1. Hunan Key Laboratory of Nanophotonics and Devices, School of Physics, Central South University, 932 South Lushan Road, Changsha, Hunan 410083, P. R. China
2. Department of Applied Physics, School of Microelectronics and Physics, Hunan University of Technology and Business, Changsha 410205, China
3. School of Physics and Technology, State Key Laboratory of Chemistry and Utilization of Carbon Based Energy Resources, Xinjiang University, Urumqi 830046, People’s Republic of China