1. Shanghai
Institute of Applied Physics, Chinese Academy of Sciences, Shanghai 201204, P. R. China
2. National
Synchrotron Radiation Lab, CAS Center for Excellence in Nanoscience, University of Science and Technology of China, Hefei, Anhui 230029, P. R. China
3. Max Planck Institute for Chemical Physics of Solids, Nöthnitzer Strasse 40, 01187 Dresden, Germany
4. National Synchrotron Radiation Research Center (NSRRC), 101 Hsin-Ann Road, Hsinchu 30076, Taiwan
5. Department
of Quantum Matter, ADSM, Hiroshima University, Higashi-Hiroshima 739-8530, Japan