1. Department of Electrical and Electronic Engineering, Graduate School of Engineering, Kobe University, Rokkodai, Nada, Kobe 657-8501, Japan
2. JST-PRESTO, Honcho 4-1-8, Kawaguchi, Saitama 332-0012, Japan
3. Geballe Laboratory for Advanced Materials, Stanford University, Stanford, California 94305, United States