1. Department of Physics and Key
Laboratory of Artificial Micro- and Nano-structures of Ministry of
Education, Wuhan University, Wuhan 430072,
China
2. Department of Materials Sciences & Engineering, Zhejiang University, Zhejiang 310058, China
3. Department
of Physics and Materials
Science, City University of Hong Kong,
Tat Chee Avenue, Kowloon, Hong Kong SAR, China
4. National Center for Nanoscience and Technology, Beijing, 100190, China