Two-dimensional (2D) van der Waals (vdW) magnetic materials with strong in-plane anisotropy can make possible novel applications such as optospintronics and strain sensors. In this work, the strong in-plane optical anisotropy in 2D vdW antiferromagnet VOCl has been systematically investigated. The optical brightness and absorption coefficient exhibit evident periodic variation with the change of incident polarization, unveiling the strong in-plane anisotropic optical absorption. The Raman intensity in this material shows obvious dependence on the polarization angle of incident laser, demonstrating that the phonon properties possess strong in-plane anisotropy. Besides, we have also realized in-situ visualization of in-plane optical reflection anisotropy in this material. Moreover, the strong second harmonic generation (SHG) signal can only be detected when the incident polarization is along specific in-plane crystal orientations, illustrating the presence of strong in-plane nonlinear optical anisotropy. These findings will benefit the applications of VOCl in the field of polarization-dependent electronics and spintronics.

Low-symmetry two-dimensional (2D) materials, with unique in-plane direction-dependent optical, electrical, and thermoelectric properties, have been intensively studied for their potential application values in advanced electronic and optoelectronic devices. However, since anisotropic 2D materials are highly sensitive to the environmental factors, researches on their high-performance field-effect transistors (FETs) are still limited. Here, we report a high-performance SnSe FET based on a van der Waals (vdWs) heterostructure of SnSe encapsulated in hexagonal boron nitride (hBN) together with graphene contacts. The device exhibits a high on/off ratio exceeding 1 × 10⁹, and a carrier mobility of 118 cm²·V^-1·s^-1. Our work highlights low-symmetry 2D SnSe holds potential to be used for designing excellent electronic devices.

Anisotropic materials are of considerable interest because of their unique combination of polarization- or direction-dependent electrical, optical, and thermoelectric properties. Low-symmetry two-dimensional (2D) materials formed by van der Waals stacking of covalently bonded atomic layers are inherently anisotropic. Layered SnSe exhibits a low degree of lattice symmetry, with a distorted NaCl structure and an in-plane anisotropy. Here we report a systematic study of the in-plane anisotropic properties in layered SnSe, using angle-resolved Raman scattering, optical absorption, and electrical transport studies. The optical and electrical characterization was direction-dependent, and successfully identified the crystalline orientation in the layered SnSe. Furthermore, the dependence of Raman-intensity anisotropy on the SnSe flake thickness and the excitation wavelength were investigated by both experiments and theoretical calculations. Finally, the electrical transport studies demonstrated that few-layer SnSe field-effect transistors (FETs) have a large anisotropic ratio of carrier mobility (~5.8) between the armchair and zigzag directions, which is a record high value reported for 2D anisotropic materials. The highly-anisotropic properties of layered SnSe indicate considerable promise for anisotropic optics, electronics, and optoelectronics.