1. Department of Electrical and Electronic Engineering, The University of Hong Kong, Pokfulam Road, Hong Kong, Special Administrative Region 999077, China
2. Department of Physics and and William Mong Institute of Nano Science and Technology, The Hong Kong University of Science and Technology, Clear Way Bay, Hong Kong, Special Administrative Region 999077, China
3. Key Laboratory of Intelligent Computing & Signal Processing, Anhui University, Hefei 230036, China
4. Core Research Facilities, Southern University of Science and Technology, Shenzhen 518055, China
5. Department of Applied Physics, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong Special Administrative Region 999077, China