1. Department of Physics, Yantai University, Yantai 264005, P. R. China
2. Department of Physics, Tsinghua University, Beijing 100084, P. R. China
3. Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, Beijing, 100190, P. R. China
4. Collaborative Innovation Center of Quantum Matter, Beijing 100084, P. R. China