Theoretical analysis of magnetic Raman scattering in La2CuO4: Two-magnon intensity with the inclusion of ring exchange

[摘要] We evaluate the Raman light-scattering intensity for the square lattice Heisenberg antiferromagnet with plaquette ring exchange J(square). With the exchange couplings as fixed before from an accurate fit to the spin-wave dispersion in La2CuO4, leading in particular to J(square)=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 B-1g scattering geometry E-max=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.

[关键词] CYCLIC 4-SPIN EXCHANGE;HIGH-ENERGY SPIN;T-J MODEL;ANTIFERROMAGNETIC INSULATORS;HEISENBERG-ANTIFERROMAGNET;SQUARE LATTICE;HUBBARD-MODEL;EXCITATIONS;TEMPERATURE;SPECTRUM