Substrate Design and Multistate Manipulation of Ferroelectric Topological Insulators

Ferroelectric topological insulators realized in heterostructures of two topologically trivial two-dimensional materials have recently attracted significant interest. Using first-principles calculations combined with topological quantum chemistry, we investigate bilayer α-In₂Se₃ (2L-In₂Se₃) in van der Waals heterostructures with XSe (X = Ga, In, Tl) substrates within space group P3m1 (No. 156). We show that the emergence of ferroelectricity-driven topological phase transitions in these systems is dictated by fundamental symmetry principles rather than material-specific effects. The band bending at the XSe/2L-In₂Se₃ interface enables topological band inversions, with higher-electron-affinity substrates such as GaSe and TlSe favoring the transition. Remarkably, GaSe/2L-In₂Se₃ exhibits a reversible transition between topological and trivial insulating phases upon polarization switching, while TlSe/2L-In₂Se₃ undergoes sequential transitions from a topological insulator to a trivial insulator and eventually to a metallic state. This multistate manipulation highlights a viable route for designing tunable, low-power, multi-functional electronic devices.