Non-trivial topological phases in transition metal rich half-Heusler oxides

Abstract

Topological insulators with gapless surface states and insulating bulk in non-centrosymmetric cubic systems have been extensively explored following the discovery of two-dimensional quantum spin hall effect in zincblende HgTe. In such systems the negative band inversion strength E (= E E 0) governs the robustness of the non-trivial topological states at ambient conditions. Hence, realizing large negative values of E has been a guiding motivation of several investigations reported in literature. Here, we present a material design approach which can be employed to realize large negative values of E in cubic materials such as half-Heusler (HH) oxides with 18 valence electron configurations. We explore 27 HH oxides of the form ABO (A = Li, K, Rb; B = Cu, Ag, Au) in α-, β-, and γ-phase (by placing transition metal atom at different Wyckoff positions) for their non-trivial topological phase. Off these three phases, we found that, the α-phase of nine HH oxides (wherein the transition metal atoms occupy 4a Wyckoff positions in the crystal structure) is the most promising with non-trivial topological phase which is governed by the mass-Darwin fully-relativistic effects enhancing E. Whereas the other phases were found to be either trivial semiconductors or semimetals or metals and most of them being dynamically unstable. We focus on RbAuO in α-phase with E of −1.29 eV and the effect of strain fields on the topological surface states of this compound. We conclude that the α-phase of HH oxide presented here can be synthesized experimentally for diverse room temperature applications in spintronics and nanoelectronics.