Topological Flat Bands in 2D Breathing‐Kagome Lattice Nb₃TeCl₇

Abstract

Flat bands (FBs) can appear in two‐dimensional (2D) geometrically frustrated systems caused by quantum destructive interference (QDI). However, the scarcity of pure 2D frustrated crystal structures in natural materials makes FBs hard to be identified, let alone modulate FBs relating to electronic properties. Here, the experimental evidence of the complete electronic QDI induced FB contributed by the 2D breathing‐kagome layers of Nb atoms in Nb3TeCl7 (NTC) is reported. An identical chemical state and 2D localization characteristics of the Nb breathing‐kagome layers are experimentally confirmed, based on which NTC is demonstrated to be a superior concrete candidate for the breathing‐kagome tight‐binding model. Furthermore, it theoretically establishes the tunable roles of the on‐site energy over Nb sites on bandwidth, energy position, and topology of FBs in NTC. This work opens an avenue to manipulate FBs characteristics in these 4d transition‐metal‐based breathing‐kagome materials.This article is protected by copyright. All rights reserved

Cataloging High‐Quality Two‐Dimensional van der Waals Materials with Flat Bands

“…Moreover, we note that Nb 3 TeI 7 's cousin, that is, Nb 3 TeCl 7 , has been proposed theoretically [60] and recently confirmed experimentally. [61] Screening results showcase that flatband vdW materials are abundant, implying the great potential for realizing flat-band characteristics of different realistic applications. Future experiments could more easily access these flat bands with a high density of states, which renders more exciting physics phenomena.…”

Artificial kagome lattices of Shockley surface states patterned by halogen hydrogen-bonded organic frameworks

“…Several kagome lattices with slight changes at the triangles can give rise to additional exotic quantum phenomena, such as the emerging topological edge states 15 , 16 and high-order topological corner states 17 , 18 in the breathing kagome lattice and the presence of two FBs in the diatomic-kagome lattice consisting of two atoms sitting on each kagome lattice site 19 , 20 . Although thousands of compound crystals are known to have the kagome net in their certain sublattices, only a few compounds have been identified to have electronic properties corresponding to the kagome lattice 9 – 12 and breathing kagome lattice 13 , 21 , 22 . Theoretical calculations show that only approximately 7% of the potential kagome compounds possess electronic properties related to the kagome sublattice because the complicated interactions from the interlayer atoms can significantly alter and even destroy the kagome electronic bands 23 .…”

Strain-Modulated Phase Transition in 2D V3F8 Kagome Lattice with Topological Flat Band

“…To date, topological flat bands have been evidenced in 2D Kagome semiconductors Nb 3 Cl 8 15 and Nb 3 TeCl 7 . 16 However, the TFBs in Nb 3 Cl 8 and Nb 3 TeCl 7 are far away from the Fermi energy (the distance is about 1−1.5 eV), hindering the potential for utilization. Consequently, there exists a compelling imperative to achieve layered semiconducting Kagome materials with controllable TFBs around the Fermi level, enabling their application in the aforementioned fields.…”

“…Currently, achieving layered Kagome materials that possess TFBs remains a formidable obstacle. To date, topological flat bands have been evidenced in 2D Kagome semiconductors Nb 3 Cl 8 and Nb 3 TeCl 7 . However, the TFBs in Nb 3 Cl 8 and Nb 3 TeCl 7 are far away from the Fermi energy (the distance is about 1–1.5 eV), hindering the potential for utilization.…”