1. Department of Materials Physics, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8603, Japan
2. Institute for Technical Physics, Karlsruhe Institute of Technology, Hermann-von-Helmholtz-Platz 1, D-76344 Eggenstein-Leopoldshafen, Germany
3. Applied Superconductivity Center, National High Field Laboratory, Florida State University, Tallahassee, Florida 32310, USA