1. National Laboratory of Solid State Microstructure, School of Physics, Nanjing University 1 , Nanjing 210093, China
2. Department of Physics, Hong Kong University of Science and Technology (HKUST) 2 , Clear Water Bay, Hong Kong, China
3. Vacuum Interconnected NanoTech Workstation (Nano-X), Suzhou Institute of Nano-Tech and Nano-Bionics (SINANO), Chinese Academy of Sciences 3 , Suzhou 215123, China
4. Collaborative Innovation Center of Advanced Microstructures, Nanjing University 4 , Nanjing 210093, China
5. School of Physics and Electronic Sciences, Changsha University of Science and Technology 5 , Changsha 410114, China
6. Hefei National Laboratory 6 , Hefei 230088, China