Competitions of magnetism and superconductivity in FeAs-based materials

Using the numerical unrestricted Hartree--Fock approach, we study the ground state of a two-orbital model describing newly discovered FeAs-based superconductors. We observe the competition of a (0, \pi) mode spin-density wave and the superconductivity as the doping concentration changes. There might be a small region in the electron-doping side where the magnetism and superconductivity coexist. The superconducting pairing is found to be spin singlet, orbital even, and coexisting s_xy + d_x²-y² wave (even parity).