1. Department of Physics, Chongqing University, Chongqing 401331, China
2. State Key Laboratory of Power Transmission Equipment and System Security and New Technology, Chongqing University, Chongqing 400044, China
3. Tianjin Key Laboratory of Low Dimensional Materials Physics and Preparing Technology, Department of Applied Physics, School of Science, Tianjin University, Tianjin 300354, China