Edge state stabilization and control in 2D topological crystalline insulators

In a practical electronic device using a topological crystalline insulator (TCI), nontrivial topological states need to be stable against local perturbations while at the same time, allow for tuning via external controls such as an applied electric field. In this work, we use systematic first principles calculations to study the robustness of the topological states of planar bismuthene, a two-dimensional TCI. We show that the mirror symmetry-protected nontrivial topological phase can be maintained when the bismuthene monolayer has weak interactions with a substrate, or placed in a symmetry-protected heterostructure configuration. Our study also shows that edge terminations play an important role in modulating the electronic response of topological behaviours of 2D TCIs. We find that the edge states and the band gap for armchair edges become highly tunable with respect to modulated interfacial distance, symmetry, and external control means such as transverse electric field or pressure. These results provide guidelines for the selection of appropriate substrates for the experimental realization of TCI edge states, and could be useful for the design of novel electronic and spintronic devices.