1. School of Science and Engineering, The Chinese University of Hong Kong, Shenzhen, Guangdong 518172, China
2. College of Physics and Electronic Engineering, Sichuan Normal University, Chengdu 610068, China
3. Department of Applied Physics, The University of Tokyo, 7-3-1 Hongo, Tokyo 113-8656, Japan
4. School of Physics, The University of New South Wales, Sydney 2052, Australia