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Atomically thin layered semiconductors reveal unique properties such as strong excitonic emission and valley degree of freedom, which are expected for exotic physics and valleytronics applications at 2D limit. To achieve 2D valleytronics and enable new functionality, efforts from both property understanding and device engineering are in need. In this talk, I will present recent progress from my group aiming for realization of 2D valleytronics. To begin with, I will discuss our work on valley selection rules for nonlinear optical process in monolayer WS21. The finding of such nonlinear optical selection in a 2D valleytronic system is crucial for potential valley optoelectronic device applications such as 2D valley-polarized THz sources and coherent control for quantum computing. I will then focus on device engineering to achieve first electrical generation and control of valley polarization in 2D materials2. With unique spin–valley locking property in monolayer WS2, valley carrier injection was achieved via a diluted ferromagnetic semiconductor with efficiency up to 45%. In the last, our discovery of new functional 2D materials will be overviewed3,4, which may not only boost the development of valleytronics but inspire new interdisciplinary topics.
1. Xiao, J. et al. Nonlinear optical selection rule based on valley-exciton locking in monolayer ws2. Light Sci. Appl. 4, e366 (2015).
2. Ye, Y. et al. Electrical generation and control of the valley carriers in a monolayer transition metal dichalcogenide. Nat. Nanotechnol. 11, 598–602 (2016).
3. Lu, A.-Y. et al. Janus monolayers of transition metal dichalcogenides. Nat. Nanotechnol. 12, 744–749 (2017).
4. Gong, C. et al. Discovery of intrinsic ferromagnetism in two-dimensional van der Waals crystals. Nature 546, 265–269 (2017).
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