1. National Laboratory of Solid State Microstructures, School of Physics,
and Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing 210093, China
2. College of Electronics
and Information, Hangzhou Dianzi University, Xiasha Campus, Hangzhou 310018, China
3. State Key Laboratory on Integrated Optoelectronics and College of
Electronic Science and Engineering, Jilin University, Changchun 130012, China
4. Department of Physics, University of Arkansas, Fayetteville, Arkansas 72701, United States