Thermal Hall Effect in the Van Der Waals Ferromagnet CrI3

CrI3 is a prototypical van der Waals ferromagnet with a magnetic honeycomblattice. Previous inelastic neutron scattering studies have suggestedtopological nature of its magnetic excitations with a magnon gap at the Diracpoints, which are anticipated to give rise to magnon thermal Hall effect. Herewe report thermal transport properties of CrI3 and show that the long-soughtthermal Hall signal anticipated for topological magnons is fairly small. Incontrast, we find that CrI3 exhibits an appreciable anomalous thermal Hallsignal at lower temperature which may arise from magnon-phonon hybridization ormagnon-phonon scattering. These findings are anticipated to stimulate furtherneutron scattering studies on CrI3 single crystal, which can shed light notonly on the intrinsic nature of magnetic excitations but also on themagnon-phonon interaction.