Purely rotational symmetry-protected topological crystalline insulator $\alpha$-Bi4Br4

Abstract

Recent theoretical advances have proposed a new class of topological crystalline insulator (TCI) phases protected by rotational symmetries. Distinct from topological insulators (TIs), rotational symmetry-protected TCIs are expected to show unique topologically protected boundary modes: First, the surface normal to the rotational axis features unpinned Dirac surface states whose Dirac points are located at generic k points. Second, due to the higher-order bulk boundary correspondence, a 3D TCI also supports 1D helical edge states. Despite the unique topological electronic properties, to date, purely rotational symmetry-protected TCIs remain elusive in real materials. Using first-principles band calculations and theoretical modeling, we identify the van der Waals material $\alpha$-Bi4Br4 as a TCI purely protected by rotation symmetry. We show that the Bi4Br4's (010) surface exhibits a pair of unpinned topological Dirac fermions protected by the two-fold rotational axis. These unpinned Dirac fermions show an exotic spin texture highly favorable for spin transport and a band structure consisting of van Hove singularities due to Lifshitz transition. We also identify 1D topological hinge states along the edges of an $\alpha$-Bi4Br4 rod. We further discuss how the proposed topological electronic properties in $\alpha$-Bi4Br4 can be observed by various experimental techniques.

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• All Topological Bands of All Nonmagnetic Stoichiometric Materials
• Topological Materials Discovery from Crystal Symmetry
• Material design with the van der Waals stacking of bismuth-halide chains realizing a higher-order topological insulator
• Room-temperature quantum spin Hall edge state in a higher-order topological insulator Bi${}_4$Br${}_4$
• Spin-Resolved Topology and Partial Axion Angles in Three-Dimensional Insulators
• A Higher-Order Topological Insulator Phase in a Modulated Haldane Model
• Topological electronic structure and spin texture of quasi-one-dimensional higher-order topological insulator Bi4Br4
• Transport response of topological hinge modes in $\alpha$-Bi${}_4$Br${}_4$
• The hybrid-order topology of weak topological insulators
• Generation of higher-order topological insulators using periodic driving
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• Facet Dependent Topological Phase Transition in Bi4Br4
• Topological crystalline insulator state with type-II Dirac fermions in transition metal dipnictides
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