Atomically-Defined Topological Edge Modes in Functionalized Stanene

The xene family of two-dimensional topological insulators plays a key role in many proposals for realizing topological electronic, spintronic, and valleytronic devices. Often, these proposals use the application of electric fields, proximity magnetism and superconductivity, or chemical functionalization to create topological edge modes in xenes.<br/> <br/>However, these techniques lack control of the interface geometry between the topological regions, a critical aspect of engineering topological devices. Motivated by recent advances in adatom deposition technology, we propose surface functionalization by atomically-precise adatom decoration as a novel method for engineering topological edge modes in xenes. We show through first-principles calculations that decorating monolayer stanene with zinc adatoms on either of the two sublattice sites induces a topological phase transition from the quantum spin Hall (QSH) to the quantum valley Hall (QVH) phase. The zinc adatoms interact weakly with the stanene surface, operating as a precisely applied local perturbation that shifts the relative energies of the sublattice sites to induce the phase transition. After establishing the QSH to QVH transition, we performed additional calculations to confirm the existence of valley and spin-valley polarized edge modes propagating at QVH/QVH and QVH/QSH interfaces constructed from regions of different adatom decoration. This method not only allows for precisely-controlled interfaces but also produces well-localized edge modes, making them ideal for potential applications. We conclude by discussing such technological applications of these decorated xene structures.