Emergence of nanoscale inhomogeneity in the superconducting state of a homogeneously disordered conventional superconductor, NbN

TL;DR

This study demonstrates that strong homogeneous disorder in NbN causes the superconducting state to spontaneously form nanoscale inhomogeneous domains, which persist above Tc and vanish near T*, revealing intrinsic inhomogeneity in disordered superconductors.

Contribution

The paper provides experimental evidence of spontaneous nanoscale inhomogeneity in a homogeneously disordered superconductor, advancing understanding of disorder effects in superconductivity.

Findings

Superconducting domains persist above Tc.

Domains disappear near pseudogap temperature T*.

Inhomogeneity arises from strong disorder and superconducting correlations.

Abstract

The notion of spontaneous formation of an inhomogeneous superconducting state is at the heart of most theories attempting to understand the superconducting state in the presence of strong disorder. Using scanning tunneling spectroscopy and high resolution scanning transmission electron microscopy, we experimentally demonstrate that under the competing effects of strong homogeneous disorder and superconducting correlations, the superconducting state of a conventional superconductor, NbN, spontaneously segregates into domains. Tracking these domains as a function of temperature we observe that the superconducting domains persist across the bulk superconducting transition, Tc, and disappear close to the pseudogap temperature, T*, where signatures of superconducting correlations disappear from the tunneling spectrum and the superfluid response of the system.