Interplay between magnetism and superconductivity in the iron pnictides

We consider phase transitions and potential coexistence of spin-density-wave (SDW) magnetic order and extended s -wave (s+) superconducting order within a two-band itinerant model of iron pnictides in which SDW magnetism and s+ superconductivity are competing orders. We show that depending on parameters, the transition between these two states is either first order or involves an intermediate phase in which the two orders coexist. We demonstrate that such coexistence is possible when SDW order is incommensurate.