A generalized non-local optical response theory for plasmonic nanostructures

Abstract

Metallic nanostructures exhibit a multitude of optical resonances associated with localized surface plasmon excitations. Recent observations of plasmonic phenomena at the sub-nanometre to atomic scale have stimulated the development of various sophisticated theoretical approaches for their description. Here instead we present a comparatively simple semiclassical generalized non-local optical response theory that unifies quantum pressure convection effects and induced charge diffusion kinetics, with a concomitant complex-valued generalized non-local optical response parameter. Our theory explains surprisingly well both the frequency shifts and size-dependent damping in individual metallic nanoparticles as well as the observed broadening of the crossover regime from bondingdipole plasmons to charge-transfer plasmons in metal nanoparticle dimers, thus unravelling a classical broadening mechanism that even dominates the widely anticipated short circuiting by quantum tunnelling. We anticipate that our theory can be successfully applied in plasmonics to a wide class of conducting media, including doped semiconductors and low-dimensional materials such as graphene.

Resonance shifts and spill-out effects in self-consistent hydrodynamic nanoplasmonics

“…While in the present work we have mainly focused on size-dependent frequency shifts, we envisage that in the future this model can be extended to also include sizedependent damping 69 mechanisms such as Landau damping 34 .…”

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.…”

Landau damping of surface plasmons in metal nanostructures

“…In subsequent quantum-mechanical studies carried within random phase approximation (RPA) [45][46][47][48][49][50][51] and timedependent local density approximation (TDLDA) [52][53][54][55][56][57][58][59] approaches, a more complicated picture has emerged involving the role of confining potential and nonlocal effects. These are dominant at the spatial scale ξ nl = v F /ω that defines the characteristic length for nonlocal effects [60,61] (e.g., for noble metals, v F /ω < 1 nm in the plasmon frequency range), whereas for larger systems with L ≫ v F /ω (i.e., several nm and larger), they mainly affect the overall magnitude of γ sp , while preserving intact its size dependence [56,58]. The latter implies that in a wide size range v F /ω ≪ L ≪ c/ω, which includes most plasmonic systems used in applications, the detailed structure of electronic states is unimportant, and the confinement effects can be reasonably described in terms of electron surface scattering, which can be incorporated, along with phonon and impurity scattering, in the metal dielectric function ε(ω) = ε ′ (ω) + iε ′′ (ω).…”