Novel Functionality in Switchable Polar Materials

In research on functional materials, the focus of attention has increasingly shifted from ferroelectrics, with electric-field-driven switching between two or more symmetry-related insulating polar states, to materials with functional behavior based on the competition of antipolar and polar states, or two or more symmetry inequivalent polar states, with switching driven by applied electric fields and/or stresses. When the competing states are not symmetry related, they can have quite distinct magnetic, optical, transport, and topological properties, with functionality derived from modulating these properties or even turning them on and off. In this perspective, the authors set out joint experimental–theoretical strategies for the discovery and development of new functional materials in this class.