We present inelastic neutron scattering measurements of magnetic excitations in ${\mathrm{YbMnBi}}_2$, which reveal features consistent with a direct coupling of magnetic excitations to Dirac fermions. In contrast with the large broadening of magnetic spectra observed in antiferromagnetic metals such as the iron pnictides, here the spin waves exhibit a small but resolvable intrinsic width, consistent with our theoretical analysis. The subtle manifestation of spin-fermion coupling is a consequence of the Dirac nature of the conduction electrons, including the vanishing density of states near the Dirac points. Accounting for the Dirac fermion dispersion specific to ${\mathrm{YbMnBi}}_2$ leads to particular signatures, such as the nearly wave-vector-independent damping observed in the experiment.

中文翻译：

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YbMnBi2中自旋波与狄拉克费米子之间的耦合特征

我们提出了磁激发中的非弹性中子散射测量 ${\mathrm{铌锰铋}}_2$揭示了与磁激发直接耦合到狄拉克费米子的特征一致的特征。与在反铁磁性金属（例如铁的铁化物）中观察到的大的光谱拓宽相反，自旋波显示出很小但可分辨的本征宽度，这与我们的理论分析一致。自旋-费米子耦合的微妙表现是传导电子的狄拉克性质的结果，包括狄拉克点附近状态的消失。解释特定于Dirac的费米子分散体${\mathrm{铌锰铋}}_2$ 导致特殊的特征，例如在实验中观察到的几乎与波矢无关的阻尼。