Institution: | 1.School of Physics and Microelectronics and Key Lab for Micro-Nano Physics and Technology of Hunan Province,Hunan University,Changsha,P.R. China;2.Department of Physics and Electronics Science,Hengyang Normal University,Hengyang,P.R. China;3.Department of Physics and Mathematics,Hunan Institute of Engineering,Xiangtan,P.R. China |