1. Beijing
National Laboratory for Condensed Matter Physics, and Institute of
Physics, Chinese Academy of Sciences, Beijing, 100190, P. R. China
2. Peking University, Beijing, 100871, P. R. China
3. Collaborative Innovation
Center of Quantum Matter, Beijing, 100190, P. R. China
4. Department of Materials Science & Engineering, State Key Laboratory of Silicon Materials, Zhejiang University, Hangzhou, Zhejiang 310027, P. R. China
5. Department
of Physics and Astronomy, California State University Northridge, Northridge, California 91330-8268, United States