[1] Cent South Univ, Sch Phys & Elect, Hunan Key Lab Supermicrostruct & Ultrafast Proces, Changsha 410083, Hunan, Peoples R China
[2] Fudan Univ, State Key Lab Surface Phys, Shanghai 200433, Peoples R China
[3] Fudan Univ, Dept Phys, Shanghai 200433, Peoples R China
[4] Xi An Jiao Tong Univ, State Key Lab Mech Behav Mat, Ctr Spintron & Quantum Syst, Xian 710049, Peoples R China
[5] Univ Rochester, Dept Phys & Astron, Rochester, NY 14627 USA