1. Changchun Institute of Optics, Fine Mechanics and Physics, Chinese Academy of Sciences, Changchun 130033, P. R. China
2. University of Chinese Academy of Sciences, Beijing 100049, P. R. China
3. Key Laboratory of Functional Materials Physics and Chemistry (Ministry of Education), College of Physics, Jilin Normal University, Changchun 130103, China
4. College of Science, Changchun University, Changchun 130022, P. R. China