Institution: | Department of Physics, Changwei Teachers College, Weifang 261043, China; Department of Metalurgy, Guizhou University of Technology, Guiyang 550003, China; Institut fur Experimental Physik, Universitat Innsbruck Technikerstrasse 25, A-6020, Innsbruck, Austria;Department of Modern Physics, University of Science and Technology of China, Hefei 230027, China |