Ferroelectric heterobilayer with tunable first- and higher-order topological states

As conceptual milestones of nontrivial phenomenon, ${\mathbb{Z}}_{2}$ topological insulators (TIs) and higher-order TIs (HOTIs) have greatly reshaped the landscape of fundamental physics and materials. However, despite the exciting progress, a tunable topological phase transition between ${\mathbb{Z}}_{2}$ TIs and HOTIs remains elusive. Here, using a tight-binding model and first-principles calculations, we propose that ferroelectric switching can be a straightforward and efficient way for engineering the ${\mathbb{Z}}_{2}$ TIs and HOTIs phases with strikingly different bulk-boundary correspondence. Remarkably, based on the Wannier charge centers, edge states, and corner states analysis, we identify the ferroelectric heterobilayer composed of ${\mathrm{MgAl}}_{2}{\mathrm{Se}}_{4}$ and ${\mathrm{In}}_{2}{\mathrm{S}}_{3}$ as a material candidate of the predicted topological phase transition. Obviously, the ferroelectric switching opens up a technological avenue to bridge the first- and higher-order topologies with high possibility of innovative applications in topotronic and ferroelectric devices.