[1] Nankai Univ, Sch Phys, Tianjin 300071, Peoples R China
[2] Shangqiu Normal Univ, Sch Elect & Elect Engn, Shangqiu 476000, Peoples R China
[3] Zhoukou Normal Univ, Sch Phys & Telecommun Engn, Zhoukou 466001, Peoples R China
[4] Henan Normal Univ, Coll Phys & Mat Sci, Xinxiang 453007, Peoples R China