Affiliation: | a College of Physics Science and Technology, Guangxi University, Nanning, Guangxi 530004, People’s Republic of Chinab Key Laboratory of Polar Materials and Devices, Ministry of Education, East China Normal University, Shanghai 200062, People’s Republic of Chinac National Laboratory for Infrared Physics, Shanghai Institute of Technical Physics, Chinese Academy of Sciences, Shanghai 200083, People’s Republic of Chinad State Key Laboratory of Artificial Microstructure and Mesoscopic Physics, School of Physics, Peking University, Beijing 100871, People’s Republic of China |