Evolutionary trade-offs between reproduction and dispersal in populations at expanding range boundaries

During recent climate warming, some species have expanded their ranges northwards to keep track of climate changes. Evolutionary changes in dispersal have been demonstrated in these expanding populations and here we show that increased dispersal is associated with reduced investment in reproduction in populations of the speckled wood butterfly, Pararge aegeria. Evolutionary changes in flight versus reproduction will affect the pattern and rate of expansion at range boundaries in the future, and understanding these responses will be crucial for predicting the distribution of species in the future as climates continue to warm

Dielectric Metamaterials with Toroidal Dipolar Response

Toroidal multipoles are the terms missing in the standard multipole expansion; they are usually overlooked due to their relatively weak coupling to the electromagnetic fields. Here we propose and theoretically study all-dielectric metamaterials of a special class that represent a simple electromagnetic system supporting toroidal dipolar excitations in the THz part of the spectrum. We show that resonant transmission and reflection of such metamaterials is dominated by toroidal dipole scattering, the neglect of which would result in a misunderstanding interpretation of the metamaterials macroscopic response. Due to the unique field configuration of the toroidal mode the proposed metamaterials could serve as a platform for sensing, or enhancement of light absorption and optical nonlinearities

"Slow" light in metamaterials

We demonstrate that propagation of microwave pulses can be significantly affected by the presence of a planar fish-scale metamaterial, which is at least 30 times thinner than the wavelength. In the resonant band of the fish-scale structure, a spectrally narrow pulse (18 ns) can be significantly delayed (by 5.6 ns) as if propagating through an 84 cm thick dielectric (epsilon=3.77), while a short pulse (220 ps) will split in two roughly equal pulses propagating with subluminal and superluminal velocity respectively. We also interpret the response of the metamaterial in terms of effective material parameters

Superconducting analogue of optical plasmonic waveguides

We demonstrate a direct analogy between electromagnetic properties of superconductors at frequencies up to 6 THz (superconducting gap) and plasmonic metals in the optical part of the spectrum. We also identify the existence of a surface bound mode in superconducting waveguide structures, "superconducting plasmon", that closely connected to surface plasmon polaritons in the noble metals. This is a peculiar low-frequency, low-loss mode that can be guided for tens of centimetres and confined on the scale of just few tens of nanometres, demonstrating an incredible application potential

Wavevector Selective Metasurfaces and Tunnel Vision Filters

Metasurfaces offer unprecedented flexibility in the design and control of light propagation, replacing bulk optical components and exhibiting exotic optical effects. One of the basic properties of the metasurfaces, which renders them as frequency selective surfaces, is the ability to transmit or reflect radiation within a narrow spectral band that can be engineered on demand. Here we introduce and demonstrate experimentally in the THz domain the concept of wavevector selective surfaces -- metasurfaces transparent only within a narrow range of light propagation directions operating effectively as tunnel vision filters. Practical implementations of the new concept include applications in wavefront manipulation, observational instruments, vision and free-space communication in light-scattering environments, as well as passive camouflage

Asymmetric transmission of light through a planar chiral metamaterial

We report that normal incidence transmission of circularly polarized light through lossy anisotropic planar chiral meta-material is asymmetric for opposite directions. The new effect is fundamentally distinct from conventional gyrotropy of bulk chiral media and the Faraday Effect

Point-dipole approximation for small systems of strongly coupled radiating nanorods

Systems of closely-spaced resonators can be strongly coupled by interactions mediated by scattered electromagnetic fields. In large systems the resulting response has been shown to be more sensitive to these collective interactions than to the detailed structure of individual resonators. Attempts to describe such systems have resulted in point-dipole approximations to resonators that are computationally efficient for large resonator ensembles. Here we provide a detailed study for the validity of point dipole approximations in small systems of strongly coupled plasmonic nanorods, including the cases of both super-radiantand subradiant excitations, where the characteristics of the excitation depends on the spatial separation between the nanorods. We show that over an appreciable range of rod lengths centered on 210 nm, when the relative separation kl in terms of the resonance wave number of light k satisfies kl >pi/2, the point electric dipole model becomes accurate. However, when theresonators are closer, the finite-size and geometry of the resonators modifies the excitation modes, in particular the cooperative mode line shifts of the point dipole approximation begin to rapidly diverge at small separations. We also construct simplified effective models by describing a pair of nanorods as a single effective metamolecule

Giant microwave and optical gyrotropy in bilayered chiral metamaterials

We report on a novel type of artificial material, which exhibits a very strong gyrotropy in the microwave and optical part of the spectrum, the bilayered chiral metamaterial. The specific rotary power of the optical metamaterial exceeds 600°/mm