1. Department of Physics, Tokyo Institute of Technology, Meguro-ku, Tokyo 152-8551
2. Department of Chemistry, Tokyo Institute of Technology, Meguro-ku, Tokyo 152-8551
3. Research Center for Materials Science at Extreme Conditions, Osaka University, Toyonaka, Osaka 560-0043
4. CREST, Japan Science and Technology, Kawaguchi, Saitama 332-0012