The coupling between electronic excitations and lattice deformation in van der Waals ferroelectrics is governed by a competition between the electron deformation potential and the inverse piezoelectric effect. While theory predicts that piezoelectric screening should drive a polar-axis contraction in monolayer group-IV monochalcogenides, we demonstrate that in multilayer SnS, the deformation potential provides the dominant contribution, driving a polar-axis expansion even within ferroelectric domains. By correlating polarization-resolved second-harmonic generation microscopy with ultrafast reflectance spectroscopy and first-principles calculations, we resolve the anisotropic lattice response and disentangle intrinsic photostrictive strain from extrinsic thin-film interference artifacts. These results establish a microscopic hierarchy of photostrictive mechanisms and position stacking-engineered SnS as a platform for ultrafast optomechanical transduction.
@article{arxiv.2602.09275,
title = {Deformation potential driven photostriction in layered ferroelectrics},
author = {S. Puri and R. Rodriguez and C. Dansou and L. Bouric and A. Sheibani and C. Paillard and L. Bellaiche and H. Nakamura},
journal= {arXiv preprint arXiv:2602.09275},
year = {2026}
}