Crossover from bad to good metal in BaFe2(As1−xPx)2induced by isovalent P substitution

Abstract

Bad metallic behavior or incoherent charge dynamics is characteristic of the normal state of high-transition-temperature copper-oxide superconductors. A parent compound of iron-based superconductors, BaFe${}_{2}$As${}_{2}$, is also a bad metal in the high-temperature phase, whereas its phosphorous counterpart, BaFe${}_{2}$P${}_{2}$, is a good metal. Combined measurements of in-plane resistivity and optical conductivity for BaFe${}_{2}$(As${}_{1\ensuremath{-}x}$P${}_{x}$)${}_{2}$ make it possible to disentangle the coherent channel from the incoherent one in the charge transport. The isovalent P substitution promotes coherent motion of carriers without changing the balance of the electron and hole Fermi-surface volume and hence transforms a bad metal into a good metal.