1. National Laboratory of Solid State Microstructures, School of Physics, and Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing 210093, China
2. State Key Laboratory of Integrated Optoelectronics and College of Electronic Science and Engineering, Jilin University, Changchun 130012, China
3. ISP/Applied Sciences Laboratory, Washington State University, Spokane, Washington 99210, United States
4. Department of Physics and Astronomy, Washington State University, Pullman, Washington 99164, United States
5. Department of Physics, University of Arkansas, Fayetteville, Arkansas 72701, United States