1. Institute of Life Science and Technology, University of Electronic Science and Technology of China, Chengdu 610065, China
2. International Centre for Material Physics, Chinese Academy of Sciences, Shenyang 110015, China
3. School of Microelectronics and Solid-State Electronics, University of Electronic Science and Technology of China, Chengdu 610054, China
4. Department of Physics, National University of Singapore, 2 Science Drive 3, Singapore 117542, Singapore