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

Area of Science:

• Condensed Matter Physics
• Materials Science
• Quantum Chemistry

Background:

• Topological insulators (TIs) are materials exhibiting unique electronic properties.
• Band inversion, a key characteristic of TIs, is primarily driven by spin-orbit (SO) coupling.
• Understanding factors influencing band inversion is crucial for TI design.

Purpose of the Study:

• To theoretically investigate the interplay between SO coupling and crystal-field effects on band inversion in bismuth and antimony chalcogenide TIs.
• To develop a simplified model that captures these interactions.
• To identify strategies for controlling band inversion and material properties.

Main Methods:

• Ab initio density-functional calculations were employed.
• Calculations focused on the SO-induced energy shifts in valence and conduction bands.
• A one-atom model incorporating crystal-field effects was developed and validated.

Main Results:

• Crystal-field splitting was found to compete with SO coupling, reducing the SO-induced band shift.
• Stronger crystal-field splitting resulted in a weaker SO band shift.
• Both SO coupling and crystal-field effects can be modulated by chemical composition.
• Uniaxial strain offers a method to tune crystal-field splitting.

Conclusions:

• The study provides a fundamental understanding of the competing roles of SO coupling and crystal-field effects in TIs.
• These findings offer practical guidance for the rational design of novel topological insulators.
• The results enable precise control over the electronic properties of existing TI materials.