Stress-induced nematicity in EuFe2As2 studied by phononic 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 using 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 Ts, cutting the side surface induces a permanent four-fold rotational symmetry C4 breaking spanning tens of degrees above Ts.