1. School of Physics, Southeast University, Nanjing 211189, China
2. Department of Physics, College of Sciences, Northeastern University, Shenyang 110819, China
3. Department of Physics, Changshu Institute of Technology, Changshu 215500, China
4. National Laboratory of Solid State Microstructures, Department of Materials Science and Engineering, Jiangsu Key Laboratory for Artificial Functional Materials, Nanjing University, Nanjing 210093, China
5. Department of Physics, Nanjing University, Nanjing 210093, China
6. National Laboratory of Solid State Microstructures, Nanjing 210008, China