1. Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China
2. School of Physical Sciences, University of Chinese Academy of Sciences, Beijing 100049, China
3. College of Materials Science and Opto-Electronic Technology, University of Chinese Academy of Sciences, Beijing 100049, China
4. National Synchrotron Radiation Research Center, Hsinchu 30076, Taiwan
5. Department of Electrophysics, National Yang Ming Chiao Tung University, Hsinchu 30010, Taiwan
6. Max Planck Institute for Chemical Physics of Solids, Dresden 01187, Germany
7. Songshan Lake Materials Laboratory, Dongguan 523808, Guangdong, China