1. National Laboratory of Solid State Microstructures & Department of Materials Science and Engineering, College of Engineering and Applied Sciences, Nanjing University, Nanjing 210093, China
2. Institute of Materials Science and Engineering, Jiangsu University of Science and Technology, Zhenjiang 212003, China
3. National Laboratory of Solid State Microstructures & Department of Physics, Nanjing University, Nanjing 210093, China
4. Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing 210093, China