Electronic correlations and unconventional spectral weight transfer in BaFe$_{2-x}$Co$_{x}$As$_{2}$

We report an infrared optical study of the pnictide high-temperature superconductor BaFe$_{1.84}$Co$_{0.16}$As$_{2}$ and its parent compound BaFe$_{2}$As$_{2}$. 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 \emph{J} is the primary mechanism that gives rise to correlations.