# Photostrictive two-dimensional materials in the monochalcogenide family

## TL;DR

This paper predicts significant photostrictive effects in SnS and SnSe monolayers, two-dimensional ferroelectric materials, induced by photoexcited electronic states, with potential applications in light-controlled devices.

## Contribution

It introduces the prediction of large photostriction in 2D monochalcogenide monolayers, a novel effect not previously observed in such materials.

## Key findings

- Photostriction is induced by a screened electric polarization in photoexcited states.
- The structural change is ten times larger than in BiFeO3.
- Observable under feasible experimental conditions with existing samples.

## Abstract

Photostriction is predicted for SnS and SnSe monolayers, two-dimensional ferroelectrics with rectangular unit cells (the lattice vector $\mathbf{a}_1$ is larger than $\mathbf{a}_2$) and an intrinsic dipole moment parallel to $\mathbf{a}_1$. Photostriction in these two-dimensional materials is found to be induced by a screened electric polarization in the photoexcited electronic state (i.e., a converse piezoelectric effect) 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 ten times larger than that observed in BiFeO$_3$, 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-opto-electronic applications.