1. School of Materials Science and Engineering, Nanjing University of Science and Technology, Nanjing 210094, China
2. Department of Physics, Southeast University, Nanjing 211189, China
3. Department of Physics and Electron Engineering, Hainan Normal University, Haikou 571158, China
4. National Laboratory of Solid Microstructures, Nanjing University, Nanjing 210093, China