Recently, a novel material with a bilayer kagome lattice ${\mathrm{Ca}}_{10}{\mathrm{Cr}}_7{\mathrm{O}}_{28}$ was proposed to be a gapless quantum spin liquid, due to the lack of long-range magnetic order and the observation of broad diffuse excitations. Here, we present the ultralow-temperature thermal conductivity measurements on single crystals of ${\mathrm{Ca}}_{10}{\mathrm{Cr}}_7{\mathrm{O}}_{28}$ to detect its low-lying magnetic excitations. At finite temperatures, with increasing magnetic fields, the thermal conductivity exhibits a clear dip around 6 T, which may correspond to a crossover in the magnetic ground state. At the zero-temperature limit, no residual linear term is found at any fields, indicating the absence of gapless itinerant fermionic excitations. Therefore, if the spinons do exist, they are either localized or gapped. In the gapped case, the fitting of our data gives a small gap, $\mathrm{\Delta }\sim 0.27\left(2\right)$ K. These results put strong constraints on the theoretical description of the ground state in this quantum spin liquid candidate.

中文翻译：

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具有双层kagome晶格的量子自旋液体候选Ca10Cr7O28中的超低温传热

最近，一种具有双层kagome晶格的新型材料 ${钙}_{10}{铬}_7{\mathrm{Ø}}_{\mathrm{28岁}}$由于缺乏长程磁阶和观察到广泛的弥散激发，因此有人提出将其作为无间隙量子自旋液体。在这里，我们介绍了单晶硅的超低温热导率测量${钙}_{10}{铬}_7{\mathrm{Ø}}_{\mathrm{28岁}}$以检测其低洼的磁激发。在有限的温度下，随着磁场的增加，热导率在6 T附近表现出明显的下降，这可能对应于磁性基态的交叉。在零温度极限下，在任何场均未发现任何残留线性项，这表明不存在无间隙的迭代铁电离子激发。因此，如果存在棘刺，则它们将被局域化或被缝隙化。在这种情况下，我们的数据拟合会产生很小的差距，$\mathrm{\Delta }〜0.27（\mathrm{2个}）$ K.这些结果对这种量子自旋液体候选物的基态的理论描述施加了强烈的约束。