1. Beijing National Laboratory for Condensed Matter Physics, Beijing Key Laboratory for Nanomaterials and Nanodevices; Institute of Physics, Chinese Academy of Sciences; Beijing 100190 China
2. The Beijing Key Laboratory for Nano-Photonics and Nano-Structure, Center for Condensed Matter Physics, Department of Physics; Capital Normal University; Beijing 100048 China
3. Key Laboratory of Cluster Science, Ministry of Education of China, Beijing Key Laboratory of Photoelectronic/Electrophotonic Conversion Materials; School of Chemistry, Beijing Institute of Technology; Beijing 100081 China
4. School of Physics; Peking University; Beijing 100871 China