title: Extraordinary Light-Induced Local Angular Momentum near Metallic Nanoparticles.
abstract: The intense local field induced near metallic nanostructures provides strong enhancements for surface-enhanced spectroscopies, a major focus of plasmonics research over the past decade. Here we consider that plasmonic nanoparticles can also induce remarkably large electromagnetic field gradients near their surfaces. Sizeable field gradients can excite dipole-forbidden transitions in nearby atoms or molecules and provide unique spectroscopic fingerprinting for chemical and bimolecular sensing. Specifically, we investigate how the local field gradients near metallic nanostructures depend on geometry, polarization, and wavelength. We introduce the concept of the local angular momentum (LAM) vector as a useful figure of merit for the design of nanostructures that provide large field gradients. This quantity, based on integrated fields rather than field gradients, is particularly well-suited for optimization using numerical grid-based full wave electromagnetic simulations. The LAM vector has a more compact structure than the gradient matrix and can be straightforwardly associated with the angular momentum of the electromagnetic field incident on the plasmonic structures.
authors.forename: Alessandro
authors.initials: A
authors.lastname: Alabastri
authors.forename: Xiao
authors.initials: X
authors.lastname: Yang
authors.affiliation: Department of Physics and Astronomy, University of New Mexico , Albuquerque, New Mexico 87131, United States.
authors.forename: Alejandro
authors.initials: A
authors.lastname: Manjavacas
authors.affiliation: Army Aviation and Missile RD&E Center at Redstone Arsenal , Huntsville, Alabama 35898, United States.|Department of Physics, Duke University , Durham, North Carolina 27708, United States.
authors.forename: Henry O
authors.initials: HO
authors.lastname: Everitt
authors.forename: Peter
authors.initials: P
authors.lastname: Nordlander
keywords: dipole-forbidden transitions; electric field gradient; local angular momentum; optical angular momentum; plasmonic nanoparticles; quadrupolar transitions