Class of diatomic ferroelectrics with multifunctional properties: IV-VI compounds in the distorted NiAs-type structure

Ferroelectrics have attracted a great deal of attention, but diatomic ferroelectrics are less common. Here we establish a class of diatomic ferroelectrics in the distorted NiAs-type structure based on state-of-the-art first-principles calculations. These compounds, with giant Rashba effect, possess rich phases, ranging from ferroelectric semiconductors to ferroelectric semimetals. Topological surface states and type-II bulk Dirac fermions are found in the undistorted phases. This class of multifunctional materials has potential applications in spin-orbitronics.