We report a comprehensive neutron scattering study on the spin excitations in the magnetic Weyl semimetal Co₃Sn₂S₂ with a quasi-two-dimensional structure. Both in-plane and out-of-plane dispersions of the spin waves were revealed in the ferromagnetic state. Similarly, dispersive but damped spin excitations were found in the paramagnetic state. The effective exchange interactions were estimated using a semi-classical Heisenberg model to consistently reproduce the experimental T_C and spin stiffness. However, a full spin wave gap below E_g = 2.3 meV was observed at T = 4 K. This value was considerably larger than the estimated magnetic anisotropy energy (~0.6 meV), and its temperature dependence indicated a significant contribution from the Weyl fermions. These results suggest that Co₃Sn₂S₂ is a three-dimensional correlated system with a large spin stiffness, and the low-energy spin dynamics can interplay with the topological electron states.

中文翻译：

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铁磁Weyl半金属Co 3 Sn 2 S 2中的自旋激发和自旋波隙

我们报告了具有准二维结构的磁性Weyl半金属Co ₃ Sn ₂ S _2中的自旋激发的全面中子散射研究。自旋波的面内和面外色散均在铁磁状态下显示。类似地，在顺磁状态下发现了弥散但阻尼的自旋激发。使用半经典的海森堡模型估计有效的交换相互作用，以一致地再现实验的T _C和自旋刚度。然而，在T处观察到低于E _g = 2.3 meV的完整自旋波隙= 4K。该值大大大于估计的磁各向异性能（〜0.6 meV），并且其温度依赖性表明Weyl费米子有很大贡献。这些结果表明，Co ₃ Sn ₂ S ₂是具有大自旋刚度的三维相关系统，低能自旋动力学可以与拓扑电子态相互作用。