1. School of Physical Sciences and CAS Center for Excellence in Topological Quantum Computation, University of Chinese Academy of Sciences, Beijing 100049, China.
2. Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA.
3. Department of Physics and Astronomy and Department of Electrical Engineering and Computer Science, Vanderbilt University, Nashville, TN 37235, USA.
4. Department of Chemistry and Centre for Advanced 2D Materials, National University of Singapore, 3 Science Drive 3, Singapore 117546, Singapore.
5. School of Materials Science and Engineering, Nanyang Technological University, Singapore 639798, Singapore.