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 multi-orbital case are discussed, as are the implications for the strength of superconducting pairing amplitude in the iron-based superconductors. 
Wenxin Ding, Rong Yu, Qimiao Si, and Elihu Abrahams
cond-mat.str-el cond-mat.supr-con