[1] Fudan Univ, Surface Phys Lab, Shanghai 200433, Peoples R China
[2] Fudan Univ, Dept Phys, Shanghai 200433, Peoples R China
[3] Chinese Acad Sci, Inst Solid State Phys, Hefei 230031, Peoples R China
[4] Chinese Acad Sci, Interdisciplinary Ctr Theoret Studies, Beijing 100080, Peoples R China