Stress-induced nematicity in EuFe2As2 studied by Raman spectroscopy

We use polarized Raman scattering to study the structural phase transition in EuFe₂As₂, the parent compound of the 122-ferropnictide superconductors. The in-plane lattice anisotropy is characterized by measurements of the side surface with different strains induced by different preparation methods. We show that while a fine surface polishing leaves the samples free of residual internal strain, in which case the onset of the C₄ symmetry breaking is observed at the nominal structural phase transition temperature T_S, cutting the side surface induce a permanent fourfold rotational symmetry breaking spanning tens of degrees above T_S.