Giant Valley Coherence at Room Temperature in 3R WS2 with Broken Inversion Symmetry

Luojun Du; Jian Tang; Jing Liang; Mengzhou Liao; Zhiyan Jia; Qinghua Zhang; Yanchong Zhao; Rong Yang; Dongxia Shi; Lin Gu; Jianyong Xiang; Kaihui Liu; Zhipei Sun; Guangyu Zhang

doi:10.34133/2019/6494565

Giant Valley Coherence at Room Temperature in 3R WS₂ with Broken Inversion Symmetry

Research (Wash D C). 2019 Oct 13:2019:6494565. doi: 10.34133/2019/6494565. eCollection 2019.

Authors

Luojun Du^{1

2}, Jian Tang¹, Jing Liang³, Mengzhou Liao¹, Zhiyan Jia⁴, Qinghua Zhang¹, Yanchong Zhao¹, Rong Yang¹, Dongxia Shi^{1

5

6}, Lin Gu¹, Jianyong Xiang⁴, Kaihui Liu³, Zhipei Sun^{2

7}, Guangyu Zhang^{1

5

6

8}

Affiliations

¹ Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China.
² Department of Electronics and Nanoengineering, Aalto University, Tietotie 3, FI-02150, Finland.
³ State Key Laboratory for Mesoscopic Physics, Collaborative Innovation, Center of Quantum Matter, School of Physics, Peking University, Beijing, China.
⁴ State Key Laboratory for Metastable Materials Science and Technology, Yanshan University, Qinhuangdao 066004, China.
⁵ School of Physical Sciences, University of Chinese Academy of Science, Beijing 100190, China.
⁶ Beijing Key Laboratory for Nanomaterials and Nanodevices, Beijing 100190, China.
⁷ QTF Centre of Excellence, Department of Applied Physics, Aalto University, FI-00076 Aalto, Finland.
⁸ Songshan-Lake Materials Laboratory, Dongguan, 523808 Guangdong Province, China.

Abstract

Breaking the space-time symmetries in materials can markedly influence their electronic and optical properties. In 3R-stacked transition metal dichalcogenides, the explicitly broken inversion symmetry enables valley-contrasting Berry curvature and quantization of electronic angular momentum, providing an unprecedented platform for valleytronics. Here, we study the valley coherence of 3R WS₂ large single-crystal with thicknesses ranging from monolayer to octalayer at room temperature. Our measurements demonstrate that both A and B excitons possess robust and thickness-independent valley coherence. The valley coherence of direct A (B) excitons can reach 0.742 (0.653) with excitation conditions on resonance with it. Such giant and thickness-independent valley coherence of large single-crystal 3R WS₂ at room temperature would provide a firm foundation for quantum manipulation of the valley degree of freedom and practical application of valleytronics.