Doping-Dependent and Orbital-Dependent Band Renormalization in   Ba(Fe_1-xCo_x)_2As_2 Superconductors
  Angle resolved photoemission spectroscopy of Ba(Fe1-xCox)2As2 (x = 0.06, 0.14, and 0.24) shows that the width of the Fe 3d yz/zx hole band depends on the doping level. In contrast, the Fe 3d x^2-y^2 and 3z^2-r^2 bands are rigid and shifted by the Co doping. The Fe 3d yz/zx hole band is flattened at the optimal doping level x = 0.06, indicating that the band renormalization of the Fe 3d yz/zx band correlates with the enhancement of the superconducting transition temperature. The orbital-dependent and doping-dependent band renormalization indicates that the fluctuations responsible for the superconductivity is deeply related to the Fe 3d orbital degeneracy. 
T. Sudayama, Y. Wakisaka, T. Mizokawa, S. Ibuka, R. Morinaga, T. J.   Sato, M. Arita, H. Namatame, M. Taniguchi, and N. L. Saini
cond-mat.supr-con cond-mat.str-el