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J. Knolle, I. Eremin, and R. Moessner
The phase diagram of ferro-pnictides (FP) exhibits spin-density wave (SDW) like magnetic order at low doping and unconventional superconductivity (SC) at larger doping. Some compounds may even have a regime in which both orders coexist on a microscopic scale. Starting from an itinerant description and taking into account the Fermi surface topology we study theoretically longitudinal and transverse magnetic excitations in the various phases of FPs. In the magnetic phase we find spin waves in the transverse channel. In the superconducting phase a spin resonance emerges in the longitudinal channel below the superconducting transition temperature reflecting the unconventional symmetry of the order parameter. Assuming that in the coexistence regime the same electrons take part in the SDW, as well as, the SC ordering, we discuss the fate of the spin waves and the superconducting resonance. We compare our results with the available inelastic neutron scattering data and discuss the importance of the orbital degrees of freedom. |
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