Competing Pairing Symmetries in a Generalized Two-Orbital Model for the Pnictides

TL;DR

This paper introduces an extended two-orbital model for pnictides incorporating Heisenberg interactions, revealing competing pairing symmetries and low-lying states that depend on model parameters.

Contribution

It develops a generalized

Findings

Enhanced spin order due to Heisenberg terms promotes pairing states.

Competition among A1g, B2g, and B1g pairing symmetries is observed.

Small parameter changes can stabilize different pairing channels.

Abstract

We introduce and study an extended "t-U-J" two-orbital model for the pnictides that includes Heisenberg terms deduced from the strong coupling expansion. Including these J terms explicitly allows us to enhance the strength of the (pi, 0)-(0, pi) spin order which favors the presence of tightly bound pairing states even in the small clusters that are here exactly diagonalized. The A1g and B2g pairing symmetries are found to compete in the realistic spin-ordered and metallic regime. The dynamical pairing susceptibility additionally unveils low-lying B1g states, suggesting that small changes in parameters may render any of the three channels stable.