1 Center for Terahertz Waves and College of Precision Instrument and Optoelectronics Engineering, Tianjin University, and the Key Laboratory of Optoelectronics Information and Technology Tianjin, Ministry of Education of China, Tianjin 300072, China
2 Physical Science and Engineering Division, King Abdullah University of Science and Technology, Thuwal 23955-6900, Saudi Arabia
3 Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University, 21 Nanyang Link, Singapore 637371, Singapore
4 Research Institute of Superconductor Electronics (RISE), School of Electronic Science and Engineering, Nanjing University, Nanjing 210093, China
5 School of Electrical and Computer Engineering, Oklahoma State University, Stillwater, Oklahoma 74078, USA
6 e-mail: weili.zhang@okstate.edu