  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 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-orbital-filtering 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 large topological
gap of ~1 eV at the K point. The corresponding topological edge states are
identified through scanning tunneling spectroscopy combined with density
functional theory calculations. Our findings provide general strategies to
design large-gap QSH systems and further explore their topology-related
physics.
