S-wave superconductivity with orbital dependent sign change in the checkerboard models of iron-based superconductors

TL;DR

This study investigates multi-orbital models of iron-based superconductors, revealing that orbital-dependent sign changes in pairing can lead to unconventional superconducting gap structures.

Contribution

It introduces a theoretical analysis of orbital-dependent sign changes in pairing within checkerboard models, highlighting their impact on superconducting gap anisotropy.

Findings

Strongest pairing in the A1g s-wave channel

Sign reversal between d_{xy} and d_{xz}/d_{yz} orbitals

Potential for gapless or anisotropic gaps in electron pockets

Abstract

We study three different multi-orbital models for iron-based superconductors (iron-SCs) in the solvable limit of weakly coupled square plaquettes. The strongest superconducting (SC) pairing is in the $A_{1g}$ $s$-wave channel and its development is correlated with the emergence of the next-nearest-neighbour antiferromagnetism (NNN-AFM). For the models with more than three orbitals, this study suggests that the signs of the intra-orbital pairing order parameters of the $d_{xy}$ and the $d_{xz}$ (or $d_{yz}$) orbitals must be {\it opposite}. Such sign difference stems from the intrinsic symmetry properties of inter-orbital hoppings and might, ultimately, lead to the sign-change of the SC orders between the hole Fermi pockets at the $\Gamma$ point and produce anisotropic or even gapless SC gaps in the electron Fermi pockets around the $M$ point in reciprocal space, as restoring back to the homogeneous limit.