Quadrupole topological insulators in Ta2M3Te5 (M= Ni, Pd) monolayers

Abstract

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${}_2{M}_3$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 $T{C}_{2z}$. 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-$\Gamma$. Then, we construct an eight-band quadrupole model with $M_x$ and $M_y$ successfully for electronic materials. These transition-metal compounds of $A_2{M}_{1,3}{X}_5$ ($A$ = 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.

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• Pressure-induced nontrivial $Z_2$ band topology and superconductivity in transition metal chalcogenide ${\mathrm{Ta}}_2{\mathrm{Ni}}_3{\mathrm{Te}}_5$
• High-Order Topological Phase Diagram Revealed by Anomalous Nernst Effect in Janus ScClI Monolayer
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• Hybrid-order topology in unconventional magnets of Eu-based Zintl compounds with surface-dependent quantum geometry
• Topological Phase Transition in Quasi-One-Dimensional Bismuth Iodide Bi4I4
• Weak antilocalization in the transition metal telluride Ta${}_2$Pd${}_3$Te${}_5$
• Real Chern insulators in two-dimensional altermagnetic Fe${}_2$S${}_2$O and Fe${}_2$Se${}_2$O
• Layer-dependent Raman spectroscopy of ultrathin Ta${}_2$Pd${}_3$Te${}_5$
• Generalization of the Nested Wilson Loop Formalism in Topological Dirac Semimetals with Higher-order Fermi Arcs
• Axion insulator, Weyl points, quantum anomalous Hall effect and magnetic topological phase transition in Eu3In2As4
• Hinge Majorana Flat Band in Type-II Dirac Semimetals
• Zeeman field induced corner states in the Kane-Mele-Hubbard model