Consistent picture for the electronic structure around a vortex core in   iron-based superconductors
  Based on a two-orbital model and taking into account the presence of the impurity, we studied theoretically the electronic structure in the vortex core of the iron-Pnictide superconducting materials. The vortex is pinned when the impurity is close to the vortex core. The bound states shows up for the unpinned vortex and are wiped out by a impurity. Our results are in good agreement with recent experiments and present a consistent explanation for the different electronic structure of vortex core revealed by experiments on different materials. 
Tao Zhou, Z. D. Wang, Yi Gao, and C. S. Ting
cond-mat.supr-con