Possibility of Unconventional Pairing Due to Coulomb Interaction in Fe-Based Pnictide Superconductors: Perturbative Analysis of Multi-Band Hubbard Models

TL;DR

This study investigates the potential for unconventional superconducting pairing in iron-pnictide materials through perturbative analysis of multi-band Hubbard models, revealing that a 5-band model can account for high Tc and specific pairing states.

Contribution

It introduces a perturbative approach to analyze Coulomb interaction effects in realistic multi-band Hubbard models for iron-pnictide superconductors, highlighting the importance of a 5-band model.

Findings

5-band model predicts high Tc with s-wave pairing without nodes

Eigenvalues of Eliashberg equation are large enough to explain high Tc

2-band model is insufficient for high Tc explanation

Abstract

Possibility of unconventional pairing due to Coulomb interaction in iron-pnictide superconductors is studied by applying a perturbative approach to realistic 2- and 5-band Hubbard models. The linearized Eliashberg equation is solved by expanding the effective pairing interaction perturbatively up to third order in the on-site Coulomb integrals. The numerical results for the 5-band model suggest that the eigenvalues of the Eliashberg equation are sufficiently large to explain the actual high Tc for realistic values of Coulomb interaction and the most probable pairing state is spin-singlet s-wave without any nodes just on the Fermi surfaces, although the superconducting order parameter changes its sign between the small Fermi pockets. On the other hand the 2-band model is quite insufficient to explain the actual high Tc.