Topologically trivial gap-filling in superconducting Fe(Se,Te) by one dimensional defects

TL;DR

This study investigates line defects in Fe(Se,Te) superconductors, revealing that certain 1D defects are topologically trivial and do not host Majorana modes, contrasting previous claims of topological superconductivity at these defects.

Contribution

The paper demonstrates that atomic lattice displacements at line defects are caused by sub-surface impurities and shows that some 1D defects are topologically trivial, challenging prior assumptions about their role in topological superconductivity.

Findings

Displacement shifts at line defects are due to sub-surface impurities.

Repositioning impurities visualizes the defect-free lattice.

Some 1D defects are fully gapped and topologically trivial.

Abstract

Structural distortions and imperfections are a crucial aspect of materials science, on the macroscopic scale providing strength, but also enhancing corrosion and reducing electrical and thermal conductivity. At the nanometre scale, multi-atom imperfections, such as atomic chains and crystalline domain walls have conversely been proposed as a route to topological superconductivity, whose most prominent characteristic is the emergence of Majorana Fermions that can be used for error-free quantum computing. Here, we shed more light on the nature of purported domain walls in Fe(Se,Te) that may host 1D dispersing Majorana modes. We show that the displacement shift of the atomic lattice at these line-defects results from sub-surface impurities that warp the topmost layer(s). Using the electric field between the tip and sample, we manage to reposition the sub-surface impurities, directly visualizing the displacement shift and the underlying defect-free lattice. These results, combined with observations of a completely different type of 1D defect where superconductivity remains fully gapped, highlight the topologically trivial nature of 1D defects in Fe(Se,Te).