Persistent spin dynamics in magnetically ordered honeycomb-lattice cobalt oxides

In the quest to find quantum spin liquids, layered cobalt oxides Na₂Co₂TeO₆ and Na₃Co₂SbO₆ have been proposed as promising candidates for approximating the Kitaev honeycomb-lattice model. Yet, their suitability has been thrown into question due to observed long-range magnetic order at low temperatures and indications of easy-plane, rather than Kitaev-type, spin anisotropy. Here, we use muon-spin relaxation to reveal an unexpected picture: Contrary to the anticipated static nature of the long-range order, the systems show prevalent spin dynamics with a spatially uneven distribution and varied correlation times. This underlines that the magnetic ground states cannot be solely described by the long-range order, suggesting a significant role of quantum fluctuations. Our findings not only shed light on the complex physics of these systems but also underscore the need for a refined approach in the search for realizable quantum spin liquids.