[Ren, Yi; Zhou, Guanghui; Zhou, Xiaoying] Hunan Normal Univ, Dept Phys, Synerget Innovat Ctr Quantum Effects & Applicat H, Minist Educ, Changsha 410081, Hunan, Peoples R China.
[Ren, Yi; Zhou, Guanghui; Zhou, Xiaoying] Hunan Normal Univ, Key Lab Low Dimens Quantum Struct & Manipulat, Synerget Innovat Ctr Quantum Effects & Applicat H, Minist Educ, Changsha 410081, Hunan, Peoples R China.
[Cheng, Fang] Changsha Univ Sci & Technol, Dept Phys & Elect Sci, Changsha 410004, Hunan, Peoples R China.
[Chang, Kai] Chinese Acad Sci, SKLSM, Inst Semicond, POB 912, Beijing 100083, Peoples R China.