Hole-s_± state induced by coexisting ferro- and antiferromagnetic and antiferro-orbital fluctuations in iron pnictides

The five-orbital Hubbard model for iron-based superconductors is investigated using the dynamical mean-field theory combined with the Eliashberg equation to clarify the local correlation effects on the electronic states and the superconductivity. In the specific case where the antiferromagnetic (AFM) and antiferro-orbital (AFO) fluctuations are comparably enhanced, the orbital dependence of the vertex function is significantly large, while that of the self-energy is small, in contrast to the AFM fluctuation-dominated case where the vertex function (the self-energy) shows a small (large) orbital dependence. The orbital-dependent vertex function together with the nesting between the inner and outer hole Fermi surfaces results in the enhancement of the inter-orbital ferromagnetic (FM) fluctuation in addition to the AFM and AFO fluctuations. In this case, the hole-s_±-wave pairing with the sign change of the two hole Fermi surfaces is mediated by the coexisting three fluctuations as expected to be observed in the specific compound LiFeAs.