Contrasting the signatures of nematic order in 122 iron pnictides and 11 iron chalcogenides: a group theoretical analysis

Iron-based unconventional superconductors (FeSC) continue to draw interest because of the exotic electronic phases they host. The nematic order, which lowers the 4-fold rotational symmetry of the crystal structure, is widely observed in the normal phase of different FeSC families. Experiments reveal strong in-plane electronic anisotropy upon the onset of nematicity, however, a complete symmetry analysis of how the band structures of different FeSC families are affected by different types of nematic order parameters is still missing. In this work, we use group theory to contrast signatures of nematic order on the band dispersions of FeSC with space group P4/nmm (such as FeSe) and space group I4/mmm (such as BaFe₂As₂). We also perform density functional theory calculations to extract coefficients that determine the nematic-induced splittings of the relevant band degeneracies. Our predictions shed light on the interpretation of observed electronic degeneracies in these systems.