Unconventional pairing originating from disconnected Fermi surfaces in superconducting LaFeAsO$_{1-x}$F$_x$}

TL;DR

This paper investigates the superconducting mechanism in LaFeAsO$_{1-x}$F$_x$ by constructing a five-band model and applying RPA, revealing that spin fluctuations from disconnected Fermi surfaces favor extended s-wave pairing.

Contribution

The study introduces a minimal five-band model for LaFeAsO$_{1-x}$F$_x$ and identifies spin fluctuation modes as the origin of superconductivity, highlighting the role of disconnected Fermi surfaces.

Findings

Multiple spin fluctuation modes from Fermi surface nesting induce extended s-wave pairing.

D-wave pairing is also a plausible alternative.

All five Fe d-bands are essential in the minimal model.

Abstract

For a newly discovered iron-based high $T_c$ superconductor LaFeAsO$_{1-x}$F$_x$, we have constructed a minimal model, where inclusion of all the five Fe $d$ bands is found to be necessary. 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.