The excitations in the Kitaev spin liquid (KSL) can be described by Majorana fermions, which have characteristic field dependence of bulk gap and topological edge modes. In the high-field state of layered honeycomb magnet $\alpha \text{−}{\mathrm{RuCl}}_3$, experimental results supporting these Majorana features have been reported recently. However, there are challenges due to sample dependence, and the impact of inevitable disorder on the KSL is poorly understood. Here, we study how low-energy excitations are modified by introducing point defects in $\alpha \text{−}{\mathrm{RuCl}}_3$ using electron irradiation, which induces site vacancies and exchange randomness. High-resolution measurements of the temperature dependence of specific heat $C(T)$ under in-plane fields $H$ reveal that, while the field-dependent Majorana gap is almost intact, additional low-energy states with $C/T=A(H)T$ are induced by introduced defects. At low temperatures, we obtain the data collapse of $C/T\sim H^{-\gamma }(T/H)$ expected for a disordered quantum spin system but with an anomalously large exponent $\gamma$. This leads us to find a power-law relationship between the coefficient $A(H)$ and the field-sensitive Majorana gap. These results are consistent with the picture that the disorder induces low-energy linear Majorana excitations, which may be considered as a weak localization effect of Majorana fermions in the KSL.

中文翻译：

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Kitaev 磁体α−RuCl3 中缺陷引起的低能马约拉纳激发

基塔耶夫自旋液体 (KSL) 中的激发可以通过马约拉纳费米子来描述，其具有体能隙和拓扑边缘模式的特征场依赖性。层状蜂窝磁体在高场状态下$\alpha \text{-}{\mathrm{氯化钌}}_3$，最近报道了支持这些马约拉纳特征的实验结果。然而，由于样本依赖性，存在挑战，并且人们对不可避免的无序对 KSL 的影响知之甚少。在这里，我们研究了如何通过在中引入点缺陷来修改低能激发$\alpha \text{-}{\mathrm{氯化钌}}_3$使用电子辐照，引起位点空缺和交换随机性。比热的温度依赖性的高分辨率测量$C（\mathrm{时间}）$面内场下$H$表明，虽然场相关的马约拉纳能隙几乎完好无损，但额外的低能态$C/\mathrm{时间}=A（H）\mathrm{时间}$由引入的缺陷引起。在低温下，我们得到的数据崩溃为$C/\mathrm{时间}～H^{-\gamma }（\mathrm{时间}/H）$预期无序量子自旋系统但具有异常大的指数$\gamma$。这使我们发现系数之间的幂律关系$A（H）$和场敏感的马约拉纳间隙。这些结果与无序引起低能量线性马约拉纳激发的情况一致，这可以被认为是马约拉纳费米子在 KSL 中的弱局域化效应。