Superconductivity in Multi-orbital t-J1-J2 Model and its Implications for Iron Pnictides

TL;DR

This paper investigates superconducting pairing mechanisms in a multi-orbital t-J1-J2 model relevant to iron pnictides, revealing competing pairing states, the role of magnetic frustration, and potential time-reversal symmetry breaking states.

Contribution

It introduces a detailed analysis of pairing symmetries in a multi-orbital model, highlighting the effects of magnetic frustration and kinetic energy on superconducting states in iron pnictides.

Findings

Dominance of A_{1g} s_{x^2 y^2} pairing in phase diagram

Presence of near-degenerate B_{1g} d_{x^2 - y^2} pairing

Possible time-reversal symmetry breaking A_{1g}+i B_{1g} state

Abstract

Motivated by the bad metal behavior of the iron pnictides, we study a multi-orbital $\mathrm{t-J_1-J_2}$ model and investigate possible singlet superconducting pairings. Magnetic frustration by itself leads to a large degeneracy in the pairing states. The kinetic energy breaks this into a quasi-degeneracy among a reduced set of pairing states. For small electron and hole Fermi pockets, an $A_{1g}$ state dominates over the phase diagram but a $B_{1g}$ state has close-by energy. In addition to the nodeless $A_{1g}$ $s_{x^2y^2}$ channel, the nodal $A_{1g}$ $s_{x^2+y^2}$ and $B_{1g}$ $d_{x^2-y^2}$ channels are also competitive in the magnetically frustrated $J_1 \sim J_2$ parameter regime. An $A_{1g}+i B_{1g}$ state, which breaks time-reversal symmetry, occurs at low temperatures in part of the phase diagram. Implications for the experiments in the iron pnictides are discussed.