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. 
A. A. Schafgans, S. J. Moon, B. C. Pursley, A. D. LaForge, M. M.   Qazilbash, A. S. Sefat, D. Mandrus, K. Haule, G. Kotliar,...
cond-mat.str-el cond-mat.supr-con