Spin-dependent dipole excitation in alkali-metal nanoparticles

We study the spin-dependent electronic excitations in alkali-metal nanoparticles. Using numerical and analytical approaches, we focus on the resonances in the response to spin-dependent dipole fields. In the spin-dipole absorption spectrum for closed-shell systems, we investigate in detail the lowest-energy excitation, the "surface paramagnon" predicted by L. Serra et al. [Phys. Rev. A 47, R1601 (1993)]. We estimate its frequency from simple assumptions for the dynamical magnetization density. In addition, we numerically determine the dynamical magnetization density for all low-energy spin-dipole modes in the spectrum. Those many-body excitations can be traced back to particle-hole excitations of the noninteracting system. Thus, we argue that the spin-dipole modes are not of collective nature. In open-shell systems, the spin-dipole response to an electrical dipole field is found to increase proportionally with the ground-state spin polarization.Comment: 12 pages, 9 figure

Surface plasmon resonance in C60 revealed by photoelectron imaging spectroscopy

Within the framework of the time-dependent local-density approximation and the self-interaction correction, we have estimated the photoionization cross-section and the photoelectron angular asymmetry parameter of C60. The latter exhibits large variation around the surface plasmon resonance of the π electrons near 20 eV. Based on a semiclassical electrodynamics model, we show that this behaviour is generic for any surface plasmon resonance in the continuum and is a signature of the correlated motion of the electrons. It is related to the change of sign of the real part of the dynamical polarizability at resonance. Possible experiments to investigate this new plasmon signature are discussed

Collective Electron Dynamics in Metallic and Semiconductor nanostructures

International audienceWe review different approaches to the modeling and numerical simulation of the nonlinear electron dynamics in metallic and semiconductor nanostructures. Depending on the required degree of sophistication, such models go from the full N-body dynamics (configuration interaction), to mean-field approaches such as the time-dependent Hartree equations, down to macroscopic models based on hydrodynamic equations. The time-dependent density functional theory and the localdensity approximation - which have become immensely popular during the last two decades - can be understood as an upgrade of the Hartree approach allowing one to include, at least approximately, some effects that go beyond the mean-field. Alternative methods, based onWigner's phase-space representation of quantum mechanics, are also described. Wigner's approach has the advantage of permitting a more straightforward comparison between semiclassical and fully quantum results. As an illustrative example, the many-electron dynamics in a semiconductor quantum well is studied numerically, using both a mean-field approach (Wigner-Poisson system) and a quantum hydrodynamical model. Finally, the above methods are extended to include the spin degrees of freedom of the electrons. The local-spin-density approximation is used to investigate the linear electron response in metallic nanostructures. The modeling of nonlinear spin effects is sketched within the framework of Wigner's phase-space dynamics