Electron–phonon coupling in BaFe₂As₂: A possible origin of nematic phase

Highlights: • Strong electron–phonon coupling is observed for B_1g phonon mode. • B_1g mode can be effectively coupled with d_xz and d_yz orbits. • Electron–phonon coupling may be the origin of nematic phase. - Abstract: Iron-based superconductors have the second-highest superconducting transition temperature next to cuprate superconductors. There are many electronic phases such as superconducting, antiferromagnetic and nematic phases, coexisting in the family of iron pnictides. The charge/spin orders are the key factors for understanding the mechanism of high-temperature superconductivity. In this paper we have performed a Raman scattering study of parent compound BaFe₂As₂. A relatively strong electron–phonon coupling is observed for B_1g phonon mode and is weakened after the structural transition at ∼140 K. Through a careful symmetry analysis, we revealed the possibility that B_1g mode can be effectively coupled with d_xz and d_yz orbits. The coupling can remove the degeneracy of the two orbits and further cause the fluctuations of electronic nematic phases. The study suggests that electron–phonon coupling can be a possible origin of nematic phase.