∗Supported by the National Natural Science Foundation of China under Grant Nos 11765005, 11305040, IRG11521064, 11775097 and 11465021, the Fund of Science and Technology Department of Guizhou Province under Grant No [2015]2114, and the Education Department of Guizhou Province under Grant No.KY[2017]004. **Corresponding author. Email: wxiangphy@gmail.com © 2017 Chinese Physical Society and IOP Publishing Ltd