1. Quantum Nanoelectronics Research Center, Tokyo Institute of Technology, 2-12-1-H-52 Oh-okayama, Meguro-ku, Tokyo 152-8551, Japan
2. JST−CREST, 7-gobancho, Chiyoda-ku, Tokyo 102-0075, Japan
3. School of Materials Science I, Japan Advanced Institute of Science and Technology, 1-1 M1-61 Asahidai, Nomi, Ishikawa 923-1292, Japan
4. Energy Technology Research Institute, National Institute of Advanced Industrial Science and Technology, 1-1-1 Umezono, Tsukuba, 305-8568, Japan
5. Department of Electronic Chemistry, Tokyo Institute of Technology, 4259 G1-1 Nagatsuta, Midori-ku, Yokohama 226-8502, Japan
6. Department of Physics, Tokyo Institute of Technology, 2-12-1-H-51 Oh-okayama, Meguro-ku, Tokyo 152-8551, Japan