High-Order Harmonic Generation and Its Unconventional Scaling Law in the Mott-Insulating Ca2RuO4

Competition and cooperation among orders is at the heart of many-body physics in strongly correlated materials and leads to their rich physical properties. It is crucial to investigate what impact many-body physics has on extreme nonlinear optical phenomena, with the possibility of controlling material properties by light. However, the effect of competing orders and electron-electron correlations on highly nonlinear optical phenomena has not yet been experimentally clarified. Here, we investigated high-order harmonic generation from the Mott-insulating phase of Ca2RuO4. Changing the gap energy in Ca2RuO4 as a function of temperature, we observed a strong enhancement of high order harmonic generation at 50 K, increasing up to several hundred times compared to room temperature. We discovered that this enhancement can be well reproduced by an empirical scaling law that depends only on the material gap energy and photon emission energy. Such a scaling law can hardly be explained by the electronic structure change in the single particle model and has not been predicted by previous theoretical studies on HHG in the simple Mott-Hubbard model. Our results suggest that the highly nonlinear optical response of strongly correlated materials is influenced by competition among the multiple degrees of freedom and electron-electron correlations.

Automated summary

Competition and cooperation among orders play a crucial role in the physical properties of strongly correlated materials. This study investigates the impact of many-body physics on extreme nonlinear optical phenomena, focusing on high-order harmonic generation from the Mott-insulating phase of Ca2RuO4. The results show a significant enhancement of harmonic generation at low temperatures, which can be explained by a scaling law dependent on the material's gap energy and photon emission energy. These findings suggest that the highly nonlinear optical response in strongly correlated materials is influenced by the competition among multiple degrees of freedom and electron-electron correlations.