[1] Peking Univ, Sch Phys, State Key Lab Mesoscop Phys, Beijing 100871, Peoples R China
[2] Univ Cambridge, Dept Mat Sci & Met, 27 Charles Babbage Rd, Cambridge CB3 0FS, England
[3] Chinese Acad Sci, Inst Elect Engn, Dept Micronano Fabricat Technol, Beijing 100190, Peoples R China
[4] Beijing Key Lab Magnetoelect Mat & Devices, Beijing 100871, Peoples R China
[5] Collaborat Innovat Ctr Quantum Matter, Beijing 100871, Peoples R China