High-harmonic generation in Weyl semimetal β-WP₂ crystals

Area of Science:

• Condensed Matter Physics
• Quantum Materials Science
• Nonlinear Optics

Background:

• Weyl semimetals possess unique electronic band structures with Weyl points and Berry curvature.
• These features can lead to unusual nonlinear optical properties, such as high-order harmonic generation (HHG), which were previously unexplored in these materials.

Purpose of the Study:

• To investigate and demonstrate high-order harmonic generation (HHG) in type-II Weyl semimetal β-WP2 crystals.
• To explore the relationship between HHG and the electronic band structure, including Berry curvature, of Weyl semimetals.
• To establish an all-optical method for characterizing quantum topological materials.

Main Methods:

• Experimental generation and spectral analysis of high-order harmonic generation (HHG) in β-WP2 crystals under femtosecond laser excitation.
• Crystallographic orientation-dependent measurements of HHG spectra.
• Theoretical interpretation of odd and even harmonic generation mechanisms related to Bloch oscillations and Berry curvature.

Main Results:

• Effective HHG was achieved in β-WP2, with both odd and even orders observed.
• Harmonic spectra extended into the vacuum ultraviolet region (190 nm, 10th order) even at low laser intensities.
• Quantitative retrieval of the electronic band structure and Berry curvature of β-WP2 was accomplished through orientation-dependent HHG measurements.

Conclusions:

• The study demonstrates the potential of Weyl semimetals for generating deep ultraviolet radiation.
• HHG in Weyl semimetals provides a powerful all-optical tool for characterizing their complex electronic structures and Berry curvature.
• This work opens new avenues for exploring quantum topological materials and their nonlinear optical responses.