Topological electronic structure and Weyl semimetal in the TlBiSe2 class of semiconductors

We present an analysis of bulk and surface electronic structures of thallium-based ternary III-V-VI2 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 TlSbSe2, TlSbTe2, TlBiSe2, and TlBiTe2 to be nontrivial topological insulators with a single Dirac cone at the Gamma point and TlSbS2 and TlBiS2 to be trivial band insulators. Our predicted topological phases agree well with available angle-resolved photoemission spectroscopy measurements, in particular, the topological phase changes between TlBiSe2 and TlBiS2. Moreover, we propose that Weyl semimetal can be realized at the topological critical point in TlBi(S1-x Se-x)(2) and TlBi(S1-x Te-x)(2) alloys by breaking the inversion symmetry in the layer-by-layer growth in the order Tl-Se(Te)-Bi-S, yielding six Dirac cones centered along the Gamma-L directions in the bulk band structure.