1. State Key Laboratory for Mesoscopic Physics, Department of Physics, Peking University, Beijing 100871, P. R. China
2. International Center for Quantum Materials, Peking University, Beijing 100871, P. R. China
3. EMAT (Electron Microscopy for Materials Science), University of Antwerp, Groenenborgerlaan 171, B-2020 Antwerp, Belgium
4. Qian Xuesen Laboratory of Space Technology, China Academy of Space Technology, Beijing 100094,P. R. China
5. Collaborative Innovation Center of Quantum Matter, Beijing 100084, P. R. China