[1] Hebei Normal Univ, Coll Phys, Shijiazhuang 050016, Peoples R China
[2] Hebei Univ Technol, Inst Phys, Tianjin 300130, Peoples R China
[3] Tsinghua Univ, Dept Phys, Beijing 100084, Peoples R China
[4] Tsinghua Univ, Key Lab Atom & Mol Nanosci, Beijing 100084, Peoples R China