1. Department of Physics, The University of Hong Kong, Pokfulam Road, Hong Kong, Hong Kong
2. Department of Physics, The Hong Kong University of Science and Technology, Clearwater Bay, 999077 Hong Kong, Hong Kong
3. Department of Electronic and Information Engineering, The Hong Kong Polytechnic University, 11 Yuk Choi Rd, Hung Hom, Kowloon, Hong Kong
4. School of Physics, The University of Sydney, Sydney, NSW 2006, Australia
5. Ruđer Bošković Institute, Bijenička 54, 10000 Zagreb, Croatia
6. Core Research Facilities, Southern University of Science and Technology, No. 1088, Xueyuan Rd., Shenzhen 518055, Guangdong, P. R. China