb repulsion enhances the smearing effects.

Strong peak smearing occurs near the quantum critical point.

Abstract

In disordered superconductors, the local pairing field fluctuates in space, leading to the smearing of the BCS peak in the density of states and appearance of the subgap tail states. We analyze the universal mesoscopic contributions to these effects and show that they are enhanced by the Coulomb repulsion. In the vicinity of the quantum critical point, where superconductivity is suppressed by the "fermionic mechanism", strong smearing of the peak due to mesoscopic fluctuations is predicted.