1. Graduate School of Material Science, University of Hyogo, Kamigori, Hyogo 678-1297, Japan
2. Department of Physics, Yokohama National University, Yokohama 240-8501, Japan
3. College of Science, China Jiliang University, Hangzhou 310018, China
4. Department of Physics, Northwest University, Xian 710127, China
5. The Institute for Solid State Physics, The University of Tokyo, Kashiwa, Chiba 277-8581, Japan