论文标题
TA2M3TE5（M = NI，PD）单层中的四极拓扑绝缘子
Quadrupole topological insulators in Ta2M3Te5 (M= Ni, Pd) monolayers
论文作者
论文摘要
在预寿命的Benalcazar-Bernevig-Hughes四极杆模型中已经引入了高阶拓扑绝缘子，但尚未提出电子化合物是四极杆拓扑绝缘子（QTI）。在这项工作中，我们预测TA $ _2M_3 $ TE $ _5 $（$ M = $ PD，NI）单层可以是2D QTI，这是由于双波段倒置而具有二阶拓扑的2D QTI。由于组合的对称性$ TC_ {2Z} $，可以通过Stiefel-Whitney编号（$ W_1，W_2 $）对具有两个镜像反射（m $ _x $和m $ _y $）的时间反向不变系统进行分类。使用Wilson Loop方法，我们计算$ W_1 = 0 $和$ W_2 = 1 $ ta $ _2 $ _2 $ ni $ _3 $ te $ _5 $，表明具有$ q^{xy} = e/2 $的QTI。因此，获得边缘状态和局部角状态。通过分析原子频段表示，我们证明了其非常规性质，在一个空的站点（即$ a_g@4e $）中具有必不可少的频段代表，这是由于y- $γ$的非凡双波段倒置所致。然后，我们成功地使用$ m_x $和$ m_y $构建了一个八波形四极型型号，用于电子材料。这些过渡金属化合物$ a_2m_ {1,3} x_5 $（$ a $ = ta，nb; $ m $ = pd，ni; $ x $ = se，te）家族为实现QTI提供了一个很好的平台，并探索拓扑和互动之间的相互作用。
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 Ta$_2M_3$Te$_5$ ($M=$ 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 ($w_1, w_2$) due to the combined symmetry $TC_{2z}$. Using the Wilson loop method, we compute $w_1=0$ and $w_2=1$ for Ta$_2$Ni$_3$Te$_5$, 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 $A_2M_{1,3}X_5$ ($A$ = 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.
