Asymmetric Cavity Mode Engineering in a Single Plasmonic Nanowire

Plasmon mode engineering enables the ability to manipulate the highly localized electromagnetic fields at the deep-subwavelength scale. Here, without introducing geometrical asymmetry, we propose a scheme to generate and control the asymmetric plasmon mode in a single nanowire cavity by the interference of cavity modes with opposite parities. Through a rigorous theoretical derivation and further verification with finite-element analysis, we show that the simultaneous excitation of odd and even cavity modes with mutual spectral and spatial overlap in a single nanowire enables a new hybridized plasmon mode with strong near-field directionality and high extinction ratio. By full exploitation of the incident electromagnetic field including its amplitude, phase, and spin components, the behavior of the asymmetric plasmon mode with its asymmetric field can be readily controlled over a broad wavelength range, offering versatility for controlling the cavity plasmon's spatial and spectral distribution at the nanoscale. Our approach can be applied to modulate the light-matter interaction and other functional devices in applications such as cavity quantum electrodynamics, information processing, sensing and lasing.