The Nodal SDW Gap and the Superconducting Gap in BaFe2−xCoxAs2

The spin density wave (SDW) transition in BaFe2As2 and the superconducting transition in BaFe1.84Co0.16As2 were investigated by Raman scattering. The symmetries of the nodal SDW gap at 400 cm−1 and the superconducting gap at 75 cm−1 are both B 2g. The superconducting coherent peak energy is smaller than the gap energy of the hole pocket, indicating that the peak is the resonant peak in the S ± superconductor. The superconducting symmetry is given by B 2g in the orbital combination and A 1g (S ±) in the momentum space. The exchange interaction energies are estimated from the two-magnon peak.