Engineering Interlayer Hybridization in Energy Space via Dipolar Overlayers

The interlayer hybridization (IH) of van der Waals (vdW) materials is thought to be mostly associated with the unignorable interlayer overlaps of wavefunctions (t) in real space. Here, we develop a more fundamental understanding of IH by introducing a new physical quantity, the IH admixture ratio α. Consequently, an exotic strategy of IH engineering in energy space can be proposed, i.e., instead of changing t as commonly used, α can be effectively tuned in energy space by changing the on-site energy difference (2Δ) between neighboring-layer states. In practice, this is feasible via reshaping the electrostatic potential of the surface by deposing a dipolar overlayer, e.g., crystalline ice. Our first-principles calculations unveil that IH engineering via adjusting 2Δ can greatly tune interlayer optical transitions in transition-metal dichalcogenide bilayers, switch different types of Dirac surface states in Bi₂Se₃ thin films, and control magnetic phase transition of charge density waves in 1H/1T-TaS₂ bilayers, opening new opportunities to govern the fundamental optoelectronic, topological, and magnetic properties of vdW systems beyond the traditional interlayer distance or twisting engineering.