Room-temperature quantum spin Hall edge state in a higher-order topological insulator Bi${}_4$Br${}_4$

Abstract

Room-temperature realization of macroscopic quantum phenomena is one of the major pursuits in fundamental physics. The quantum spin Hall state, a topological quantum phenomenon that features a two-dimensional insulating bulk and a helical edge state, has not yet been realized at room temperature. Here, we use scanning tunneling microscopy to visualize a quantum spin Hall edge state on the surface of the higher-order topological insulator Bi4Br4. We find that the atomically resolved lattice exhibits a large insulating gap of over 200meV, and an atomically sharp monolayer step edge hosts a striking in-gap gapless state, suggesting the topological bulk-boundary correspondence. An external magnetic field can gap the edge state, consistent with the time-reversal symmetry protection inherent to the underlying topology. We further identify the geometrical hybridization of such edge states, which not only attests to the Z2 topology of the quantum spin Hall state but also visualizes the building blocks of the higher-order topological insulator phase. Remarkably, both the insulating gap and topological edge state are observed to persist up to 300K. Our results point to the realization of the room-temperature quantum spin Hall edge state in a higher-order topological insulator.

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• Higher-order topological phases in crystalline and non-crystalline systems: a review
• Topological electronic structure and spin texture of quasi-one-dimensional higher-order topological insulator Bi4Br4
• Topological edge and corner states in Bi fractals on InSb
• Transport response of topological hinge modes in $\alpha$-Bi${}_4$Br${}_4$
• Discovery of a hybrid topological quantum state in an elemental solid
• Towards Layer-Selective Quantum Spin Hall Channels in Weak Topological Insulator Bi4Br2I2
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• Quasicrystalline second-order topological semimetals
• Sublattice-enriched tunability of bound states in second-order topological insulators and superconductors
• Topology hierarchy of transition metal dichalcogenides built from quantum spin Hall layers
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• Floquet second-order topological Anderson insulator hosting corner localized modes
• Third-order topological insulator induced by disorder
• Optical bulk-boundary dichotomy in a quantum spin Hall insulator
• Effective action approach to the filling anomaly in crystalline topological matter
• Coalescence of multiple topological orders in quasi-one-dimensional bismuth halide chains
• Fast electrically switchable large gap quantum spin Hall states in MGe${}_2$Z${}_4$
• Quantum transport evidence of the boundary states and Lifshitz transition in Bi${}_4$Br${}_4$
• A robust weak topological insulator in a bismuth halide Bi4Br2I2
• Discovery of a Topological Charge Density Wave
• Topological Phase Transition in Quasi-One-Dimensional Bismuth Iodide Bi4I4
• Mass Acquisition of Dirac Fermions in Bi4I4 by Spontaneous Symmetry Breaking
• Integration of Scanning Probe Microscope with High-Performance Computing: fixed-policy and reward-driven workflows implementation
• Fractional second-order topological insulator from a three-dimensional coupled-wires construction
• Two-channel Kondo problem in coupled interacting helical liquids
• Enhancement of temperature of quantum anomalous Hall effect in two-dimensional germanene/magnetic semiconductor heterostructures
• Characterization of higher-order topological superconductors using Bott indices
• Corner states of two-dimensional second-order topological insulators with a chiral symmetry and broken time reversal and charge conjugation
• Optical Berry Curvature of Hinge State and Its Detection
• Shear-resistant topology in quasi one-dimensional van der Waals material Bi${}_4$Br${}_4$
• Observation of the surface hybridization gap in the electrical transport properties of the ultrathin topological insulator (Bi${}_{1-x}$Sb${}_x$)${}_2$Te${}_3$
• Signature of quantum phase transition manifested in quantum fidelity at finite temperature
• Closing of the Mott gap near step edges in NiS2
• Interface engineering of van der Waals heterostructures towards energy-efficient quantum devices operating at high temperatures
• Interacting Crystalline Topological Insulators in two-dimensions with Time-Reversal Symmetry
• RKKY interaction in helical higher-order topological insulators
• Parity-protected superconducting qubit based on topological insulators
• Quantum Coherent Transport of 1D ballistic states in second order topological insulator Bi${}_4$Br${}_4$
• Field manipulation of Weyl modes in an ideal Dirac semimetal
• Quasiperiodic Quadrupole Insulators
• Origin of Robust ${\mathbb{Z}}_2$ Topological Phases in Stacked Hermitian Systems: Non-Hermitian Level Repulsion
• Unveiling Topological Hinge States in the Higher-Order Topological Insulator WTe${}_2$ Based on the Fractional Josephson Effect
• Floquet first- and higher-order topological superconductors: A review
• Emergent One-Dimensional Helical Channel in Higher-Order Topological Insulators with Step Edges
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• Phonons Drive the Topological Phase Transition in Quasi-One-Dimensional Bi${}_4$I${}_4$