Interplay between spin-orbit coupling and crystal-field effect in topological insulators

TL;DR

This study uses ab initio calculations to explore how spin-orbit coupling and crystal-field effects interact to influence band inversion in topological insulators, offering insights for material design.

Contribution

It reveals the competition between spin-orbit coupling and crystal-field splitting and demonstrates how chemical composition and strain can tune these effects in topological insulators.

Findings

Stronger crystal-field splitting weakens spin-orbit band shifts.

Chemical composition changes can control spin-orbit and crystal-field effects.

Uniaxial strain adjusts crystal-field splitting, influencing topological properties.

Abstract

Band inversion, one of the key signatures of time-reversal invariant topological insulators (TIs), arises mostly due to the spin-orbit (SO) coupling. Here, based on ab initio density-functional calculations, we report a theoretical investigation of the SO-driven band inversion in isostructural bismuth and antimony chalcogenide TIs from the viewpoint of its interplay with the crystal-field effect. We calculate the SO-induced energy shift of states in the top valence and bottom conduction manifolds and reproduce this behavior using a simple one-atom model adjusted to incorporate the crystal-field effect. The crystal-field splitting is shown to compete with the SO coupling, that is, stronger crystal-field splitting leads to weaker SO band shift. We further show how both these effects can be controlled by changing the chemical composition, whereas the crystal-field splitting can be tuned by means of uniaxial strain. These results provide a practical guidance to the rational design of novel TIs as well as to controlling the properties of existing materials.