Contrasting Scenarios for Organic Spin Liquids

The ultimate ground state of organic spin-liquid candidates, such as κ-(ET)₂Cu₂(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 of spin-vortex order in the related compound κ-(BETS)₂Mn[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. Here, we contrast these scenarios in view of recent experimental results.