Engineering topologically nontrivial structures by stacking topologically trivial materials

Nonmagnetic topological insulators (TIs) are crystalline materials with conserved time-reversal symmetry that feature robust metallic surface states coexisting with an insulating bulk phase and are characterized by non-zero topological invariants. Certain non-centrosymmetric crystals exhibit remarkably strong Rashba spin-orbit coupling, leading to a significant splitting of the uppermost valence band from the other bands, with the former surpassing the bottom-most conduction band. This often results in a band inversion near the Fermi level, transforming a topologically trivial material into a nontrivial one. In 2D TIs, this kind of transformation gives rise to the emergence of 1D metallic edge states, which form the basis of the quantum spin Hall effect. In this work, we theoretically propose a novel approach to create topologically nontrivial 2D structures by strategically layering multiple topologically trivial constituent layers of Rashba semiconductors. We present our findings by considering the BiSb and GeTe monolayer structures as prototypes. In their free-standing form, these monolayers are topologically trivial. However, by strategically stacking these seemingly trivial layers, we unveil the potential for generating intriguing topologically nontrivial properties.