Pairing symmetry in a two-orbital exchange coupling model of oxypnictides

We study the pairing symmetry of a two-orbital J1-J2 model for FeAs layers in oxypnictides. We show that the mixture of an intraorbital unconventional sx2y2∼cos(kx)cos(ky) pairing symmetry, which changes sign between the electron and hole Fermi surfaces, and a very small dx2-y2∼cos(kx)-cos(ky) component is favored in a large part of the J1-J2 phase diagram. A pure sx2y2 pairing state is favored for J2>J1. The signs of the dx2-y2 order parameters in the two different orbitals are opposite. While a small dxy∼sin(kx)sin(ky) interorbital pairing coexists in the above phases, the intraorbital dxy pairing is not favored even for large J2.