1. Key Lab of Artificial Micro- and Nano-Structures of Ministry of Education of China, School of Physics and Technology, Wuhan University, Wuhan 430072, PR China
2. Shenzhen Institute, Wuhan University, Shenzhen, Guangdong 518055, PR China
3. International School of Microelectronics, Dongguan University of Technology, Dongguan, Guangdong 523808, PR China
4. Department of Physics, The Chinese University of Hong Kong, 999077 Hong Kong SAR, China