Optical and hidden transport properties of BaFe1.91Ni0.09As2 film

Optical spectroscopy was used to study the electrodynamics and hidden transport properties of a BaFe1.91Ni0.09As2 thin superconducting (SC) 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 SC state, two gaps with 2 Δ 0 ( 2 ) / k B T c = 1.9 -2.0 and 2 Δ 0 ( 1 ) / k B T c = 4.0 -4.3 are formed from the narrow component D1 while the broad component D2 remains 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 (λ tot) and representative energy (Ω0) in the normal state with respect to the SC state is typical of other iron-based materials as well as high-temperature superconducting (HTSC) cuprates.