1. Department of Physics, Stony Brook University, Stony Brook, New York 11794, United States
2. Nanophotonics Research Division, CAS Center for Excellence in Nanoscience, National Center for Nanoscience and Technology, Beijing 100190, China
3. Skolkovo Institute of Science and Technology, Skolkovo, Moscow Region 143026, Russia
4. Department of Physics and Astronomy, Iowa State University, Ames, Iowa 50011, United States
5. Key Laboratory of Terahertz Solid State Technology, Shanghai Institute of Microsystem and Information Technology, Chinese Academy of Sciences, Shanghai 200050, China
6. State Key Laboratory of Transducer Technology, Shanghai Institute of Microsystem and Information Technology, Chinese Academy of Sciences, Shanghai 200050, China