Spin dynamics simulations of spin wave spectrum of ferromagnetic monolayer CrI₃

Inelastic neutron scattering experiments show that magnons in bulk CrI₃ present a two-band spin-wave dispersion, and the band crossings at the Brillouin zone corners are not observed. Instead, a finite gap between the two bands was reported. The microscopic origin of the gap and its very existence in the monolayer (ML) limit are still controversial. Using the Heisenberg spin model with parameters extracted from first-principles calculations, we perform spin dynamics simulations to study ML ferromagnetic honeycomb CrI₃ and pay particular attention to its spin wave spectrum near high symmetry points, in an effort to examine whether the gap persists in the ML limit and, if it does, the size of it.