M. Auslender

Low-temperature resistivity minimum in ceramic manganites

Measurements of magnetoresistance and magnetization were carried out on ceramic samples of La0.5Pb0.5MnO3 and La0.5Pb0.5MnO3, containing 10 at. % Ag in a dispersed form. The results obtained for the resistivity at zero applied magnetic field exhibit a shallow minimum at the temperature T∼25–30 K which shifts towards lower temperatures upon applying a magnetic field and disappears at a certain field Hcr. Also the resistivity at helium temperature decreases upon applying magnetic fields. It is shown that the model of charge carriers tunneling between antiferromagnetically coupled grains may account for the results observed.

Sensitivity enhancement of guided-wave surface-plasmon resonance sensors

It is demonstrated theoretically and experimentally that, by using the guided-wave surface-plasmon sensor configuration with a top layer of dielectric thin film (10-15 nm) having a high value of the real part of the dielectric function, it is possible to improve the sensitivity of the sensor up to 1 order of magnitude. The stability is improved because the thin nanolayer acts as a protection layer for the metal. The enhancement is due to the increase in the interaction volume and the evanescent field enhancement near the top layer-analyte interface.

Low-temperature resistivity minima in single-crystalline and ceramic La0.8Sr0.2MnO3: Mesoscopic transport and intergranular tunneling

A slight minimum in the zero-field resistivity of a single crystalline La0.8Sr0.2MnO3 and shallow one for ceramic La0.8Sr0.2MnO3 samples were observed at T∼4 K and at T∼25–30 K, respectively. The minimum for the ceramic shifts towards lower temperatures, flattens with increasing magnetic fields (H), and vanishes at some critical H. The above effects are accompanied by an appreciable negative magnetoresistance (MR). On the other hand, the minimum for the single-crystalline sample is almost field independent and the MR in the relevant temperature range is very small. Two different mechanisms were found to account for the results observed in the single crystal and the polycrystalline samples: (i) mesoscopic corrections to the bulk resistivity that include Coulomb interaction and weak localization and (ii) intergranular tunneling. The resistivity of the large-grain ceramic sample comprises both types of behavior. The minimum of the bulk contribution becomes clearly seen under H, which suppresses the ceramic-t...

Variable gratings for optical switching: rigorous electromagnetic simulation and design

Ben-Gurion University of the NegevDepartment of Electrical andComputer EngineeringP.O. Box 653Beer-Sheva 84105IsraelE-mail: hava@bguee.bgu.ac.ilAbstract. This paper is devoted to rigorous electromagnetic diffractionanalysis, in the near infrared, for micromechanical silicon interdigitatedbeam gratings with both lateral and vertical displacement of movablebeams. In the wavelength-to-period ratio domain where the gratings sup-port three diffraction orders, the specific designs of high-efficiencyswitches for polarized radiation, such as switches from a transmitter to a133 transmission beamsplitter and from a retroreflector to an 1 32 re-flection beam divider, are presented. The possibility of light modulation,which follows from these designs, is discussed. The analysis with re-spect to wavelength, beam-width, beam-height, and incidence-anglevariations shows a good tolerance of the devices’ performance to spec-tral shifts and to fabrication and mounting errors. In addition, with the useof our software we simulated the diffraction efficiency versus displace-ment at a visible wavelength for a micromechanical grating reported inthe literature. There is good agreement between theory and experiment.

Scattering-matrix propagation algorithm in full-vectorial optics of multilayer grating structures.

The scattering of an electromagnetic plane wave incident upon an inhomogeneous multilayer structure is considered in symbolic form. In this framework a scattering-matrix propagation algorithm that decouples recurrences for backward- and forward-scattered wave amplitudes is developed. By construction the scattering-matrix solution procedure is stable against increase of truncation order and depths and number of layers, irrespective of numerical implementation. For grating structures a numerical study using Fouriertransform discretization is performed. In this implementation the convergence issue for TM polarization is recapitulated.

Zero infrared reflectance anomaly in doped silicon lamellar gratings. I. From antireflection to total absorption

Abstract Zero-reflectance phenomenon for a binary lamellar grating on n-Si substrate irradiated by normally incident TE polarized plane electromagnetic wave of wavelength 10.6 μm is studied. The treatment is performed in the strong diffraction regime, where the structural dimensions and the wavelength are of the same order of magnitude, using data on the IR dielectric function of bulk doped silicon and a version of rigorous coupled-wave analysis. The evolution of normal reflectance zeros with increasing electron concentration from dielecric to metallic-like n-Si is traced. It is shown that the groove height undergoes sharp increase and the period shrinks when plasma wavelength becomes equal to the radiation wavelength. This marks the transition from the antireflection to the total absorption regime where most of incident power is absorbed in the grating region. The cavity-resonance origin of total absorption and satellite peaks in the spectral response are discussed.

The nature of the low-temperature minimum of resistivity in ceramic manganites

Abstract Electrical transport measurements were carried out on a ceramic samples of La 0.5 Pb 0.5 MnO 3 containing 10 at.% of Ag in a dispersed form and La 0.8 Sr 0.2 MnO 3 . Their resistivity at zero applied magnetic field exhibits a shallow minimum at the interval of T ∼25–30 K. This minimum shifts towards lower T upon applying a magnetic field ( H ) and disappears at a certain field H cr , while residual resistivity decreases notably with increasing of H . It is found that the bulk-scattering model is not adequate for describing of such behavior of ρ in the presence of H . It seems that the proposed model of charge-carrier tunneling between antiferromagnetically coupled grains accounts for the results obtained in spite of significant difference in the crystallinity (grain size) of the samples.

Inherent inhomogeneity in the crystals of low-doped lanthanum manganites

The X-band electron paramagnetic resonance (EPR) technique and the model analysis of the EPR susceptibility versus temperature were employed to characterize the dopant distribution in a number of La-manganite crystals, low doped with Ca, Sr, and Ba in a La site. Such distribution appears to be inhomogeneous as a result of technological-driven effect. It is emphasized that the above chemical disorder influences strongly both magnetic state and transport of the low-doped manganite crystals.

One-dimensional antireflection gratings in (100) silicon: a numerical study

The antireflection properties of V-grooved gratings in (100)crystalline silicon are studied numerically by use of rigorouselectromagnetic theory. This study shows that these gratings canexhibit antireflective behavior only for TM-polarizedradiation. The V-grooved structures are analyzed as a function ofgrating period, duty cycle, and depth of a SiO(2) mask layerthat is added to the tops of the V-grooved mesas. Specificantireflection grating designs (the duty cycle and depth versus theperiod) are presented that illustrate TM-polarized reflectivity muchless than 10(-3) with periods as high as 80% the wavelengthof incident radiation. These designs exhibit good tolerance tofabrication errors and gratings plane deviations in aplanar-diffraction mounting.

Silicon grating-based mirror for 1.3-μm polarized beams: matlab-aided design

A dielectric lamellar-grating layer-substrate structure is proposed to be capable, under some conditions, of acting as a 100% efficiency mirror when operated at fixed wavelengths and incidence angles. The design of such mirrors for 1.3 µm and near normal incidence is achieved with silicon as the grating-layer material and glass substrates of two types. The study is based on a new matrix-vector procedure for the solution of rigorous coupled-wave equations. The computations use MATLAB, and, in particular, its goal-attainment routine. Design parameter tolerances are also discussed.