[1] Beijing Inst Technol, Sch Life Sci, Beijing 100081, Peoples R China
[2] Tsinghua Univ, State Key Lab Low Dimens Quantum Phys, Beijing 100084, Peoples R China
[3] Tsinghua Univ, Ctr Atom & Mol Nanosci, Dept Phys, Beijing 100084, Peoples R China
[4] Collaborat Innovat Ctr Quantum Matter, Beijing 100084, Peoples R China