1. College of Applied Sciences
2. Beijing University of Technology
3. Beijing 100124
4. P. R. China
5. State Key Laboratory of Low-Dimensional Quantum Physics
6. Tsinghua-Foxconn Nanotechnology Research Center
7. Department of Physics
8. Collaborative Innovation Center of Quantum Matter
9. Tsinghua University
10. State Key Laboratory of New Ceramics and Fine Processing
11. School of Material Science and Engineering
12. Beijing 100084