1. School
of Fundamental Science and Technology, Keio University, Yokohama 223-8522, Japan
2. Department
of Physics, ETH Zurich, Schafmattstrasse 16, 8093 Zurich, Switzerland
3. Correlated
Electronics
Group, Electronics and Photonics Research Institute, National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba Central 4, 1-1-1, Higashi, Tsukuba, Ibaraki 305-8562, Japan
4. Nanoscale
Material Science, EMPA, Ueberlandstr. 129, 8600 Duebendorf, Switzerland
5. Research
Center for Advanced Science and Technology (RCAST), The University of Tokyo, Komaba, Meguro-ku, Tokyo 153-8904, Japan
6. Diamond Research Group, Research Institute for Ubiquitous
Energy Devices, National Institute of Advanced Industrial Science and Technology (AIST), 1-8-31, Midorigaoka, Ikeda, Osaka 563-8577, Japan