Gyrotropic impact upon negatively refracting surfaces

Surface wave propagation at the interface between different types of gyrotropic materials and an isotropic negatively refracting medium, in which the relative permittivity and relative permeability are, simultaneously, negative is investigated. A general approach is taken that embraces both gyroelectric and gyromagnetic materials, permitting the possibility of operating in either the low GHz, THz or the optical frequency regimes. The classical transverse Voigt configuration is adopted and a complete analysis of non-reciprocal surface wave dispersion is presented. The impact of the surface polariton modes upon the reflection of both plane waves and beams is discussed in terms of resonances and an example of the influence upon the Goos–Hänchen shift is given

Percolation model for the superconductor-insulator transition in granular films

We study the temperature dependence of the superconductor-insulator transition in granular superconductors. Empirically, these systems are characterized by very broad resistance tails, which depend exponentially on the temperature, and the normal state resistance. We model these systems by a two-dimensional random resistor percolation networks in which the resistance between two grains is governed either by Josephson junction coupling or by quasi particle tunneling. Our numerical simulations as well as an effective medium evaluation explain the experimental results over a wide range of temperatures and resistances. Using effective medium approximation we find an analytical expression for the effective resistance of the system and the value of the critical resistance separating conducting from insulating branches.Comment: 4 pages, 2 figure

Phase-transition–like behavior of strong-field classical magnetotransport in a composite medium with a periodic columnar microstructure

A phase-transition–like change from saturating to non-saturating behavior is found in the longitudinal bulk effective magnetoresistivity $\rho^{\rm (e)}_\parallel$ along some fixed directions of a two-dimensional periodic array of long, parallel, perfectly insulating inclusions embedded in a simple, free-electron conducting host. Near the transition, $\rho^{\rm (e)}_\parallel$ exhibits scaling behavior, with a scaling variable that is the ratio of two physical lengths which are tending to 0. At the transition, the local current is constrained to flow in some very narrow boundary layers

Magneto-optical properties of metal-dielectric composites with a periodic microstructure

The AC magneto-electric properties (including Faraday rotation, etc.) of a metal-dielectric composite are considered in the quasi-static regime. Resonances appear at modified values of the surface plasmon and cyclotron frequencies, which depend on the applied magnetic field as well as on the microstructure. When the microstructure is periodic and has more than one characteristic length scale, the electric permittivity can exhibit a strong dependence on both the magnitude and the direction of the applied DC magnetic field in the vicinity of one of those resonances. The possibility of observing this effect in a suitably fabricated composite film is discussed

Controlling the optical spectra of gold nano-islands by changing the aspect ratio and the inter-island distance: theory and experiment

The extinction spectrum of a dielectric film with periodic array of metallic islands of different shapes and different mutual distances was studied both theoretically and experimentally. It is shown, analytically, numerically and experimentally, that the positions of the surface plasmon resonances depend on the nano-structural details. We propose two ways of controlling plasmon resonance frequency: changing the aspect ratio of the elliptical (or rectangular) islands and changing their mutual distances. A new analytical asymptotic approach for calculating the optical properties of such plasmonic systems is developed. The results of our analytical and numerical studies are in good qualitative agreement with experiment

Anisotropic Magnetoresistance of a Classiscal Antidot Array

A periodic array of cylindrical voids, embedded in a thin film of n-doped GaAs, displays a pronounced anisotropy of the classical magnetoresistance. For a geometry where the magnetic field lies in the plane of the film, we observe a characteristic dependence on the angle between current and magnetic field. This experimental finding provides a first verification of a recently predicted effect and agrees well with theoretical calculations. The observed anisotropy is due to interactions among current distortions by neighboring voids

Control of extraordinary light transmission through perforated metal films using liquid crystals

We calculate the effective dielectric tensor of a metal film penetrated by cylindrical holes filled with a nematic liquid crystal (NLC). We assume that the director of the NLC is parallel to the film, and that its direction within the plane can be controlled by a static magnetic field, via the Freedericksz effect. To calculate the effective dielectric tensor, we consider both randomly distributed holes (using a Maxwell-Garnett approximation) and a square lattice of holes (using a Fourier technique). Both the holes and the lattice constant of the square lattice are assumed small compared to the wavelength. The films are found to exhibit extraordinary light transmission at special frequencies related to the surface plasmon resonances of the composite film. Furthermore, the frequencies of peak transmission are found to be substantially split when the dielectric in the holes is anisotropic. For typical NLC parameters, the splitting is of order 5–10% of the metal plasma frequency. Thus, the extraordinary transmission can be controlled by a static magnetic or electric field whose direction can be rotated to orient the director of the NLC. Finally, as a practical means of producing the NLC-filled holes, we consider the case where the entire perforated metal film is dipped into a pool of NLC, so that all the holes are filled with the NLC, and there are also homogeneous slabs of NLC on both sides of the film. The transmission in this geometry is shown to have similar characteristics to that in which the NLC-filled screen is placed in air. Copyright EDP Sciences/Società Italiana di Fisica/Springer-Verlag 200678.67.-n Optical properties of low-dimensional, mesoscopic, and nanoscale materials and structures, 78.66.Sq Composite materials,

Peculiarities of Tamm states formed in degenerate photonic band gaps

The structure of the Tamm state localized at the interface between anisotropic magnetophotonic crystal (anisotropic MPC) and a photonic crystal (PC) made of isotropic dielectrics is studied. It is shown that if the frequency of this state appears within the degenerate band gap then its structure qualitatively differs from the structure of a well-known Tamm state localized at the interface between two one-dimensional PC made of isotropic materials. Since inside the degenerate BG the real part of the Bloch wavenumber differs from the Brillouin value, two Bloch waves with different signs in the real part of the wavenumber and the same sign in the imaginary part have different input impedance values. Moreover, contrary to the case of a PC made of isotropic materials the impedance of each Bloch wave is a tensor. As a consequence to construct a surface state at least three evanescent Bloch waves are required. The conditions that determine the Tamm state frequency also change. © 2010 Elsevier B.V. All rights reserved