Structure of Neutron-Scattering Peak in both s++ wave and s+- wave states of an Iron pnictide Superconductor

TL;DR

This study analyzes neutron scattering spectra in iron pnictide superconductors, revealing that a broad spectral peak can be explained by an s++ wave state with quasiparticle damping effects, aligning with experimental observations.

Contribution

It demonstrates that the broad spectral peak in iron pnictides can be explained by the s++ wave state considering quasiparticle damping, challenging the exclusive association with s+- states.

Findings

Hump structure appears above the spectral gap in s++ state due to damping effects.

Broad spectral peak observed experimentally can be reproduced with s++ wave state.

Resonance-like peak in s+- state is larger than in s++ state.

Abstract

We study the neutron scattering spectrum in iron pnictides based on the random-phase approximation in the five-orbital model, for fully-gapped s-wave states with sign reversal (s+-) and without sign reversal (s++). In the s++ wave state, we find that a prominent hump structure appears just above the spectral gap, by taking account of the quasiparticle damping gamma due to strong electron-electron correlation: As the superconductivity develops, the reduction in gamma gives rise to the large overshoot in the spectrum above the gap. The obtained hump structure looks similar to the resonance peak in the s+- wave state, although the height and weight of the peak in the latter state is much larger. In the present study, experimentally observed broad spectral peak in iron pnictides is naturally reproduced by assuming the s++ wave state.