Computational design of mixed-dimensional heterostructures for mid-gap state engineering and enhanced second-order optical nonlinearities (A08*)

• Subject Area: Theoretical Condensed Matter Physics
• Term: since 2025
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 398816777

Mixed-dimensional heterostructures consisting of 2D substrates and molecules on them are a promising platform for tailoring nonlinear optical properties at the atomic scale. Using an efficient combination of accurate ab initio calculations based on density functional theory, effective embedding models, and efficient high-throughput computational screening, this project aims to identify design rules for mixed-dimensional heterostructures with type-II level alignment and a spatially localized mid-gap state combined with an enhanced second-order nonlinear response to an external field. To do so, we will screen functionalized rylene dyes and characterize their electronic structure in terms of orbital energies and spatial distribution, assuming hexagonal boron nitride and transition metal dichalcogenides as 2D substrates, including their conventional compositions, selected Janus structures, and model alloys. We will perform symmetry and dipole analyses of the collected data to identify mixed-dimensional heterostructures with the targeted characteristics. Atomistic simulations based on real-time time-dependent density-functional theory will validate the data-driven method and deliver the nonlinear response of selected systems, focusing on the second-order polarizability and the role of the mid-gap state in photoexcitation for potential single-photon emission. This project addresses central questions of NOA related to the fundamental mechanisms driving nonlinear optical processes at the atomic scale.

• DFG Programme: Collaborative Research Centres
• Subproject of: SFB 1375: Nonlinear Optics down to Atomic scales (NOA)
• Applicant Institution: Friedrich-Schiller-Universität Jena
• Project Head: Professorin Dr. Caterina Cocchi