Magnetic quantum criticality in the iron pnictides

The prominence of antiferromagnetic ordering in the phase diagram of the iron pnictides naturally raises the question of the relevance of magnetic quantum criticality. We address this issue in the undoped parent compounds using the fact that they are “bad metals.” Localized magnetic moments with frustrating interactions, which model the incoherent electronic excitations, are coupled to the itinerant carriers associated with the coherent electronic excitations. Varying the spectral weight of the latter leads to a magnetic quantum critical point. Our theory provides a mechanism to understand the experimental observation that the ordered moment varies across the undoped iron arsenides, and suggests P substitution for As in the undoped iron pnictides as a means to access the magnetic quantum criticality in an unmasked fashion.