# Exploring a proximity-coupled Co chain on Pb(110) as a possible Majorana platform

## TL;DR

This study investigates cobalt chains on Pb(110) as a potential platform for Majorana zero modes, using spin-polarized spectroscopy, but finds no clear evidence of Majorana states due to multiple band crossings.

## Contribution

It provides experimental insights into the magnetic and electronic properties of Co chains on Pb(110) and evaluates their suitability for hosting Majorana modes, highlighting the role of band crossings.

## Key findings

- Ferromagnetic order observed in Co chains.
- Spin-polarized YSR bands detected with zero-energy resonances.
- No clear evidence of Majorana modes found.

## Abstract

Linear, suspended chains of magnetic atoms proximity coupled to an s-wave superconductor are predicted to host Majorana zero modes at the chain ends in the presence of strong spin-orbit coupling. Specifically, iron (Fe) chains on Pb(110) have been explored as a possible system to exhibit topological superconductivity and host Majorana zero-modes [Nadj-Perge, et al., Science 346, 602 (2014)]. Here, we study chains of the transition metal cobalt (Co) on Pb(110) and check for topological signatures. Using spin-polarized scanning tunneling spectroscopy, we resolve ferromagnetic order in the $d$ bands of the chains. Interestingly, also the subgap Yu-Shiba-Rusinov (YSR) bands carry a spin polarization as was predicted decades ago. Superconducting tips allow us to resolve further details of the YSR bands and in particular resonances at zero energy. We map the spatial distribution of the zero-energy signal and find it delocalized along the chain. Hence, despite of the ferromagnetic coupling within the chains and the strong-spin orbit coupling in the superconductor, we do not find clear evidence of Majorana modes. Simple tight-binding calculations suggest that the spin-orbit-split bands may cross the Fermi level four times which suppresses the zero-energy modes.