1. Department of Physics; Capital Normal University; Beijing Key Lab for Metamaterials and Devices and Key Laboratory of Terahertz Optoelectronics; Ministry of Education; Beijing 100048 China
2. Department of Physics; Harbin Institute of Technology; Harbin 150001 China
3. Department of Physics; Capital Normal University; The Beijing Key Laboratory for Nano-Photonics and Nano-Structure; Center for Condensed Matter Physics; Beijing 100048 China
4. Institute of Information Photonics Technology and College of Applied Sciences; Beijing University of Technology; Beijing 100124 China
5. Physikalisches Institut; Justus-Liebig-Universität; Giessen 35392 Germany