Stress-induced nematicity inEuFe2As2studied by Raman spectroscopy

We use polarized Raman scattering to study the structural phase transition in ${\mathrm{EuFe}}₂{\mathrm{As}}₂$, 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 ${C}₄$ symmetry breaking is observed at the nominal structural phase transition temperature ${T}_S$, cutting the side surface induces a permanent fourfold rotational symmetry breaking spanning tens of degrees above ${T}_S$.