Point-contact Andreev-reflection spectroscopy in Fe(Te,Se) films: multiband superconductivity and electron-boson coupling

Abstract

We report on a study of the superconducting order parameter in thin films (with different Se contents: ) by means of point-contact Andreev-reflection spectroscopy (PCARS). The PCARS spectra show reproducible evidence of multiple structures, namely two clear conductance maxima associated to a superconducting gap of amplitude and additional shoulders at higher energy that, as we show, are the signature of the strong interaction of charge carriers with a bosonic mode whose characteristic energy coincides with the spin-resonance energy. The details of some PCARS spectra at low energy suggest the presence of a smaller and not easily discernible gap of amplitude . The existence of this gap and its amplitude are confirmed by PCARS measurements in single crystals. The values of the two gaps and , once plotted as a function of the local critical temperature , turn out to be in perfect agreement with the results obtained by various experimental techniques reported in literature.