1. Department of Physics, National Taiwan University, Taipei 10617, Taiwan
2. Department of Physics and Astronomy, University of California, Riverside, California 92521, USA
3. Department of Physics, The Pennsylvania State University, University Park, Pennsylvania 16802, USA
4. National Synchrotron Radiation Research Center, Taiwan, 101 Hsin Ann Road, Hsinchu Science Park, Hsinchu 30076, Taiwan
5. Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei 10617, Taiwan
6. Research Center for Applied Sciences, Academia Sinica, Taipei 11529, Taiwan