1. School of Materials Science and Engineering Zhejiang Sci‐Tech University Hangzhou 310018 P. R. China
2. Department of Physics The Chinese University of Hong Kong Shatin Hong Kong SAR 999077 P. R. China
3. Department of Physics Hong Kong Baptist University Kowloon Tong Kowloon Hong Kong SAR 999077 P. R. China
4. Department of Applied Physics The Hong Kong Polytechnic University Hung Hom Hong Kong SAR 999077 P. R. China
5. Department of Materials Science and Engineering City University of Hong Kong 83 Tat Chee Avenue Kowloon Hong Kong SAR 999077 P. R. China