Superconductivity in multi-orbital t-J₁-J₂ model and its implications for iron pnictides

Department of Physics and Astronomy, Rice University - Houston, TX 77005, USA

^a qmsi@rice.edu

Received: 6 July 2010
Accepted: 31 July 2010

Abstract

Motivated by the bad metal behavior of the iron pnictides, we study a multi-orbital t-J₁-J₂ 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_x²y² channel, the nodal A_1g s_x²+y² and B_1g d_{x²- y²} channels are also competitive in the magnetically frustrated J₁∼J₂ parameter regime. An A_1g+iB_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.