[Cao, Liemao; Deng, Xiaohui] Hengyang Normal Univ, Coll Phys & Elect Engn, Hengyang 421002, Peoples R China.
[Zhou, Guanghui] Hunan Normal Univ, Dept Phys, Key Lab Low Dimens Struct & Quantum Manipulat, Minist Educ, Changsha 410081, Peoples R China.
[Zhou, Guanghui] Shaoyang Univ, Coll Sci, Dept Phys, Shaoyang 422001, Peoples R China.
[Liang, Shi-Jun] Nanjing Univ, Collaborat Innovat Ctr Adv Microstruct, Sch Phys, Natl Lab Solid State Microstruct, Nanjing 210093, Peoples R China.
[V. Nguyen, Chuong] Le Quy Don Tech Univ, Dept Mat Sci & Engn, Hanoi 100000, Vietnam.