Acoustic plasmon modes tightly coupled between a two-dimensional material and another conducting layer can exhibit optical confinement not possible with conventional plasmons. Here, we investigate acoustic plasmons supported in a monolayer and multilayers of black phosphorus (BP) placed shortly above a conducting plate. In the presence of a conducting plate, the acoustic plasmon dispersion for the armchair direction is found to exhibit the characteristic linear scaling in the mid- and far-infrared regime while it largely deviates from that in the long-wavelength limit and near-infrared regime. For the zigzag direction, such scaling behavior is not evident due to relatively tighter plasmon confinement. Further, we demonstrate a novel design for an acoustic plasmon resonator that exhibits higher plasmon confinement and resonance efficiency than BP ribbon resonators in the mid-infrared and longer wavelength regime. The theoretical framework and new resonator designs studied here provide a practical route toward the experimental verification of acoustic plasmons in BP and open up the possibility to develop novel plasmonic and optoelectronic devices that can leverage its strong in-plane anisotropy and thickness-dependent band gap.

中文翻译：

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黑磷中的各向异性声等离子体

在二维材料和另一个导电层之间紧密耦合的声等离振子模式可以表现出常规等离激子不可能实现的光学限制。在这里，我们研究了放置在导电板上方不久的单层和多层黑磷（BP）中所支撑的声等离子体激元。在存在导电板的情况下，发现扶手椅方向的声等离振子色散在中红外和远红外条件下表现出特征性的线性标度，而与长波长极限和近红外条件下的线性等比例极大地偏离。对于锯齿形方向，由于等离子激元限制相对较紧，因此这种缩放行为并不明显。进一步，我们展示了一种新颖的声学等离振子谐振器设计，在中红外和更长的波长范围内，与BP带状谐振器相比，它具有更高的等离激元限制和谐振效率。本文研究的理论框架和新的谐振器设计为实现BP中的声等离子体激元的实验验证提供了一条实用的途径，并为开发能够利用其强大的平面各向异性和厚度依赖性带隙的新型等离子体和光电器件提供了可能性。