1. Department of Applied Science Okayama University of Science Okayama 700‐0005 Japan
2. Institute of Applied Physics Graduate School of Pure and Applied Sciences University of Tsukuba Tsukuba Ibaraki 305‐8573 Japan
3. Department of Physics Graduate School of Science Tohoku University Sendai 980‐8578 Japan
4. Advanced Institute for Materials Research Tohoku University Sendai 980‐8577 Japan
5. Department of Physics Osaka University Osaka 560‐0043 Japan
6. Institute for Materials Research Tohoku University Sendai 980‐8577 Japan
7. Department of Physics Graduate School of Science The University of Tokyo Tokyo 113‐0033 Japan
8. RIKEN Nishina Center Wako 351‐0198 Japan
9. Department of Materials Science and Engineering Hopkins Extreme Materials Institute Johns Hopkins University Baltimore MD 21218 USA