Reflection in a mirror changes the handedness of the real world, and right-handed objects turn left-handed and vice versa (M. Gardner, The Ambidextrous Universe, Penguin Books, 1964). Also, we learn from electromagnetism textbooks that a flat metallic mirror transforms an electric charge into a virtual opposite charge. Consequently, the mirror image of a magnet is another parallel virtual magnet as the mirror image changes both the charge sign and the curl handedness. Here we report the dramatic modification in the optical response of a silicon nanocavity induced by the interaction with its image through a flat metallic mirror. The system of real and virtual dipoles can be interpreted as an effective magnetic dipole responsible for a strong enhancement of the cavity scattering cross section.

Several configurations of colloidal wires are obtained by infiltration of charge‐stabilized polystyrene spheres into cylindrical pores of a silicon membrane (see figure). As channel dimensions are comparable to those of particles, wirelike arrangements are governed by the ratio between the pore diameter and the particle diameter. Also, Coulomb repulsion between particles plays a very important role in the particle ordering.

We show that hard spheres confined between two parallel hard plates pack denser with periodic adaptive prismatic structures which are composed of alternating prisms of spheres. The internal structure of the prisms adapts to the slit height which results in close packings for a range of plate separations, just above the distance where three intersecting square layers fit exactly between the plates. The adaptive prism phases are also observed in real-space experiments on confined sterically stabilized colloids and in Monte Carlo simulations at finite pressure.PACS numbers: 82.70. Dd, 05.20.Jj, 68.65.Ac How to pack the largest number of hard objects in a given volume is a classic optimization problem in pure geometry [1]. The close-packed structures obtained from such optimizations are also pivotal in understanding the basic physical mechanisms behind freezing [2,3] and glass formation [4]. Moreover, close-packed structures are highly relevant to numerous applications ranging from packaging macroscopic bodies and granulates [5] to the self-assembly of colloidal [6] and biological [7,8] soft matter. For the case of hard spheres, Kepler conjectured that the highest-packing density should be that of a periodic face-centered-cubic (fcc) lattice composed of stacked hexagonal layers; it took until 2005 for a strict mathematical proof [9]. More recent studies on close packing concern either non-spherical hard objects [10] such as ellipsoids [11,12], convex polyhedra [13,14] (in particular tetrahedra [15]), and irregular non-convex bodies [16] or hard spheres confined in hard containers [17][18][19] or other complex environments.If hard spheres of diameter σ are confined between two hard parallel plates of distance H, as schematically illustrated in Fig. 1, the close-packed volume fraction φ and its associated structure depend on the ratio H/σ. Typically, the complexity of the observed phases increases tremendously on confining the system. Parallel slices from the fcc bulk crystal are only close-packed for certain values of H/σ: A stack of n hexagonal (square) layers aligned with the walls, denoted by n△ (n ), is bestpacked at the plate separation H n△ (H n ) where the layers exactly fit between the walls. Clearly, for the minimal plate distance H ≡ H 1△ = σ, packing by a hexagonal monolayer is optimal. Increasing H/σ up to H 2△ , a buckled monolayer [20] and then a rhombic bilayer [21] become close-packed. However, for H 2△ < H < H 4△ , the close-packed structures are much more complex and still debated. Both, prism phases with alternating parallel prism-like arrays composed of hexagonal and square base [22,23] and morphologies derived from the hexagonalclose-packed (hcp) structure [24,25] were proposed as possible candidates.For confined hard spheres, the knowledge and control over the close-packed configuration is of central relevance for at least two reasons: First, the hard sphere system away from close-packing is of fundamental interest as a quasi-two-dimensional statistical mechanics model. At low densities, a ha...

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This paper investigates the sequence of morphological transitions in a nearly hard sphere arrangement confined in a wedge cell. A model that shows smooth transitions between the different particle orderings for a small number of layers is proposed. In this model, both the buckling and the (100) hexagonal close packed (hcp) phases are particular cases of a much more general particle arrangement tendency that we call hcp-like ordering. This phase, which does not correspond to any known close packed ordering, is able to adopt packing arrangements commensurate with the cell thickness. More striking, the hcp-like phase adapts itself to the progressive changes of the cell thickness by a smooth change in the interlayer spacing. We present hcp-like orderings up to six layers and a complete sequence of transformations between two and four layers. Finally, a packing model of the transition from two to three layers is also presented.

We study light transmission and reflection from an integrated microresonator device, formed by a circular microresonator coupled to a bus waveguide, with an embedded S-shaped additional crossover waveguide element that selectively couples counter-propagating modes in a propagation-direction-dependent way. The overall shape of the device resembles a “taiji” symbol, hence its name. While Lorentz reciprocity is preserved in transmission, the peculiar geometry allows us to exploit the non-Hermitian nature of the system to obtain high-contrast unidirectional reflection with negligible reflection for light incident in one direction and a significant reflection in the opposite direction.

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We report on a combined theoretical and experimental study of the optical coupling between a microdisk resonator and a waveguide laying on different planes. While the lateral coupling between a planar resonator and a waveguide is characterized by a unique distance at which the resonant waveguide transmission vanishes because of destructive interference, the vertical coupling geometry exhibits an oscillatory behavior in the coupling amplitude as a function of the vertical gap. This effect manifests experimentally as oscillations in both the waveguide transmission and the mode quality factor. An analytical description based on coupled-mode theory and a two-port beamsplitter model of the waveguide-resonator coupling is developed, which compares successfully both to experimental data and numerical simulations.