Higher-order topological insulators have been introduced in the precursory Benalcazar-Bernevig-Hughes quadrupole model, but no electronic compound has been proposed to be a quadrupole topological insulator (QTI) yet. In this work, we predict that Ta₂M₃Te₅ (M = Pd, Ni) monolayers can be 2D QTIs with second-order topology due to the double-band inversion. A time-reversal-invariant system with two mirror reflections (M_x and M_y) can be classified by Stiefel-Whitney numbers (w₁, w₂) due to the combined symmetry TC_2z. Using the Wilson loop method, we compute w₁ = 0 and w₂ = 1 for Ta₂Ni₃Te₅, indicating a QTI with q^xy = e/2. Thus, gapped edge states and localized corner states are obtained. By analyzing atomic band representations, we demonstrate that its unconventional nature with an essential band representation at an empty site, i.e., A_g@4e, is due to the remarkable double-band inversion on Y–Γ. Then, we construct an eight-band quadrupole model with M_x and M_y successfully for electronic materials. These transition-metal compounds of A₂M_1,3X₅ (A = Ta, Nb; M = Pd, Ni; X = Se, Te) family provide a good platform for realizing the QTI and exploring the interplay between topology and interactions.

在早期的 Benalcazar-Bernevig-Hughes 四极模型中引入了高阶拓扑绝缘体，但尚未提出电子化合物作为四极拓扑绝缘体 (QTI)。在这项工作中，我们预测 Ta ₂ M ₃ Te ₅ ( M  = Pd, Ni) 单分子层可以是由于双带反转而具有二阶拓扑的二维 QTI。由于组合对称性T C _{2 z} ，具有两个镜面反射（M _x和 M _y）的时间反演不变系统可以通过 Stiefel-Whitney 数 ( w ₁ ,  w _{2 ) 进行分类}. 使用威尔逊环法，我们计算 Ta ₂ Ni ₃ Te _5的w ₁  = 0 和w ₂ = 1 ，表示 QTI q ^{x y}  =  e /2。因此，获得间隙边缘状态和局部角状态。通过分析原子能带表示，我们证明了它的非常规性质，在空位处具有基本能带表示，即A _g @ 4 e，是由于 Y-Γ 上显着的双带反转。然后，我们构建了一个具有M _x和M _y的八波段四极模型成功用于电子材料。这些A ₂ M _1,3 X ₅ ( A = Ta, Nb; M = Pd, Ni; X = Se, Te)族的过渡金属化合物为实现QTI和探索拓扑与相互作用之间的相互作用提供了良好的平台.