Theory of slidetronics in ferroelectric van der Waals layers

Vertically stacked layers derived from non-ferroelectric monolayers offer a promising route to two-dimensional (2D) ferroelectrics, where polarization switching occurs via interlayer sliding at sub-unit cell scales. Here, we develop a theory of slidetronics based on the notion that sliding-induced switching $P \rightarrow P'$ can also be achieved by applying an appropriate point-group operator $G$ to the entire system, such that $P' = G P$. Interlayer sliding and the transformation induced by the generator $G$ are thus equivalent in describing the relationship between the initial and final layer configurations. From this symmetry principle, we deduce that slidetronics can be classified by generators $G$; the generator $G$ must act as a symmetry operator for the constituent layers, while it is not a symmetry operator for the stacked layers as a whole; for a given 2D material, $G$ determines the interlayer sliding required for polarization switching; and sliding-induced complete polarization inversion is impossible in bilayers but can be realized in multilayers (e.g., PdSe$_2$ trilayers). These findings provide a framework for designing 2D ferroelectrics with targeted polarization-switching properties, as demonstrated through case studies of real materials.