1. Institutes of Physical Science and Information Technology, Anhui University, Hefei 230601, P. R. China
2. Anhui Province Key Laboratory of Condensed Matter Physics at Extreme Conditions, High Magnetic Field Laboratory (HMFL), Chinese Academy of Science, Hefei 230031, P. R. China
3. University of Science and Technology of China, Hefei 230026, P. R. China
4. Institute of Functional Nano & Soft Materials (FUNSOM), Jiangsu Key Laboratory for Carbon-Based Functional Materials and Devices, Soochow University, Suzhou 215123, P. R. China