Stacking-dependent electronic structure of ultrathin perovskite bilayers

Twistronics has received much attention as a method to manipulate the properties of two-dimensional van der Waals structures by introducing moir\'e patterns through a relative rotation between two layers. Here, we begin a theoretical exploration of twistronics beyond the realm of van der Waals materials by developing a first-principles description of the electronic structure and interlayer interactions of ultrathin perovskite bilayers. We construct both an ab initio tight-binding model as well as a minimal three-band effective model for the valence bands of monolayers and bilayers of oxides derived from the Ruddlesden-Popper phase of perovskites, which is amenable to thin-layer formation. We illustrate the approach with the specific example of Sr₂TiO₄ layers but also provide model parameters for Ca₂TiO₄ and Ba₂TiO₄.