1. Department of Applied Physics, National Defense Academy, 1-10-20, Hashirimizu, Yokosuka239-8686, Japan
2. Department of Physics, Tohoku University, 6-3, Aramaki-aza-Aoba, Aoba-ku, Sendai980-8578, Japan
3. Department of Mathematics, Saitama University, 255, Shimo-Okubo, Sakura-ku, Saitama338-8570, Japan
4. Department of Physics, Ochanomizu University, 2-1-1, Otsuka, Bunkyo-ku, Tokyo112-8610, Japan
5. Department of Mathematics, Ochanomizu University, 2-1-1, Otsuka, Bunkyo-ku, Tokyo112-8610, Japan
6. Faculty of Materials Science and Engineering, Kyoto Institute of Technology, Matsugasaki,
Sakyo-ku, Kyoto606-8585, Japan