Contrasting Scenarios for Organic Spin Liquids

The ultimate ground state of organic spin-liquid candidates, such as $\kappa$-(ET)$_2$Cu$_2$(CN)$_3$ has long remained elusive. While a variety of apparently conflicting experimental results have favored various scenarios over the years, a comprehensive view has yet to emerge. It has long been thought that conventional magnetic order is destabilized by strong ring-exchange, occasioned by proximity to the Mott transition. Such interactions are known to promote either chiral spin-liquid phases or unconventional spin-vortex order if sufficiently strong. On the one hand, this scenario is now supported by the recent observation [1] of spin-vortex order in the related compound $\kappa$-(BETS)$_2$Mn[N(CN)$_2$]$_3$, which definitely confirms the importance of ring-exchange. On the other hand, there is mounting evidence for an important role of disorder in the low-temperature response [2]. Here, we contrast these scenarios in view of recent experimental results. [1] Phys. Rev. Lett. 127, 147204 (2021). [2] Nat. Commun. 10, 2561 (2019).