[1] Shandong Univ, Sch Phys, Jinan 250100, Peoples R China
[2] Shandong Univ, State Key Lab Crystal Mat, Jinan 250100, Peoples R China
[3] Univ Autonoma Madrid, Dept Fis Mat C4, Fac Ciencias, E-28049 Madrid, Spain
[4] Peking Univ, State Key Lab Nucl Phys & Technol, Beijing 100871, Peoples R China