Resonant two-magnon Raman scattering in antiferromagnetic insulators

We propose a theory of two-magnon resonant Raman scattering from antiferromagnetic insulators, which contains information not only on magnetism but also on the electronic properties in these materials. We argue that the conventional theory does not work in the resonant regime, in which the energy of the incident photon is close to the gap between the conduction and valence bands. We identify the diagram which gives the dominant contribution to Raman intensity in this regime and show that it can explain the unusual features in the two-magnon profile and in the two-magnon peak intensity dependence on the incoming photon frequency.