1. School of Physics and Technology, Center for Nanoscience and Nanotechnology, and Key Laboratory of Artificial Micro- and Nano-structures of Ministry of Education , Wuhan University , Wuhan 430072 , China
2. Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences , Beijing 100190 , China
3. Institute of Microscale Optoelectronics, Shenzhen University , Shenzhen 518060 , China
4. School of Microelectronics , Wuhan University , Wuhan 430072 , China
5. Songshan Lake Materials Laboratory , Dongguan 523808 , China