[1] Xidian Univ, Sch Phys & Optoelect Engn, Xian 710071, Peoples R China
[2] Chinese Acad Sci, Inst Phys, Beijing Natl Lab Condensed Matter Phys, Beijing 100190, Peoples R China
[3] Shandong Univ, State Key Lab Crystal Mat, Jinan 250100, Peoples R China
[4] Shandong Univ, Inst Crystal Mat, Jinan 250100, Peoples R China