1. School of Physics and Electronics, Hunan Key Laboratory of Nanophotonics and Devices, Central South University, 932 South Lushan Road, Changsha, Hunan 410083, People's Republic of China
2. Key Laboratory of Super Microstructure and Ultrafast Process, Central South University, Changsha, Hunan 410083, People's Republic of China
3. College of Materials Science and Engineering, Hunan University, Changsha, Hunan 410082, China