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Molecularchemistry offers a unique toolkit to draw inspirationfor the design of artificial metamolecules. For a long time, opticalcircular dichroism has been exclusively the terrain of natural chiralmolecules, which exhibit optical activity mainly in the UV spectralrange, thus greatly hindering their significance for a broad rangeof applications. Here we demonstrate that circular dichroism can begenerated with artificial plasmonic chiral nanostructures composedof the minimum number of spherical gold nanoparticles required forthree-dimensional (3D) chirality. We utilize a rigid addressable DNAorigami template to precisely organize four nominally identical goldnanoparticles into a three-dimensional asymmetric tetramer. Becauseof the chiral structural symmetry and the strong plasmonic resonantcoupling between the gold nanoparticles, the 3D plasmonic assembliesundergo different interactions with left and right circularly polarizedlight, leading to pronounced circular dichroism. Our experimentalresults agree well with theoretical predictions. The simplicity ofour structure geometry and, most importantly, the concept of resortingon biology to produce artificial photonic functionalities open a newpathway to designing smart artificial plasmonic nanostructures forlarge-scale production of optically active metamaterials. [ABSTRACT FROM AUTHOR]

We introduce a theory to describe the interaction of swift electrons with strong evanescent light fields. This allows us to explain recent experimental results of multiple energy losses and gains for electrons passing near illuminated nanostructures. A complex evolution of the electron state over attosecond time scales is unveiled, giving rise to non-Poissonian distributions of multiphoton features in the electron spectra. Prospects for application to nanoscale-resolved transmission electron microscopy and spectroscopy are discussed.