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 Engineering and Applied Sciences, Nanjing University, Nanjing 210093, China
3. Sivananthan Laboratories, Bolingbrook, Illinois 60440, 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