With infrared spectroscopy, we studied the bulk electronic properties of the topological antiferromagnet $\mathrm{Mn}{\mathrm{Bi}}_2{\mathrm{Te}}_4$ with $T_N\simeq 25\mathrm{K}$. With the support of band-structure calculations, we assign the intra- and interband excitations and determine the band gap of $E_g\approx 0.17$ eV. We also obtain evidence for two types of conduction bands with light and very heavy carriers. The multiband free-carrier response gives rise to an unusually strong increase of the combined plasma frequency, ${\omega }_{\mathrm{pl}}$, below 300 K. The band reconstruction below $T_N$ yields an additional increase of ${\omega }_{\mathrm{pl}}$ and a splitting of the transition between the two conduction bands by about 54 meV. Our study thus reveals a complex and strongly temperature-dependent multiband low-energy response that has important implications for the study of the surface states and device applications.

中文翻译：

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拓扑反铁磁体MnBi2Te4的多频带低能激发的红外研究

通过红外光谱，我们研究了拓扑反铁磁体的体电子性质 $锰{双}_{\mathrm{2个}}{特}_4$ 和 ${Ť}_{ñ}\simeq 25\mathrm{ķ}$。在带结构计算的支持下，我们分配带内和带间激励，并确定${Ë}_G\approx 0.17$ eV。我们还获得了载流子很轻和很重的两种导带的证据。多频带自由载波响应会导致组合等离子体频率异常强劲地增加，${\omega }_{\mathrm{PL}}$，低于300K。下面的频段重建 ${Ť}_{ñ}$ 产生额外的增加 ${\omega }_{\mathrm{PL}}$两个导带之间的跃迁分裂约54 meV。因此，我们的研究揭示了一个复杂且强烈依赖温度的多频带低能量响应，这对表面状态和器件应用的研究具有重要意义。