1. Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China
2. College of Materials Science and Opto-Electronic Technology, University of Chinese Academy of Sciences, Beijing 100049, China
3. Department of Physics, Yancheng Institute of Technology, Yancheng, Jiangsu 224051, China
4. School of Physical Sciences, University of Chinese Academy of Sciences, Beijing, 100049, China
5. Max Planck Institute for Chemical Physics of Solids, Nöthnitzer Straße 40, 01187 Dresden, Germany
6. National Synchrotron Radiation Research Center, 101 Hsin-Ann Road, Hsinchu Science Park, Hsinchu 300092, Taiwan
7. Songshan Lake Materials Laboratory, Dongguan, Guangdong 523808, China
8. State Key Laboratory of Low Dimensional Quantum Physics and Department of Physics, Tsinghua University, Beijing 100084, China