Two-magnon Raman scattering inA0.8Fe1.6Se2systems (A=K, Rb, Cs, and Tl): Competition between superconductivity and antiferromagnetic order
Physical Review B
We have performed Raman-scattering measurements on high-quality single crystals of A_0.8Fe_1.6Se_2 superconductors of several compositions. We find a broad, asymmetric peak around 1600 cm^-1 (200 meV), which we identify as a two-magnon process involving optical magnons. The intensity of the two-magnon peak falls sharply on entering the superconducting phase. This effect, which is entirely absent in the non-superconducting system KFe_1.5Se_2, requires a strong mutual exclusion between
... gnetism and superconductivity arising from proximity effects within regions of microscale phase separation.