1. Research Center for Materials Science at Extreme Conditions, Osaka University, Toyonaka, Osaka 560-8531
2. Department of Physical Science, Grasuate School of Engineering Science, Osaka University, Toyonaka, Osaka 560-8531
3. Oarai Branch, Institute for Materials Research, Tohoku University, Oarai, Ibaraki 311-1313
4. Physics Department, Graduate School of Science, Tohoku University, Sendai 980-8545