Infrared Spectroscopy on superconducting and non-superconducting iron pnictide compounds

We performed infrared reflectivity measurements on single crystals of the hole-doped BaK-122 iron pnictide superconductor ($T_{c}\approx 33$~K) and on the non-superconducting compound CaFe$_{4}$As$_{3}$. In BaK-122, similar to previous reports, we observed an increases in optical reflectance in the infrared below T$_{c}$, associated with the superconducting condensate. The non-superconducting CaFe$_{4}$As$_{3}$ shows two magnetic transitions: one associated with a spin density wave (SDW) transition at $T_{N}\approx88$~K and another one at lower temperature ($T_{2}\approx 26$~K), with unclear origin up to date. The change in measured reflectivity and in optical conductivity, obtained from Kramers-Kronig analysis, at the two transitions will be discussed in the framework of Drude and Lorentz models.