Direct electrical modulation of surface response in a single plasmonic nanoresonator

TL;DR

This study demonstrates electrical control over the surface response of a single plasmonic nanoresonator, revealing changes in resonance frequency and width due to surface charge modulation, with implications for ultrafast plasmonic devices.

Contribution

It provides the first experimental evidence of direct electrical modulation of surface responses in a single nanoresonator, incorporating nonlocal and anisotropic effects in the analysis.

Findings

Resonance frequency shifts with surface charge modulation

Resonance narrowing indicates reduced losses

Surface response can be electrically tuned in nanoscale plasmonic systems

Abstract

Classical electrodynamics describes the optical response of systems using bulk electronic properties and infinitesimally thin boundaries. However, due to the quantum nature of electrons, interfaces have a finite thickness. Non-classical surface effects become increasingly important as ever smaller nanoscale systems are realized and eventually dominate over volume-related phenomena. Investigating the response of surface electrons in such systems, therefore, becomes imperative. One way to gain control over non-classical interface effects and study them is through electrical gating, as the static screening charges reside exclusively at the surface. Here, we investigate the modulation of the surface response upon direct electric charging of a single plasmonic nanoresonator by measuring the resulting changes in resonance. We analyze the observed effects within the general framework of surface-response functions and provide a basic model derived from electron spill-out within the local-response approximation (LRA). Our observed change in resonance frequency is well accounted for by assuming a modulation of the in-plane surface current. Surprisingly, we also measure a change in the resonance width, where adding electrons to the surface leads to a narrowing of the plasmonic resonance, i.e., reduced losses. The description of such effects requires considering nonlocal effects and the inclusion of a possible anisotropy of the perturbed surface permittivity. Our experiment, therefore, opens a vast field of investigations on how to gain control over the surface response in plasmonic resonators and to develop ultrafast and extremely small electrically driven plasmonic modulators and metasurfaces by leveraging electrical control over non-classical surface effects.