[1] Nanyang Technol Univ, Sch Phys & Math Sci, Div Phys & Appl Phys, Singapore, Singapore
[2] Peking Univ, Sch Phys, Int Ctr Quantum Mat, Beijing, Peoples R China
[3] Peking Univ, Sch Phys, Electron Microscopy Lab, Beijing, Peoples R China
[4] Tsinghua Univ, State Key Lab Low Dimens Quantum Phys, Beijing, Peoples R China
[5] Tsinghua Univ, Dept Phys, Beijing, Peoples R China
[6] Beijing Acad Quantum Informat Sci, Beijing, Peoples R China
[7] Nanyang Technol Univ, Sch Elect & Elect Engn, Singapore, Singapore