1. Institute of Modern Physics, Chongqing University of Post and Telecommunications, Chongqing 400065, People's Republic of China
2. Department of Physics, Structure Research Laboratory, Academica Sinica, University of Science and Technology of China, Hefei, Anhui 230026, People's Republic of China
3. Department of Biology and Chemistry, City University of Hong Kong, Tat Chee Avenue, Kowloon, Hong Kong S.A.R., People's Republic of China