Doping-Dependent and Orbital-Dependent Band Renormalization in Ba(Fe(1-x)Co(x))(2)As(2) Superconductors

Angle resolved photoemission spectroscopy of Ba(Fe(1-x)Co(x))(2)As(2) (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(x2-y2) 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