1. State Key Laboratory of Functional Materials for Informatics; Shanghai Institute of Microsystem and Information Technology; Chinese Academy of Sciences; 865 Changning Road Shanghai 200050 China
2. School of Physical Science and Technology; Lanzhou University; Lanzhou 730000 China
3. Department of Physics; Beihang University; Beijing 100191 China
4. Department of Physics and Materials Science; City University of Hong Kong; Tat Chee Avenue; Kowloon Hong Kong China
5. International Centre for Quantum and Molecular Structures and Department of Physics; Shanghai University; Shanghai 200444 China