1. Department of Physics, Harbin Institute of Technology, Harbin 150001, People's Republic of China
2. Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China
3. Department of Physics & Astronomy, University of Wyoming, Laramie, Wyoming 82071, USA
4. Academy of Fundamental and Interdisciplinary Sciences, Harbin Institute of Technology, Harbin 150001, People's Republic of China