Model-independent determination of the gap function of nearly localized superconductors

TL;DR

This paper introduces a model-independent method to extract the superconducting gap function in nearly localized superconductors with non-constant density of states, demonstrated on TiN films, revealing unconventional features.

Contribution

A novel, model-independent approach for determining the gap function in complex superconductors with non-constant density of states.

Findings

Extracted gap function from TiN films showing unconventional features.

Indicated coupling to a soft pair-breaking mode.

Method applicable to other nearly localized superconductors.

Abstract

The gap function $\Delta(\omega)$ carries essential information on both, the pairing glue as well as the pair-breaking processes in a superconductor. Unfortunately, in nearly localized superconductors with a non-constant density of states in the normal state, the standard procedure for extraction of $\Delta(\omega)$ cannot be applied. Here, we introduce a model-independent method that makes it possible to extract $\Delta(\omega)$ also in this case. The feasibility of the procedure is demonstrated on the tunneling data for the disordered thin films of TiN. We find an unconventional feature of $\Delta(\omega)$ which suggests that the electrons in TiN are coupled to a very soft pair-breaking mode.