The smallest free-electron sphere sustaining multipolar surface plasmon oscillation

Transverse spinning of a sphere in a plasmonic field

We evaluate optical forces and torques induced by a surface plasmon to a sphere of arbitrary size, i.e. beyond the point-like dipolar limit. Through a multipolar decomposition of the plasmonic field, we demonstrate that the induced torque is purely transverse to the plasmon propagation direction. Our approach removes the inherent ambiguities of the dipolar regime with respect to rotations and emphasizes the crucial role played by dissipation in the onset of the plasmonic torque. We also give realistic estimates of such plasmon-induced spinning of gold spheres immersed in water or air.

铝纳米盘中紫外等离激元模式的电子能量损失

Electron-Energy Loss of Ultraviolet Plasmonic Modes in Aluminum Nanodisks

本研究理论探究铝纳米盘紫外等离激元的EELS特性，区分扁平与厚纳米盘的模式行为，提出改进的有效波长模型模拟扁平结构色散关系，并指出厚结构需结合EELS与阴极荧光测量。

Plasmonic lateral forces on chiral spheres

We show that the optical force exerted on a finite size chiral sphere by a surface plasmon mode has a component along a direction perpendicular to the plasmon linear momentum. We reveal how this chiral lateral force, pointing in opposite directions for opposite enantiomers, stems from an angular-to-linear crossed momentum transfer involving the plasmon transverse spin angular momentum density and mediated by the chirality of the sphere. Our multipolar approach allows us discussing the inclusion of the recoil term in the force on a small sphere taken in the dipolar limit and observing sign inve…

Decay dynamics of Localised Surface Plasmons: damping of coherences and populations of the oscillatory plasmon modes

Properties of plasmonic materials are associated with surface plasmons - the electromagnetic excitations coupled to coherent electron charge density oscillations on a metal/dielectric interface. Although decay of such oscillations cannot be avoided, there are prospects for controlling plasmon damping dynamics. In spherical metal nanoparticles (MNPs) the basic properties of Localized Surface Plasmons (LSPs) can be controlled with their radius. The present paper handles the link between the size-dependent description of LSP properties derived from the dispersion relation based on Maxwell's equat…

Plasmon oscillations in ellipsoid nanoparticles: beyond dipole approximation

The plasmon oscillations of a metallic triaxial ellipsoid nanoparticle have been studied within the framework of the quasistatic approximation. A general method has been proposed for finding the analytical expressions describing the potential and frequencies of the plasmon oscillations of an arbitrary multipolarity order. The analytical expressions have been derived for an electric potential and plasmon oscillation frequencies of the first 24 modes. Other higher orders plasmon modes are investigated numerically.

本地化表面等离子体衰减的自淬灭效应：经典与量子视角

Self-Quenching Effect of the Decay of Localized Surface Plasmons: Classical and Quantum Perspectives

本文提出一种结合经典电动力学与量子发射视角的自洽模型，研究金属纳米颗粒中本地化表面等离子体（LSPs）的衰减动力学，强调等离子体准粒子的玻色特性及自淬灭效应的影响。

Plasmon-Emitter Interactions at the Nanoscale

Plasmon-emitter interactions are of paramount importance in modern nanoplasmonics and are generally maximal at short emitter-surface separations. However, when the separation falls below 10-20 nm, the classical theory progressively deteriorates due to its neglect of quantum mechanical effects such as nonlocality, electronic spill-out, and Landau damping. Here, we show how this neglect can be remedied by presenting a unified theoretical treatment of mesoscopic electrodynamics grounded on the framework of Feibelman $d$-parameters. Crucially, our technique naturally incorporates nonclassical reso…

Nonlocal Response of Metallic Nanospheres Probed by Light, Electrons, and Atoms

Inspired by recent measurements on individual metallic nanospheres that can not be explained with traditional classical electrodynamics, we theoretically investigate the effects of nonlocal response by metallic nanospheres in three distinct settings: atomic spontaneous emission, electron energy loss spectroscopy, and light scattering. These constitute two near-field and one far-field measurements, with zero-, one-, and two-dimensional excitation sources, respectively. We search for the clearest signatures of hydrodynamic pressure waves in nanospheres. We employ a linearized hydrodynamic model …