近日，新加坡南洋理工大学的Qi Jie Wang&Zheng Liu及其研究小组与哈尔滨工业大学的李兴冀等人合作并取得一项新进展。经过不懈努力，他们证实逆对称破缺二维PdPSe中具有特殊偏振各向异性的强非线性光学过程。相关研究成果已于2024年5月27日在国际知名学术期刊《光：科学与应用》上发表。

该研究团队证明了偶层PdPSe的二阶和三阶磁化率分别为64pm/V和6.2×10^-19 m²/V²，这在其他常见的TMDCs(例如MoS₂)中没有发现。引人注目的是，它同时也表现出强烈的SHG各向异性，各向异性比约为45，据研究人员所知，这是迄今为止所有2D材料中最大的。此外，由于X^（2）值的色散，通过改变激发波长，SHG各向异性比可以从0.12控制到45(375倍)。作为一个示例，研究人员进一步展示了偏振SHG成像在晶体取向识别和偏振相关空间编码中的潜在应用。这些发现对非线性纳米光子和光电子应用具有重要的意义。

据悉，非线性光学活性，特别是二次谐波的产生是逆对称破缺二维(2D)过渡金属二硫族化合物(TMDCs)中的关键现象。另一方面，各向异性非线性光学过程对于具有偏振功能的纳米非线性光子器件的独特应用具有重要意义，已成为非线性光子学领域的研究热点之一。然而，在普通的二维材料中，强非线性和强光学各向异性并不同时存在。

附：英文原文

Title: Strong nonlinear optical processes with extraordinary polarization anisotropy in inversion-symmetry broken two-dimensional PdPSe

Author: Zhu, Song, Duan, Ruihuan, Xu, Xiaodong, Sun, Fangyuan, Chen, Wenduo, Wang, Fakun, Li, Siyuan, Ye, Ming, Zhou, Xin, Cheng, Jinluo, Wu, Yao, Liang, Houkun, Kono, Junichiro, Li, Xingji, Liu, Zheng, Wang, Qi Jie

Issue&Volume: 2024-05-27

Abstract: Nonlinear optical activities, especially second harmonic generation (SHG), are key phenomena in inversion-symmetry-broken two-dimensional (2D) transition metal dichalcogenides (TMDCs). On the other hand, anisotropic nonlinear optical processes are important for unique applications in nano-nonlinear photonic devices with polarization functions, having become one of focused research topics in the field of nonlinear photonics. However, the strong nonlinearity and strong optical anisotropy do not exist simultaneously in common 2D materials. Here, we demonstrate strong second-order and third-order susceptibilities of 64pm/V and 6.2×10^-19 m²/V², respectively, in the even-layer PdPSe, which has not been discovered in other common TMDCs (e.g., MoS₂). Strikingly, it also simultaneously exhibited strong SHG anisotropy with an anisotropic ratio of ~45, which is the largest reported among all 2D materials to date, to the best of our knowledge. In addition, the SHG anisotropy ratio can be harnessed from 0.12 to 45 (375 times) by varying the excitation wavelength due to the dispersion of X^（2） values. As an illustrative example, we further demonstrate polarized SHG imaging for potential applications in crystal orientation identification and polarization-dependent spatial encoding. These findings in 2D PdPSe are promising for nonlinear nanophotonic and optoelectronic applications.

DOI: 10.1038/s41377-024-01474-6

Source: https://www.nature.com/articles/s41377-024-01474-6