Projected Dipole Model for Quantum Plasmonics

Abstract

Quantum effects of plasmonic phenomena have been explored through ab initio studies, but only for exceedingly small metallic nanostructures, leaving most experimentally relevant structures too large to handle. We propose instead an effective description with the computationally appealing features of classical electrodynamics, while quantum properties are described accurately through an infinitely thin layer of dipoles oriented normally to the metal surface. The nonlocal polarizability of the dipole layer-the only introduced parameter-is mapped from the free-electron distribution near the metal surface as obtained with 1D quantum calculations, such as time-dependent density-functional theory (TDDFT), and is determined once and for all. The model can be applied in two and three dimensions to any system size that is tractable within classical electrodynamics, while capturing quantum plasmonic aspects of nonlocal response and a finite work function with TDDFT-level accuracy. Applying the theory to dimers, we find quantum corrections to the hybridization even in mesoscopic dimers, as long as the gap itself is subnanometric.

Classification of scalar and dyadic nonlocal optical response models

“…This is confirmed in Ref. [25] where it is shown that besides damping due to electron-hole pair creation in forward-scattering processes across the gap (i.e. tunneling) also backward scattering processes at metal-air interfaces are important, the latter processes both for monomers and dimers.…”

On the origin of nonlocal damping in plasmonic monomers and dimers

“…42 We consider a simple metal, such as Na, described within a jellium approximation, and exploit TDDFT to obtain its response to a timedependent electrical field. 42,62 The calculation provides both the (space dependent) equilibrium density n 0 (r) and the induced charge density n 1 (r).…”

“…42 We consider a simple metal, such as Na, described within a jellium approximation, and exploit TDDFT to obtain its response to a timedependent electrical field. 42,62 The calculation provides both the (space dependent) equilibrium density n 0 (r) and the induced charge density n 1 (r). Additionally, one also obtains the displacement field D generated by the perturbing E field, and from this one may again infer an effective relative dielectric function ε eff (r, ω), where the imaginary part holds key information about damping and its spatial localization.…”

Spatial dispersion in two-dimensional plasmonic crystals: Large blueshifts promoted by diffraction anomalies

“…The successful observation of such quantum effects [26][27][28][29][30] has fueled the interest in an accurate description of electrons in the nonlocal regime and electron dynamics in photonic systems was studied in recent years with semiclassical [21,22,25,[31][32][33][34] and ab initio methods [35][36][37][38][39][40][41]. There has naturally been a large emphasis on localized plasmons in subwavelength metallic nanostructures and basic planar geometries [42], * chrida@fotonik.dtu.dk while only few works have considered plasmons in periodic structures [43][44][45][46][47].…”