Tuning the topological band gap of bismuthene with silicon-based substrates

Some metastable polymorphs of bismuth monolayers (bismuthene) can host non-trivial topological phases. However, it remains unclear whether these polymorphs can become stable through interaction with a substrate, whether their topological properties are preserved, and how to design an optimal substrate to make the topological phase more robust. Using first-principles techniques, we demonstrate that bismuthene polymorphs can become stable over silicon carbide (SiC), silicon (Si), and silicon dioxide (SiO2) and that proximity interaction in these heterostructures has a significant effect on the electronic structure of the monolayer, even when bonding is weak. We show that van der Waals interactions and the breaking of the sublattice symmetry are the main factors driving changes in the electronic structure in non-covalently binding heterostructures. Our work demonstrates that substrate interaction can strengthen the topological properties of bismuthene polymorphs and make them accessible for experimental investigations and technological applications.