Figure 3: Optical response of a small metallic dimer within quantum and classical models.
From: Bridging quantum and classical plasmonics with a quantum-corrected model
Comparison of the optical properties of a metallic dimer obtained with (a–c) the full-QM, (d–f) with the QCM and (g–i) with a clasical electromagnetic model (CEM).The dimer consists of two Na spheres of radius R~2.17 nm (40.96 a.u.) in vacuum, separated by a distance D. The incoming field is a plane wave with electric field E0 polarized along the dimer axis z. The centre of the particles are at z=±(R+D/2), and D is negative for overlapping spheres. D=−2R would correspond to the limit of a single sphere. (a,d,g) show colour plots of the extinction spectra σext of the dimers (far-field) as a function of separation distance D. D is expressed in Ångströms, and the extinction cross-section in nm2. Zero-separation distance is marked as a vertical dashed line separating the classical non-touching regime and the overlapping regime. Each of these regimes is schematically represented by separated and overlapping yellow dots, respectively. The most relevant modes are identified within the three treatments followed: bonding dimer plasmon (BDP), bonding quadrupolar plasmon (BQP), charge transfer plasmon (CTP) and higher-order charge transfer plasmon (CTP′). (b,e,h) Far-field spectra from selected distances in (a), (d) and (g), respectively. For clarity, a vertical shift proportional to the separation distance is used. Traces in red correspond to separation distances of D=−5.29, −2.65, 0, 2.65 and 5.29 Å, as indicated on each graph. (c,f,i) Colour plots of the local field enhancement |E/E0| (near-field) at the centre of the junction for separations D>0.5 Å. The yellow dots schematically represent the particles in the non-touching regime.
