Nematic fluctuations and the magneto-structural phase transition in ${\rm Ba(Fe_{1-x}Co_x)_2As_2}$

TL;DR

This study uses Raman scattering to investigate nematic fluctuations in Ba(Fe_{1-x}Co_x)_2As_2, revealing their magnetic origin and their role in the material's structural and magnetic phase transitions.

Contribution

It provides experimental evidence linking nematic fluctuations to magnetic order and offers a theoretical explanation for the observed symmetry and temperature dependence.

Findings

Fluctuation response appears only in B_{1g} symmetry.

Fluctuation amplitude increases near the structural transition.

Magnetic order gap opens below T_{SDW}.

Abstract

An inelastic light (Raman) scattering study of nematicity and critical fluctuations in ${\rm Ba(Fe_{1-x}Co_x)_2As_2}$ ($0\le x \le 0.051$) is presented. It is shown that the response from fluctuations appears only in $B_{1g}$ (${x^2-y^2}$) symmetry. The scattering amplitude increases towards the structural transition at $T_s$ but vanishes only below the magnetic ordering transition at $T_{\rm SDW} < T_s$, suggesting a magnetic origin of the fluctuations. The theoretical analysis explains the selection rules and the temperature dependence of the fluctuation response. These results make magnetism the favorite candidate for driving the series of transitions.%Below $T_{\rm SDW}$ the gap of the magnetically ordered phase opens up.