Classical spin dynamics based on SU(N) coherent states

We introduce a classical limit of the dynamics of quantum spin systems based on coherent states of SU(N), where N is the dimension of the local Hilbert space. This approach, which generalizes the well-known Landau-Lifshitz dynamics (LLD) from SU(2) to SU(N), provides a better approximation to the exact quantum dynamics for a large class of realistic spin Hamiltonians, including S≥1 systems with large single-ion anisotropy and weakly-coupled multi-spin units, such as dimers or trimers. We illustrate this idea by applying the SU(3) LLD to model the finite-temperature inelastic neutron scattering data of a spin-one antiferromagnet Ba₂FeSi₂O₇. Unlike the traditional LLD based on SU(2) coherent states, the results  obtained with classical SU(3) spins reproduce the measured spectrum in the whole temperature range.