1. Department of Chemistry, National University of Singapore, 3 Science Drive 3, Singapore 117543
2. Institute of Advanced Energy, Kyoto University, Uji, Kyoto 611-0011, Japan
3. Department of Physics, National Sun Yat-sen University, Kaohsiung 80424, Taiwan
4. Physics Division, National Center for Theoretical Sciences, Taipei, 10617, Taiwan
5. Zhejiang Province Key Laboratory of Quantum Technology and Device, Department of Physics, Zhejiang University, Hangzhou, People's Republic of China
6. Centre for Advanced 2D Materials (CA2DM), National University of Singapore, 6 Science Drive 2, Singapore 117546, Singapore