1. Department of Physics, Condensed Matter Science and Technology Institute, Harbin Institute of Technology, Harbin 150080, China
2. National Synchrotron Radiation Laboratory and CAS Key Laboratory of Materials for Energy Conversion, University of Science and Technology of China, Hefei, Anhui 230026, China
3. Advanced Photon Source, Argonne National Laboratory, Argonne, Illinois 60439, USA
4. Department of Mathematics and Materials Research Institute, The Pennsylvania State University, University Park, Pennsylvania 16802, USA