1. Institute of Super-Microstructure and Ultrafast Process in Advanced Materials, School of Physics and Electronics, Central South University, Changsha 410083, People's Republic of China
2. College of Electronic Information and Electrical Engineering, Xiangnan University, Chenzhou 423000, People's Republic of China
3. Department of Physics, Kashgar University, Kashgar 844006, People's Republic of China
4. Department of Physics and Astronomy, University of Rochester, Rochester, New York 14627, USA