Persistent spin dynamics in magnetically ordered honeycomb cobalt oxides

Abstract: 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 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 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 new 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.