作者机构:[1]Department of Physics, College of Science, Yanbian University, Yanji 133002, China, [2]Center for the Condensed-Matter Science and Technology, Harbin Institute of Technology, Harbin 150001, China
相关基金:Project supported by the National Natural Science Foundation of China (Grant No 60667001) and the Science Foundation of Yanbian University, China (Grant No 2007-35).