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

Abstract

The gap function Δ(ω) 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 nonconstant density of states in the normal state, the standard procedure for extraction of Δ(ω) cannot be applied. Here we introduce a model-independent method that makes it possible to extract Δ(ω) 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 Δ(ω) which suggests that the electrons in TiN are coupled to a very soft pair-breaking mode.