Photostrictive Two-Dimensional Materials in the Monochalcogenide Family

Photostriction is predicted for group-IV monochalcogenide monolayers, two-dimensional ferroelectrics with rectangular unit cells (the lattice vector a(1) is larger than a(2)) and an intrinsic dipole moment parallel to a(1). Photostriction is found to be related to the structural change induced by a screened electric polarization (i.e., a converse piezoelectric effect) in photoexcited electronic states with either p(x) or p(y) (in-plane) orbital symmetry that leads to a compression of a(1) and a comparatively smaller increase of a(2) for a reduced unit cell area. The structural change documented here is 10 times larger than that observed in BiFeO3, making monochalcogenide monolayers an ultimate platform for this effect. This structural modification should be observable under experimentally feasible densities of photexcited carriers on samples that have been grown already, having a potential usefulness for light-induced, remote mechano-optoelectronic applications.