Theoretical analysis of magnetic Raman scattering in (formula presented) Two-magnon intensity with the inclusion of ring exchange

Abstract

We evaluate the Raman light-scattering intensity for the square lattice Heisenberg antiferromagnet with plaquette ring exchange (formula presented) With the exchange couplings as fixed before from an accurate fit to the spin-wave dispersion in (formula presented) leading in particular to (formula presented) 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 (formula presented) scattering geometry (formula presented) 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. © 2003 The American Physical Society.