1. International Center for Materials Nanoarchitectonics (MANA) National Institute for Materials Science (NIMS) Tsukuba Ibaraki 305‐0044 Japan
2. Research Center for Functional Materials National Institute for Materials Science (NIMS) Tsukuba Ibaraki 305‐0044 Japan
3. Department of Condensed Matter Physics Graduate School of Science Hokkaido University Sapporo 060‐0810 Japan