1. Department of Physics, University of Oxford, Oxford OX1 3PU, UK.
2. School of Physical Science and Technology, ShanghaiTech University and Chinese Academy of Sciences–Shanghai Science Research Center, 393 Middle Huaxia Road, Shanghai 201210, People’s Republic of China.
3. Center for Nanochemistry, Beijing National Laboratory for Molecular Sciences, College of Chemistry and Molecular Engineering, Peking University, Beijing 100871, People’s Republic of China.
4. Department of Condensed Matter Physics, Weizmann Institute of Science, Rehovot 7610001, Israel.
5. Max Planck Institute for Chemical Physics of Solids, D-01187 Dresden, Germany.
6. State Key Laboratory of Low Dimensional Quantum Physics, Department of Physics, Tsinghua University, Beijing 100084, People’s Republic of China.
7. Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA.
8. Accelerator Laboratory, Pohang University of Science and Technology, Pohang 790-784, Korea.
9. Paul Scherrer Institute, 5232 Villigen, Switzerland.
10. National Laboratory of Solid-State Microstructures, College of Engineering and Applied Sciences, and Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing 210093, People’s Republic of China.
11. Key Laboratory of Artificial Structures and Quantum Control (Ministry of Education), Department of Physics and Astronomy, Shanghai Jiao Tong University, Shanghai 200240, People’s Republic of China.