The magnetoelectric coupling in possible Kitaev spin liquid $\alpha -{\mathrm{RuCl}}_3$ with the layered honeycomb structure was examined. We observed a remarkable anisotropic magnetodielectric effect in the zigzag-type antiferromagnetic phase; there is a large suppression in dielectric constant, when both electric and magnetic fields were applied parallel to the in-plane direction. A possible origin of the observed anisotropic magnetodielectric effect is discussed in terms of a magnetically induced local electric polarization with antiferroelectric correlation. Our results stimulate the model calculation including not only exchange coupling but also magnetoelectric coupling to understand the ground state of the spin system in $\alpha -{\mathrm{RuCl}}_3$.

• Received 16 February 2017

DOI:https://doi.org/10.1103/PhysRevB.95.245104