Searching for two-dimensional (2D) realistic materials able to realize room-temperature quantum spin Hall (QSH) effects is currently a growing field. Here, we through ab initio calculations to identify arsenene oxide, AsO, as an excellent candidate, which demonstrates high stability, flexibility, and tunable spin-orbit coupling (SOC) gaps. In contrast to known pristine or functionalized arsenene, the maximum nontrivial band gap of AsO reaches 89 meV, and can be further enhanced to 130 meV under biaxial strain. By sandwiching 2D AsO between BN sheets, we propose a quantum well in which the band topology of AsO is preserved with a sizeable band gap. Considering that AsO having fully oxidized surfaces are naturally stable against surface oxidization and degradation, this functionality provides a viable strategy for designing topological quantum devices operating at room temperature.One of the grand challenges in condensed matter physics and materials science is to develop dissipationless electron conduction operating at room temperature. The appearance of band topology opens the door to fields of topological quantum states (TQSs), e.g., topological Dirac semimetal 1,2 , Weyl semimetal 3,4 , and node-line semimetal 5,6 , as well as topological insulators (TIs) 7 and so on.Remarkably, two-dimensional (2D) TIs hosts quantum spin Hall (QSH) effect with one-dimensional helical edge states, which can serve as a "two-lane highway" protected by time-reversal symmetry (TRS), making it more suited for coherent spin transport than 3D TIs. 8,9 However, the * Corresponding author: C. W. Zhang: ss_zhangchw@ujn.edu.cn experimental observations of quantized Hall conductance through QSH effect are only reported in HgTe/CdTe 10,11 and InAs/GaSb 12,13 quantum-wells with a ultralow temperature (<10 K). Hence considerable effort has been devoted to design new materials with QSH effect, and a variety of large-gap 2D TIs have been proposed, including the honeycomb lattices of silicene, 14,15 germanene, 16,17 stanene, 18-21 plumbene, 22 transition-metal halide 23 , ZrTe 5 /HfTe 5 24 , III-V bilayers 25 , BiF 26 , and Bi/Sb 27 , but none of them has been directly confirmed in experiments. Searching for realistic 2D TIs with large gap that can support high-temperature applications is vitally essential.
Quantum spin Hall (QSH) effect of two-dimensional (2D) materials features edge states that are topologically protected from backscattering by time-reversal symmetry. However, the major obstacles to the application for QSH effect are the lack of suitable QSH insulators with a large bulk gap. Here, we predict a novel class of 2D QSH insulators in X-decorated plumbene monolayers (PbX; X = H, F, Cl, Br, I) with extraordinarily giant bulk gaps from 1.03 eV to a record value of 1.34 eV. The topological characteristic of PbX mainly originates from s-px,y band inversion related to the lattice symmetry, while the effect of spin-orbital coupling (SOC) is only to open up a giant gap. Their QSH states are identified by nontrivial topological invariant Z2 = 1, as well as a single pair of topologically protected helical edge states locating inside the bulk gap. Noticeably, the QSH gaps of PbX are tunable and robust via external strain. We also propose high-dielectric-constant BN as an ideal substrate for the experimental realization of PbX, maintaining its nontrivial topology. These novel QSH insulators with giant gaps are a promising platform to enrich topological phenomena and expand potential applications at high temperature.
Quantum spin Hall (QSH) effect is promising for achieving dissipationless transport devices which can be achieved only at extremely low temperature presently. The research for new large-gap QSH insulators is critical for their realistic applications at room temperature. Based on first-principles calculations, we propose a QSH insulator with a sizable bulk gap as large as ∼0.22 eV in stanene film functionalized with the organic molecule ethynyl (SnC 2 H), whose topological electronic properties are highly tunable by the external strain. This large-gap is mainly due to the result of the strong spinorbit coupling related to the p xy orbitals at the Γ point of the honeycomb lattice, significantly different from that consisting of the p z orbital as in free-standing group IV ones. The topological characteristic of SnC 2 H film is confirmed by the Z 2 topological order and an explicit demonstration of the topological helical Dirac type edge states. The SnC 2 H film on BN substrate is observed to support a nontrivial large-gap QSH, which harbors a Dirac cone lying within the band gap. Owing to their high structural stability, this two-dimensional large-gap QSH insulator is promising platforms for topological phenomena and new quantum devices operating at room temperature in spintronics.
A great obstacle for the practical applications of the quantum anomalous Hall (QAH) effect is the lack of suitable two-dimensional (2D) materials with a sizable nontrivial band gap, high Curie temperature, and high carrier mobility.
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