Prominent Dimensional Effects on High-order Harmonic Generation in Strongly Correlated Electron Systems

Dimensionality strongly affects elementary excitations in correlated quantum materials, yet its impact on extreme nonlinear optical responses remains largely unexplored. Here, we combine high-harmonic generation (HHG) experiments on quasi-one-dimensional SrCuO${}_2$ and quasi-two-dimensional Pr${}_2$CuO${}_4$ with nonequilibrium simulations of Hubbard models. We find a pronounced dimensional contrast: SrCuO${}_2$ exhibits a robust plateau-like high-harmonic spectrum with weak temperature dependence, whereas Pr${}_2$CuO${}_4$ shows a monotonic decrease in harmonic yield and strong thermal suppression, especially at higher harmonics. The simulations qualitatively reproduce these trends and identify dimensionality-dependent doublon–holon dephasing, governed by spin–charge coupling, as their microscopic origin. These results establish dimensionality and spin–charge coupling as key control parameters for extreme nonlinear optical responses in correlated insulators.