Geometry changes the optical response
The strongest calculated near-field enhancements—increases in electric field close to the modeled metal—appeared at sharper corners and smaller gaps in a new modeling study of silver nanowire structures. The work compared cylindrical dimers, bowtie dimers and a triangular nanowire monomer, using local and nonlocal descriptions of the metal’s optical response.
The calculations treated the structures as infinitely extended, high-aspect-ratio nanowires rather than finite particles. They varied shape, corner curvature, separation between paired wires and illumination direction, then tracked optical-extinction spectra, resonance positions and the strength and location of the calculated near fields.
For the cylindrical dimer, the authors considered illumination parallel to the x-axis more favorable for light harvesting because it produced a broader spectral response and a larger extinction efficiency. The comparison was qualitative and confined to the simulations.
Nonlocal calculations revealed extra structure
A central comparison was between a local Drude model and the nonlocal Halevi model. The latter generally lowered the calculated resonant field amplitudes, while the maxima of averaged near-field enhancement usually stayed close to the peaks in optical extinction.
The calculations also pointed to a curvature effect that would be easy to miss if a corner were described only by a reference radius. In the triangular nanowire, the quadrupolar nonlocal blueshift—a shift toward higher frequency—changed as the corner curvature changed, rather than remaining fixed by that reference radius.
All three modeled structures showed non-degenerate high-order localized surface-plasmon spectra associated with longitudinal nonlocality. These higher-order resonances can overlap and couple less efficiently to an incoming plane wave, limiting how precisely their amplitudes can be interpreted.
In the bowtie geometry, the spectra contained pairs of resonances on either side of the corresponding monomer quadrupolar resonance. The authors identified these as bonding and antibonding hybrid quadrupolar modes.
The largest fields appeared in gaps and at corners
At the smallest cylindrical-dimer gap tested, enhancement around the edge of the gap reached roughly two orders of magnitude in both material models. With illumination perpendicular to the x-axis, the maximum enhancement centered in the gap was about 80 in the Drude calculation and 68 in the Halevi calculation.
The triangular monomer showed a similar curvature dependence: sharper modeled curvature was accompanied by stronger enhancement at the corner. For the sharpest triangular wire, mean corner enhancement was approximately 94 with the Drude model and 76 with the Halevi model.
The bowtie produced still larger gap-centered values in the reported scans. Reducing the gap raised enhancement above 100 in both models; increasing the curvature raised the values to 152 with Drude and 132 with Halevi.
A separate area measure based on a chosen enhancement threshold suggested that curvature broadened the modeled nonlocal sequence more than gap-size variation did. In the bowtie curvature scan, the sequence extended from about 0.72 to 0.92 ωp,Ag for both illumination directions, although individual peaks were irregular and more strongly displaced.
The boundaries of the model
These findings are computational predictions from effectively two-dimensional cross sections of infinitely extended, homogeneous, high-aspect-ratio nanowires. The study used a Bézier-type corner parametrization to tune curvature and a DGTD finite-element solver, leaving finite-length end effects outside its scope.
The dimer gaps were restricted to no smaller than two nanometers to suppress tunneling effects. The results therefore do not address the behavior of smaller gaps within the assumptions of this study.
The reported enhancement values are tied to the modeled geometry, illumination conditions and material descriptions. They indicate how the calculated structures respond under those settings, rather than establishing performance for finite particles or an experimental device.
The document is an arXiv preprint, version 1, dated 26 August 2026. The work acknowledged support from the German Research Foundation through Collaborative Research Centre 1375, Project ID 398816777, Project A06.
Paper data and sources
Original title: Optical extinction and near-field properties of plasmonic dimers: Role of particle shape and separation
Authors: Gino Wegner, Bill Antonio Bernhardt, Ulf Peschel, Kurt Busch
Journal/Repository: arXiv
Status: Preprint, not yet peer-reviewed
First online: 2026-08-26
DOI: Not available
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