Theoretical prediction of topological insulators in thallium-based III-V-VI ₂ ternary chalcogenides

Abstract

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