Bond-dependent anisotropy and magnon decay in cobalt-based Kitaev triangular antiferromagnet

The Kitaev model, a honeycomb network of spins with bond-dependent anisotropic interactions, is a rare example that gives the quantum spin liquid state as an exact solution. Although most Kitaev model candidate materials eventually order magnetically due to additional non-Kitaev interactions, their bond-dependent anisotropy manifests in unusual spin dynamics. It has recently been suggested that bond-dependent anisotropy can stabilize exotic magnetic phases on the geometrically frustrated triangular lattice. Unfortunately, few materials have been identified with simultaneous geometric frustration and bond-dependent anisotropy. In this talk, I will present spin dynamics of iodine-based van der Waals triangular antiferromagnet CoI₂. We found evidence of finite bond-dependent anisotropy in CoI­₂ using inelastic neutron scattering. From the paramagnetic scattering and observed magnetic structure, we conclude that the Kitaev interaction plays an essential role in explaining. Moreover, momentum and energy-resolved inelastic neutron scattering measurements show substantial magnon decay and level repulsion in CoI₂. Our results provide the basis for future studies of the interplay between Kitaev magnetism and geometric frustration.