1. State Key Laboratory of Catalysis CAS Center for Excellence in Nanoscience Dalian Institute of Chemical Physics Chinese Academy of Sciences 457 Zhongshan Road Dalian 116023 China
2. University of Chinese Academy of Sciences Beijing 100049 China
3. Department of Physics Department of Chemistry and JILA University of Colorado Boulder CO 80309 USA
4. Hefei National Laboratory for Physical Sciences at the Microscale University of Science and Technology of China 96 Jin Zhai Road Hefei 230026 China
5. Beijing National Laboratory for Condensed Matter Physics Institute of Physics Chinese Academy of Sciences Beijing 100190 China
6. Advanced Light Source Lawrence Berkeley National Laboratory Berkeley CA 94720 USA
7. Materials Sciences Division Lawrence Berkeley National Laboratory Berkeley CA 94720 USA