Persistent spin dynamics in magnetically ordered honeycomb-lattice cobalt oxides
Ping Miao, Xianghong Jin, Weiliang Yao, Yue Chen, A. Koda, Zhenhong Tan, Wu Xie, Wenhai Ji, Takashi Kamiyama, Yuan Li
Abstract
In the quest to find quantum spin liquids, layered cobalt oxides ${\mathrm{Na}}_{2}{\mathrm{Co}}_{2}{\mathrm{TeO}}_{6}$ and ${\mathrm{Na}}_{3}{\mathrm{Co}}_{2}{\mathrm{SbO}}_{6}$ 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.