Nontrivial topological properties in two-dimensional half-Heusler compounds

Abstract

With the experimental synthesis of two-dimensional (2D) half-Heusler compounds, the need for comprehensive investigations of their material properties is rising. Using exhaustive materials search through first-principles computations, we explore the structural stability, electronic, and topological properties of 60 monolayer half-Heusler compounds with a chemical formula of ABX (A = Li, Na, K, Rb, or Cs; B = Be, Mg, Ca, Sr, Ba, or Zn; X = Sb or Bi) under the P4/nmm crystal structure. Regarding stability, three structural configurations were examined, namely pristine (d0), one-sided distortion (d1), and two-sided distortion (d2). Interestingly, 6 compounds exhibit nontrivial topological properties as confirmed by the calculated Z2 invariant under the hybrid functional approach, with RbBeBi having the largest system bandgap of 0.217 eV. Orbital analyses show that the band inversion along the Γ-point was driven by the s-orbital of the B element and the px+py-orbital of the X element. The calculated edge states also manifest gapless states, thus further confirming the topological insulating phase. Additionally, we conjecture that the monolayer RbBeBi may exhibit the charge density wave (CDW) phase as a consequence of periodic lattice distortion. Our research identifies a new 2D material family derived from the bulk half-Heusler possessing various stable distortions for the development of 2D topological materials platforms, paving the way for discovering 2D topological materials for future technological applications.