Epitaxial Growth of Ultraflat Bismuthene with High-Temperature Quantum Spin Hall Effect Enabled by Substrate-Orbital-Filtering Effect

Quantum spin Hall (QSH) systems hold promises of low-power-consuming spintronic devices, yet their practical applications are extremely impeded by the small energy gaps. Fabricating QSH materials with large gaps, especially under the guidance of new design principles, is essential for both scientific research and practical applications. Here, we demonstrate that large on-site atomic spin-orbit coupling can be directly exploited via the intriguing substrate-orbitalfiltering effect to generate large-gap QSH systems and experimentally realized on the epitaxially synthesized ultraflat bismuthene on Ag(111). Theoretical calculations reveal that the underlying substrate selectively filters Bi pz orbitals away from the Fermi level, leading pxy orbitals with nonzero magnetic quantum numbers, resulting in a large QSH gap of ~1 eV. The corresponding topological edge states are identified through scanning tunneling spectroscopy combined with density functional theory calculations. Our findings provide new strategies to design large-gap QSH systems for room-temperature applications and further explore their topology-related physics. INTRODUCTION Two-dimensional (2D) topological materials (such as the quantum spin Hall (QSH) insulators), which exhibit one-dimensional topological edge states within the bulk band gap, are potential candidates to realize dissipationless transport. With graphene as the first predicted 2D topological insulator to possess the QSH effect,1,2 many other 2D topological materials have also been