1. a Department of Physics , National Central University , Chung-Li, Taiwan , 32054 , ROC
2. b Department of Physics , Millsaps College , Jackson , Mississippi , 39210 , USA
3. c School of Physics and Astronomy, University of Minnesota , Minneapolis , Minnesota , 55455 , USA
4. d Department of Physics , Kent State University , Kent , Ohio , 44242 , USA
5. e Department of Physics , State University of New York at Buffalo , Buffalo , New York , 14260 , USA