Transitions on triangles

摘要

Contrary to expectation and experience, cooling a material will not always freeze it, no matter how low the temperature falls. Two factors can act to preserve the liquid state even down to absolute zero: fluctuations away from order and towards disorder, which are especially important when atoms are confined to sheets and chains; and geometrical frustration, a failure to simultaneously satisfy all the constraints imposed by interactions between neighbouring atoms. On page 612 of this issue, Pratt et aV probe a model two-dimensional frustrated system that has magnetic spins as stand-ins for atoms and a quantum spin-liquid phase that is stable down to the lowest temperatures accessible. This is the layered molecular system denoted k-(BEDT-TTF)_2Cu_2(CN)_3.