The conventional theory for two-magnon Raman scattering applied to ${\mathrm{La}}_2$${\mathrm{CuO}}_4$ and other nonsuperconducting precursor phases of the cuprate-based high-$T_c$ materials yields a line shape much narrower than is observed. We modify this theory to allow for a finite magnon lifetime and to allow for a relaxation of momentum conservation in the scattering process. The former modification gives results in good agreement with the experiments; the latter does not. We argue that a probable source of the magnon damping is electronic excitations associated with the free carriers.

• Received 13 March 1989

DOI:https://doi.org/10.1103/PhysRevB.40.6890