Pairing symmetry of the multiorbital pnictide superconductor BaFe1.84Co0.16As2 from Raman scattering

The pairing symmetry of BaFe(2-)xCo(x)As(2) was investigated by Raman scattering. The gap structure appears only in the B-2g symmetry inconsistent with Muschler et al. [Phys. Rev. B 80, 180510 (R) (2009)]. They concluded that the gap symmetry is the extended s with the argument that the B-2g spectra probe the electron pocket. Our calculation using the realistic band parameter, however, shows that the B-2g spectra are derived from mainly the hole pocket. The calculated intensity is much stronger in A(1g) than in B-2g but the observed A1g spectra have no gap structure. This inconsistency is removed, if the orbital combination is introduced in the pairing symmetry. That is, the symmetry of orbital combination is B-2g and that of momentum space is A1g. The energy of the gap peak is smaller than the gap energy of the hole pocket, indicating the observed peak is the resonant peak created in the gap of the s +/- superconductor.