# Nematic Fluctuations and Phase Transitions in LaFeAsO: a Raman Scattering Study

## TL;DR

This study uses Raman scattering to investigate nematic fluctuations and phase transitions in LaFeAsO, revealing that magnetic fluctuations drive the structural transition and highlighting differences in nematic dynamics compared to related compounds.

## Contribution

It provides new insights into the role of magnetic degrees of freedom in structural transitions of LaFeAsO through Raman scattering analysis.

## Key findings

- Nematic fluctuations are observed via a quasi-elastic peak in Raman spectra.
- Magnetic degrees of freedom drive the structural transition in LaFeAsO.
- Nematic fluctuations exhibit slower dynamics compared to BaFe2As2.

## Abstract

Raman scattering experiments on LaFeAsO with splitted antiferromagnetic (T_AFM = 140 K) and tetragonal-orthorhombic (T_S = 155 K) transitions show a quasi-elastic peak (QEP) in B2g symmetry (2 Fe tetragonal cell) that fades away below ~T_AFM and is ascribed to electronic nematic fluctuations. A scaling of the reported shear modulus with the T-dependence of the QEP height rather than the QEP area indicates that magnetic degrees of freedom drive the structural transition. The large separation between T_S and T_AFM in LaFeAsO compared with their coincidence in BaFe2As2 manifests itself in slower dynamics of nematic fluctuations in the former.