[1] Natl Taiwan Univ, Ctr Condensed Matter Sci, Taipei 106, Taiwan
[2] Chinese Acad Sci, Dalian Inst Chem Phys, Dalian 116023, Peoples R China
[3] Natl Synchrotron Radiat Res Ctr, Hsinchu 300, Taiwan
[4] Acad Sinica, Inst Atom & Mol Sci, Taipei 106, Taiwan