Confinement of superconducting fluctuations due to emergent electronic inhomogeneities

Abstract

How a disordered superconductor evolves into an insulator is still a matter of intense debate. Disorder and reduced screening of Coulomb repulsion may simply break the pairs or, alternatively, the Cooper pairs themselves may localize. Thin disordered NbN films fall between these two extremes and display intermediate scale inhomogeneity with anomalous properties, which are studied by the authors using Scanning Tunneling Spectroscopy and transport measurements. While STS exhibits inhomogeneity at distances much larger the typical size of the nanocrystals constituting the NbN films, the conductivity fluctuations near the superconductor-insulator transition have effectively a zero-dimensional character similar to the one previously found only in granular systems.