In many realistic topological materials, more than one kind of fermions contribute to the electronic bands crossing the Fermi level, leading to various novel phenomena. Here, using momentum-resolved inelastic electron scattering, we investigate the plasmons and their evolution across the phase transition in a type-II Weyl Semimetal MoTe$_2$, in which both Weyl fermions and trivial nonrelativistic fermions contribute to the Fermi surface in the Td phase. One plasmon mode in the 1T' phase at high temperature and two plasmon modes in the topological T$_d$ phase at low temperature are observed. Combining with first-priciples calculations, we show that all the plasmon modes are dominated by the interband correlations between the inverted bands of MoTe$_2$. Especially in the T$_d$ phase, since the electronic bands split due to inversion symmetry breaking and spin-orbit coupling, the plasmon modes manifest the interband correlation between the topological Weyl fermions and the trivial nonrelativistic electrons. Our work emphasizes the significance of the interplay between different kinds of carriers in plasmons of topological materials.

中文翻译：

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II型外尔半金属MoTe2中的拓扑非平凡带间等离子体

在许多现实的拓扑材料中，不止一种费米子有助于跨越费米能级的电子能带，从而导致各种新现象。在这里，使用动量分辨非弹性电子散射，我们研究了等离子激元及其在 II 型外尔半金属 MoTe$_2$ 相变过程中的演化，其中外尔费米子和平凡的非相对论费米子都对 Td 中的费米表面有贡献阶段。观察到高温1T'相中的一种等离子体模式和低温拓扑T$_d$相中的两种等离子体模式。结合第一性原理计算，我们表明所有等离子体模式都由 MoTe$_2$ 的倒置带之间的带间相关性主导。尤其是在T$_d$阶段，由于反转对称性破坏和自旋轨道耦合导致电子能带分裂，等离子体模式表现出拓扑外尔费米子和平凡的非相对论电子之间的带间相关性。我们的工作强调了拓扑材料等离子激元中不同类型载流子之间相互作用的重要性。