Department of Physics, Graduate School of Science, Kyoto University, Kitashirakawa-oiwake, Sakyo, Kyoto, Japan.
Chemphyschem. 2012 Jan 16;13(1):74-8. doi: 10.1002/cphc.201100556. Epub 2011 Oct 19.
Quantum spin liquids (QSLs) are fluidlike states of quantum spins in which the long-range ordered state is destroyed by quantum fluctuations. The ground state of QSLs and their exotic phenomena, which have been extensively discussed for decades, have yet to be identified. We employ thermal-transport measurements on newly discovered QSL candidates κ-(BEDT-TTF)(2)Cu(2)(CN)(3) and EtMe(3)SbPd(dmit)(2), and report that the two organic insulators have different QSLs characterized by different elementary excitations. In κ-(BEDT-TTF)(2)Cu(2)(CN)(3), heat transport is thermally activated at low temperatures, and this suggests the presence of a spin gap in this QSL. In stark contrast, in EtMe(3)SbPd(dmit)(2), a sizable linear temperature dependence of thermal conductivity is clearly resolved in the zero-temperature limit, and shows gapless excitation with a long mean free path (ca. 1000 lattice distances). Such a long mean free path demonstrates a novel feature of QSL as a quantum-condensed state with long-distance coherence.
量子自旋液体 (QSL) 是量子自旋的流变体相，其中长程有序状态被量子涨落破坏。QSL 的基态及其奇异现象已经被广泛讨论了几十年，但仍未被确定。我们对新发现的 QSL 候选物 κ-(BEDT-TTF)(2)Cu(2)(CN)(3) 和 EtMe(3)SbPd(dmit)(2) 进行了热输运测量，并报告说这两种有机绝缘体具有不同的 QSL，其特征是不同的基本激发。在 κ-(BEDT-TTF)(2)Cu(2)(CN)(3)中，热输运在低温下被热激活，这表明这个 QSL 中存在自旋能隙。相比之下，在 EtMe(3)SbPd(dmit)(2)中，在零温极限下可以清楚地分辨出热导率的相当大的线性温度依赖性，并显示出具有长平均自由程 (约 1000 个晶格距离) 的无能隙激发。这种长平均自由程展示了 QSL 的一个新特征，即具有长程相干性的量子凝聚态。
