1. School of Physics, Southeast University, Nanjing 211189, China
2. Department of Physics, City University of Hong Kong, Tat Chee Avenue, Kowloon, 999077 Hong Kong, China
3. Department of Materials Science and Engineering, City University of Hong Kong, Tat Chee Avenue, Kowloon, 999077 Hong Kong, China
4. Department of Biomedical Engineering, City University of Hong Kong, Tat Chee Avenue, Kowloon, 999077 Hong Kong, China