Nonlocal Correlations in Iron Pnictides and Chalcogenides

Deviations of low-energy electronic structure of iron-based superconductors from density functional theory predictions have been parameterized in terms of band-dependent mass renormalizations and energy shifts. Theoretically, these have typically been described either in terms of a local self-energy within the framework of Dynamical Mean Field Theory, or in terms of nonlocal effects due to interband scattering. By calculating the renormalized bandstructure in both random phase approximation and the two-particle self-consistent approximation, we show that correlations in pnictide systems like LaFeAsO and LiFeAs can be described rather well by nonlocal correlations. In particular, Fermi pocket shrinkage as seen in experiment occurs along the paradigm of interband scattering scenario. We also show agreement with experimentally observed non-local scattering lifetime data for LiFeAs. Next, we compare with the canonical iron chalcogenide system FeSe in its bulk tetragonal phase, and show that band renormalizations are completely inconsistent with this picture. We discuss possible reasons for this discrepancy.