1. Department of Physics, Tokyo Institute of Technology,
Oh-Okayama, Meguro-ku, Tokyo 152-8551
2. Institute for Solid State Physics, University of Tokyo,
Roppongi, Tokyo 106-8666
3. Department of Material Science and Technology,
Niigata University, Niigata 950-2181
4. Department of Physics, Tokyo Metropolitan University,
Hachioji, Tokyo 192-0397