1. National Laboratory of Solid State Microstructures, Nanjing University, Nanjing 210093, China
2. Department of Physics, Nanjing University, Nanjing 210093, China
3. Jiangsu Key Laboratory of Artificial Functional Materials, Nanjing University, Nanjing 210093, China
4. Department of Materials Science and Engineering, Nanjing University, Nanjing 210093 China
5. Institute of Materials Science and Engineering, Jiangsu University of Science and Technology, Zhenjiang 212003, China
6. Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing 210093, China