1. Department of Electronic Science and Engineering, Kyoto University, Kyoto, Kyoto 615-8510, Japan
2. Center for Spintronics Research Network, Institute for Chemical Research, Kyoto University, Gokasho, Uji, Kyoto 611-011, Japan
3. Department of Materials Science and Engineering, Monash University, Clayton, Victoria 3800, Australia
4. ARC Centre of Excellence in Future Low Energy Electronics Technologies, Clayton, Victoria 3800, Australia
5. Robinson Research Institute, Victoria University of Wellington, Wellington 6140, New Zealand
6. The MacDiarmid Institute for Advanced Materials and Nanotechnology, Wellington 6011, New Zealand
7. PRESTO, Japan Science and Technology Agency, Honcho, Kawaguchi, Saitama 332-0012, Japan