Magnetodielectric small spheres present unusual electromagnetic scattering features, theoretically predicted a few decades ago. However, achieving such behaviour has remained elusive, due to the non-magnetic character of natural optical materials or the difficulty in obtaining low-loss highly permeable magnetic materials in the gigahertz regime. Here we present unambiguous experimental evidence that a single low-loss dielectric subwavelength sphere of moderate refractive index (n ¼ 4 like some semiconductors at near-infrared) radiates fields identical to those from equal amplitude crossed electric and magnetic dipoles, and indistinguishable from those of ideal magnetodielectric spheres. The measured scattering radiation patterns and degree of linear polarization (3-9 GHz/33-100 mm range) show that, by appropriately tuning the a/l ratio, zero-backward ('Huygens' source) or almost zeroforward ('Huygens' reflector) radiated power can be obtained. These Kerker scattering conditions only depend on a/l. Our results open new technological challenges from nanoand micro-photonics to science and engineering of antennas, metamaterials and electromagnetic devices.

The optical and structural properties of dense colloidal suspensions in the presence of long-range electrostatic repulsion are determined from both light and small-angle neutron scattering experiments. Short-range structural order induces an enhancement of the scattering strength while at the same time the total transmission shows strong wavelength dependence, reminiscent of a photonic crystal. Interestingly, the interplay between diffusive scattering and local order leads to negative values of the scattering anisotropy parameter. The tunable optical properties of these liquids furthermore suggest potential applications such as transparency switches or filters. DOI: 10.1103/PhysRevLett.93.073903 PACS numbers: 42.25.Bs, 42.70.Qs, 82.70.Dd When light is incident on a nonabsorbing material, its further propagation is strongly influenced by the microscopic structure of the material itself. For a bulk homogeneous medium, light is refracted according to Snell's law. Local variations in the dielectric properties lead to isolated scattering events that disperse the light beam. The scatterer density and cross section define the scattering mean free path l. As the number of scattering events increases, the transport of light becomes diffusive and the material appears turbid or ''white'' [1,2]. The relevant scattering length for diffusive light transport is the transport mean free path l . Both quantities are connected by the scattering anisotropy parameter g defined as the average of the cosine of the scattering angle g hcosi, l=l 1 ÿ g. Our current understanding of the diffusive transport is based on the knowledge of these key quantities. In the absence of positional correlations, l is usually equal to or larger than l [2 -5]. For instance, Mie particles (or human tissue [1]) scatter strongly in the forward direction (small scattering angles ) and hence g ' 1 while for Rayleigh scatterers g ' 0. Here we show that these common properties of diffusive transport can be manipulated by tuning the interaction between scatterers. By the appropriate control of the Coulomb repulsion between highly charged particles in suspension, we are now able to access the whole possible interval of g values (from forward scattering g ! 1 to the unusual case of strong backscattering g ! ÿ1).When mesoscopic variations of the dielectric constant can be neatly controlled over macroscopic distances, totally new, so-called photonic properties may appear [6]. At the core of the design of new photonic materials lies the intelligent way structures are assembled on length scales comparable to the wavelength of light. There are two main promising concepts to achieve lossless guidance and manipulation of light based on seemingly opposite principles: order or disorder. Photonic band gap materials are based on periodic structures predicted to inhibit light propagation completely [6]. In the case of disorder, light cannot propagate in the material due to recurrent interference called strong Anderson localization [7].Tailoring microstructures with an app...

A method to form and manipulate the properties of nanometer-size liquid bridges by an external electric field is discussed. The properties of bridges are shown to be the result of an interplay among the field-induced polarization of the water layer adsorbed on the surface, the surface energy, and the water condensation from the humid air. For a given tip-sample separation, a simple model predicts the existence of a threshold voltage V(th) to form the bridge in full agreement with experiments.

A method to calculate electrostatic forces in the context of atomic force microscopy that is useful for the calculation of the electrostatic forces when different length scales are included in the simulation is presented. The versatility of the method allowed for an analysis of the behavior of forces as a function of the tip apex geometry. For example, for flattened, worn out tips, the force at the point of contact with a dielectric sample could be 2.5 times larger than that of a sharp tip. A simple analytical approximation has been also developed for the local characterization of thin films at the nanoscale.