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. Songshan Lake Materials Laboratory, Dongguan, Guangdong 523808, China
4. National Synchrotron Radiation Research Center, Hsinchu 30076, Taiwan, R.O.C.
5. Max Planck Institute for Chemical Physics of Solids, Dresden 01187, Germany