[1] Hong Kong Univ Sci & Technol, Dept Phys, Kowloon, Hong Kong, Peoples R China
[2] Hong Kong Univ Sci & Technol, Nano Sci & Technol Program, Kowloon, Hong Kong, Peoples R China
[3] Hong Kong Univ Sci & Technol, Dept Phys, Kowloon, Hong Kong, Peoples R China
[4] Chinese Acad Sci, Inst Phys, Beijing, Peoples R China