Possible origin of the reduced ordered magnetic moment in iron pnictides: A dynamical mean-field theory study

We investigate the phase diagram of a two-band frustrated Hubbard model in the framework of dynamical mean-field theory. While a first-order phase transition occurs from a paramagnetic (PM) metal to an antiferromagnetic (AF) insulator when both bands are equally frustrated, an intermediate AF metallic phase appears in each band at different Uc values if only one of the two bands is frustrated, resulting in continuous orbital-selective phase transitions from PM metal to AF metal and AF metal to AF insulator, regardless of the strength of the Ising Hund's coupling. We argue that our minimal-model calculations capture the frustration behavior in the undoped iron-pnictide superconductors as well as local quantum-fluctuation effects and that the intermediate phases observed in our results are possibly related to the puzzling AF metallic state with small staggered magnetization observed in these systems as well as to the pseudogap features observed in optical experiments.