1. Key Laboratory for Intelligent Nano Materials and Devices of Ministry of Education, State Key Laboratory of Mechanics and Control of Mechanical Structures, and Institute for Frontier Science, Nanjing University of Aeronautics and Astronautics , Nanjing 210016 , China
2. Centre for Advanced 2D Materials, National University of Singapore , Singapore 117546 , Singapore
3. School of Physics and Electronics, Hunan University , Changsha 410082 , China
4. Centre for Quantum Physics, Key Laboratory of Advanced Optoelectronic Quantum Architecture and Measurement, School of Physics, Beijing Institute of Technology , Beijing 100081 , China
5. Leibniz Institute für Kristallzüchtung , Berlin 12489 , Germany