Robust large-gap quantum spin Hall states in stabilized bismuthene on Si(111)-α-√3×√3-Au

Bismuthene is a promising large-gap two-dimensional topological material with potential applications in quantum devices. However, fabricating a stable bismuthene on a substrate that preserves its edge states and large energy gap at room temperature has been challenging. In this study, we successfully stabilized bismuthene on the 2D electron gas Si(111)-α-√3×√3-Au surface despite its delicate atomic structures, enabling direct access to its quantum spin Hall states. Scanning tunneling microscopy (STM) with localized dI/dV mapping on in-situ prepared structures revealed that the bismuthene surface exhibits a stable, shallow-buckled, insulative interior and an almost planar metallic edge. We found a 0.75 eV-bandgap throughout the interior and a closing gap at the island’s boundary. By using island-based differential conductance mapping, we identified localized edge states and the Dirac point at an energy of −0.10 eV within the bandgap. These results support the 2D-TI nature of bismuthene in Au / Si(111), paving the way for the development of bismuthene-based quantum devices.