The spin-1/2 kagome Heisenberg antiferromagnets are believed to host exotic quantum entangled states. Recently, the reports of 1/9 magnetization plateau and magnetic oscillations in a kagome antiferromagnet YCu3(OH)6Br2[Brx(OH)1−x] (YCOB) have made this material a promising candidate for experimentally realizing quantum spin liquid states. Here, we present measurements of the specific heat Cp in YCOB in high magnetic fields (up to 41.5 T) down to 0.46 K, and the 1/9 plateau feature has been confirmed. Moreover, the temperature dependence of Cp/T in the vicinity of 1/9 plateau region can be fitted by a linear in T term which indicates the presence of a Dirac spectrum, together with a constant term, which indicates a finite density of states contributed by other spinon Fermi surfaces. Surprisingly, the constant term is highly anisotropic in the direction of the magnetic field. Additionally, we observe a double-peak feature near 30 T above the 1/9 plateau which is another hallmark of fermionic excitations in the specific heat. This combination of gapless behavior and the double-peak structure strongly suggests that the 1/9 plateau in YCOB is nontrivial and hosts fermionic quasiparticles. Published by the American Physical Society 2025

中文翻译：

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Kagome 反铁磁体中 1-9 高原附近费米子行为的热力学证据

自旋 1/2 笼目海森堡反铁磁体被认为具有奇异的量子纠缠态。最近，关于笼目反铁磁体 YCu3（OH）6Br2[Brx（OH）1−x] （YCOB） 中 1/9 磁化平台和磁振荡的报道使这种材料成为实验实现量子自旋液态的有前途的候选材料。在这里，我们展示了在低至 0.46 K 的高磁场（高达 41.5 T）中 YCOB 中比热 Cp 的测量值，并且 1/9 平台特征已得到证实。此外，Cp/T 在 1/9 高原区域附近的温度依赖性可以用线性 T 项来拟合，前者表示存在狄拉克谱，后者表示其他自旋费米表面贡献的有限态密度。令人惊讶的是，常数项在磁场方向上是高度各向异性的。此外，我们在 1/9 平台上方 30 T 附近观察到双峰特征，这是比热中费米子激发的另一个标志。这种无间隙行为和双峰结构的结合强烈表明，YCOB 中的 1/9 平台是非平凡的，并且含有费米子准粒子。 美国物理学会 2025 年出版