Ferroelectric higher-order topological insulator in two dimensions

The interplay between ferroelectricity and band topology can give rise to a wide range of both fundamental and applied research. Here, we map out the emergence of nontrivial corner states in two-dimensional ferroelectrics and, remarkably, demonstrate that ferroelectricity and corner states are coupled together by crystallographic symmetry to realize the electric control of higher-order topology. Implementing density functional theory, we identify a series of experimentally synthesized two-dimensional ferroelectrics, such as ${\mathrm{In}}_{2}{\mathrm{Se}}_{3}$, BN, and SnS, as realistic material candidates for the proposed ferroelectric higher-order topological insulators. Our work not only sheds light on traditional ferroelectric materials but also opens an avenue to bridge the higher-order topology and ferroelectricity that provides a nonvolatile handle to manipulate the topology in next-generation electronic devices.