Out-of-plane ferroelectricity and multiferroicity in elemental bilayer phosphorene, arsenene, and antimonene

Developing out-of-plane ferroelectricity in a two-dimensional (2D) lattice is becoming increasingly important due to its high potential for miniaturized device applications. Current research efforts for 2D out-of-plane ferroelectrics mainly focus on compounds, while 2D elemental material-based ferroelectrics have been rarely explored. Herein, we show first-principles evidence of the existence of out-of-plane ferroelectricity in elemental 2D lattices, bilayer phosphorene, arsenene, and antimonene, which can be easily synthesized in a controllable manner in experiments. Our results reveal that their sizable out-of-plane polarizations are attributed to the charge redistribution caused by the unique stacking pattern. Upon doping holes, bilayer phosphorene and arsenene are shown to be multiferroic, presenting a strong coupling between ferroelectricity and ferromagnetism. Moreover, reversible spin texture induced by ferroelectric switching is achieved in all these three systems. These findings thereby not only broaden the class of 2D out-of-plane ferroelectrics but also enable future multifunctional nanodevice designs.