Extended Drude model and role of interband transitions in the midinfrared spectra of pnictides

We analyze the outcomes of an extended-Drude-model approach to the optical spectra of pnictides, where the multiband nature of the electronic excitations requires a careful analysis of the role of interband processes in the optical conductivity. Through a direct comparison between model calculations of the intraband optical spectra, experimental data, and first-principles calculations we show that interband transitions give a non-negligible contribution already in the infrared region. This leads to a substantial failure of the extended-Drude-model analysis on the measured optical data without subtraction of interband contributions.