Giant Magnetic In-Plane Anisotropy and Competing Instabilities in Na3Co2SbO6

We report magnetometry data obtained on twin-free single crystals of Na3Co2SbO6, which is considered a candidate material for realizing the Kitaev honeycomb model for quantum spin liquids. Contrary to a common belief that such materials can be modeled with the symmetries of an ideal honeycomb lattice, our data reveal a pronounced twofold symmetry and in-plane anisotropy of over 200%, despite the honeycomb layer's tiny orthorhombic distortion of less than 0.2%. We further use magnetic neutron diffraction to elucidate a rich variety of field-induced phases observed in the magnetometry. These phases manifest themselves in the paramagnetic state as diffuse scattering signals associated with competing ferromagnetic and antiferromagnetic instabilities, consistent with a theory that also predicts a quantum spin liquid phase nearby. Our results call for theoretical understanding of the observed in-plane anisotropy and render Na3Co2SbO6 a promising ground for finding exotic quantum phases by targeted external tuning.

Automated summary

We present magnetometry data on twin-free single crystals of Na3Co2SbO6, a candidate material for realizing the Kitaev honeycomb model for quantum spin liquids. Contrary to the belief that such materials can be modeled with the symmetries of an ideal honeycomb lattice, our data show a pronounced twofold symmetry and in-plane anisotropy of over 200%, despite the small orthorhombic distortion of the honeycomb layer. Magnetic neutron diffraction is used to study the field-induced phases observed in the magnetometry, which manifest as diffuse scattering signals in the paramagnetic state and are consistent with a theory predicting a nearby quantum spin liquid phase. These findings call for a theoretical understanding of the observed in-plane anisotropy and make Na3Co2SbO6 a promising candidate for studying exotic quantum phases through targeted external tuning.