High-Harmonic Generation Approaching the Quantum Critical Point of Strongly Correlated Systems

By employing the exact diagonalization method, we investigate the high-harmonic generation (HHG) of the correlated systems under the strong laser irradiation. For the extended Hubbard model on a periodic chain, HHG close to the quantum critical point (QCP) is more significant compared to two neighboring gapped phases (i.e., charge-density-wave and spin-density wave states), especially in low frequencies. We confirm that the systems in the vicinity of the QCP are supersensitive to the external field and more optical-transition channels via excited states are responsible for HHG. This feature holds the potential of obtaining high efficiency harmonics by making use of materials approaching QCP. Based on the two-dimensional Haldane model, we further propose that the even-or odd-order components of generated harmonics can be promisingly regarded as spectral signals to distinguish the topologically ordered phases from locally ordered ones. Our findings in this Letter pave the way to achieve ultrafast light source from HHG in strongly correlated materials and to study quantum phase transition by nonlinear optics in strong laser fields.

Automated summary

This research investigates the high-harmonic generation (HHG) of correlated systems under strong laser irradiation using the exact diagonalization method. The results show that systems close to the quantum critical point (QCP) are highly sensitive to the external field and exhibit more significant HHG at low frequencies. HHG is attributed to the additional optical-transition channels via excited states. This study highlights the potential of obtaining high-efficiency harmonics from materials approaching QCP.