High harmonic generation from Kagome lattice based on multi-band semiclassical trajectory method.

We develop a multi-band semiclassical trajectory (MBSCT) method for studying the high harmonic generation (HHG) from solids, which is fundamentally similar to the Boltzmann equation but describe the electron density distribution in a different way and can simulate the electron transitions between bands, thereby depicting a richer array of physical processes. Compared to other theoretical methods, such as the time-dependent Schrödinger equation, the semiconductor Bloch equation, and time-dependent density functional theory, our MBSCT method avoids issues like massive consumption of computational resources and the need for wave function phase correction. Moreover, we focus on Kagome-type materials to justify the MBSCT method and investigate the influence of flat band on HHG in strong laser fields. The simulated results show that the intensity of certain harmonic orders is suppressed by the flat band, implying harmonic spectroscopy as a potential all-optical approach for characterising nonequilibrium physics of flat-band quantum materials.