1. Department of Physics, The Chinese University of Hong Kong, Shatin, New Territories, Hong Kong, China
2. Department of Physics, Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong, China
3. Department of Electronic and Information Engineering, Shenzhen Graduate School, Harbin Institute of Technology, Shenzhen 518055, China
4. Department of Applied Physics, Graduate School of Engineering, Hokkaido University, N13-W8, Sapporo 060-8628
5. Institute of Theoretical Physics, The Chinese University of Hong Kong, Shatin, New Territories, Hong Kong, China