Topological magnons in CrI${}_3$ monolayers: an itinerant fermion description

Abstract

Magnons dominate the magnetic response of the recently discovered insulating ferromagnetic two dimensional crystals such as CrI${}_3$. Because of the arrangement of the Cr spins in a honeycomb lattice, magnons in CrI${}_3$ bear a strong resemblance with electronic quasiparticles in graphene. Neutron scattering experiments carried out in bulk CrI${}_3$ show the existence of a gap at the Dirac points, that has been conjectured to have a topological nature. Here we propose a theory for magnons in ferromagnetic CrI${}_3$ monolayers based on an itinerant fermion picture, with a Hamiltonian derived from first principles. We obtain the magnon dispersion for 2D CrI${}_3$ with a gap at the Dirac points with the same Berry curvature in both valleys. For CrI${}_3$ ribbons, we find chiral in-gap edge states. Analysis of the magnon wave functions in momentum space further confirms their topological nature. Importantly, our approach does not require to define a spin Hamiltonian, and can be applied to both insulating and conducting 2D materials with any type of magnetic order.

Includes supplementary material

Cited by in corpus (3)

• Magnetic Two-Dimensional Chromium Trihalides: A Theoretical Perspective
• Topological magnonics in the two-dimensional van der Waals magnet CrI3
• Non-reciprocal magnons in a two dimensional crystal with off-plane magnetization