Defect-induced activation of symmetry forbidden infrared resonances in individual metallic nanorods

3 páginas, 4 figuras.-- et al.We report on the observation of second-order infrared (IR) plasmon resonances in lithographically prepared gold nanorods investigated by means of far-field microscopic IR spectroscopy. In addition to the fundamental antennalike mode, even and odd higher order resonances are observed under normal incidence of light. The activation of even-order modes under normal incidence is surprising since even orders are dipole-forbidden because of their centrosymmetric charge density oscillation. Performing atomic force microscopy and calculations with the boundary element method, we determine that excitation of even modes is enabled by symmetry breaking by structural deviations of the rods from an ideal, straight shape.We gratefully thank P. Nordlander and acknowledge funding within the “Nanoantenna” collaborative European project (No. HEALTH-F5-2009-241818). The authors from the University of Heidelberg, University of Troyes, and University of Paris 13 acknowledge financial support by the DAAD and Partenariat Hubert Curien Procope Program, the Egide Organisation, and the Conseil Régional de Champagne Ardenne. D.W. acknowledges financial support by the Heidelberg Graduate School of Fundamental Physics, F.N. acknowledges financial support by the FRONTIER project. J.A. and A.G.E. acknowledge financial support from National Project No.FIS2007-66711-C02-01 from the Spanish Ministry of Innovation and Science.Peer reviewe