Strong Coupling Theory for Superconducting Iron Pnictides

TLDR

The study employs a two‑orbital Hubbard model in the large‑U limit, showing that Coulomb repulsion drives orbital‑dependent pairing of charge carriers. Pairing originates mainly from intrapocket scattering, while interpocket scattering fixes the symmetry: extended s‑wave at low Hund’s coupling and d‑wave at high Hund’s coupling and large U, matching recent ARPES and Andreev reflection experiments.

Abstract

Superconductivity in iron pnictides is studied by using a two-orbital Hubbard model in the large U limit. The Coulomb repulsion induces an orbital-dependent pairing between charge carriers. The pairing is found mainly from the scattering within the same Fermi pocket. The interpocket pair scatterings determine the symmetry of the superconductivity, which is extended s wave at small Hund's coupling, and d wave at large Hund's coupling and large U. The former is consistent with recent experiments of angle-resolved photoemission spectroscopy and Andreev reflection spectroscopy.