1. School
of Optical and Electronic Information, Huazhong University of Science and Technology, LuoYu Road, Wuhan 430074, China
2. The
Institute of Scientific and Industrial Research, Osaka University, 8-1
Mihogaoka, Ibaraki, Osaka 567-0047, Japan
3. Division
of Materials Theory, Department of Physics and Astronomy, Angström
Laboratory, Uppsala University, Box 516, SE-751 20, Uppsala, Sweden