We present comprehensive electron spin resonance (ESR) studies of in-plane oriented single crystals of $\alpha \text{−}{\mathrm{RuCl}}_3$, a quasi-two-dimensional material with honeycomb structure, focusing on its high-field spin dynamics. The measurements were performed in magnetic fields up to 16 T, applied along the [110] and [100] directions. Several ESR modes were detected. Combining our findings with recent inelastic neutron- and Raman-scattering data, we identified most of the observed excitations. Most importantly, we show that the low-temperature ESR response beyond the boundary of the magnetically ordered region is dominated by single- and two-particle processes with magnons as elementary excitations. The peculiarities of the excitation spectrum in the vicinity of the critical field are discussed.

中文翻译：

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α-RuCl_{3}高场相中的磁激发性质。

我们目前对面内取向的单晶进行全面的电子自旋共振（ESR）研究 $\alpha \text{-}{\mathrm{氯化钌}}_3$是一种具有蜂窝结构的准二维材料，专注于其高场自旋动力学。测量是在沿[110]和[100]方向施加的最大16 T磁场中进行的。检测到几种ESR模式。结合我们的发现与最新的非弹性中子和拉曼散射数据，我们确定了大多数观测到的激发。最重要的是，我们表明，超出磁有序区域边界的低温ESR响应受单磁和双磁过程控制，其中磁振子为基本激发。讨论了临界场附近激发光谱的特殊性。