Inhomogeneity-assisted plasmon hybridization in subwavelength plasmas

Resonance mode hybridization in plasmonic systems exhibits great theoretical significance and practical value in various fields, particularly in sensing, light harvesting, and information processing. However, existing modulation techniques for plasmon hybridization in the optical regime predominantly rely on the design of diverse structures. In this work, we propose a new degree of freedom, namely density profiles, to manipulate plasmon hybridization characteristics using a hollow inhomogeneous plasma shell, where two typical hybridization schemes, namely, split and interference states, are identified and analyzed. We further demonstrate that the impact of inhomogeneity on plasmon hybridization manifests in two key aspects: (1) inhomogeneity-induced polarized charge redistribution, which includes surface and volume polarized charges, and (2) inhomogeneity-induced modulation on the relative energy levels of sphere and cavity eigenmodes, as well as the spectral interval or coupling strength between the symmetrically and anti-symmetrically hybridized modes. Additionally, the resonance line shape of the inhomogeneous plasma system is explained from the perspective of Fano resonance and the phase of Mie scattering coefficients. The two hybridization schemes are further observed in extended core-shell plasma structures where the relative permittivity of the inner core is greater than unity. Our results not only broaden the application scopes of plasmon hybridization theories from homogeneous to inhomogeneous media but also open new avenues of functional gradient plasma in advanced electromagnetic manipulation, including efficient electrically small antenna, resonate cavity, and scattering control.