1. School of Physics and Information Technology, Shaanxi Normal University, Xi’an 710062, P. R. China
2. School of Science, Xian University of Posts and Telecommunications, Xi’an 710121, P. R. China
3. School of Physics and Materials Science, Guangzhou University, Guangzhou 510006, P. R. China
4. Institute of Physics and Electronic Information, Yunnan Normal University, Kunming 650500, P. R. China
5. State Key Lab of Loess and Quaternary Geology (SKLLQG), Institute of Earth Environment, Chinese Academy of Sciences, Xi’an 710061, P. R. China
6. Institut für Chemie, Technische Universität Berlin, Straße des 17. Juni 135, 10623 Berlin, Germany