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arXiv 2007.03764cond-mat.str-el
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蜂窝晶格磁体CoTiO $_3$中的自旋轨道激子:揭示稀土和过渡金属磁性之间的联系

Spin-Orbit Exciton in a Honeycomb Lattice Magnet CoTiO$_3$: Revealing Link Between Rare Earth and Transition Metal Magnetism

Bo Yuan, M. B. Stone, Guo-Jiun Shu, F. C. Chou, Xin Rao, J. P. Clancy, Young-June Kim

摘要:

利用非弹性中子散射研究了CoTiO $_3$单晶样品中的自旋轨道激子随温度的变化。CoTiO $_3$是一种蜂窝状磁体,具有主导的XY型磁相互作用和低于$\mathrm{T_N} \approx 38$ ~K的A型反铁磁序。我们发现,SO激子变得更软,但获得了更大的带宽,在顺磁相相比,在磁有序相。此外,仅在中间温度范围内观察到额外模式,因为样本被加热到高于低于$\mathrm{T_N}$的最低可达温度。在这种材料中观察到的这种不寻常的温度依赖性表明,它的基态($S_{\mathrm{eff}}=\frac{1}{2}$双峰)和激发态多重态是强耦合的,因此不能像在伪自旋模型中经常做的那样独立处理。我们的观察结果可以解释的多层次理论内的随机相位近似,明确考虑到地面和激发多重态。我们的理论最初是为了解释稀土磁体中磁激发的温度依赖性而发展的,它的成功突出了稀土系统中磁激发与具有强自旋轨道耦合的过渡金属系统中磁激发之间的相似性。

英文摘要:

We carried out inelastic neutron scattering to study the spin-orbital (SO) exciton in a single crystal sample of CoTiO$_3$ as a function of temperature. CoTiO$_3$ is a honeycomb magnet with dominant XY-type magnetic interaction and an A-type antiferromagnetic order below $\mathrm{T_N} \approx 38$~K. We found that the SO exciton becomes softer, but acquires a larger bandwidth in the paramagnetic phase, compared to that in the magnetically ordered phase. Moreover, an additional mode is only observed in the intermediate temperature range, as the sample is warmed up above the lowest accessible temperature below $\mathrm{T_N}$. Such an unusual temperature dependence observed in this material suggests that its ground states (an $S_{\mathrm{eff}}=\frac{1}{2}$ doublet) and excited states multiplets are strongly coupled, and therefore cannot be treated independently, as often done in a pseudo-spin model. Our observations can be explained by a multi-level theory within random phase approximation that explicitly takes into account both the ground and excited multiplets. The success of our theory, which is originally developed to explain temperature dependence of magnetic excitations in the rare-earth magnets, highlight the similarity between the magnetic excitations in rare-earth systems and those in transition metal systems with strong spin orbit coupling.

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