Research progress of high-order harmonics in topological insulators

In recent years, with the advancement of the infrared laser technology, the study of high-order harmonic generation has expanded to solid materials. Numerous experimental and theoretical studies have revealed that the high-order harmonics in topological insulators exhibit unique properties, such as enhanced harmonic yields, the specific ellipticity dependence, and the circular dichroism. This work reviews the recent progress in the study of high-order harmonics in topological insulators, focusing on the harmonic characteristics of the SSH model (one-dimensional system), the Haldane model (twodimensional system), and the Z2 topological insulator (three-dimensional system). These characteristics are related to the Berry curvature and boundary states (surface states) of topological phase materials. Finally, the potential of high-order harmonics as a reliable indicator for probing the topology of materials is discussed, along with future research directions. The study of high-order harmonics in topological materials not only deepens the understanding of the mechanisms of high- order harmonics in solid materials, but also has the potential to reveal the profound significance of topological properties.