We evaluate the Raman light- scattering intensity for the square lattice Heisenberg antiferromagnet with plaquette ring exchange J□. With the exchange couplings as fixed before from an accurate fit to the spin-wave dispersion in La2CuO4, leading in particular to J□ = 0.24J, we demonstrate in a parameter-free calculation that the inclusion of the plaquette exchange contribution to the dispersion and the magnon-magnon interaction vertex gives a peak position in B1g scattering geometry Emax = 2.71J which is in excellent agreement with the experimental data. Yet, the intrinsic width and the line shape of the two-magnon remain beyond a description in terms of a spin-only Hamiltonian.
|Number of pages||4|
|Journal||Physical Review B - Condensed Matter and Materials Physics|
|Publication status||Published - 15 Mar 2003|