1. Department of Physics and William Mong Institute of Nano Science and Technology The Hong Kong University of Science and Technology Clearwater Bay Hong Kong P. R. China
2. School of Physics Sun Yat‐sen University No.135 Xingangxi Road Guangzhou Guangdong 510275 P. R. China
3. Department of Electronic Engineering and Department of Chemistry The Chinese University of Hong Kong Shatin New Territories Hong Kong P. R. China
4. Department of Electrical and Electronic Engineering The University of Hong Kong Pokfulam Road Hong Kong P. R. China
5. Institute of Physics Zagreb 10000 Croatia
6. Division of Theoretical Physics Ruđer Bošković Institute Zagreb 10000 Croatia