Orbital Degeneracy and the Microscopic Model of the FeAs Plane in the   Iron-Based Superconductors
  A microscopic model for the FeAs plane in the newly discovered Iron-based superconductors is proposed with the emphasis on the role of the orbital degeneracy between the Fe $3d_{xz}$ and $3d_{yz}$ orbital in the crystal field environment. The model predicts commensurate antiferromagnetic ordered ground state for the parent compounds and a d-wave superconducting ground state at finite doping. Inter-orbital couplings plays an interesting role in enhancing both orders. Correlated variational wave functions are proposed for both ordered phases. 
Tao Li