Effect of electron correlations on spin excitation bandwidth in Ba$_{0.75}$K$_{0.25}$Fe$_{2}$As$_{2}$ as seen via time-of-flight inelastic neutron scattering

TL;DR

This study uses inelastic neutron scattering and theoretical analysis to show that electron correlations significantly narrow the spin excitation bandwidth in Ba$_{0.75}$K$_{0.25}$Fe$_{2}$As$_{2}$, emphasizing their role in spin dynamics of iron-based superconductors.

Contribution

The paper combines experimental neutron scattering data with first-principles calculations to demonstrate how electron correlations affect spin excitation bandwidth in an iron-based superconductor.

Findings

Spin-wave-like dispersive spin excitations with 200 meV zone boundary energy.

Electron correlations lead to a mass renormalization factor of 3.

Correlations cause a substantial narrowing of the spin excitation bandwidth.

Abstract

We use inelastic neutron scattering (INS) to investigate the effect of electron correlations on spin dynamics in the iron-based superconductor Ba$_{0.75}$K$_{0.25}$Fe$_{2}$As$_{2}$. Our INS data show a spin-wave-like dispersive feature, with a zone boundary energy of 200 meV. A first principles analysis of dynamical spin susceptibility, incorporating the mass renormalization factor of 3, as determined by angle-resolved photoemission spectroscopy, provides a reasonable description of the observed spin excitations. This analysis shows that electron correlations in the Fe-3$d$ bands yield enhanced effective electron masses, and consequently, induce substantial narrowing of the spin excitation bandwidth. Our results highlight the importance of electron correlations in an itinerant description of the spin excitations in iron-based superconductors.