Electronic Correlations and Unconventional Spectral Weight Transfer in the High-Temperature Pnictide BaFe2-xCoxAs2 Superconductor Using Infrared Spectroscopy

We report an infrared optical study of the pnictide high-temperature superconductor BaFe1.84Co0.16As2 and its parent compound BaFe2As2. We demonstrate that electronic correlations are moderately strong and do not change across the spin-density wave transition or with doping. By examining the energy scale and direction of spectral weight transfer, we argue that Hund's coupling J is the primary mechanism that gives rise to correlations.