Two-band model of Raman scattering on iron pnictide Ba (Fe_1-X Co _x) ₂ As ₂ superconductors

Based on a two-band model, we theoretically study the electronic Raman scattering spectra in both normal and superconducting states of iron-pnictide Ba(_Fe1-xCo_x2As₂ superconductors. In the normal state, due to the match or mismatch of band hybridization and Raman vertex symmetries, overall B2_g Raman intensity is found to be much stronger than that of the B1_g channel. Besides, in the non-resonant limit, there could exhibit an interband excitation peak at high frequency ω7.3^t1(6.8^t1) in the B1 _gB2_g) channel with ^t1 the nearest-neighbor hopping. In the superconducting state, due to the composite effect of Raman vertex, gap symmetry, and Fermi surface topology, both B1_g and B2_g Raman intensities are dominated by α- (β-) band contribution for the extended s-wave (d^x2-^y2-wave) pairing, whereas both bands are equally important for the ^s±- wave pairing. It is shown that both extended s- and ^s±-wave pairings can lead to a good fitting for the reported B1_g data Muschler et al. (2009) [11], while the d^x2-^y2-wave pairing seems not favorable.