1. Key Laboratory of Materials Physics Institute of Solid State Physics HFIPS Chinese Academy of Sciences Hefei 230031 P. R. China
2. University of Science and Technology of China Hefei 230026 P. R. China
3. Department of Physics Southern University of Science and Technology Shenzhen 518055 P. R. China
4. Institute of Plasma Physics Chinese Academy of Sciences HFIPS Chinese Academy of Sciences Hefei 230031 P. R. China
5. School of Science Jiangsu University of Science and Technology Zhenjiang 212003 P. R. China
6. High Magnetic Field Laboratory HFIPS Chinese Academy of Sciences Hefei 230031 P. R. China
7. Collaborative Innovation Centre of Advanced Microstructures Nanjing University Nanjing 210093 P. R. China