Impurity-induced smearing of the spin resonance peak in Fe-based superconductors

TL;DR

This paper investigates how nonmagnetic disorder affects the spin resonance peak in iron-based superconductors, showing that disorder broadens and shifts the peak, but the $s_$ state remains distinguishable from the $s_{++}$ state.

Contribution

It provides a theoretical analysis of impurity effects on the spin resonance in Fe-based superconductors using multi-band models and RPA calculations.

Findings

Disorder broadens the resonance peak.

Resonance energy shifts to higher frequencies with disorder.

The $s_$ state remains distinguishable from the $s_{++}$ state despite disorder.

Abstract

The spin resonance peak in the iron-based superconductors is observed in inelastic neutron scattering experiments and agrees well with predicted results for the extended s-wave ($s_\pm$) gap symmetry. On the basis of four-band and three-orbital tight binding models we study the effect of nonmagnetic disorder on the resonance peak. Spin susceptibility is calculated in the random phase approximation with the renormalization of the quasiparticle self-energy due to the impurity scattering in the static Born approximation. We find that the spin resonance becomes broader with the increase of disorder and its energy shifts to higher frequencies. For the same amount of disorder the spin response in the $s_\pm$ state is still distinct from that of the $s_{++}$ state.