Recent experiments on bulk Zintl CaAl₂Si₂ reveal the presence of nontrivial topological states. However, the large family of two-dimensional (2D) Zintl materials remains unexplored. Using first-principles calculations, we discuss the stability and topological electronic structures of 12 Zintl single-quintuple-layer (1-QL) AM₂X₂ compounds in the CaAl₂Si₂-structure (A = Ca, Sr, or Ba; M = Zn or Cd; and X = Sb or Bi). Considering various layer-stackings, we show that the M-X-A-X-M stacking, where the transition metal M is exposed, is energetically most favorable. Phonon dispersion computations support the thermodynamic stability of all the investigated compounds. Nontrivial topological properties are ascertained through the calculation of Z₂ invariants and edge states using the hybrid functional. Insulating topological phases driven by a band inversion at the Γ-point involving Bi-(p_x + p_y) orbitals are found in CaZn₂Bi₂, SrZn₂Bi₂, BaZn₂Bi₂, CaCd₂Bi₂, SrCd₂Bi₂, and BaCd₂Bi₂ with bandgaps (eV) of 0.571, 0.500, 0.025, 0.774, 0.650, and 0.655, respectively. Interestingly, van Hove singularities are found in CaCd₂Bi₂ and BaCd₂Bi₂, implying the possibility of coexisting insulating and superconducting topological phases. We discuss how topological 1-QL Zintl compounds could be synthesized through atomic substitutions resulting in Janus materials (1-QL AM₂XY). In particular, the thermodynamically stable Janus BaCd₂SbBi film is shown to exhibit both an insulating topological state and the Rashba effect. Our study identifies a new family of materials for developing 2D topological materials platforms and paves the way for the discovery of 2D topological superconductors.

中文翻译：

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Zintl 单五重层 AM2X2（A = Ca、Sr 或 Ba；M = Zn 或 Cd；X = Sb 或 Bi）族中的量子自旋霍尔绝缘相和范霍夫奇点

最近对块状 Zintl CaAl ₂ Si ₂的实验揭示了非平凡拓扑状态的存在。然而，二维 (2D) Zintl 材料的大家族仍未开发。使用第一性原理计算，我们讨论了 12 Zintl 单五层 (1-QL) AM ₂ X ₂化合物在 CaAl ₂ Si _{2中的稳定性和拓扑电子结构}-结构（A = Ca、Sr 或 Ba；M = Zn 或 Cd；和 X = Sb 或 Bi）。考虑到各种层堆叠，我们表明，过渡金属 M 暴露的 MXAXM 堆叠在能量上是最有利的。声子色散计算支持所有研究化合物的热力学稳定性。通过使用混合泛函计算 Z ₂不变量和边缘状态来确定非平凡拓扑性质。_{在 CaZn 2} Bi ₂、SrZn ₂ Bi ₂、BaZn ₂ Bi _{2中发现了由涉及 Bi-(} p _x + p _y ) 轨道的Γ点处的能带反转驱动的绝缘拓扑相、CaCd ₂ Bi ₂、SrCd ₂ Bi ₂和 BaCd ₂ Bi ₂的带隙 (eV) 分别为 0.571、0.500、0.025、0.774、0.650 和 0.655。有趣的是，在 CaCd ₂ Bi ₂和 BaCd ₂ Bi ₂中发现了范霍夫奇点，这暗示了绝缘和超导拓扑相共存的可能性。我们讨论了如何通过原子取代合成拓扑 1-QL Zintl 化合物，从而产生 Janus 材料 (1-QL AM ₂ XY)。特别是，热力学稳定的 Janus BaCd ₂SbBi 薄膜显示出绝缘拓扑状态和 Rashba 效应。我们的研究确定了用于开发二维拓扑材料平台的新材料家族，并为发现二维拓扑超导体铺平了道路。