Engineering Second‐Order Corner States in 2D Multiferroics

The understanding and manipulate of the second‐order corner states are central to both fundamental physics and future topotronics applications. Despite the fact that numerous second‐order topological insulators (SOTIs) are achieved, the efficient engineering in a given material remains elusive. Here, the emergence of 2D multiferroics SOTIs in SbAs and BP5 monolayers is theoretically demonstrated, and an efficient and straightforward way for engineering the nontrivial corner states by ferroelasticity and ferroelectricity is remarkably proposed. With ferroelectric polarization of SbAs and BP5 monolayers, the nontrivial corner states emerge in the mirror symmetric corners and are perpendicular to orientations of the in‐plane spontaneous polarization. And remarkably the spatial distribution of the corner states can be effectively tuned by a ferroelastic switching. At the intermediate states of both ferroelectric and ferroelastic switchings, the corner states disappear. These finding not only combines exotic SOTIs with multiferroics but also pave the way for experimental discovery of 2D tunable SOTIs. In this article, the manipulation of second‐order corner states in 2D multiferroics of SbAs and BP5 monolayers is identified. The charge spatial distribution is well located at the corners of nanoflakes for both SbAs and BP5 when they possess the in‐plane polarization and under a ferroelastic switching from the initial to final states, the spatial distribution of the corner states are effectively rotated by 90°.