1. Department of Physics and State Key Laboratory of Silicon Materials, Zhejiang University, Hangzhou 310027, China
2. Department of Physics, Hangzhou Normal University, Hangzhou 310036, China
3. Zhejiang California International NanoSystems Institute, Zhejiang University, Hangzhou 310058, China
4. Collaborative Innovation Centre of Advanced Microstructures, Nanjing 210093, China