High-Order Harmonic Generation and Its Unconventional Scaling Law in the Mott-Insulating Ca_{2}RuO_{4}

Area of Science:

• Condensed Matter Physics
• Strongly Correlated Materials
• Nonlinear Optics

Background:

• Competition and cooperation among orders drive complex properties in many-body physics.
• Understanding many-body physics' impact on nonlinear optical phenomena is key for light-based material control.
• Experimental clarification of competing orders and electron-electron correlations' effects on nonlinear optics is lacking.

Purpose of the Study:

• Investigate high-order harmonic generation (HHG) in the Mott-insulating phase of Ca_{2}RuO_{4}.
• Explore the influence of competing orders and electron-electron correlations on nonlinear optical responses.
• Determine the relationship between material gap energy and HHG enhancement.

Main Methods:

• Studied HHG from Ca_{2}RuO_{4} across varying temperatures.
• Manipulated the material's gap energy by temperature changes.
• Analyzed the observed HHG enhancement using an empirical scaling law.

Main Results:

• Observed a significant enhancement (hundreds of times) of HHG at 50 K compared to room temperature.
• Found HHG enhancement scales with material gap energy and photon emission energy.
• This scaling law is not explained by single-particle models or previous HHG theories for Mott-Hubbard systems.

Conclusions:

• Highly nonlinear optical responses in strongly correlated materials are significantly influenced by competing degrees of freedom and electron-electron correlations.
• The observed scaling law suggests a novel mechanism beyond single-particle physics governing HHG in these materials.
• This work opens new avenues for controlling material properties through light-matter interactions in correlated systems.