Topological electronic structure and Weyl semimetal in the TlBiSe$_2$ class of semiconductors

TL;DR

This paper investigates the electronic structures of TlBiSe2 and related compounds, predicting topological insulator phases and proposing Weyl semimetal realization at critical points, supported by ab initio calculations and experimental agreement.

Contribution

It provides a comprehensive ab initio analysis of the topological phases in TlBiSe2 and similar compounds, predicting Weyl semimetal states through inversion symmetry breaking.

Findings

TlSbSe2, TlSbTe2, TlBiSe2, TlBiTe2 are topological insulators with Dirac cones.

TlSbS2 and TlBiS2 are trivial insulators.

Weyl semimetal phase can be realized in alloy compositions at critical points.

Abstract

We present an analysis of bulk and surface electronic structures of thallium based ternary III-V-VI$_2$ series of compounds TlMQ$_2$, where M=Bi or Sb and Q=S, Se or Te, using the ab initio density functional theory framework. Based on parity analysis and (111) surface electronic structure, we predict TlSbSe$_2$, TlSbTe$_2$, TlBiSe$_2$ and TlBiTe$_2$ to be non-trivial topological insulators with a single Dirac cone at the $\Gamma$-point, and TlSbS$_2$ and TlBiS$_2$ to be trivial band insulators. Our predicted topological phases agree well with available angle-resolved photoemission spectroscopy (ARPES) measurements, in particular the topological phase changes between TlBiSe$_2$ and TlBiS$_2$. Moreover, we propose that Weyl semimetal can be realized at the topological critical point in TlBi(S$_{1-x}$Se$_x$)$_2$ and TlBi(S$_{1-x}$Te$_x$)$_2$ alloys by breaking the inversion symmetry in the layer by layer growth in the order of Tl-Se(Te)-Bi-S, yielding six Dirac cones centered along the $\Gamma-L$ directions in the bulk band structure.