Sliding ferroelectrics, which exhibit out-of-plane polarization arising from specific stacking rather than conventional ionic displacements, are new types of ferroelectrics whose underdeveloped physics needs to be explored. Here, we investigate the electro-optic (EO) response of these materials using first-principles calculations, focusing on ZrI2 as a prototype. We reveal that, contrary to conventional ferroelectrics, the EO effect in ZrI2 is dominated by its electronic contribution rather than the ionic one, which promises faster EO responses. Furthermore, both biaxial and uniaxial strains significantly enhance this response, and a universal-like linear relationship between the band gap and such response is discovered. We also report a large elasto-optic coefficient that is independent of biaxial strain. Similar large linear EO coefficients and properties are found in other sliding ferroelectrics, including different zirconium dihalides, as well as BN and BP bilayers. These findings highlight sliding ferroelectrics as highly promising candidates for ultrafast nonlinear optical devices and reveal unusual mechanisms.
@article{arxiv.2510.03738,
title = {Electro-optic effects in some sliding ferroelectrics},
author = {Xueqing Wan and Zhenlong Zhang and Charles Paillard and Jinyang Ni and Lei Zhang and Zhijun Jiang and Laurent Bellaiche},
journal= {arXiv preprint arXiv:2510.03738},
year = {2025}
}