Vertical ferroelectric switching by in-plane sliding of two-dimensional bilayer WTe₂

Based on first-principles calculations, we studied the ferroelectric properties of bilayer 1T'-WTe₂. In this work, we discovered that the polarization stems from uncompensated out-of-plane interlayer charge transfer, which can be switched upon interlayer sliding of an in-plane translation. Our differential charge density results also confirmed that such ferroelectricity in the bilayer WTe₂ is derived from interlayer charge transfer. The ferroelectric polarization directions further control the spin texture of the bilayer WTe₂, which may have important applications in spintronics. Therefore, we propose a spin field effect transistor (spin-FET) design that may effectively improve the spin-polarized injection rate. In addition, the lattice strain has been found to have an important influence on the ferroelectric properties of the bilayer WTe₂. One can effectively increase the polarization with a maximum at 3% tensile strain, whereas a 3% compressive strain can transform the bilayer WTe₂ from the ferroelectric to paraelectric phase.