Affiliation: | 1Department of Physics, Southeast University, Nanjing 210096 2 Department of Physics and Institute of Innovations and Advanced Studies (IIAS), National Cheng Kung University, Tainan 701 3 jiangsu Provincial Laboratory for Nanotechnology, National Laboratory of Solid State Mierostructure, and Department of Physics, Nanjing University, Nanjing 210093) |