Research Article

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2017, 10(5): 1618–1626

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https://doi.org/10.1007/s12274-016-1329-x

Valley polarization in stacked MoS2 induced by circularly polarized light

Juan Xia1, Xingli Wang2, Beng Kang Tay2,3, Shoushun Chen4, Zheng Liu2,3,5, Jiaxu Yan1,6 (*), and Zexiang Shen1,3,7 (*)

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1 Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University, Singapore 637371, Singapore
2 NOVITAS, Nanoelectronics Centre of Excellence, School of Electrical and Electronic Engineering, Nanyang Technological University, Singapore 639798, Singapore
3 CINTRA CNRS/NTU/THALES, UMI 3288, Research Techno Plaza, Singapore 637553, Singapore
4 School of Electrical and Electronic Engineering, Nanyang Technological University, Singapore 639798, Singapore
5 Center for Programmable Materials, School of Materials Science and Engineering, Nanyang Technological University, Singapore 639798, Singapore
6 Institute of Advanced Materials (IAM), Jiangsu National Synergistic Innovation Center for Advanced Materials (SICAM), Nanjing Tech University (NanjingTech), 30 South Puzhu Road, Nanjing 211816, China
7 Centre for Disruptive Photonic Technologies, Nanyang Technological University, Singapore 637371, Singapore

Keywords: circularly polarized photoluminescence, first-principles calculations, molybdenum disulfide, ultra-low-frequency Raman spectroscopy, valley polarization
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ABSTRACT Manipulation of valley pseudospins is crucial for future valleytronics. The emerging transition metal dichalcogenides (TMDs) provide new possibilities for exploring the interplay among the quantum degrees of freedom, including real spin, valley pseudospin, and layer pseudospin. For example, spin–valley coupling results in valley-dependent circular dichroism in which electrons with particular spin (up or down) can be selectively excited by chiral optical pumping in monolayer TMDs, whereas in few-layer TMDs, the interlayer hopping further affects the spin–valley coupling. In addition to valley and layer pseudospins, here we propose a new degree of freedom—stacking pseudospin—and demonstrate new phenomena correlated to this new stacking freedom that otherwise require the application of external electrical or magnetic field. We investigated all possible stacking configurations of chemical-vapor-deposition-grown trilayer MoS2 (AAA, ABB, AAB, ABA, and 3R). Although the AAA, ABA, 3R stackings possess a sole peak with lower degree of valley polarization than that in monolayer samples, the AAB (ABB) stackings exhibit two distinct peaks, one similar to that observed in monolayer MoS2 and an additional unpolarized peak at lower energy. Our findings provide a more complete understanding of valley quantum control for future valleytronics.
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Valley polarization in stacked MoS2 induced by circularly polarized light. Nano Res. 2017, 10(5): 1618–1626 https://doi.org/10.1007/s12274-016-1329-x

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