Anomalous Shiba states in topological iron-based superconductors

TL;DR

This paper investigates zero energy modes near magnetic impurities in FeSe$_{1-x}$Te$_x$, revealing topological, spin-triplet pairing states that produce robust, protected zero modes consistent with recent experiments.

Contribution

It introduces a topological spin-triplet pairing mechanism induced by magnetic impurities in iron-based superconductors, explaining the formation of robust zero modes.

Findings

Zero energy modes are stabilized near magnetic impurities.

Spin-triplet inter-orbital pairing is favored over intra-orbital pairing.

Zero modes form Kramers doublets insensitive to impurity spin orientation.

Abstract

We demonstrate the formation of robust zero energy modes close to magnetic impurities in the iron-based superconductor FeSe$_{1-x}$Te$_x$. We find that the Zeeman field generated by the impurity favors a spin-triplet inter-orbital pairing as opposed to the spin-singlet intra-orbital pairing prevalent in the bulk. The preferred spin-triplet pairing preserves time-reversal symmetry and is topological, as robust, topologically-protected zero modes emerge at the boundary between regions with different pairing states. Moreover, the zero modes form Kramers doublets that are insensitive to the direction of the spin polarization or to the separation between impurities. We argue that our theoretical results are consistent with recent experimental measurements on FeSe$_{1-x}$Te$_x$.