Photoabsorption by Volume Plasmons in Metal Nanoclusters

TL;DR

This paper demonstrates that volume plasmons in metal nanoclusters can be optically excited, unlike in bulk metals, due to different selection rules in finite systems, confirmed by photodepletion measurements on sodium clusters.

Contribution

It provides experimental evidence of volume plasmon excitation in nanoclusters, revealing a new optical excitation pathway in finite metallic systems.

Findings

Identification of a broad volume plasmon absorption peak above 4 eV in Na clusters

Demonstration of optical excitation of volume plasmons in nanoclusters

Different selection rules enable volume plasmon excitation in finite systems

Abstract

It is well known that plasmons in bulk metals cannot be excited by direct photoabsorption, that is, by coupling of volume plasmons to light. Here we demonstrate that the situation in nanoclusters of the same metals is entirely different. We have carried out a photodepletion measurement for Na_20 and Na_92 and identified a broad volume plasmon absorption peak centered slightly above 4 eV, revealing the possibility of optical excitation of volume-type collective electronic modes in a metallic system. The observed phenomenon is related to different selection rules for finite systems.