1. Institute of Super-Microstructure and Ultrafast Process in Advanced Materials, School of Physics and Electronics, Central South University, Changsha, 410083, P. R. China
2. School of Electronics and Information Engineering, Central South University of Forestry and Technology, Changsha, 410004, P. R. China
3. Department of Physics and Astronomy, University of Rochester, Rochester, New York 14627, United States