Asymptotics of surface-plasmon redshift saturation at sub-nanometric separations

Abstract

Many promising nanophotonics endeavours hinge upon the unique plasmonic properties of nanometallic structures with narrow non-metallic gaps, which support super-concentrated bonding modes that singularly redshift with decreasing separations. In this letter, we present a descriptive physical picture, complemented by elementary asymptotic formulae, of a nonlocal mechanism for plasmon-redshift saturation at subnanometric gap widths. Thus, by considering the electron-charge and field distributions in the close vicinity of the metal-vacuum interface, we show that nonlocality is asymptotically manifested as an effective potential discontinuity. For bonding modes in the near-contact limit, the latter discontinuity is shown to be effectively equivalent to a widening of the gap. As a consequence, the resonance-frequency near-contact asymptotics are a renormalisation of the corresponding local ones. Specifically, the renormalisation furnishes an asymptotic plasmon-frequency lower bound that scales with the $1/4$-power of the Fermi wavelength. We demonstrate these remarkable features in the prototypical cases of nanowire and nanosphere dimers, showing agreement between our elementary expressions and previously reported numerical computations.

References in corpus (5)

• Generalized nonlocal optical response in nanoplasmonics
• Nonlocal optical response in metallic nanostructures
• Resonance shifts and spill-out effects in self-consistent hydrodynamic nanoplasmonics
• Nonlocal study of ultimate plasmon hybridization
• Singular perturbations approach to localized surface-plasmon resonance: Nearly touching metal nanospheres

Cited by in corpus (9)

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• Surface-plasmon resonances of arbitrarily shaped nanometallic structures in the small-screening-length limit
• Hybridization of Singular Plasmons via Transformation Optics
• Electromagnetic reflection, transmission and energy density at boundaries of nonlocal media
• Interplay between anisotropy and spatial dispersion in metamaterial waveguide
• Plasmonic resonances of slender nanometallic rings
• Reflection and transmission in nonlocal susceptibility models with multiple resonances