1. Institute for Nationalities Attached to Hebei Normal University, Shijiazhuang 050091, China
2. Shijiazhuang Institute of Technology, Shijiazhuang 050200, China
3. College
of Physics, Hebei Normal University, Shijiazhuang 050024, China
4. Department
of Physics, Xingtai University, Xingtai 054001, China
5. College
of Physics, and Hebei Advanced Thin Films Laboratory, Hebei Normal University, Shijiazhuang 050024, China