1. Graduate School of Engineering Science, Osaka University, Toyonaka, Osaka 560-8531, Japan
2. Graduate School of Science, Osaka University, Toyonaka, Osaka 560-0043, Japan
3. Low Temperature Center, Osaka University, Toyonaka, Osaka 560-0043, Japan
4. Center for Quantum Science and Technology under Extreme Conditions, Osaka University, Toyonaka, Osaka 560-0043, Japan
5. The Institute for Solid State Physics, The University of Tokyo, Kashiwanoha, Kashiwa, Chiba 277-8581, Japan