Observation of Bond-Dependent Frustrated Spins via Spin-Exciton Coupling in the Cobalt Honeycomb Antiferromagnet Cu₃Co₂SbO₆

Two-dimensional honeycomb antiferromagnets are an appealing class of materials, offering a pathway to realize exactly solvable Kitaev quantum spin liquids, distinguished by a disordered phase even at zero temperature and exotic fractionalized excitations. Indicators of proximity to a Kitaev quantum spin liquid include in-plane anisotropy, bond-dependent magnetic properties, and fluctuation regions within the disordered phase. In this study, we propose Cu₃Co₂SbO₆ heterostructures as a promising candidate for exploring Kitaev quantum spin liquid physics. A notable feature of Cu₃Co₂SbO₆ is the interaction between excitons and magnetic properties, enabling the examination of anisotropic magnetic characteristics and magnetic phase transitions using light. The redistribution of spectral weight under differently polarized light reveals anisotropic Kitaev spin exchange interactions and robust short-range spin-spin correlations that persist at temperatures exceeding twice the magnetic ordering temperature. Magneto-optic studies of the spin-fluctuation region underscore the robustness of this fluctuating region. Our findings suggest the potential to detect and even control the spin Hamiltonian of Cu₃Co₂SbO₆ through light.