1. Research Center for Crystal Materials CAS Key Laboratory of Functional Materials and Devices for Special Environments Xinjiang Technical Institute of Physics and Chemistry, CAS 40-1 South Beijing Road Urumqi 830011 P. R. China
2. University of Chinese Academy of Sciences Beijing 100049 P. R. China
3. Beijing National Laboratory for Condensed Matter Physics Institute of Physics Chinese Academy of Sciences Beijing 100190 P. R. China