Non-Fermi-liquid behavior, Lifshitz transitions, and Hund’s metal behavior of iron-based superconductors from ARPES

Recent ARPES studies on iron-based high-Tc superconductors reveal non-Fermi-liquid scattering rates and Lifshitz transitions near optimal doping which lead together with correlation effects to a large mass enhancement. The scattering rates do not show a huge enhancement near optimal doping as naively expected in a quantum critical scenario. Rather they are enhanced near a 3d⁵ configuration, i.e., in the hole doped Fe compounds, and decrease in the corresponding Cr compound. This indicates that they are determined by local interactions and in particular by the Hund’s exchange interactions. Furthermore, from the ARPES experiments we have evidence for hot and cold spots on the Fermi surface, depending on the orbital character of the bands. The cold spots determine the transport properties in the normal state. Probably the superconducting properties and the thermal properties in the normal state are determined by the hot spots, composed of rather incoherent charge carriers. The strange normal state transport and thermal properties can be explained on the basis of a co-action of Lifshitz transitions and correlation effects.