Dipole resonance conditions and field redistributions of charged nanoparticles

Abstract

For charged nanoparticles, no relation of the near fields to the resonance conditions has yet been documented. Hence, the “singular” near fields induced by the excess charges have not yet been well explained. In this paper, using the charge-amended scattering theory, we study in detail the excess-charge-regulated resonance conditions and the blue shifts of resonances for a 2D charged cylinder made of polar materials. We show that the blue-shifted resonance of the charged nanoparticles may extend to wavelengths below the longitudinal optical (LO) wavelength, breaking the limit of a neutral nanoparticle. We give the theoretical threshold of the surface charge density, which shifts the resonance to the LO wavelength. Under the resonance shifts, the mechanism of the “singular” near-field redistribution due to the excess charges can be understood. Specifically, the on- and off-resonance distributions can swap with each other excited by the surface charges, which leads to the redistribution of the internal and near external intensities.