Affiliation: | Department of Physics, College of Science, Yanbian University, Yanji 133002, China; Centre for the Condensed-Matter Science and Technology, Department of Physics, Harbin Institute of Technology, Harbin 150001, China; BK21 Program Physics & Department of Physics, College of Natural Science, Chungbuk National University, Cheonju, Chungbuk 361–763, Republic of Korea; |