1. Department of Electrophysics, National Chiao Tung University, 1001 University Road, Hsinchu 30010, Taiwan, Republic of China
2. International College of Semiconductor Technology, National Chiao Tung University, Hsinchu 30010, Taiwan, Republic of China
3. Center for Emergent Matter Science, RIKEN, Wako-Shi 351-0198, Japan
4. Department of Physics, National Chung Hsing University, Taichung 40227, Taiwan, Republic of China
5. Graduate Institute of Applied Science and Technology, National Taiwan University of Science and Technology, Taipei 106, Taiwan, Republic of China