1. National Laboratory
of Solid State Microstructures, College of Engineering and Applied Sciences, and
Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing 210093, China
2. Institute of Functional Nano and Soft Materials (FUNSOM), Soochow University, Suzhou 215123, China
3. School of Physics, Nanjing University, Nanjing 210093, China