Performance of Nonlocal Optics When Applied to Plasmonic Nanostructures

Abstract

Semi-classical non-local optics based on the hydrodynamic description of conduction electrons might be an adequate tool to study complex phenomena in the emerging field of nanoplasmonics. With the aim of confirming this idea, we obtain the local and non-local optical absorption spectra in a model nanoplasmonic device in which there are spatial gaps between the components at nanometric and sub-nanometric scales. After a comparison against time-dependent density functional calculations, we conclude that hydrodynamic non-local optics provides absorption spectra exhibiting qualitative agreement but not quantitative accuracy. This lack of accuracy, which is manifest even in the limit where induced electric currents are not established between the constituents of the device, is mainly due to the poor description of induced electron densities.

A generalized non-local optical response theory for plasmonic nanostructures

“…Finally, we note that in the anticipated tunnelling regime the extinction spectra are strongly broadened by the complex non-local response. In fact, our semiclassical approach is in remarkable agreement with the TD-DFT results [48][49][50] , with the diffusion contribution being responsible for 'repairing' the apparent incompatibility of TD-DFT calculations and earlier hydrodynamic predictions 49,50 . Our semiclassical GNOR theory thereby pinpoints induced charge diffusion as the dominant broadening mechanism in recent EELS and optical experiments on plasmonic dimers 13,30 , thus challenging tunnelling-current interpretations for which the phenomenological QCM was constructed.…”

“…Ab initio approaches show a crossing from the classical hybridization of localized surface plasmon resonances to tunnelling-mediated charge-transfer plasmons (CTPs) 36,[48][49][50] . Being able to push experiments into this intriguing regime 13,30,51 , commonly associated with expectations of quantum physics, leaves an open question: Can this regime be adequately described with semiclassical models?…”

“…Being able to push experiments into this intriguing regime 13,30,51 , commonly associated with expectations of quantum physics, leaves an open question: Can this regime be adequately described with semiclassical models? While non-local response within the hydrodynamic semiclassical model has been found unsuccessful in explaining features from TD-DFT [48][49][50] , there have been phenomenological attempts of classically modelling the crossover regime. The 'quantumcorrected model' (QCM) 52 adds an artificial conducting and lossy material in the gap to mimic short-circuiting currents associated with quantum tunnelling.…”

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.…”

Visualizing hybridized quantum plasmons in coupled nanowires: From classical to tunneling regime

“…1,18,19 However, the validity and predictive power of such an approach in the true quantum regime is not fully clarified, and the standard hydrodynamic approximation, not including spill-out, has been found to fail for calculations on small nanometric gabs due to a insufficient description of induced charges in the interface. 20 One important hallmark of the quantum regime is electron tunneling, which occurs when two systems are brought into close proximity. In fact, tunneling leads to a break down of the local field enhancement predicted by the classical theory at subnanometer separations, and leads to the formation of a charge-transfer plasmon.…”