Designing Dirac semimetals with a honeycomb Na3Bi-lattice via isovalent cation substitution

Abstract

Functionality driven materials design for crystalline symmetry enabled quantum phases such as Dirac semimetals often faces the challenge of stabilizing a crystal structure with targeted functionality. Here, we propose an iso-symmetry isovalent cation substitution approach for stabilizing a honeycomb (P6₃/mmc) lattice analogous to Na₃Bi that was predicted as the first Dirac semimetal with conical linear band dispersion at the Fermi level protected by high-order rotational symmetry. Such isovalent substitution on the inequivalent cation sites in dynamically unstable Na₃Bi (P6₃/mmc) maintains the crystalline symmetry and reduces the strain energy, leading to the prediction of three dynamically stable compounds K₂NaBi, Rb₂NaBi and Rb₂KBi that are also thermodynamically stable against disproportionation into the competing phases. Electronic structure analysis reveals that the predicted ternaries have Dirac cones mainly consisting of Bi-6p and metal s states at the Fermi level, with interesting hidden spin textures. Our study suggests a rational approach for designing functional materials, and could stimulate future predictions of new stable materials based on inequivalent-site isovalent-cation substitution.