1. Key Laboratory of Material Physics Ministry of Education School of Physics and Microelectronics Zhengzhou University Zhengzhou 450001 P. R. China
2. Beijing National Laboratory for Condensed Matter Physics and Institute of Physics Chinese Academy of Sciences Beijing 100190 P. R. China
3. School of Physical Sciences University of Chinese Academy of Sciences Beijing 100190 P. R. China
4. School of Physics and Information Technology Shaanxi Normal University Xi'an 710119 P. R. China
5. Departments of Chemistry and Mechanical Engineering The University of Hong Kong Hong Kong 999077 P. R. China
6. HKU Zhejiang Institute of Research and Innovation The University of Hong Kong Hangzhou 311305 P. R. China