1. Nagano National College of Technology, 716 Tokuma, Nagano 381-8550, Japan
2. Department of Physics, Department of Materials Science and Engineering & Materials Research Institute, The Pennsylvania State University, 104 Davey Lab., University Park, Pennsylvania 16802-6300, United States
3. Department of Electrical Engineering and Computer Science and Department of Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139-4307, United States