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

We study three different multiorbital 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- neighbor antiferromagnetism (NNN AFM). Increasing the NNN AFM interactions can drastically enhance the s-wave SC pairing. For the models with more than two orbitals, our study suggests that the signs of the intraorbital pairing superconducting order of the d _xy and the d _xz (or d _yz) orbitals must be opposite. Such a sign difference stems from the intrinsic symmetry properties of interorbital hoppings and might, in the homogeneous case, lead to the sign change of the SC orders between the hole Fermi pockets at the Γ and M points in the unfolded Brillouin zone.