1. Department of Physics, Taiyuan University of Science and Technology, Taiyuan 030024, China
2. The Institute of Technological Sciences, Wuhan University, Wuhan 430072, China
3. School of Materials Science and Engineering, Hubei University, Wuhan 430062, China
4. Department of Materials Science and Engineering and State Key Laboratory of Terahertz and Millimeter Waves, City University of Hong Kong, Hong Kong 999077, SAR, China
5. College of Electronic Information and Optical Engineering, Taiyuan University of Technology, Taiyuan 030024, China