Spatial Nonlocality in the Optical Response of Metal Nanoparticles

Abstract

Spatial nonlocality is known to play an important role in nano-optics when small nanometer-sized structures are involved, but few efforts have been made to assess nonlocal effects in a rigorous way. We present two different approaches to account for nonlocality in metal nanoparticles: (i) the nonretarded specular reflection model and (ii) the retarded hydrodynamical model. Excellent agreement with available experiments is obtained from our parameter-free simulations, which lead to dramatic differences with respect to local theory. Both models predict sizable plasmon blue shifts and broadenings in individual metal nanoparticles, nanoshells, particle dimers, and Yagi–Uda antennas. An analysis of plasmon resonances for varying particle size and spacing allows us to separate nonlocal and retardation effects within the hydrodynamical model. We find a wide range of geometrical parameters for which nonlocal effects coexist with significant retardation. This study is particularly relevant for broad, active areas involving applications of local field enhancement to biosensing and nonlinear optics in plasmonics.

Performance of Nonlocal Optics When Applied to Plasmonic Nanostructures

“…The hydrodynamic equation (1) together with Maxwell's equations defines a self-consistent problem that can be solved analytically for selected geometries and numerically by using, for instance, finite-elements methods. 12,18,[21][22][23][24][25][26][27] The HDA dispersion relation for longitudinal bulk plasmons is ω 2 = ω 2 P + β 2 k 2 , where ω P = (4πe 2n /m e ) 1/2 is the bulk plasma frequency. 28 Therefore, the velocity β quantifies the dispersion in the EM response.…”

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.…”

Low-damping epsilon-near-zero slabs: Nonlinear and nonlocal optical properties

“…The phenomenology of nonlocal contributions of free electrons on the optical response of nanoscale plasmonic structures has been widely discussed in literature. [22][23][24][25][26][27][28] Typical manifestations of the nonlocal, free-electron gas pressure are blue shift and broadening of plasmonic resonances, anomalous absorption, 29 unusual resonances above the plasma frequency, 25 and limitation of field enhancements. 28 These effects are more pronounced when the electron wavelength (~1 nm) becomes comparable to the radius of curvature of metallic nanostructures or to the distance between the metal boundaries of larger structures.…”