1. School of Physics and AstronomyYunnan University Kunming 650091 P. R. China
2. Key Laboratory of LCR Materials and Devices of Yunnan ProvinceSchool of Materials Science and EngineeringYunnan University Kunming 650091 P. R. China
3. State Key Laboratory of Structural ChemistryFujian Institute of Research on the Structure of MatterChinese Academy of Sciences Fuzhou 350002 P. R. China