The relative atomic-scale motion between layers in van der Waals layered materials offers a new route to realizing two-dimensional ferroelectricity. However, directly measuring the extent of interlayer sliding remains challenging. Here, we use wide-field second-harmonic generation (SHG) imaging to quantitatively map interlayer sliding in few-layer 1T'-ReS2, a model platform enabled by centrosymmetry in each monolayer and weak coupling between layers. We discover multiple discrete stacking configurations in the trilayer and four-layer samples, manifested as characteristic SHG intensity values. Corroborated by Raman and photoluminescence (PL) spectroscopy, we demonstrate that these states arise from anisotropy-confined translational interlayer sliding along the b-axis, which also subtly modulates the electronic structure by ∼5 meV. Our results present the quantitative optical imaging of discrete interlayer sliding in 1T'-ReS2, offering direct evidence to understand and manipulate two-dimensional sliding ferroelectricity.
Fu et al. (Thu,) studied this question.