Orbital differentiation and the role of orbital ordering in the magnetic state of Fe superconductors

TL;DR

This paper investigates the orbital differentiation and ordering in the magnetic state of iron superconductors, revealing a complex interplay between itinerant and localized behaviors influenced by interactions and doping.

Contribution

It introduces a detailed analysis of orbital differentiation and ordering in a five-orbital model, highlighting the non-trivial evolution from itinerant to localized regimes.

Findings

Orbital differentiation occurs between xy, yz, and zx orbitals.

Orbital ordering arises from exchange and kinetic energy interplay.

Iron superconductors are near the boundary between regimes, tunable by doping.

Abstract

We analyze the metallic (pi,0) antiferromagnetic state of a five-orbital model for iron superconductors. We find that with increasing interactions the system does not evolve trivially from the pure itinerant to the pure localized regime. Instead we find a region with a strong orbital differentiation between xy and yz, which are half-filled gapped states at the Fermi level, and itinerant zx, 3z^2-r^2 and x^2-y^2. We argue that orbital ordering between yz and zx orbitals arises as a consequence of the interplay of the exchange energy in the antiferromagnetic x direction and the kinetic energy gained by the itinerant orbitals along the ferromagnetic y direction with an overall dominance of the kinetic energy gain. We indicate that iron superconductors are close to the boundary between the itinerant and the orbital differentiated regimes and that it could be possible to cross this boundary with doping.