Optical and hidden transport properties of BaFe1.91Ni0.09As2film.

Optical spectroscopy was used to study the electrodynamics and hidden transport properties of a BaFe1.91Ni0.09As2thin superconducting film. We analyzed the normal state data using a Drude-Lorentz model with two Drude components: one narrow (D1) and another broad one (D2). In the superconducting state, two gaps with 2Δ(2)0/kBTc= 1.9-2.0 and 2Δ(1)0/kBTc= 4.0-4.3 are formed from the narrow component D1while the broad component D2remains ungapped. The calculated total DC resistivity of the film and the low-temperature scattering rate for the narrow Drude component show a hidden Fermi-liquid behavior. The change of total electron-boson coupling (λtot) and representative energy (Ω0) in the normal state with respect to the superconducting state is typical of other iron-based materials as well as high-temperature superconducting (HTSC) cuprates.