[1] Univ Chinese Acad Sci, Sch Phys Sci, Beijing 100049, Peoples R China
[2] Tsinghua Univ, Dept Phys, State Key Lab Low Dimens Quantum Phys, Beijing 100084, Peoples R China
[3] Collaborat Innovat Ctr Quantum Matter, Beijing 100084, Peoples R China
[4] Capital Normal Univ, Dept Phys, Beijing 100037, Peoples R China