As one of the simplest systems for realizing Majorana fermions, topological superconductor plays an important role in both condensed matter physics and quantum computations. Based on \emph{ab~initio} calculations and the analysis of an effective 8-band model with the superconducting pairing, we demonstrate that the three dimensional extended s-wave Fe-based superconductors such as Fe1+ySe0.5Te0.5 have a metallic topologically nontrivial band structure, and exhibit a normal-topological-normal superconductivity phase transition on the (001) surface by tuning the bulk carrier doping level. In the topological superconductivity (TSC) phase, a Majorana zero mode is trapped at the end of a magnetic vortex line. We further show that, the surface TSC phase only exists up to a certain bulk pairing gap, and there is a normal-topological phase transition driven by the temperature, which has not been discussed before. These results pave an effective way to realize the TSC and Majorana fermions in a large class of superconductors.
@article{arxiv.1511.06942,
title = {Topological superconductivity on the surface of Fe-based superconductors},
author = {Gang Xu and Biao Lian and Peizhe Tang and Xiao-Liang Qi and Shou-Cheng Zhang},
journal= {arXiv preprint arXiv:1511.06942},
year = {2016}
}