Non-Majorana modes in diluted spin chains proximitized to a superconductor

TL;DR

This study investigates spin chains coupled to superconductors, revealing that zero-energy boundary modes often mimic Majorana signatures but are actually topologically trivial Shiba states, challenging assumptions about their topological nature.

Contribution

It demonstrates that zero-energy modes in proximitized spin chains are not necessarily Majorana modes, highlighting the importance of careful topological identification and proposing new experimental platforms.

Findings

Boundary modes are ubiquitous in the studied spin chains.

Most boundary modes are topologically trivial Shiba states.

The work suggests new methods to distinguish trivial from topological states.

Abstract

Spin chains proximitized with superconducting condensates have emerged as one of the most promising platforms for the realization of Majorana modes. Here, we craft diluted spin chains atom-by-atom following seminal theoretical proposal suggesting indirect coupling mechanisms as a viable route to trigger topological superconductivity. Starting from single adatoms hosting deep Shiba states, we use the highly anisotropic Fermi surface of the substrate to create spin chains characterized by different magnetic configurations along distinct crystallographic directions. By scrutinizing a large set of parameters we reveal the ubiquitous emergence of boundary modes. Although mimicking signatures of Majorana modes, the end modes are identified as topologically trivial Shiba states. Our work demonstrates that zero-energy modes in spin chains proximitized to superconductors are not necessarily a link to Majorana modes while simultaneously identifying new experimental platforms, driving mechanisms, and test protocols for the determination of topologically non-trivial superconducting phases.