1. State Key Laboratory for Mesoscopic Physics and Electron Microscopy Laboratory, School of Physics; Peking University, and Collaborative Innovation Center of Quantum Matter; Beijing 100871 China
2. International Center for Quantum Materials; School of Physics, Peking University and Collaborative Innovation Center of Quantum Matter; Beijing 100871 China
3. Department of Nuclear Science and Engineering and Department of Materials Science and Engineering; Massachusetts Institute of Technology; Cambridge Massachusetts 02139 USA
4. Key Laboratory of Intelligent Nano Materials and Devices of MOE; Institute of Nano Science; Nanjing University of Aeronautics and Astronautics; 29 Yudao Street Nanjing 210016 China