1. Department of Physics, Ningbo University, Ningbo 315211, China
2. State Key Laboratory of Surface Physics and Department of Physics, Fudan University, Shanghai 200433, P. R. China
3. Department of Sport and Exercise Science, Zhejiang University, Hangzhou 310058, China
4. Department of Physics and Astronomy, Clemson University, Clemson, South Carolina 29634, United States