1. School of Physics and Electron, Mianyang Normal University, Mianyang, 621000, China
2. Department of Physics and Electronic Engineering, Neijiang Normal College, Neijiang, 641112, China
3. Department of Applied Physics, Chongqing University of Technology, Chongqing, 400054, P.R. China
4. International Centre for Materials Physics, Chinese Academy of Sciences, Shenyang, 110016, P.R. China