1. School of Physics and Telecommunication Engineering South China Normal University Guangzhou 510006 China
2. Advanced Energy Science and Technology Guangdong Laboratory Huizhou 516000 China
3. Institute of Modern Physics Chinese Academy of Sciences Lanzhou 730000 China
4. School of Nuclear Science and Technology University of Chinese Academy of Sciences Beijing 100049 China
5. State Key Laboratory of Superlattices and Microstructures Institute of Semiconductors Chinese Academy of Sciences Beijing 100083 China