Tuning of the Valley Structures in Monolayer In₂Se₃/WSe₂ Heterostructures via Ferroelectricity

Recent findings of two-dimensional ferroelectric (FE) materials have enabled the integration of nonvolatile FE functions into device applications based on van der Waals (vdW) heterojunctions (HJs), resulting in versatile technological advances. In this paper, we report the results of direct probing of the electronic structures of In₂Se₃/WSe₂ heterostructures at the single-layer limit, where monolayer (ML)-In₂Se₃ was found to be either antiferroelectric (AFE, β') or ferroelectric (β*) at sufficiently low temperatures. A general type-II band alignment was revealed for this heterostructure. Moreover, we observed significant modulations of the valley structures of WSe₂, and in situ transformations between the FE and AFE In₂Se₃ phases demonstrated the dominant role of the polarizations in the top ML-In₂Se₃ layer. The observed phenomena can be attributed to the combination of both the linear and quadratic Stark shifts from the out-of-plane electric field, which has only been previously theoretically explored for ML-transition metal dichalcogenides (TMDs).