Nematicity at the Hund's metal crossover in iron superconductors

Abstract

The theoretical understanding of the nematic state of iron-based superconductors and especially of FeSe is still a puzzling problem. Although a number of experiments call for a prominent role of local correlations and place iron superconductors at the entrance of a Hund's metal state, the effect of the electronic correlations on the nematic state has been theoretically poorly investigated. In this work we study the nematic phase of iron superconductors accounting for local correlations, including the effect of the Hund's coupling. We show that Hund's physics strongly affects the nematic properties of the system. It severely constrains the precise nature of the feasible orbital-ordered state and induces a differentiation in the effective masses of the $zx/yz$ orbitals in the nematic phase. The latter effect leads to distinctive signatures in different experimental probes overlooked so far in the interpretation of experiments. As notable examples the splittings between $zx$ and $yz$ bands at $\mathrm{\ensuremath{\Gamma}}$ and $M$ points are modified, with important consequences for angle-resolved photoemission spectroscopy measurements.