1. School of Physics and Optoelectronic Engineering, Guangdong University of Technology, Guangzhou Higher Education Mega Center, Guangzhou, 510006, P. R. China
2. School of Advanced Materials and Nanotechnology, Xidian University, Xian 710126, China
3. Ningbo Institute of Materials Technology and Engineering, Chinese Academy of Sciences, Ningbo 315201, China
4. Shenzhen Institutes of Advanced Technology, Chinese Academy of Sciences, Shenzhen 518055, China
5. Department of Physics, The University of Hong Kong, Hong Kong 999077, P. R. China