Effects of disorder induced by heavy-ion irradiation on (Ba K )FeAs single crystals, within the three-band Eliashberg s± wave model.

One of the open issues concerning iron-based superconductors is whether the s± wave model is able to account for the overall effects of impurity scattering, including the low rate of decrease of the critical temperature with the impurity concentration. Here we investigate Ba K FeAs crystals where disorder is introduced by Au-ion irradiation. Critical temperature, T , and London penetration depth, λ , were measured by a microwave resonator technique, for different values of the irradiation fluence. We compared experimental data with calculations made on the basis of the three-band Eliashberg equations, suitably accounting for the impurity scattering. We show that this approach is able to explain in a consistent way the effects of disorder both on T and on λ (T), within the s± wave model. In particular, a change of curvature in the low-temperature λ (T) curves for the most irradiated crystals is fairly well reproduced.