This paper investigates the magnetic interactions and electron-correlation effects in 2D van der Waals materials using CrI₃ as a model. Calculations incorporating nonlocal electron correlations show spin excitations consistent with inelastic neutron-scattering measurements. A correlation-enhanced interlayer super-superexchange interaction is identified, causing a magnon gap along the high-symmetry Γ-K-M path. This finding offers a novel explanation for the gap opening in CrI₃, differing from previous attributions to spin-orbit coupling. The study highlights the importance of explicitly treating electron correlations in understanding spin ordering and dynamics in 2D magnetic materials.

Liqin Ke, Mikhail I. Katsnelson