1. State Key Laboratory of Artificial Microstructure and Mesoscopic Physics
2. School of Physics
3. Peking University
4. Beijing 100871
5. China
6. Beijing National Laboratory for Condensed Matter Physics
7. Institute of Physics
8. University of Chinese Academy of Sciences
9. Chinese Academy of Sciences
10. Beijing 100190
11. State Key Laboratory for Superlattices and Microstructures
12. Institute of Semiconductors
13. Beijing 100083