Does the Heisenberg model describe the multimagnon spin dynamics in antiferromagnetic CuO layers ?

TL;DR

This study investigates whether the Heisenberg model accurately describes multimagnon spin excitations in antiferromagnetic CuO layers, using exact diagonalization to compare theoretical spectra with experimental observations.

Contribution

The paper demonstrates that an extended Heisenberg model with cyclic exchange better matches experimental multimagnon spectra in CuO layers.

Findings

Standard Heisenberg model reproduces main peak but underestimates side band weights.

Including cyclic four-site exchange improves agreement with experimental spectra.

The extended model provides a more accurate description of spin dynamics in cuprates.

Abstract

We compute the absorption spectrum for multimagnon excitations assisted by phonons in insulating layered cuprates using exact diagonalization in clusters of up to 32 sites. The resulting line shape is very sensitive to the underlying magnetic Hamiltonian describing the spin dynamics. For the usual Heisenberg description of undoped Cu-O planes we find, in accordance with experiment, a two-magnon peak followed by high energy side bands. However the relative weight of the side bands is too small to reproduce the experiment. An extended Heisenberg model including a sizable four-site cyclic exchange term is shown to be consistent with the experimental data.