Unusual resonances in nanoplasmonic structures due to nonlocal response

TL;DR

This paper investigates the nonlocal electromagnetic response in nanoplasmonic structures using the hydrodynamical Drude model, revealing that nonlocal resonances occur only above the plasma frequency, challenging previous quasi-static approximation results.

Contribution

It demonstrates that nonlocal resonances in nanoplasmonic structures are physically valid only above the plasma frequency, correcting earlier predictions based on quasi-static approximation.

Findings

Nonlocal resonances occur only above the plasma frequency.

Quasi-static approximation predicts unphysical resonances at optical frequencies.

Analytical calculations for nanosized metallic cylinders support these conclusions.

Abstract

We study the nonlocal response of a confined electron gas within the hydrodynamical Drude model. We address the question whether plasmonic nanostructures exhibit nonlocal resonances that have no counterpart in the local-response Drude model. Avoiding the usual quasi-static approximation, we find that such resonances do indeed occur, but only above the plasma frequency. Thus the recently found nonlocal resonances at optical frequencies for very small structures, obtained within quasi-static approximation, are unphysical. As a specific example we consider nanosized metallic cylinders, for which extinction cross sections and field distributions can be calculated analytically.