Normal-state charge dynamics in doped BaFe2As2: Roles of doping and necessary ingredients for superconductivity

We carried out a comparative study of the in-plane resistivity and optical spectrum of doped BaFe2As2 and investigated the doping evolution of the charge dynamics. For BaFe2As2, charge dynamics is incoherent at high temperatures. Electron (Co) and isovalent (P) doping into BaFe2As2 increase coherence of the system and transform the incoherent charge dynamics into highly coherent one. On the other hand, charge dynamics remains incoherent for hole (K) doping. It is found in common with any type of doping that superconductivity with high transition temperature emerges when the normal-state charge dynamics maintains incoherence and when the resistivity associated with the coherent channel exhibits dominant temperature-linear dependence.