1. Department of Physics, University of Science and Technology of China, Hefei, Anhui, 230026, P. R. China
2. Center for Basic Research on Materials, National Institute for Materials Science, Tsukuba, Ibaraki 305-0044, Japan
3. State Key Laboratory of Structural Chemistry, Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences, Fuzhou 350002, China
4. Research Network and Facility Services Division, National Institute for Materials Science, Tsukuba, Ibaraki 305-0044, Japan
5. Department of Physics, Xiamen University, Xiamen, Fujian 361-005, China