[1] Fudan Univ, Dept Phys, Surface Phys Lab, Natl Key Lab, Shanghai 200433, Peoples R China
[2] Fudan Univ, Dept Phys, Shanghai 200433, Peoples R China
[3] Chinese Ctr Adv Sci & Technol, World Lab, Beijing 100080, Peoples R China
[4] Fudan Univ, Ctr Theoret Phys, Shanghai 200433, Peoples R China