Speaker
Description
Spin wave theory (SWT), in particular at lowest order, is often used to extract spin exchanges from scattering experiments such as inelastic neutron scattering and resonant inelastic X-ray scattering. However, this approach has limitations in accounting for large quantum fluctuations and possible fractional excitations that go beyond a magnon description. To address this, we employ a large-scale matrix product state method to compute the dynamical spin structure factor for an effective spin model on the square-lattice that is relevant to various cuprate materials. When comparing our results with experimental data for La$_2$CuO$_4$ and CaCuO$_2$, we observe a significant disparity in the strength of Hubbard-parameterized interactions with respect to those inferred from SWT. An empirical relation is derived in terms of the interaction strength and data from experimental measurements to obtain better estimates of the Hubbard parameter. Our simulations are in good agreement with ab initio studies and a modified spin wave theory analysis for La$_2$CuO$_4$, while for CaCuO$_2$ we provide a new estimate. We extent our analysis by including first order corrections to SWT, which result in a wave-vector-dependent rescaling of the magnon bands and partially recover the discrepancy with experiment and numerics. Furthermore, we provide a detailed discussion of spin dynamics in La$_2$CuO$_4$.
