1. School of Science and Engineering The Chinese University of Hong Kong Shenzhen Guangdong 518172 China
2. Department of Physics, International Center for Quantum and Molecular Structures Shanghai University Shanghai 200444 China
3. School of Physics Nanjing University Nanjing 210093 China
4. Department of Materials Science and Engineering Nanjing University Nanjing 210093 China
5. National Laboratory of Solid State Microstructures Nanjing University Nanjing 210093 China