Effective exchange interactions for bad metals and implications for iron-based superconductors

The experimentally observed bad-metal behavior in parent iron pnictides and chalcogenides suggests that these systems contain strong electronic correlations and are on the verge of a metal-to-insulator transition. The magnetic excitations in this bad-metal regime mainly derive from the incoherent part of the electronic spectrum away from the Fermi energy. We present a microscopic study of the exchange interactions in such a regime within a slave rotor approach. We find that the exchange interaction is maximized near the Mott transition. Generalizations to the multiorbital case are discussed, as are the implications for the strength of superconducting pairing amplitude in iron-based superconductors.