Atomically defined topological edge modes in functionalized xenes: an ab-initio study

The xene family of two-dimensional topological insulators plays a key role in many proposals for realizing topological electronic, spintronic, and valleytronic devices. These proposals use either the application of electric fields, proximity magnetism and superconductivity, or chemical functionalization to create topological edge modes in xenes. A key drawback of these techniques is their lack of control over the geometry of interfaces between topological regions, a critical aspect of engineering topological devices. Motivated by recent advances in adatom deposition technology, we propose atomically precise adatom decoration as a novel method for engineering topological edge modes in xenes. We show through first-principles calculations that decorating stanene with zinc adatoms exclusively on one of two sublattice sites induces a topological phase transition from the quantum spin Hall (QSH) to quantum valley Hall (QVH) phase. We confirm the existence of valley and spin-valley polarized edge modes propagating at QVH/QVH and QVH/QSH interfaces through further first-principles simulations. We conclude by discussing technological applications of these edge modes that are enabled by the atomic precision of the technique.