Thermal-transport measurements in a quantum spin-liquid state of the frustrated triangular magnet κ-

Abstract

Low-temperature thermal-transport measurements of a frustrated organic magnet in which a quantum spin-liquid is believed to exist, suggest that the emergence of this state is accompanied by a spin-gap. This contradicts previous studies conducted at higher temperatures, suggesting that our understanding of this system should be re-evaluated. The notion of quantum spin-liquids (QSLs), antiferromagnets with quantum fluctuation-driven disordered ground states, is now firmly established in one-dimensional (1D) spin systems as well as in their ladder cousins. The spin-1/2 organic insulator κ-(bis(ethylenedithio)-tetrathiafulvalene)2Cu2(CN)3 (κ-(BEDT-TTF)2Cu2(CN)3; ref. 1) with a 2D triangular lattice structure is very likely to be the first experimental realization of this exotic state in D≥2. Of crucial importance is to unveil the nature of the low-lying elementary spin excitations2,3, particularly the presence/absence of a ‘spin gap’, which will provide vital information on the universality class of this putative QSL. Here, we report on our thermal-transport measurements carried out down to 80 mK. We find, rather unexpectedly, unambiguous evidence for the absence of a gapless excitation, which sharply contradicts recent reports of heat capacity measurements4. The low-energy physics of this intriguing system needs be reinterpreted in light of the present results indicating a spin-gapped QSL phase.

Cite this article

Yamashita, M., Nakata, N., Kasahara, Y. et al. Thermal-transport measurements in a quantum spin-liquid state of the frustrated triangular magnet κ-(BEDT-TTF)₂Cu₂(CN)₃. Nature Phys 5, 44–47 (2009). https://doi.org/10.1038/nphys1134

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