Strong Nonlinear Optical Response and Transient Symmetry Switch in Type‐II Weyl Semimetal β‐WP2

• Published in: Advanced optical materials 2023-05, Vol.11 (9), p.n/a
• Main Authors: Hu, Tianchen, Su, Bo, Shi, Liyu, Wang, Zixiao, Yue, Li, Xu, Shuxiang, Zhang, Sijie, Liu, Qiaomei, Wu, Qiong, Li, Rongsheng, Zhou, Xinyu, Yuan, Jiayu, Wu, Dong, Chen, Zhiguo, Dong, Tao, Wang, Nanlin
• Format: Article
• Language: English
• Subjects: Carrier density; Conduction electrons; Femtosecond pulsed lasers; Femtosecond pulses; Interlayers; Materials science; Metalloids; Metastable state; Nonlinear optics; Nonlinear response; Optical properties; Optics; Optoelectronic devices; Second harmonic generation; Symmetry; Topology; ultrafast symmetry switch; Weyl semimetals
• ISSN: 2195-1071; 2195-1071
• DOI: 10.1002/adom.202202639

The topological Weyl semimetals (WSMs) with peculiar band structures exhibit novel nonlinear optical enhancement phenomena, even for light at optical wavelengths. While many intriguing nonlinear optical effects are constantly uncovered in type‐I WSMs, few experimental works focuse on basic nonlinear optical properties in type‐II WSMs. Here a static and time‐resolved second harmonic generation (SHG) is performed on the 3D type‐II WSM candidate β‐WP2. Although β‐WP2 exhibits extremely high conductivity and a high carrier density (≈1021 cm−3), the SHG is unscreened by conduction electrons, and a rather strong SHG response is observed, comparing with non‐topological polar metals. Additionally, the time‐resolved SHG experiment traces ultrafast symmetry switch and reveals that polar metal β‐WP2 tends to form an inversion symmetric metastable state after photo‐excitation. Intense femtosecond laser pulse can optically drive symmetry switch and tune nonlinear optical response on ultrafast timescales although the interlayer coupling of β‐WP2 is very strong. These findings are illuminating for the polar metal nonlinear optics and provide a new perspective for future ultrafast topological optoelectronic devices. A strong second harmonic generation (SHG) response at 400 nm is observed in a topological Weyl semimetal β‐WP2 crystal. More novelty, the strong SHG response can be controlled in picosecond timescales by near‐infrared laser light, indicating an ultrafast symmetry switch process. The discovery paves the way for practical topological optoelectronic applications.