The pairing symmetry of ${\text{BaFe}}_{2-x}{\text{Co}}_x{\text{As}}_2$ was investigated by Raman scattering. The gap structure appears only in the $B_{2\text{g}}$ 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 $B_{2\text{g}}$ spectra probe the electron pocket. Our calculation using the realistic band parameter, however, shows that the $B_{2\text{g}}$ spectra are derived from mainly the hole pocket. The calculated intensity is much stronger in $A_{1\text{g}}$ than in $B_{2\text{g}}$ but the observed $A_{1\text{g}}$ 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 $B_{2\text{g}}$ and that of momentum space is $A_{1\text{g}}$. 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 $s\pm$ superconductor.

• Received 23 March 2010

DOI:https://doi.org/10.1103/PhysRevB.82.140504