Wu Shuang, Fei Zaiyao, Sun Zeyuan, Yi Yangfan, Xia Wei, Yan Dayu, Guo Yanfeng, Shi Youguo, Yan Jiaqiang, Cobden David H, Liu Wei-Tao, Xu Xiaodong, Wu Shiwei
State Key Laboratory of Surface Physics, Key Laboratory of Micro and Nano Photonic Structures (MOE), and Department of Physics, Fudan University, Shanghai 200433, China.
Department of Physics, University of Washington, Seattle, Washington 98195, United States.
ACS Nano. 2023 Oct 10;17(19):18905-18913. doi: 10.1021/acsnano.3c04153. Epub 2023 Sep 28.
Topological properties in quantum materials are often governed by symmetry and tuned by crystal structure and external fields, and hence, symmetry-sensitive nonlinear optical measurements in a magnetic field are a valuable probe. Here, we report nonlinear magneto-optical second harmonic generation (SHG) studies of nonmagnetic topological materials including bilayer WTe, monolayer WSe, and bulk TaAs. The polarization-resolved patterns of optical SHG under a magnetic field show nonlinear Kerr rotation in these time-reversal symmetric materials. For materials with 3-fold rotational symmetric lattice structure, the SHG polarization pattern rotates just slightly in a magnetic field, whereas in those with mirror or 2-fold rotational symmetry, the SHG polarization pattern rotates greatly and distorts. These different magneto-SHG characters can be understood by considering the superposition of the magnetic field-induced time-noninvariant nonlinear optical tensor and the crystal-structure-based time-invariant counterpart. The situation is further clarified by scrutinizing the Faraday rotation, whose subtle interplay with crystal symmetry accounts for the diverse behavior of the extrinsic nonlinear Kerr rotation in different materials. Our work illustrates the application of magneto-SHG techniques to directly probe nontrivial topological properties, and underlines the importance of minimizing extrinsic nonlinear Kerr rotation in polarization-resolved magneto-optical studies.
量子材料中的拓扑性质通常由对称性决定，并受晶体结构和外场调控，因此，磁场中对对称性敏感的非线性光学测量是一种有价值的探测手段。在此，我们报告了对包括双层WTe₂、单层WSe₂和块状TaAs在内的非磁性拓扑材料的非线性磁光二次谐波产生（SHG）研究。磁场下光学SHG的偏振分辨模式在这些时间反演对称材料中显示出非线性克尔旋转。对于具有三重旋转对称晶格结构的材料，SHG偏振模式在磁场中仅轻微旋转，而对于具有镜面对称或二重旋转对称的材料，SHG偏振模式则大幅旋转并畸变。通过考虑磁场诱导的时间非不变非线性光学张量与基于晶体结构的时间不变对应张量的叠加，可以理解这些不同的磁SHG特性。通过仔细研究法拉第旋转进一步阐明了这种情况，其与晶体对称性的微妙相互作用解释了不同材料中外在非线性克尔旋转的多样行为。我们的工作展示了磁SHG技术在直接探测非平凡拓扑性质方面的应用，并强调了在偏振分辨磁光研究中最小化外在非线性克尔旋转的重要性。
