Possible mixed coupling mechanism in FeTe1−xSex within a multiband Eliashberg approach

Abstract

We show that the phenomenology of the iron chalcogenide superconductor FeTe1−xSex can be explained within an effective three-band -wave Eliashberg model. In particular, various experimental data reported in literature—the critical temperature, the energy gaps, the upper critical field, the superfluid density—can be reproduced by this model in a moderate strong-coupling regime provided that both an intraband phononic term and an interband antiferromagnetic spin-fluctuations term are included in the coupling matrix. The intraband coupling is unusual in Fe-based compounds and is required to explain the somehow anomalous association between gap amplitudes and Fermi surfaces, already evidenced by ARPES.