Unconventional Pairing Originating from the Disconnected Fermi Surfaces of Superconducting LaFeAsO 1-x F x

TLDR: It is concluded that the multiple spin-fluctuation modes arising from the nesting across the disconnected Fermi surfaces realize an extended s-wave Pairing, while d-wave pairing can also be another candidate.

Abstract: For a newly discovered iron-based high ${T}_{c}$ superconductor ${\mathrm{LaFeAsO}}_{1\ensuremath{-}x}{\mathrm{F}}_{x}$, we have constructed a minimal model, where inclusion of all five Fe $d$ bands is found to be necessary. The random-phase approximation is applied to the model to investigate the origin of superconductivity. We conclude that the multiple spin-fluctuation modes arising from the nesting across the disconnected Fermi surfaces realize an extended $s$-wave pairing, while $d$-wave pairing can also be another candidate.