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

TL;DR

This paper provides a theoretical analysis of magnetic Raman scattering in La2CuO4, showing that including ring exchange interactions accurately predicts the two-magnon peak position, but lineshape details remain complex.

Contribution

It introduces a parameter-free theoretical calculation incorporating ring exchange effects to match experimental two-magnon Raman scattering data in La2CuO4.

Findings

Predicted two-magnon peak at 2.71J in agreement with experiments

Ring exchange significantly influences magnon dispersion and scattering intensity

Lineshape complexity suggests additional factors beyond spin-only models

Abstract

We evaluate the Raman light scattering intensity for the square lattice Heisenberg antiferromagnet with plaquette ring exchange J_\Box. With the exchange couplings as fixed before from an accurate fit to the spin-wave dispersion in La2CuO4, leading in particular to J_\Box=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 lineshape of the two-magnon remain beyond a descriptions in terms of a spin-only Hamiltonian.