Large-Gap Quantum Spin Hall Insulator in single layer bismuth monobromide Bi${}_4$Br${}_4$

Abstract

Quantum spin Hall (QSH) insulators have gapless topological edge states inside the bulk band gap, which can serve as dissipationless spin current channels protected by the time-reversal symmetry. The major challenge currently is to find suitable materials for this topological state. Here, we predict a new large-gap QSH insulator with bulk direct band gap of $\sim$0.18 eV, in single-layer Bi${}_4$Br${}_4$, which could be exfoliated from its three-dimensional bulk material due to the weakly-bonded layered structure. The band gap of single-layer Bi${}_4$Br${}_4$ is tunable via strain engineering, and the QSH phase is robust against external strain. In particular, because this material consists of special one-dimensional molecular chain as its basic building block, the single layer Bi${}_4$Br${}_4$ could be easily torn to ribbons with clean and atomically sharp edges, which are much desired for the observation and application of topological edge states. Our work thus provides a new promising material for experimental studies and practical applications of QSH effect.

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• Quantum Spin Hall Effect in 2D Transition Metal Dichalcogenide Haeckelites
• Purely rotational symmetry-protected topological crystalline insulator $\alpha$-Bi4Br4
• Topological edge states in single- and multi-layer Bi${}_4$Br${}_4$
• Quantum Spin Hall Effect in Ta${}_2$M${}_3$Te${}_5$ (M = Pd, Ni)
• Engineering quantum spin Hall insulators by strained-layer heterostructures
• Optical bulk-boundary dichotomy in a quantum spin Hall insulator
• Topological phase in non-centrosymmetric material NaSnBi
• A new kind of 2D topological insulators BiCN with a giant gap and its substrate effects
• Realization of Kane-Mele Model in $X{\mathbf{N}}_4$-Embedded Graphene ($X$=Pt, Ir, Rh, Os)
• Robust large-gap topological insulator phase in transition-metal chalcogenide ZrTe${}_4$Se