Coexisting Itinerant and Localized Electrons in Iron-Based Superconductors

The surprising discovery of high-$T_c$ superconductivity in iron-based compounds has prompted an intensive investigation on the role of interaction and magnetism in the these materials. Based on the general features of multi-bands and intermediate coupling strengths, a phenomenological theory of coexisting itinerant and localized electrons has been proposed to describe the low-energy physics in iron-based superconductors. It provides a unified framework to understand magnetic, superconducting, and normal phases, subject to further microscopic justification and experimental verification.