Large photo-induced tuning of ferroelectricity in sliding ferroelectrics

Stacking nonpolar, monolayer materials has emerged as an effective strategy to harvest ferroelectricity in two-dimensional (2D) van de Waals (vdW) materials. At a particular stacking sequence, interlayer charge transfer allows for the generation of out-of-plane dipole components, and the polarization magnitude and direction can be altered by an interlayer sliding. In this work, we use {\it ab initio} calculations and demonstrate that in prototype sliding ferroelectrics 3R-stacked bilayer transition metal dichalcogenides MoS$_2$, the out-of-plane electric polarization can be robustly tuned by photoexcitation in a large range for a given sliding. Such tuning is associated with both a structural origin -- i.e., photoinduced structural distortion, and a charge origin -- namely, the distribution of photoexcited carriers. We elucidate different roles that photoexcitation plays in modulating sliding ferroelectricity under different light intensities, and we highlight the pivotal role of light in manipulating polarization of 2D vdW materials.