This work demonstrates significant line narrowing of surface {multipole plasmon (MP)} by modifying the surface electronic wavefunction with two-dimensional materials (2DMs): graphene and hexagonal boron nitride. This is found in an optical reflectivity of alkali atoms (Cs or K) on an Ir(111) surface covered with the 2DMs. The reduction in reflectivity induced by deposition of the alkali atoms becomes as large as 20% at $$2 eV, which is ascribed to {MP} of a composite of alkali/2DM/alkali/Ir multilayer structure. The linewidth of the {MP} band becomes as narrow as 0.2 eV by the presence of the 2DM between the two alkali layers. A numerical simulation by time-dependent density functional theory with a jellium model reveals that the density of states of the surface localized state is sharpened remarkably by the 2DMs that decouple the outermost alkali layer from the Ir bulk. {Consequently, {a local field enhancement of an order of ${10}^5$} is achieved by ultimate confinement of {MP} within the outermost alkali layer.} This work leads to a novel strategy for reducing the plasmon dissipation {in an atomically thin layer} via atomic scale modification of surface structure.

中文翻译：

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通过用二维材料修改表面电子波函数来缩小碱多极等离子体的极限宽度

这项工作演示了通过使用二维材料（2DM）：石墨烯和六方氮化硼修改表面电子波函数来显着缩小表面{多极等离子体激元（MP）}的线。这是在覆盖有2DM的Ir（111）表面上的碱原子（Cs或K）的光反射率中发现的。由碱原子的沉积引起的反射率的降低在$ 2 eV时高达20％，这归因于碱/ 2DM /碱/ Ir多层结构的复合物的{MP}。由于在两个碱层之间存在2DM，{MP}带的线宽变得窄至0.2 eV。通过时变密度泛函理论和一个Jelium模型进行的数值模拟显示，通过将最外层碱层与Ir体解耦的2DM，表面局部态的态密度显着提高。{因此，{{${10}^5$}是通过将{MP}最终限制在最外层的碱层中来实现的。}这项工作导致了一种通过对表面结构进行原子尺度修饰来降低{原子薄层中的}等离激元耗散的新策略。