Using ferroelectric polarization to regulate and preserve the valley polarization in a HfN2/CrI3/In2Se3 …

How to effectively regulate and preserve valley polarization is very important for the development of valleytronic devices in practical applications. Here, we propose a scheme of using ferroelectric polarization reversal to control valley polarization and, further, using ferroelectric nonvolatility to stably preserve the regulated valley state. We design a trilayer heterostructure, which is composed of vertically stacked two-dimensional (2D) valleytronic material ${\mathrm{HfN}}_{2}$, 2D ferromagnetic material ${\mathrm{CrI}}_{3}$, and 2D ferroelectric material ${\mathrm{In}}_{2}{\mathrm{Se}}_{3}$. Through first-principles simulation, we find that the polarization reversal of ${\mathrm{In}}_{2}{\mathrm{Se}}_{3}$ can change the orientation of the easy magnetization axis for ${\mathrm{CrI}}_{3}$, and the change of magnetic moment direction causes the change of valley polarization for ${\mathrm{HfN}}_{2}$. When ${\mathrm{In}}_{2}{\mathrm{Se}}_{3}$ is polarized upward, the easy magnetization axis of ${\mathrm{CrI}}_{3}$ is the $z$ axis, and the valley polarization is 15 meV, while when ${\mathrm{In}}_{2}{\mathrm{Se}}_{3}$ is polarized downward, the easy magnetization axis of ${\mathrm{CrI}}_{3}$ is changed to the $x\text{\ensuremath{-}}y$ plane, and the valley polarization is changed to zero. Then we study the ferroelectric bistability of the ${\mathrm{HfN}}_{2}/{\mathrm{CrI}}_{3}/{\mathrm{In}}_{2}{\mathrm{Se}}_{3}$ heterotrilayer and propose a method to preserve different valley states using ferroelectric nonvolatility.