Tuning topological surface magnetism by bulk alloying

TL;DR

This paper demonstrates that the spin structure of topological surface states in IV-VI semiconductors is highly dependent on bulk material parameters, allowing for tuning of surface magnetism through bulk alloying.

Contribution

It introduces an analytical model linking bulk band structure parameters to surface state spin textures, revealing their non-universality and tunability.

Findings

Surface state spin structure varies with bulk spin-orbit and crystal field parameters.

RKKY interaction depends qualitatively on bulk parameters.

Surface magnetism can be tuned by alloying IV-VI compounds.

Abstract

Deploying an analytical atomistic model of the bulk band structure of the IV-VI semiconductors we connect the spin structure of the topological surface state to the crystal field and spin orbit coupling parameters of the bulk material. While the Dirac-Weyl (or equivalently, Rashba) type topological surface state is often assumed universal, we show that the physics of the surface state is strikingly non-universal. To see this explicitly we calculate the RKKY interaction, which may be viewed as a probe of this surface state spin structure, finding its \emph{qualitative form} depends on the values the bulk spin-orbit and crystal field parameters take. This opens the way to tune the spin interaction on the surface of a IV-VI topological insulator by, for instance varying the composition of the IV-VI ternary compounds, as well as highlighting the importance of the connection between bulk and surface physics in topological insulators.