1. Department of Physics and State Key Laboratory of Low-Dimensional Quantum Physics; Tsinghua University; Beijing 100084 China
2. Collaborative Innovation Center of Quantum Matter; Beijing 100084 China
3. Key Laboratory of Space Utilization; Technology and Engineering Center for Space Utilization; Chinese Academy of Sciences; Beijing 100094 China
4. College of Mechatronics and Automation; National University of Defense Technology; Changsha 410073 China
5. School of Materials Science and Engineering and State Key Lab of New Ceramics and Fine Processing; Tsinghua University; Beijing 100084 China
6. Center for Nanoscale Science and Technology; National Institute of Standards and Technology; Gaithersburg MD 20899 USA
7. Department of Physics; Beijing Normal University; Beijing 100875 China
8. Beijing National Laboratory for Condensed Matter Physics; Institute of Physics; Chinese Academy of Sciences; Beijing 100190 China