As a two-dimensional semimetal, graphene offers clear advantages for plasmonic applications over conventional metals, such as stronger optical field confinement, in situ tunability, and relatively low intrinsic losses. However, the operational frequencies at which plasmons can be excited in graphene are limited by the Fermi energy E_F, which in practice can be controlled electrostatically only up to a few tenths of an electronvolt. Higher Fermi energies open the door to novel plasmonic devices with unprecedented capabilities, particularly at mid-infrared and shorter-wave infrared frequencies. In addition, this grants us a better understanding of the interaction physics of intrinsic graphene phonons with graphene plasmons. Here, we present FeCl₃-intercalated graphene as a new plasmonic material with high stability under environmental conditions and carrier concentrations corresponding to E_F > 1 eV. Near-field imaging of this highly doped form of graphene allows us to characterize plasmons, including their corresponding lifetimes, over a broad frequency range. For bilayer graphene, in contrast to the monolayer system, a phonon-induced dipole moment results in increased plasmon damping around the intrinsic phonon frequency. Strong coupling between intrinsic graphene phonons and plasmons is found, supported by ab initio calculations of the coupling strength, which are in good agreement with the experimental data.

中文翻译：

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高掺杂石墨烯的本征等离子-声子相互作用：近场成像研究

作为二维半金属，石墨烯为等离子体应用提供了优于常规金属的明显优势，例如更强的光场限制，原位可调谐性和相对较低的固有损耗。但是，费米能E _F限制了在石墨烯中激发等离激元的工作频率，实际上，费米能E _F只能通过静电将其控制到十分之一电子伏特。更高的费米能量打开了具有前所未有的功能的新型等离子设备的大门，特别是在中红外和短波红外频率下。此外，这使我们对内在的石墨烯声子与石墨烯等离子体激元的相互作用物理有了更好的理解。在这里，我们介绍FeCl ₃-插层石墨烯作为一种新的等离子体材料，在环境条件下具有很高的稳定性，并且载流子浓度对应于E _F > 1 eV。这种高掺杂形式的石墨烯的近场成像使我们能够在很宽的频率范围内表征等离子体激元，包括其相应的寿命。对于双层石墨烯，与单层系统相反，声子诱导的偶极矩导致固有声子频率附近的等离振子阻尼增加。从头开始计算了耦合强度，发现内在的石墨烯声子与等离激元之间存在强耦合，这与实验数据非常吻合。