Department of Physics He’nan University Kaifeng 475001;
Department of Physics He’nan University Kaifeng 475001;
Istituto di MAI CNR C.P.10 00016 Monterotondo S.(Rome) Italy;
Istituto di MAI CNR C.P.10 00016 Monterotondo S.(Rome) Italy;
Institute of Physics Chinese Academy of Sciences Beijing 100080;