Unconventional Pairing Originating from the Disconnected Fermi Surfaces of SuperconductingLaFeAsO1−xFx

Abstract

For a newly discovered iron-based high $T_c$ superconductor ${\mathrm{LaFeAsO}}_{1-x}{\mathrm{F}}_x$, 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.