1. Institute of Applied Physics, University of Tsukuba, Tsukuba, Ibaraki 305-8573, Japan
2. The Wakasa Wan Energy Research Center, Tsuruga, Fukui 914-0192, Japan
3. Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan
4. Japan Science and Technology Agency,
CREST, Tokyo 102-0075, Japan