1. School of Physics, Xidian University, Xi’an 710071, P. R. China
2. School of Chemistry, MOE Key Laboratory for Nonequilibrium Synthesis and Modulation of Condensed Matter, State Key Laboratory for Mechanical Behavior of Materials, Xi’an Jiaotong University, Xi’an 710049, P. R. China
3. Key Laboratory of Photonics Technology for Information, School of Electronic and Information Engineering, Xi’an Jiaotong University, Xi’an 710049, P. R. China