Change of the sign of superconducting intraband order parameters induced by interband pair hopping interaction in iron-based high-temperature superconductors

Iron based superconductors are characterized by the s_± gap symmetry, where the gap changes its sign between pockets of the Fermi surface. We discuss another sign change mechanism of the superconducting order parameter (OP)—the interband Cooper pairs hopping interaction. In the minimal two-orbital model of iron based superconductors we show that this interaction can lead to a change of the sign of the intraband superconducting OP regardless of its symmetry. (paper)