1. Key Laboratory for Soft Chemistry and Functional Materials of Ministry of Education Nanjing University of Science and Technology Nanjing 210094 China
2. Beijing National Laboratory for Condensed Matter Physics Institute of Physics Chinese Academy of Sciences Beijing 100190 China
3. Department of Physics City University of Hong Kong Hong Kong China
4. School of Materials Science and Engineering Nanjing University of Science and Technology Nanjing 210094 China