Predictions of Multiband s± Strong-Coupling Eliashberg Theory Compared to Experimental Data in Iron Pnictides

Abstract

The experimental critical temperatures and the gap values of the superconducting materials LaFeAsO1−xFx, SmFeAsO1−xFx and Ba1−xKxFe2As2, which are exponent of the most important families (1111 and 122) of iron pnic- tides, can be reproduced by an effective s-wave three-band Eliashberg model in which the dominant coupling is in the interband channel and the order parameter is nodeless but undergoes a sign reversal between hole and electron bands (s± symmetry). In particular, high values of the electron- boson coupling constants and small typical boson energies (in agreement with neutron diffraction experiments) are nec- essary to reproduce the exact Tc, the experimental gap values and their temperature dependence. The same parameters al- low fitting the experimental temperature dependence of the upper critical field and predicting the presence of character- istic structures related to the electron-boson coupling in the Andreev-reflection spectra.