Chiromagnetoptics of Au and Ag Nanoparticulate Systems

Photoelectron excitations into unoccupied energy states are fundamental in solid-state physics and many modern applications. The operation of such internal electronic transitions relies not only on photon absorption efficiency, which is pivotal in sensing, photovoltaics, active plasmonics, etc., but also on light-matter interactions and near/far-field spectroscopic techniques. Here, we report on a spectroscopic absorption fingerprint in magnetic circular dichroism (MCD) responses of various nanoparticulate systems. MCD spectra acquired at low temperatures on assemblies of uncoupled/coupled Ag and Au nanoparticles reveal asymmetric MCD spectral line shapes strongly depending on the nature and shape of nanoparticles and on their interparticular interactions. Assembling for instance the NPs into 2D networks with interparticle distances allowing dipolar interactions or transforming the spherical nanoparticles into disks was found to significantly alter the magneto-optic response in the spectral line shape. The findings are interpreted within the framework of chiral magneto-plasmonic effects by considering the k-dependent electronic states involved in both inter- and intraband electronic transitions.