Understanding temperature-dependent SU(3) spin dynamics in the S = 1 antiferromagnet Ba 2 FeSi 2 O 7

Quantum magnets admit more than one classical limit and N -level systems with strong single-ion anisotropy are expected to be described by a classical approximation based on SU( N ) coherent states. Here we test this hypothesis by modeling finite temperature inelastic neutron scattering (INS) data of the effective spin-one antiferromagnet Ba 2 FeSi 2 O 7 . The measured dynamic structure factor is calculated with a generalized Landau-Lifshitz dynamics for SU(3) spins. Unlike the traditional classical limit based on SU(2) coherent states, the results obtained with classical SU(3) spins are in good agreement with the measured temperature dependent spectrum. The SU(3) approach developed here provides a general framework to understand the broad class of materials comprising weakly coupled antiferromagnetic dimers, trimers, or tetramers, and magnets with strong single-ion anisotropy.