1. Quantum-Phase Electronics Center (QPEC) and Department of Applied Physics, University of Tokyo, Bunkyo-ku, Tokyo 113-8656, Japan
2. Materials Science Research Center, Japan Atomic Energy Agency, Tokai, Ibaraki 319-1195, Japan
3. Nanostructures Research Laboratory, Japan Fine Ceramics Center, Nagoya 456-8587, Japan
4. MDX Research Center for Element Strategy (MDXES), Tokyo Institute of Technology, Midori-ku, Yokohama, Kanagawa 226-8501, Japan
5. Department of Applied Physics, University of Tokyo, Bunkyo-ku, Tokyo 113-8656, Japan