1. Department of Physics, National Taiwan Normal University, Taipei 11677, Taiwan
2. Department of Physics, Tohoku University, Sendai 980-8578, Japan
3. Frontier Research Institute for Interdisciplinary Sciences, Tohoku University, Sendai 980-8578, Japan
4. Center for Condensed Matter Sciences, National Taiwan University, Taipei 10617, Taiwan
5. Department of Mechanical Engineering, School of Engineering, The University of Tokyo, Tokyo 113-8656, Japan
6. Department of Applied Physics, Aalto University School of Science, Espoo 15100, FI-00076 Aalto, Finland