Faraday Rotation and Circular Dichroism Spectra of Gold and Silver Nanoparticle Aggregates

TL;DR

This study investigates the magneto-optical properties of noble metal nanoparticle clusters, revealing how magnetic fields influence circular dichroism and polarization changes, especially near surface plasmon frequencies.

Contribution

It provides new insights into the magneto-optical responses of nanoparticle aggregates, highlighting the dependence of Faraday effects on cluster anisotropy and chirality.

Findings

Circular dichroism in dimers depends on magnetic field and light direction.

Faraday rotation and ellipticity are sinusoidal functions of polarization azimuth.

Enhanced effects observed near surface plasmon frequency.

Abstract

We study the magneto-optical response of noble metal nanoparticle clusters. We consider the interaction between the light-induced dipoles of particles. In the presence of a magnetic field, the simplest achiral cluster, a dimer, exhibits circular dichroism (CD). The CD of a dimer depends on the directions of the magnetic field and the light wave vector. The CD of a populous cluster weakly depends on the magnetic field. Upon scattering from the cluster, an incident linearly polarized light with polarization azimuth $\varphi$, becomes elliptically polarized. The polarization azimuth rotation and ellipticity angle variation are sinusoidal functions of $2 \varphi$. The anisotropy and the chirality of the cluster control the amplitude and offset of these sinusoidal functions. The Faraday rotation and Faraday ellipticity are also sinusoidal functions of $2 \varphi$. Near the surface plasmon frequency, Faraday rotation and Faraday ellipticity increase.