Observation of phonon splitting in BaFe$_{2}$As$_{2}$ single crystals using infrared spectroscopy

We present infrared spectroscopic results on the pnictide parent compound BaFe$_{2}$As$_{2}$ (Ba122) detailing direct observation of phonon splitting in the pnictide materials following the tetragonal to orthorhombic structural phase transition. We then compare these results with the optimally Co-doped superconductor Co-Ba122 in which only one, weak infrared-active phonon is observed. Finally, we explore these results to glean insights into the interplay between structural and spin density wave order.