A. Andreone

Experimental evidence of s-wave superconductivity in bulk CaC6

The temperature dependence of the in-plane magnetic penetration depth, lambda(ab)(T), has been measured in a c-axis oriented polycrystalline CaC(6) bulk sample using a high-resolution mutual inductance technique. A clear exponential behavior of lambda(ab)(T) has been observed at low temperatures, strongly suggesting isotropic s-wave pairing. Data fit using the standard BCS theory yields lambda(ab)(0) = (720 +/- 80) A and delta(0) = (1.79 +/- 0.08) meV. The ratio 2delta(0)/k(B)T(c) = (3.6 +/- 0.2) gives indication for a weakly coupled superconductor.

Optical sensing using dark mode excitation in an asymmetric dimer metamaterial.

We study the presence of dark and bright modes in a planar metamaterial with a double rod unit cell introducing geometric asymmetry in rod lengths. The dark mode displays a Fano-type resonance with a sharp asymmetric profile, rendering it far more sensitive than the bright mode to slight variations of the dielectric environment. This peculiar feature may envisage the possible application of the asymmetric dimer metamaterial as an optical sensor for chemical or biological analysis, provided that the effect of material losses on the dark mode quality factor is properly taken into account.

In situ growth and superconducting properties of YNi2B2C thin films

Thin films of the recently discovered intermetallic superconducting compound YNi2B2C have been grown in situ using a magnetron sputtering technique. High quality, c‐axis oriented, films were obtained on MgO substrates held at about 800 °C during the sputtering process. The best films showed maximum Tc=15.25 K (onset), a transition width of ≊0.3 K, a room‐temperature resistivity of 53±3 μΩ cm, a residual resistivity ratio up to ≊5.4, a low‐temperature critical current Jc≊105 A/cm2 and Bc2≥6 T. Superconducting films were also obtained on sapphire and LaAlO3 substrates.

Surface impedance measurements of superconducting (NbTi)N films by a ring microstrip resonator technique

In the framework of the search for new materials for sputter coated superconducting rf cavities for particle accelerators, an innovative method to measure the rf properties of superconducting films, based on an inverted microstrip ring resonator technique, is presented. Test measurements on well characterized Nb sputtered films show excellent agreement with the Bardeen, Cooper and Schrieffer theory and prove the good resolution of the method. New results obtained by this technique on the surface impedance of (NbTi)N reactively sputtered films, including the temperature dependence and the rf field amplitude dependence of the surface resistance and the temperature dependence of the magnetic field penetration depth, are then presented and discussed.

Single and double side YBCO thin films for x-band microwave filters and devices

The properties of high quality single side and double side YBa2Cu2O7-δ (YBCO) thin films deposited on LaA1O3 substrates by pure oxygen d.c. sputtering are reported. The single side films are highly c-axis oriented with their a (or b) axis parallel to that of the substrate. The critical temperature is higher than 91 K with transition width less than 0.5 K, while the critical current density Jc is higher than 3 MA/cm2 at 77 K. The best double side samples exhibit no appreciable differences in the superconducting properties of the films deposited on the two different sides. X-ray analyses show in both cases highly c-axis oriented thin films with comparable values of the c-axis length (1.169 nm). The microwave properties are tested by a microstrip resonator technique. The surface resistance is lower than 80 μΩ at 77 K and f=5.4 GHz while the penetration depth at low temperature is in the range 150-200 nm.

Dual mode cross-slotted filters realized with superconducting films

A planar superconducting single stage dual mode filter has been investigated and tested. The basic element of the device is a square patch resonator diagonally crossed by unequal slots to provide both a size reduction and a simple way to couple the two degenerate modes. The effect of further cuts, realized on the conductor surface, is also investigated with respect to the power handling capability and miniaturization requirements. Two different filter topologies operating in C band with 1% fractional bandwidth have been designed and fabricated using Nb and YBa2Cu3O7 films grown on 10×10×0.5 mm3 LaAlO3 (100) substrates. Device response is studied performing power and intermodulation measurements. Third order products start to appear above the noise floor (−120 dBm) at input power Pin≈−20 dBm, whereas thermomagnetic breakdown is observed above 20 dBm.

Selected Topics in Photonic Crystals and Metamaterials

Introduction to Photonic Crystals and Metamaterials (C Ciminelli) Out-of-Plane Propagation in Photonic Quasi-Crystals: Guided Resonances (A Ricciardi et al.) Photonic Molecules Organized by Light (J Ng et al.) EBG Superstrates for Directivity Enhancement of Antennas (F Frezza et al.) Transformation Electromagnetism (G Dupont et al.) Cloaking in Terms of Nonradiating Cancelling Currents (E Martini et al.) Photonic Crystals for Biosensing (B T Cunningham et al.) Slow Light in Negative Permeability Metamaterial Waveguides (S Savo et al.) Fabrication of 2D and 3D Photonic Crystals (E Kuramochi) and other papers.

Microwave intermodulation distortion of MgB2 thin films

The two-tone intermodulation arising in MgB2 thin films deposited in situ by planar magnetron sputtering on sapphire substrates is studied. Samples are characterized using an open-ended dielectric puck resonator operating at 8.8 GHz. The experimental results show that the third-order products increase with the two-tone input power with a slope ranging between 1.5 and 2.3. The behavior can be understood introducing a mechanism of vortex penetration in grain boundaries as the most plausible source of nonlinearities in these films. This assumption is confirmed by the analysis of the field dependence of the surface resistance, that show a linear behavior at all temperatures under test.

Experimental evidence of cut-wire-induced enhanced transmission of transverse-electric fields through sub-wavelength slits in a thin metallic screen

Recent numerical studies have demonstrated the possibility of achieving substantial enhancements in the transmission of transverse-electric-polarized electromagnetic fields through subwavelength slits in a thin metallic screen by placing single or paired metallic cut-wire arrays at a close distance from the screen. In this paper, we report on the first experimental evidence of such extraordinary transmission phenomena, via microwave (X/Ku-band) measurements on printed-circuit-board prototypes. Experimental results agree very well with full-wave numerical predictions, and indicate an intrinsic robustness of the enhanced transmission phenomena with respect to fabrication tolerances and experimental imperfections.

A metal-organic chemical vapor deposition approach to double-sided Tl2Ba2Ca1Cu2O8 superconducting films on LaAlO3(100) substrates

Double-sided Tl2Ba2CaCu2O8 (Tl-2212) films for device applications have been fabricated through thallium vapor diffusion into BaCaCuOF matrices deposited by a novel metal-organic chemical vapor deposition (MOCVD) process onto 10 × 10 mm2 LaAlO3 (100) substrates. The present approach uses a multimetal molten single source in a monocomponent hot-wall MOCVD reactor whose geometry allows simultaneous and uniform film growth on both sides of the substrate. Both sides are epitaxially coated by homogeneous and monophasic Tl-2212 films, which, even more importantly, have comparable superconducting and transport properties.