Engineering the spin couplings in atomically crafted spin chains on an elemental superconductor

TL;DR

This paper demonstrates the precise engineering of spin couplings in atomically crafted chains on a superconductor, advancing the control needed for realizing Majorana modes for quantum computing.

Contribution

It introduces a method to control YSR states and spin interactions in atomically assembled chains using a scanning tunneling microscope, enabling tailored topological superconductivity.

Findings

Engineered YSR energy levels by placing interstitial Fe atoms.

Strengthened interactions within long chains through linking Fe atoms.

Progressed towards controlled Majorana mode manipulation.

Abstract

Magnetic atoms on a superconductor give rise to Yu-Shiba-Rusinov (YSR) states within the superconducting energy gap. A spin chain of magnetic adatoms on an s-wave superconductor may lead to topological superconductivity accompanied by the emergence of Majorana modes at the chain ends. For their usage in quantum computation, it is a prerequisite to artificially assemble the chains and control the exchange couplings between the spins in the chain and in the substrate. Here, using a scanning tunneling microscope tip, we demonstrate engineering of the energy levels of the YSR states by placing interstitial Fe atoms in close proximity to adsorbed Fe atoms on an oxidized Ta surface. Based on this prototype platform, we show that the interaction within a long chain can be strengthened by linking the adsorbed Fe atoms with the interstitial ones. Our work adds an important step towards the controlled design and manipulation of Majorana end states.