Department of Science, Taiyuan Institute of Technology, Taiyuan 030008;
School of Physics, Shandong University, Jinan 250100;
Department of Science, Taiyuan Institute of Technology, Taiyuan 030008;
School of Physics, Shandong University, Jinan 250100;
School of Physics, Shandong University, Jinan 250100;
School of Physics, Shandong University, Jinan 250100;
School of Physics, Shandong University, Jinan 250100;
Department of Applied Physics, School of Information Science and Engineering,Shandong Agricultural University, Taian 271018;