近日，德国耶拿大学的Giancarlo Soavi及其研究团队取得一项新进展。他们实现了单层WSe₂中的非线性谷选择定则，及全光学时间反演对称性破缺探测。相关研究成果已于2025年1月7日在国际知名学术期刊《自然—光子学》上发表。

该研究团队提出一种基于二次谐波产生的新方法，用于检测单层WSe₂中的时间反演对称性破缺和谷不平衡。在室温下，这项研究方法能够选择性地探测由超快、相干且谷选择性的光学斯塔克效应，和布洛赫-西格特效应产生的净谷不平衡。

这项工作展示了非线性光学在探测时间反演对称性破缺方面的潜力和独特能力，同时也为超快、非破坏性的谷电子学操作提供了一种工具。

据悉，在单层过渡金属硫化物中，时间反演对称性与破缺空间反演对称性相结合，决定了自旋-谷自由度。因此，通过光学或磁场手段对时间反演对称性的调控和工程化，构成了谷电子学的基础。

附：英文原文

Title: Nonlinear valley selection rules and all-optical probe of broken time-reversal symmetry in monolayer WSe₂

Author: Herrmann, Paul, Klimmer, Sebastian, Lettau, Thomas, Weickhardt, Till, Papavasileiou, Anastasios, Mosina, Kseniia, Sofer, Zdenk, Paradisanos, Ioannis, Kartashov, Daniil, Wilhelm, Jan, Soavi, Giancarlo

Issue&Volume: 2025-01-07

Abstract: In monolayer transition metal dichalcogenides, time-reversal symmetry—combined with broken space-inversion symmetry—defines the spin–valley degree of freedom. As such, the engineering and control of time-reversal symmetry by optical or magnetic fields constitutes the foundation of valleytronics. Here we propose a new approach for the detection of broken time-reversal symmetry and valley imbalance in monolayer WSe₂ based on second-harmonic generation. At room temperature, our method can selectively probe a net valley imbalance generated by ultrafast, coherent and valley-exclusive optical Stark and Bloch–Siegert effects. This work demonstrates the potential and unique capabilities of nonlinear optics as a probe of broken time-reversal symmetry as well as a tool for ultrafast and non-destructive valleytronic operations.

DOI: 10.1038/s41566-024-01591-z

Source: https://www.nature.com/articles/s41566-024-01591-z