The idea of squeezing optical field intensity into nanoscopic dimensions can be achieved through plasmon polaritons, where the prerequisite is to bridge the unmatched momentum of plasmons and free-space photons. Conventionally, complicated subwavelength structures or artificial dipole nanostructures are adopted to impart the necessary momentum for the plasmon excitation. In this work, we show that by using the near-field imaging technique, the plasmon can be launched directly from the edge of graphene lying on the high-κ oxide substrates when illuminated by an infrared light. In addition, we show that such an edge-excited mode can be remarkably tailored by changing the angle between the graphene edge and the incident light field. Further theoretical analysis reveals the strength of the edge-excited mode and its superposition with a tip-excited mode and an edge localized mode. We attribute our findings to the reduced Coulomb scattering and phonon scattering in graphene, allowing the edge-excited mode to be identified. The conceptual edge “antenna” is found to be a very convenient approach to initiate plasmons in two-dimensional systems, which opens up a compelling route for realising nanophotonic applications.

中文翻译：

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石墨烯中边缘激发等离子体激元模式的纳米成像†

将光场强度压缩到纳米级的想法可以通过等离激元极化子来实现，前提是要弥合等离激元和自由空间光子的无与伦比的动量。常规地，采用复杂的亚波长结构或人造偶极子纳米结构来赋予等离子体激元激发所需的动量。在这项工作中，我们表明，通过使用近场成像技术，可以从位于高κ的石墨烯边缘直接发射等离子体激元。红外光照射时会氧化底材。另外，我们表明可以通过改变石墨烯边缘和入射光场之间的角度来显着调整这种边缘激发模式。进一步的理论分析揭示了边缘激发模式的强度及其与尖端激发模式和边缘局部模式的叠加。我们将发现归因于石墨烯中库仑散射和声子散射的减少，从而可以确定边缘激发模式。发现概念边缘“天线”是在二维系统中引发等离子体激元的一种非常方便的方法，这为实现纳米光子应用开辟了一条引人注目的途径。