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

Abstract

Magnetic chains on superconductors hosting Majorana zero modes (MZMs) have attracted a great deal of 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 an 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 twofold effect of spin-orbit coupling: although it tends to enlarge the topological phase regarding spin spiraling angles, it also extends the localization of MZMs. Due to the presented predictive power, our work fills a big gap between experimental efforts and theoretical models while paving the way for engineering platforms for topological quantum computation.

Source-reported materials — not catalogue approval

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