We use resonant inelastic x-ray scattering (RIXS) to investigate the magnetic dynamics of the infinite-layer cuprate ${\mathrm{CaCuO}}_2$. We find that close to the $(1/2,0)$ point, the single magnon decays into a broad continuum of excitations accounting for about 80% of the total magnetic spectral weight. Polarization-resolved RIXS spectra reveal the overwhelming dominance of the spin-flip ($\mathrm{\Delta }S=1$) character of this continuum with respect to the $\mathrm{\Delta }S=0$ multimagnon contributions. Moreover, its incident-energy dependence is identical to that of the magnon, supporting a common physical origin. We propose that the continuum originates from the decay of the magnon into spinon pairs, and we relate it to the exceptionally high ring exchange $J_c\sim J_1$ of ${\mathrm{CaCuO}}_2$. In the infinite-layer cuprates, long-range and multisite hopping integrals are very important, and they amplify the 2D quantum magnetism effects in spite of the 3D antiferromagnetic Néel order.

中文翻译：

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无限层铜酸盐CaCuO2中的分数自旋激发

我们使用共振非弹性 X 射线散射 (RIXS) 来研究无限层铜酸盐的磁动力学${\mathrm{钙铜}}_2$. 我们发现接近$(1/2,0)$点，单个磁振子衰减成一个广泛的连续激发，约占总磁谱权重的 80%。偏振分辨的 RIXS 光谱揭示了自旋翻转的压倒性优势（$\mathrm{\Delta }\mathrm{小号}=1$) 这个连续统的特征$\mathrm{\Delta }\mathrm{小号}=0$多磁子贡献。此外，它的入射能量依赖性与磁振子的相同，支持共同的物理起源。我们提出连续统起源于磁子衰变成自旋子对，我们将其与异常高的环交换联系起来${Ĵ}_C～{Ĵ}_1$的${\mathrm{钙铜}}_2$. 在无限层铜酸盐中，长程和多点跳跃积分非常重要，尽管存在 3D 反铁磁 Néel 阶，它们仍放大了 2D 量子磁效应。