1. Hunan Key Laboratory for Super-Microstructure and Ultrafast Process, School of Physics and Electronics, Central South University, Changsha, Hunan 410012, China
2. National Laboratory of Solid State Microstructure, School of Physics, Nanjing University, Nanjing 210093, China
3. School of Physics and Electronics, Central South University, Changsha 410083, China
4. School of Electronics and Information Engineering, Central South University of Forestry and Technology, Changsha 410004, China
5. Department of Physics and Astronomy, University of Rochester, Rochester, New York 14627, United States