[1]Key Laboratory of Materials Physics Institute of Solid State Physics Chinese Academy of Sciences Hefei 230031 China;
[2]University of Science and Technology of China Hefei 230026 China;
[3]Department of Physics and Astronomy and Yunnan Key Laboratory for Micro/Nano Materials and Technology Yunnan University Kunming 650091 China;
[4]Institute of Physics Chinese Academy of Sciences Beijing 100190 China;
