Possible mixed coupling mechanism in FeTe_(1-x)Se_(x) within a multiband Eliashberg approach

We show that the phenomenology of the iron chalcogenide superconductor FeTe1-x Se x can be explained within an effective three-band [Formula: see text]-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.