Hydrodynamical model for bulk and surface plasmons in cylindrical wires

Unusual resonances in nanoplasmonic structures due to nonlocal response

“…For nanowires, we find extinction resonances without making the quasistatic approximation that agree with the quasistatic modes of Ref. 13, so we do not claim a general breakdown of the approximation itself. Even though there are no nonlocal resonances in the visible, plasmonic field enhancements are affected by nonlocal response.…”

“…1) are due to the excitation of confined longitudinal modes, which are bulk-plasmon states with discrete energies abovehω p due to confinement in the cylinder. 13 These peaks are analogous to discrete absorption lines above the band gap in quantumconfined semiconductor structures. Interestingly, contrary to the common belief that light does not scatter off bulk plasmons, which is correct in the local theory (i.e., no peak around ω p in Fig.…”

“…Intuitively, one might expect that it can be extended to the nonlocal case and indeed several nonlocal treatments use this assumption. 9,11,[13][14][15][16][17] However, as we shall demonstrate, one should proceed with care.…”

“…This regime challenges the existing theoretical framework resting on a local-response picture using bulk-material parameters. In tiny metallic nanostructures, quantum confinement [3][4][5][6][7] and nonlocal response [8][9][10][11][12][13][14][15][16][17][18] are believed to change the collective plasmonic behavior with resulting strong optical fingerprints and far-reaching consequences for, e.g., field enhancement and extinction cross sections. Within nonlocal response, Maxwell's constitutive relation between the displacement and the electric fields reads D(r,ω) = ε 0 d r ε(r,r ,ω) · E(r ,ω).…”

“…It would, however, be premature to conclude that the quasistatic approximation breaks down, because in Ref. 13 the modes of cylinders in the hydrodynamical Drude model were found after making the quasistatic approximation, and the only different modes found were the confined bulk plasmon modes above ω p . Figure 1 also illustrates that for increasing radii, σ ext in the two nonlocal models converges toward the local-response value.…”