Effects of magnetism and doping on the electron-phonon coupling in BaFe$_{2}$As$_{2}$

TL;DR

This study uses density functional perturbation theory to show that magnetism increases electron-phonon coupling in BaFe$_{2}$As$_{2}$, influencing superconductivity but not enough to explain high critical temperatures.

Contribution

It demonstrates that local magnetic moments enhance electron-phonon coupling in BaFe$_{2}$As$_{2}$, highlighting the role of magnetism in superconductivity.

Findings

Magnetism increases electron-phonon coupling by ~50%.

Doping does not mirror the density of states behavior.

Enhanced coupling affects superconductivity by frustrating spin fluctuation interactions.

Abstract

We calculate the effect of local magnetic moments on the electron-phonon coupling in BaFe$_{2}$As$_{2}+\delta$ using the density functional perturbation theory. We show that the magnetism enhances the total electron-phonon coupling by $\sim 50%$, up to $\lambda \lesssim 0.35$, 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 $\lambda$ 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.