1. Graduate School of Science, Osaka University, Toyonaka, Osaka 560-0043, Japan
2. Center for Quantum Science and Technology under Extreme Conditions (KYOKUGEN), Osaka University, Toyonaka, Osaka 560-8531, Japan
3. Institute of Solid State Physics, University of Tokyo, Kashiwa, Chiba 277-8581, Japan
4. Department of Physics, College of Humanities and Sciences, Nihon University, Setagaya, Tokyo 156-8550, Japan
5. Low Temperature Center, Osaka University, Toyonaka, Osaka 560-0043, Japan