Modified field enhancement and extinction by plasmonic nanowire dimers due to nonlocal response

Abstract

We study the effect of nonlocal optical response on the optical properties of metallic nanowires, by numerically implementing the hydrodynamical Drude model for arbitrary nanowire geometries. We first demonstrate the accuracy of our frequency-domain finite-element implementation by benchmarking it in a wide frequency range against analytical results for the extinction cross section of a cylindrical plasmonic nanowire. Our main results concern more complex geometries, namely cylindrical and bow-tie nanowire dimers that can strongly enhance optical fields. For both types of dimers we find that nonlocal response can strongly affect both the field enhancement in between the dimers and their respective extinction cross sections. In particular, we give examples of blueshifted maximal field enhancements near hybridized plasmonic dimer resonances that are still large but nearly two times smaller than in the usual local-response description. For the same geometry at a fixed frequency, the field enhancement and cross section can also be significantly more enhanced in the nonlocal-response model.

A generalized non-local optical response theory for plasmonic nanostructures

“…The former is already known to cause frequency shifts (blueshifts) 17,21,22 , while the latter turns out to cause line broadening, that is the GNOR parameter x is in general a complex-valued quantity. As also anticipated from more general discussions 14 , our rigorous semiclassical treatment shows that non-local effects may manifest themselves over distances greatly exceeding atomic dimensions and become comparable to characteristic structure dimensions, such as the radius R of a nanoparticle (Fig.…”

“…Quite surprisingly, while the literature is rich on discussions of the former effect within hydrodynamic models, the importance of the latter in nanoplasmonic systems remains unexplored, and, according to our knowledge, there is no unifying real-space description applicable to realistic plasmonic nanostructures. Pioneering works focused on pressure-driven convective flow of charge in ideal geometries [16][17][18][19] , while the exploration of non-local response in arbitrarily shaped metal nanostructures has only recently been initiated 20 , emphasizing real-space rigorous formulations of semiclassical hydrodynamic equations 21 and different solution strategies [22][23][24][25][26] . Thus, large blueshifts in nanoscale noble metal plasmonic structures 11,27,28 have been interpreted in the context of the quantum pressurerelated non-local response 27,28 , while quantum confinement 11 and surface-screening 29 explanations have also been proposed.…”

Performance of Nonlocal Optics When Applied to Plasmonic Nanostructures

“…Finally, since damping processes in this system are mainly due to the scattering of moving electrons by the barrier potential at the cylinder surface, γ must be of the order of hv F /R ∼ 0.3 eV. 36 The sets of differential equations for classical local and semi-classical non-local HDA optics are solved numerically using the finite element COMSOL package 37 following the prescription by Raza et al 25,38 and Hiremath et al 39 Unlike it was done in some previous applications of the HDA to nanowires, 22,23 such an implementation does not neglect the transverse component of the induced electric field. It is known that this simplification enforces the definition of additional but artificial boundary conditions to obtain a unique solution of the HDA problem, which results in the appearance of spurious resonances in the absorption spectrum.…”

A classical treatment of optical tunneling in plasmonic gaps: extending the quantum corrected model to practical situations

“…2,[64][65][66][67][68][69][70][71][72][73] The nonlocal hydrodynamical (NLHD) description has attracted considerable interest because of its numerical efficiency for arbitrarily-shaped objects 47,[74][75][76][77][78][79][80][81][82][83][84] and the possibility to obtain semi-analytical Example of the implementation of QCM in metallic gaps. In (a), a spatially inhomogeneous effective medium whose properties depend continuously on the separation distance is introduced in the gap between two metallic spheres.…”