1. National Laboratory of Solid State Microstructures and Department of Physics, Nanjing University, Nanjing 210093, People’s Republic of China
2. Jiangsu Provincial Key Laboratory of Advanced Photonic and Electronic Materials, School of Electronic Science and Engineering, Nanjing University, Nanjing 210093, People’s Republic of China
3. School of Science, Nanjing University of Posts and Telecommunications, Nanjing 210046, People’s Republic of China
4. Collaborative Innovation Center of Advanced Microstructures, Nanjing 210093, People’s Republic of China