Gap opening and orbital character in Ba(FeCo)2As2

Polarization-dependent ARPES measurements performed at low photon energy along high-symmetry directions in the Brillouin zone made it possible to get new insight into the role of the five Fe 3d orbitals in the complex electronic structure of Ba(Fe_1−xCo_x)₂As₂ close to the Fermi level, and in particular, into the nature of the holelike pockets. Two distinct inner α pockets could be disentangled, suggesting that their origin is probably due to hybridized d_xz and d_yz, while the complex outer β pocket is mainly of d_z² nature.
The observation of momentum- and band-dependent superconducting gaps allowed us to detect the gap opening across T_c for both α and β pockets. These results confirm that the superconducting order parameter is consistent with a s± symmetry, and suggest that multiple harmonic terms may be included in its description.