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 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 (Mx and My) can be classified by Stiefel-Whitney numbers (w1, w2) due to the combined symmetry TC2z. Using the Wilson loop method, we compute w1 = 0 and w2 = 1 for Ta2Ni3Te5, indicating a QTI with qxy = 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., Ag@4e, is due to the remarkable double-band inversion on Y–Γ. Then, we construct an eight-band quadrupole model with Mx and My successfully for electronic materials. These transition-metal compounds of A2M1,3X5 (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.

Observation of Emergent Superconductivity in the Topological Insulator Ta2Pd3Te5 via Pressure Manipulation

“…17−22 Theoretical studies have proposed that the monolayer Ta 2 M 3 Te 5 (M = Pd, Ni) behaves as 2D quadrupole TIs characterized by double band-inversion interactions. 23,24 Angle-resolved photoemission spectroscopy and scanning tunneling microscopy experimentally confirm that the monolayer Ta 2 Pd 3 Te 5 behaves as quantum spin Hall insulator, with a 43 meV inverted band gap at the Fermi level. 25 Furthermore, the recent work on bulk Ta 2 Pd 3 Te 5 demonstrates the coexistence of bulk insulating gap, in-gap edge conducting state, and edge gap as signatures of 2D secondorder TI candidate, with observed tunable Luttinger liquid behavior in edge channels across different scales.…”

Orbital degree of freedom induced multiple sets of second-order topological states in two-dimensional breathing Kagome crystals

“…The exploration of higher-order TIs is at the forefront of condensed matter physics [11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30] . Unlike the d-dimensional TIs that host (d − 1) dimensional topological boundary states [31][32][33] , the higher-order TIs manifest robust boundary states with higher codimension [11][12][13][14][15][16][17] .…”

Spintronic interactions between topological edge states in chiral carbon nanotubes: a natural helical symmetry approach

“…[1][2][3][4][5][6][7][8][9][10] The quantum spin hall (QSH) effect is one of the unique properties of some twodimensional (2D) TIs, in which the bulk states are insulating while the edge states are conducting with spin-polarized currents. 1,2,[9][10][11][12][13][14][15][16][17] In the applications of the nanodevices, e.g. transistors, 2,[10][11][12]16,18 quantum dots, 3,5,15 and quantum computing, 1,3,10,12,13,17 most of the 2D TIs involve the composition of the heavy metal atoms due to their large spin-orbit coupling (SOC) interactions, which allows for the engineering of band inversion and enhances the band gaps between edge states.…”

“…1,2,[9][10][11][12][13][14][15][16][17] In the applications of the nanodevices, e.g. transistors, 2,[10][11][12]16,18 quantum dots, 3,5,15 and quantum computing, 1,3,10,12,13,17 most of the 2D TIs involve the composition of the heavy metal atoms due to their large spin-orbit coupling (SOC) interactions, which allows for the engineering of band inversion and enhances the band gaps between edge states. 1,2,[10][11][12][13][14]18 During device operations, the band gaps of 2D TIs can be controlled by the electric fields, the magnetic fields, or the applied strain.…”

“…1,2,[10][11][12][13][14]18 During device operations, the band gaps of 2D TIs can be controlled by the electric fields, the magnetic fields, or the applied strain. 2,5,[9][10][11][12][13][17][18][19][20][21] Since graphene was predicted and demonstrated to exhibit the QSH effect, 22 the carbon-based materials have also been explored for possible applications on TIs [3][4][5][6][7][8]19,21,23,24 The simplest one-dimensional (1D) carbon-based TIs can be theoretically represented by the classical Su-Schrieffer-Heeger (SSH) model. 25 The graphene nanoribbons (GNRs) and the carbon nanotubes (CNTs) can be designed to exhibit the topologically protected zero-mode interface or edge states.…”