Orbital-selective Mottness in layered iron oxychalcogenides: the case of Na2Fe2OSe2

Using a combination of local density approximation and dynamical mean-field theory calculations, we explore the correlated electronic structure of a member of the layered iron oxychalcogenides group, Na2Fe2OSe2. We find that the parent compound is a multi-orbital Mott insulator. Surprisingly, and somewhat reminiscently of the underdoped high-Tc cuprate scenario, carrier localization is found to persist upon hole doping because the chemical potential lies in a gap structure with almost vanishing density of states. On the other hand, in remarkable contrast, electron doping drives an orbital-selective metallic phase with coexisting pseudogapped (Mott-localized) and itinerant carriers. These remarkably contrasting behaviors in a single system thus stem from drastic electronic reconstruction caused by large-scale transfer of dynamical spectral weight involving states with distinct orbital character at low energies, fitting the oxychalcogenides neatly into the increasingly visible pattern for Fe-based systems of having orbital-selective Mott phases. We detail the implications that follow from our analysis, and discuss the nature and symmetries of the superconductive states that may arise upon appropriately doping or pressurizing Na2Fe2OSe2.