Signatures of multigap superconductivity in tunneling spectroscopy

Abstract

We considered a two-band superconductor with a nonzero interband quasiparticle coupling and numerically generated partial elementary excitation spectra for each band. These show deviations from the conventional Bardeen, Cooper, and Schrieffer form, resulting in characteristic signatures in the partial tunneling spectra. The total (measurable) tunneling spectra are calculated considering the $\mathbf{k}$ selection in the tunneling process. Due to the thermal smearing, the relevant spectral signatures may not be resolved in superconductor-insulator-normal-metal tunneling while they are clearly revealed in superconductor-insulator-superconductor (SIS) geometry. As an example, the excitation spectrum of $2{\text{H-NbSe}}_{2}$ is considered in the framework of the developed tunneling model. A remarkable agreement obtained with the experimental SIS data suggests the material to be a two-band superconductor rather than an anisotropic one.