Kitaev-type interactions between neighboring magnetic moments emerge in the honeycomb material $\alpha -\mathrm{Ru}{\mathrm{Cl}}_3$. It is debated, however, whether these Kitaev interactions are ferromagnetic or antiferromagnetic. With electron energy loss spectroscopy (EELS) we study the lowest excitation across the Mott-Hubbard gap, which involves a $d^4$ triplet in the final state and therefore is sensitive to nearest-neighbor spin-spin correlations. At low temperatures the spectral weight of these triplets is strongly enhanced, in accordance with optical data. We show that the magnetic correlation function that determines this EELS spectral weight is directly related to a Kitaev-type spin-spin correlator and that the temperature dependence agrees very well with the results of a microscopic magnetic Hamiltonian for $\alpha -\mathrm{Ru}{\mathrm{Cl}}_3$ with ferromagnetic Kitaev coupling.

中文翻译：

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α-RuCl3中铁磁Kitaev相关性的低温增强

蜂窝材料中出现相邻磁矩之间的基塔耶夫型相互作用 $\alpha -茹{氯}_3$。但是，这些Kitaev相互作用是铁磁的还是反铁磁的，尚有争议。利用电子能量损失谱（EELS），我们研究了整个Mott-Hubbard间隙的最低激发，其中包括$d^4$在最终状态下三元组，因此对最近邻自旋-自旋相关性敏感。在低温下，根据光学数据，这些三胞胎的光谱重量大大增强。我们表明，确定该EELS谱权重的磁相关函数与Kitaev型自旋自旋相关器直接相关，并且温度依赖性与微观磁哈密顿量的结果非常吻合。$\alpha -茹{氯}_3$与铁磁Kitaev耦合。