Anomalous magneto-elastic coupling in Au-doped BaFe2As2

TL;DR

This study investigates how Au-doping affects magneto-elastic interactions in BaFe2As2 using Raman scattering, revealing enhanced phonon intensity and asymmetric line shapes linked to magnetic order, indicating strong magneto-elastic coupling.

Contribution

It demonstrates the anomalous behavior of the $A_g$(As) phonon mode in Au-doped BaFe2As2 and models its interaction with magnetic excitations via a Fano resonance, highlighting doping-dependent magneto-elastic coupling.

Findings

Enhanced $A_g$(As) phonon intensity below $T_N$

Asymmetric phonon line shape and linewidth broadening with Au-doping

Magneto-elastic coupling proportional to magnetic order parameter

Abstract

We used polarization-resolved Raman scattering to study magneto-elastic coupling in Ba(Fe$_{1-x}$Au$_{x}$)$_2$As$_2$ crystals as a function of light Au-doping, materials for which temperatures of the structural transition ($T_S$) and of the magnetic ordering transition ($T_N$) split. We study the appearance of the $A_g$(As)phonon intensity in the $XY$ scattering geometry that is very weak just below $T_S$, but for which the intensity is significantly enhanced below $T_N$. In addition, the $A_g$(As) phonon shows an asymmetric line shape below $T_N$ and an anomalous linewidth broadening upon Au-doping in the magnetic phase. We demonstrate that the anomalous behavior of the $A_g$(As) phonon mode in the $XY$ scattering geometry can be consistently described by a Fano model involving the $A_g$(As) phonon mode interacting with the $B_{2g}$ symmetry-like magnetic continuum in which the magneto-elastic coupling constant is proportional to the magnetic order parameter.