Challenges and opportunities in proximity-driven exciton-spin engineering in van der Waals heterostructures

van der Waals heterostructures consisting of transition metal dichalcogenides (TMDs) and two-dimensional (2D) magnets offer a versatile platform to study the coexistence and transformation of different excitons. By focusing on TMD WSe$_2$ and 2D magnetic CrI$_3$, as a bilayer WSe$_2$/CrI$_3$ and a trilayer CrI$_3$/WSe$_2$/CrI$_3$, we provide their description using a parameter-free, high-fidelity many-body perturbation theory. This ab initio approach allows us to elucidate the character of magnetic Frenkel excitons in CrI3 and how the nonmagnetic Wannier-Mott excitons in WSe2 are modified by the proximity of CrI3. We reveal novel proximity-induced interlayer excitons in these heterostructures. In contrast to the sensitivity of proximity-induced modifications of excitons in WSe$_2$, which depend on the interfacial details, the interlayer magnetic excitons are remarkably robust and are present across the different stacking configurations between WSe$_2$ and CrI$_3$, simplifying their experimental demonstration. These findings suggest unexplored opportunities for information transduction using magnetic excitons and integrating photonics, electronics, and spintronics in proximitized materials.