Optical properties of plasmonic core-shell nanomatryoshkas: A quantum hydrodynamic analysis

Plasmonic response of the metallic structure characterized by sub-nanometer dielectric gaps can be strongly affected by nonlocal or quantum effects. In this paper, we investigate these effects in spherical Na and Au nanomatryoshka structures with sub-nanometer core-shell separation. We use the state-of-the-art quantum hydrodynamic theory (QHT) to study both near-field and far-field optical properties of these systems: results are compared with the classical local response approximation (LRA), Thomas–Fermi hydrodynamic theory (TF–HT), and the reference time-dependent density functional theory (TD–DFT). We find that the results obtained using the QHT method are in a very good agreement with TD–DFT calculations, whereas other LRA and TF–HT significantly overestimate the field-enhancements. Thus, the QHT approach efficiently and accurately describes microscopic details of multiscale plasmonic systems whose sizes are computationally out-of-reach for a TD–DFT approach; here, we report results for Na and Au nanomatryoshka with a diameter of 60 nm.