Pairing mechanism and symmetry of iron-based high-temperature superconductivity

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Strong correlation effects in iron-based superconductors have been investigated by using the dynamical mean-field theory with the Eliashberg equation. The renormalization factor exhibits significant orbital dependence as observed in recent ARPES experiments. The magnetic and orbital orders are largely suppressed as compared with those from the RPA due to local correlation effects. Remarkably, the s++-pairing phase due to the orbital fluctuation is largely expanded relative to the RPA result, while the s+--pairing phase due to the magnetic fluctuation is reduced. The effect of the intersite Coulomb interaction between Fe d and As p electrons has also been studied and is found to enhance the ferro-orbital (FO) fluctuation responsible for the C66 elastic softening. The FO fluctuation and the antiferromagnetic fluctuation enhanced due to the onsite d-d Coulomb interaction cooperatively enhance Tc of s+--wave superconductivity without any competition by virtue of the q-space segregation.