We study the distance-dependent quenching of fluorescence due to a metallic nanoparticle in proximity of a fluorophore. In our single-molecule measurements, we achieve excellent control over structure and stoichiometry by using self-assembled DNA structures (DNA origami) as a breadboard where both the fluorophore and the 10 nm metallic nanoparticle are positioned with nanometer precision. The single-molecule spectroscopy method employed here reports on the co-localization of particle and dye, while fluorescence lifetime imaging is used to directly obtain the correlation of intensity and fluorescence lifetime for varying particle to dye distances. Our data can be well explained by exact calculations that include dipole-dipole orientation and distances. Fitting with a more practical model for nanosurface energy transfer yields 10.4 nm as the characteristic distance of 50% energy transfer. The use of DNA nanotechnology together with minimal sample usage by attaching the particles to the DNA origami directly on the microscope coverslip paves the way for more complex experiments exploiting dye-nanoparticle interactions.

We discuss the effect of the spin-orbit interaction on the band structure, wave functions and low temperature conductance of long quasi-one-dimensional electron systems patterned in twodimensional electron gases (2DEG). Our model for these systems consists of a linear (Rashba) potential confinement in the direction perpendicular to the 2DEG and a parabolic confinement transverse to the 2DEG. We find that these two terms can significantly affect the band structure introducing a wave vector dependence to subband energies, producing additional subband minima and inducing anticrossings between subbands. We discuss the origin of these effects in the symmetries of the subband wave functions. 71.70.Ej; 73.23.Ad

A compact analytical formula up to the order of k 3 , where k is a wave vector, is derived for the depolarization field E d of a spheroidal particle by performing explicitly the steps of the recipe outlined by Meier and Wokaun [Opt. Lett. 8, 581 (1983)]. For the static component of E d a general electrostatic formula valid for a particle of a general shape is rederived within the Meier and Wokaun framework. The dynamic k 2-dependent depolarization component of E d is shown to depend on dynamic geometrical factors, which can be expressed in terms of the standard geometrical factors of electrostatics. The Meier and Wokaun recipe itself is shown to be equivalent to a long-wavelength limit of the Green's function technique. The resulting Meier and Wokaun longwavelength approximation is found to exhibit a redshift compared against exact T-matrix results. At least for a sphere, it is possible to get rid of the redshift by assuming a weak nonuniformity of the field E int inside a particle, which can be fully accounted for by a renormalization of the dynamic geometrical factors. My results may be relevant for various plasmonic, or nanoantenna, applications of spheroidal particles with a dominant electric dipole scattering, whenever it is necessary to go beyond the Rayleigh approximation and to capture the essential size-dependent features of scattering, local fields, SERS, hyper-Raman and second-harmonicgeneration enhancements, decay rates, and photophysics of dipolar arrays.

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We present a new set of artificial structures which can exhibit a negative refractive index band in excess of 6% in a broad frequency range from the deep infrared to the terahertz region. The structures are composites of two different kinds of non-overlapping spheres, one made from inherently non-magnetic polaritonic and the other from a Drude-like material. The polaritonic spheres are responsible for the existence of negative effective magnetic permeability whilst the Drude-like spheres are responsible for negative effective electric permittivity. The resulting negative refractive index structures are truly subwavelength structures with wavelength-to-structure ratio 14:1, which is almost 50% higher than has been previously achieved. Our results are explained in the context of the extended Maxwell-Garnett theory and are reproduced by calculations based on the layer Korringa-Kohn-Rostoker method, an ab initio multiple scattering theory. The role of absorption in the constituent materials is discussed. Effective medium computer F77 code is freely available at http://www.wave-scattering.com.