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.