Topological superconductivity on the surface of Fe-based superconductors

TL;DR

This paper demonstrates that Fe-based superconductors can host topological superconductivity and Majorana zero modes, with phase transitions driven by doping and temperature, offering a promising platform for quantum computing.

Contribution

It provides ab initio calculations and an effective model showing topological phases and Majorana modes in Fe-based superconductors, revealing new phase transition mechanisms.

Findings

Fe-based superconductors exhibit topologically nontrivial band structures.

Majorana zero modes are trapped at vortex ends in the topological phase.

Surface topological superconductivity exists only below a certain bulk pairing gap.

Abstract

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 Fe$_{1+\text{y}}$Se$_{0.5}$Te$_{0.5}$ 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.