Phase fluctuations in a strongly disordered s-wave superconductor close to the metal-insulator transition

TL;DR

This study investigates how phase fluctuations affect a strongly disordered NbN superconductor near the metal-insulator transition, revealing a pseudogap state caused by phase fluctuations above Tc.

Contribution

It provides experimental evidence that phase fluctuations induce a pseudogap state in a disordered s-wave superconductor close to the metal-insulator transition.

Findings

Finite electronic gap persists above Tc in strong disorder.

Superfluid density is suppressed and becomes linear with temperature.

Phase fluctuations lead to pseudogap formation in disordered superconductor.

Abstract

We explore the role of phase fluctuations in a 3-dimensional s-wave superconductor, NbN, as we approach the critical disorder for the destruction of the superconducting state. Scanning tunneling spectroscopy measurements reveal that in the presence of strong disorder, a finite gap in the electronic spectrum continues to persist at temperatures above Tc. With increase in disorder, the superfluid density is strongly suppressed at low temperatures and evolves towards a linear-T variation at higher temperatures. These observations provide strong evidence that phase fluctuation leads to the formation of a pseudogap state in a disordered conventional superconductor.