Superconducting pairing symmetry and energy gaps of the two-orbital t-t'-J-J' model: comparisons with the ARPES experiments in iron pnictides

The role of Hund's coupling in the stabilization of the (0, π) ordered spin density wave state within the minimal two-band model for iron pnictides

Spin wave excitations and the stability of the (0, π) ordered spin density wave (SDW) state are investigated within the minimal two-band model for iron pnictides including a Hund's coupling term. The SDW state is shown to be stable in two distinct doping regimes-for finite hole doping in the lower SDW band for small second-neighbour hoppings, and for low electron doping in the upper SDW band for comparable first-neighbour and second-neighbour hoppings. In both cases, Hund's coupling strongly stabilizes the SDW state due to the generation of additional ferromagnetic spin couplings involving the inter-orbital part of the particle-hole propagator. The spin wave energies for the two-band model are very similar to the one-band t-t' Hubbard model results obtained earlier, and are in agreement with the findings from inelastic neutron scattering studies of iron pnictides.

Orbital polarizations and superconducting phase diagrams in two-orbital asymmetric t-J models

We present the zero-temperature superconducting (SC) phase diagrams of the two-orbital asymmetric t-J model on a square lattice by means of the auxiliary-boson approach. Besides the two-gap SC and normal phases, we find an orbital dependent intermediate SC phase, in which one orbit is fully SC and another orbit is exponentially vanishing gapped SC. Such an intermediate phase is stable only for sufficient asymmetry in orbital space and doping concentration. The implication of the present scenario on the iron-based and other multi-orbital superconductors is discussed.