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

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 non-constant 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.

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