Spin-wave theory of two-magnon Raman scattering in iron Pnictides and Chalcogenides

• The weights of quasiparticle excitation are given in the two-mangnon Raman response.
• The (π/2, 0) collinear AF order in iron Pnictides should contain two energy branches instead of one branch.
• For the iron Chalcogenides, the exchange interaction parameters should be re-studied.

Motivated by the experimental measurement of the two-magnon Raman scattering in iron Pnictides and Chalcogenides superconductors (Okazaki et al., 2011; Sugai et al., 2012), the underlying spin excitations of the (π, 0) collinear and the (π/2, π  /2) diagonal double stripe antiferromagnetic superstructures are investigated in detail with the spin density wave approximation. By calculating the Fleury–London (FL) Raman cross-section of various quantum spin models proposed for this new class of superconductors, it is found that the unfrustrated quantum spin models are well consistent with the Raman data. Our calculation results also show that the broad peak around 2500 cm−1−1 of iron Pnictides in Bg channel come from the quasiparticle excitations of two optical magnons, whereas, in Ag   channel the Raman response is from two optical magnons and two acoustic magnons with almost the same weights. In addition, our calculation results reveal that the broad peak around 2300 cm−1−1 of the iron Chalcogenides in Bg channel is caused by one acoustic magnon and one optical magnon, which is simultaneously excited by the Raman scattering. While in Ag channel, Raman scattering will mainly excite two optical magnons.