1Department of Electrophysics, National Chiayi University, Chiayi, Taiwan 60004, R.O.C.
2Graduate Institute of Applied Physics and Department of Physics, National Taiwan University, Taipei, Taiwan 10617, R.O.C.
3National Synchrotron Radiation Research Center, Hsinchu, Taiwan 30076, R.O.C.
4Center for Condensed Matter Sciences, National Taiwan University, Taipei, Taiwan 10617, R.O.C.
5Department of Physics, National Tsing Hua University, Hsinchu, Taiwan 30013, R.O.C.