Direct Evidence for Anisotropic Magnetic Interaction in Α-Rucl_3 from Polarized Inelastic Neutron Scattering

Polarized neutron scattering experiments reveal the anisotropy of magnetic correlations in the candidate Kitaev material α-RuCl_3. The anisotropy of the inelastic response at the magnetic Bragg positions is just opposite to the expectation for a simple Heisenberg model. Near the antiferromagnetic q vector, there are no low-energy transversal magnon modes directly documenting the fully anisotropic and bond-directional character of the magnetic interaction in α-RuCl_3. However, other findings disagree with a simple or strongly dominant Kitaev component.