Deviating band symmetries and many-body interactions in a model hole-doped iron pnictide superconductor

We present a polarization-resolved study of the low-energy band structure in the optimally doped iron pnictide superconductor Ba _0.6K _0.4Fe ₂As ₂ (T _c=37 K) using angle-resolved photoemission spectroscopy. Polarization-contrasted measurements are used to identify and trace all three low-energy holelike bands predicted by local density approximation (LDA) calculations. The photoemitted electrons reveal an inconsistency with LDA-predicted symmetries along the Γ-X high-symmetry momentum axis, due to unexpectedly strong rotational anisotropy in electron kinetics. We evaluate many-body effects such as Mott-Hubbard interactions, which are likely to underlie the anomaly, and discuss how the observed deviations from LDA band structure affect the energetics of iron pnictide Cooper pairing in the hole-doped regime.