Theoretical Prediction of Topological Insulators in Thallium-based III-V-VI$_2$ Ternary Chalcogenides

TL;DR

This paper predicts a new class of three-dimensional topological insulators in thallium-based ternary chalcogenides, highlighting their surface states, potential superconductivity, and tunable topological phases under pressure.

Contribution

It introduces a new class of topological insulators in Tl-based III-V-VI$_2$ compounds, with detailed mechanisms and potential for topological superconductivity.

Findings

Robust surface states with a single Dirac cone at the $a0$ point.

TlBiTe$_2$ can become a superconductor when doped.

TlSbS$_2$ can undergo a topological phase transition under pressure.

Abstract

We predict a new class of three dimensional topological insulators in thallium-based III-V-VI$_2$ ternary chalcogenides, including TlBiQ$_2$ and TlSbQ$_2$ (Q = Te, Se and S). These topological insulators have robust and simple surface states consisting of a single Dirac cone at the $\Gamma$ point. The mechanism for topological insulating behavior is elucidated using both first principle calculations and effective field theory models. Remarkably, one topological insulator in this class, TlBiTe$_2$ is also a superconductor when doped with $p$-type carriers. We discuss the possibility that this material could be a topological superconductor. Another material TlSbS$_2$ is on the border between topological insulator and trivial insulator phases, in which a topological phase transition can be driven by pressure.