Topological Properties of Half Heusler Compounds: Tuned by the Spin-Orbit Coupling and P-D Hybridization

The topological properties of Half Heusler compounds XYZ (X=Na, K; Y=Cu, Ag, Au; Z=S, Se, Te) are studied by the density functional theory (DFT) and tight-binding model Hamiltonian. The Y-s, Y-d and Z-p states form the bands around the Fermi level and determine their topological properties. When the energy of Y-s state is much larger than the other states, the compounds are normal insulators, just like NaCuS and NaCuS. On the contrary, when the Y-s state energy is only a little higher than the other states, the compounds are topological insulators (TI) or Dirac semi-metal (DSM) depended on the effective spin orbital coupling (SOC), which can be tuned by the relation between positive SOC Z-p and Y-d states. The compounds with negative effective SOC are TI such as NaAgS, NaAuS, while the compounds possessing positive SOC are DSM, just like NaAgTe and NaAuTe. Our simple tight-binding model can be used to design topological materials before the time consuming DFT calculations.