1. National Laboratory of Solid State Microstructures and Department of Materials Science and Engineering, Nanjing University, Nanjing 210093, China
2. Department of Physics, College of Science, Shihezi University, Xinjiang 832003, China
3. National Laboratory of Solid State Microstructures and Department of Physics, Nanjing University, Nanjing 210093, China
4. Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing 210093, China