Driving Orbital Magnetism in Metallic Nanoparticles Through Circularly Polarized Light: A Real-Time TDDFT Study
Transfer of angular momentum from helicity-controlled laser fields to a nonmagnetic electronic system can lead to the creation of magnetization. The underlying mechanism in metallic nanoparticles has been studied using different theoretical approaches. Very recently light-induced magnetism in plasmonic gold nanoparticles has also been reported [Cheng et al., Nat. Photonics 2020, 14, 365-368], openning opportunities for studying the ultrafast optical control of magnetic properties in subwavelength geometries. However, an understanding of the dynamics using an orbital-based quantum-mechanical method within the many-body theoretical framework is still due. To this end, in this collaborative work we have usded the real-time formulation of time-dependent, density-functional theory (TDDFT) to study induced orbital magnetism in metallic nanoparticles (clusters) excited by circularly polarized light. The polarized laser field gives rise to an angular momentum and, hence, a magnetic moment, which is maximum at the surface plasmon frequency of the nanoparticle, revealing that this is a resonant plasmonic effect. The primary contribution to the magnetic moment comes from surface currents generated by the plasmonic field, although some bulk contributions due to the quantum-mechanical nature of the system (Friedel oscillations) still persist. A comparison of the obtained results with the known classical theoretical model confirms that the laser-induced generation of the magnetization is due to the plasmonic inverse Faraday effect. Finally, our simulations of the generation of orbital magnetic moment in gold clusters produced results having magnitudes consistent with recently reported experimental study (mentioned above).
Figure: Schematic representation of the real-time TDDFT simulation where a circularly polarized laser pulse (green) gives rise to a magnetic moment (red) in a metal cluster whose induced density (at a time after the end of the laser) is shown by an iso-surface plot.
Rajarshi Sinha-Roy, Jérôme Hurst, Giovanni Manfredi, and Paul-Antoine Hervieux
The work was carried out by Rajarshi Sinha-Roy during his postdoctoral research activities in the group TSN in Centre Interdisciplinaire de Nanoscience de Marseille (CINaM). This work is done in collaboration with Jérôme Hurst at CEA, Grenoble, and Giovanni Manfredi, and Paul-Antoine Hervieux at Institut de Physique et Chimie des Maté riaux de Strasbourg.
ACS Photonics 2020, 7, 2429−2439
A graphical artwork representing the work has also been selected as the official journal cover of the latest issue of ACS photonics (Vol. 7, Iss. 9)