1. School
of Physical Science and Technology, Inner Mongolia University, Hohhot 010021, P. R. China
2. College of Physics, Chongqing University, Chongqing 401331, P. R. China
3. School of Science, Shaanxi University Science & Technology, Xi’an 710021, P. R. China
4. College of Physics and Electronic Engineering, Xinjiang Normal University, Urumchi 830054, P. R. China