Twisted bilayer transition metal dichalcogenides are ideal platforms to study flat-band phenomena. In this paper, we investigate flat-band plasmons in the hole-doped twisted bilayer ${\mathrm{MoS}}_2$ (tb-${\mathrm{MoS}}_2$) by employing a full tight-binding model and the random phase approximation. When considering lattice relaxations in tb-${\mathrm{MoS}}_2$, the flat band is not separated from remote valence bands, which makes the contribution of interband transitions in transforming the plasmon dispersion and energy significantly different. In particular, low-damped and quasiflat plasmons emerge if we only consider intraband transitions in the doped flat band, whereas a $\sqrt{q}$ plasmon dispersion emerges if we also take into account interband transitions between the flat band and remote bands. Furthermore, the plasmon energies are tunable with twist angles and doping levels. However, in a rigid sample that suffers no lattice relaxations, lower-energy quasiflat plasmons and higher-energy interband plasmons can coexist. For rigid tb-${\mathrm{MoS}}_2$ with a high doping level, strongly enhanced interband transitions quench the quasiflat plasmons. Based on the lattice relaxation and doping effects, we conclude that two conditions, the isolated flat band and a proper hole-doping level, are essential for observing the low-damped and quasiflat plasmon mode in twisted bilayer transition metal dichalcogenides. We hope that our study on flat-band plasmons can be instructive for studying the possibility of plasmon-mediated superconductivity in twisted bilayer transition metal dichalcogenides in the future.

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扭曲的双层过渡金属二硫属化物中的平带等离子体

扭曲的双层过渡金属二硫化物是研究平带现象的理想平台。在本文中，我们研究了空穴掺杂扭曲双层中的平带等离子体${\mathrm{二硫化钼}}_2$（待定-${\mathrm{二硫化钼}}_2$) 通过采用完全紧束缚模型和随机相位近似。当考虑 tb- 中的晶格弛豫时${\mathrm{二硫化钼}}_2$，平带没有与远程价带分开，这使得带间跃迁在转换等离子体色散和能量方面的贡献显着不同。特别是，如果我们只考虑掺杂平带中的带内跃迁，则会出现低阻尼和准平坦等离激元，而$\sqrt{q}$如果我们还考虑平带和远程带之间的带间跃迁，就会出现等离子体分散。此外，等离子体能量可通过扭转角和掺杂水平进行调节。然而，在没有晶格弛豫的刚性样品中，低能准平面等离子体和高能带间等离子体可以共存。对于刚性 tb-${\mathrm{二硫化钼}}_2$具有高掺杂水平，强烈增强的带间跃迁会淬灭准平坦等离子体。基于晶格弛豫和掺杂效应，我们得出结论，隔离平带和适当的空穴掺杂水平这两个条件对于观察扭曲的双层过渡金属二硫属化物中的低阻尼和准平坦等离子体模式至关重要。我们希望我们对平带等离子体的研究能够对未来研究扭曲的双层过渡金属二硫属化物中等离子体介导的超导性的可能性具有指导意义。