Topological superconductivity from first-principles I: Shiba band structure and topological edge states of artificial spin chains

TL;DR

This paper develops a first-principles computational approach to study topological superconductivity in magnetic chains on superconductors, enabling accurate predictions of edge states and Majorana zero modes without fitting parameters.

Contribution

It introduces a microscopic relativistic theory-based method to analyze the topological nature of edge states in realistic experimental systems, bridging the gap between theory and experiment.

Findings

Ferromagnetic Fe chains on Au/Nb(110) do not support MZMs.

Spin-spirals can host robust zero energy edge states with MZM signatures.

Spin-orbit coupling influences the topological phase and MZM localization.

Abstract

Magnetic chains on superconductors hosting Majorna Zero Modes (MZMs) attracted high interest due to their possible applications in fault-tolerant quantum computing. However, this is hindered by the lack of a detailed, quantitative understanding of these systems. As a significant step forward, we present a first-principles computational approach based on a microscopic relativistic theory of inhomogeneous superconductors applied to an iron chain on the top of Au-covered Nb(110) to study the Shiba band structure and the topological nature of the edge states. Contrary to contemporary considerations, our method enables the introduction of quantities indicating band inversion without fitting parameters in realistic experimental settings, holding thus the power to determine the topological nature of zero energy edge states in an accurate ab-initio based description of the experimental systems. We confirm that ferromagnetic Fe chains on Au/Nb(110) surface do not support any separated MZM; however, a broad range of spin-spirals can be identified with robust zero energy edge states displaying signatures of MZMs. For these spirals, we explore the structure of the superconducting order parameter shedding light on the internally antisymmetric triplet pairing hosted by MZMs. We also reveal a two-fold effect of spin-orbit coupling: although it tends to enlarge the topological phase regarding spin spiraling angles, however, it also extends the localization of MZMs. Due to the presented predictive power, our work fills a big gap between the experimental efforts and theoretical models while paving the way for engineering platforms for topological quantum computation.