Half-Heusler d0-d gapless semiconductors as strong Z2 topological insulators

The discovery of non-trivial topological materials has attracted a lot of attention in the condensed matter physics. In the following we investigate the mechanical stability, electronic, and topological properties of XAuZ half-Heusler compounds (X = K, Cs; Z = S, Se, Te) using the WIEN2K full-potential electronic structure package, Wannier90, and WannierTools code. It is found that except KAuTe the other compounds are metastable in half-Heusler structure. In addition, the structural phase transition under pressure between stable and metastable phase has been investigated. The band structure without spin-orbit coupling (SOC) indicates a band-inversion and direct gapless semiconducting behavior for all compounds. The SOC effect creates a meaningful band gap in the fl-phase compounds KAuS, KAuSe, and CsAuS, thus converting them to topological insulators. The Z(2) topological quantum numbers of these compounds are found to be (1; 0 0 0). The Z(2) numbers and the surface states spectrum indicate that these compounds are strong topological insulators. The application of modest uniaxial strain is shown to open a gap in gamma-phase compounds, and turn CsAuSe and CsAuTe into their topological insulating states. Hence, true metastability together with topology of band structure are promising indicators for potential application of the above compounds as topological spintronic materials, which together with earlier findings of spin-gapless behavior in other d(0) - d half-Heusler alloys goes to show that these compounds are indeed multifaceted materials for spin-based electronics of the future.