Stable quantum spin Hall states in bismuthene supported on Si(111) with ordered gold decoration

Bismuthene is a promising two-dimensional topological material with a large energy gap, making it suitable for potential applications in quantum devices. However, it has been challenging to fabricate a stable bismuthene layer on a substrate without compromising its edge states and large energy gap at room temperature. In this study, we successfully stabilized bismuthene on the 2D electron gas surface of Si(111)-α-√3×√3-Au, allowing for direct access to its quantum spin Hall states. Using scanning tunneling microscopy along with localized dI/dV mapping on in-situ prepared structures, we observed that the bismuthene surface features a stable, shallow-buckled insulative interior and an almost planar metallic edge. We found a bandgap of 0.75 eV throughout the interior, with a closing gap at the boundary of the islands. Additionally, through island-based differential conductance mapping, we identified localized edge states and located the Dirac point at an energy of −0.10 eV within the bandgap. These findings support the two-dimensional topological insulator nature of bismuthene on Au/Si(111), paving the way for the development of bismuthene-based quantum devices.