Effects of magnetism and doping on the electron-phonon coupling in BaFe2As2

We calculate the effect of local magnetic moments on the electron-phonon coupling in BaFe2As2+δ using the density functional perturbation theory. We show that the magnetism enhances the total electron-phonon coupling by ∼ 50%, up to λ . 0.35, still not enough to explain the high critical temperature, but strong enough to have a non-negligible effect on superconductivity, for instance, by frustrating the coupling with spin fluctuations and inducing order parameter nodes. The enhancement comes mostly from a renormalization of the electron-phonon matrix elements. We also investigate, in the rigid band approximation, the effect of doping, and find that λ versus doping does not mirror the behavior of the density of states; while the latter decreases upon electron doping, the former does not, and even increases slightly.