1. Department
of Physics and Jiangsu Key Laboratory of Thin Films, Soochow University, Suzhou 215006, P. R. China
2. International
Center for Quantum Materials, School of Physics, Peking University, Beijing 100871, P. R. China
3. Collaborative Innovation Center of Quantum Matter, Beijing, P. R. China
4. Center
for Statistical and Theoretical Condensed Matter Physics and Department
of Physics, Zhejiang Normal University, Jinhua 321004, P. R. China
5. National
Laboratory of Solid State Microstructure and Department of Physics, Nanjing University, Nanjing 210093, P. R. China