Two types of s-wave pairing due to magnetic and orbital fluctuations in the two-dimensional 16-band d-p model for iron-based superconductors

TL;DR

This study investigates two distinct s-wave pairing mechanisms in a detailed 16-band model for iron-based superconductors, revealing how magnetic and orbital fluctuations lead to different pairing symmetries.

Contribution

It identifies and characterizes two types of s-wave pairing driven by magnetic and orbital fluctuations within a realistic multi-band model.

Findings

Extended s-wave pairing mediated by antiferromagnetic spin fluctuations.

Ferro-orbital fluctuation-induced s++-wave pairing without sign reversal.

Electron-phonon coupling enhances the s++-wave pairing.

Abstract

We study superconductivity in the two-dimensional 16-band d-p model extracted from a tight-binding fit to the band structure of LaFeAsO, using the random phase approximation. When the intraorbital repulsion U is larger than the interorbital one U', an extended s-wave (s+--wave) pairing with sign reversal of order parameter is mediated by antiferromagnetic spin fluctuations, while when U<U' another kind of s-wave (s++-wave) pairing without sign reversal is mediated by ferro-orbital fluctuations. The s++-wave pairing is enhanced due to the electron-phonon coupling and then can be expanded over the realistic parameter region with U>U'.