[1] Southwest Univ, Sch Phys, Chongqing 400715, Peoples R China
[2] Southwest Univ, Sch Math & Stat, Chongqing 400715, Peoples R China
[3] Xidian Univ, Sch Phys & Optoelect Engn, Xian 710071, Shaanxi, Peoples R China
[4] Chinese Acad Sci, Inst Phys, Beijing Natl Lab Condensed MatterPhys, Beijing 100190, Peoples R China