Dimensional reconstruction of dark excitons in few-layer CrI3 revealed by RIXS

Magnetic van der Waals (vdW) materials offer a versatile platform for novel, tunable many-body phenomena. Of particular interest are the rich excitons. Beyond traditional long-range Frenkel excitons, vdW systems can host correlated excitons bound by local Coulomb interactions. Recent Resonant Inelastic X-ray Scattering (RIXS) study has confirmed spin-flip dark excitons in bulk CrI3 and NiPS3, establishing RIXS as a direct probe of the otherwise optically forbidden modes [1,2]. Yet how reduced dimensionality reshapes the dark exciton manifold remains open due to the lack of concise experimental evidence. Here we use high-resolution Cr L3-edge RIXS to map incident energy dependent spectra of few-layer CrI3, benchmarked against bulk data. We resolve a set of dark excitons that are absent in bulk and consistent with large binding energies proposed in the two-dimensional limit [3], underscoring a dimensional reconstruction of the excitonic landscape. We will present a survey of the electronic character of the excitons versus thickness, guided by GW-BSE-informed multiplet modeling. We then outline routes to control these excitons via hetero-stacking and coupling to magnetism.

[1] W. He, et al., Phys. Rev. X 15, 011042 (2025).

[2] W. He, et al., Nat. Commun. 15, 3496 (2024).

[3] M. Wu, et al., Nat. Commun. 10, 2371 (2019).