1. Electrical and Electronic Engineering and Information Systems The University of Tokyo 7–3–1 Hongo Bunkyo‐ku Tokyo 113–8656 Japan
2. Department of Materials Science and Engineering The University of Texas at Dallas 800 W. Campbell Rd. Richardson Texas 75080–3021 USA
3. Exploratory Research for Advanced Technology (ERATO) Japan Science and Technology Agency (JST) 2–11–16, Yayoi Bunkyo‐ku Tokyo 113–0032 Japan