E. Farber

Enhanced Cooper pairing versus suppressed phase coherence shaping the superconducting dome in coupled aluminum nanograins

Uwe S. Pracht, ∗ Nimrod Bachar, 3, 4 Lara Benfatto, Guy Deutscher, Eli Farber, Martin Dressel, and Marc Scheffler 1. Physikalisches Institut, Universität Stuttgart, Germany Department of Quantum Matter Physics, University of Geneva, Switzerland Laboratory for Superconductivity and Optical Spectroscopy, Ariel University, Israel Raymond and Beverly Sackler School of Physics and Astronomy, Tel Aviv University, Israel ISC-CNR and Department of Physics, Sapienza University of Rome, Italy (Dated: August 20, 2015)

Evidence for a bulk complex order parameter in Y0.9Ca0.1Ba2Cu3O7-δ thin films

We have measured the penetration depth of overdoped Y0.9Ca0.1Ba2Cu3O7−δ (Ca-YBCO) thin films using two different methods. The change of the penetration depth as a function of temperature has been measured using the parallel-plate resonator (PPR), while its absolute value was obtained from a quasi-optical transmission measurement. Both sets of measurements are compatible with an order parameter of the form Δdx2 − y2 + iδdxy, with Δ = 14.5 ± 1.5 meV and δ = 1.8 meV, indicating a finite gap at low temperature. Below 15 K, the drop of the scattering rate of uncondensed carriers becomes steeper in contrast to a flattening observed for optimally doped YBCO films. This decrease supports our results on the penetration depth temperature dependence. The findings are in agreement with tunneling measurements on similar Ca-YBCO thin films.

Optical signatures of the superconducting Goldstone mode in granular aluminum: Experiments and theory

Recent advances in the experimental growth and control of disordered thin films, heterostructures, and interfaces provide a fertile ground for the observation and characterisation of the collective superconducting excitations emerging below

Attenuated Total Reflectance (ATR)-FTIR spectral measurements in MIR and FIR (THz) range

T_c

VHF multi-channel coupler for RF communication

after breaking the

Quasi-dynamical multi-channel coupler based on high temperature superconducting films

U(1)

High sensitivity high Tc superconducting Josephson junction antenna for 200 GHz detection

gauge symmetry. Here we combine THz experiments in a nano-structured granular Al thin film and theoretical calculations to demonstrate the existence of optically-active phase modes, which represent the Goldstone excitations of the broken gauge symmetry. By measuring the complex transmission trough the sample we identify a sizeable and temperature-dependent optical sub-gap absorption, which cannot be ascribed to quasiparticle excitations. A quantitative modelling of this material as a disordered Josephson array of nano-grains allows us to determine, with no free parameters, the structure of the spatial inhomogeneities induced by shell effects. Besides being responsible for the enhancement of the critical temperature with respect to bulk Al, already observed in the past, this spatial inhomogeneity provides a mechanism for the optical visibility of the Goldstone mode. By computing explicitly the optical spectrum of the superconducting phase fluctuations we obtain a good quantitative description of the experimental data. Our results demonstrate that nanograins arrays are a promising setting to study and control the collective superconducting excitations via optical means.

Phase shift combiner for multi-channel VHF communication

Mid-Infrared (MIR) spectroscopy is an extremely reliable and well recognized fingerprinting method. Far-Infrared (FIR) and THz spectroscopy is quite difficult since it requires special sources, quasi optics, special materials and sensitive detectors. The technique of Attenuated Total Reflectance (ATR) has in recent years revolutionized solid and liquid sample analyses because it combats the most challenging aspects of infrared analyses, namely sample preparation and spectral reproducibility. An attenuated total reflection accessory operates by measuring the changes that occur in a totally internally reflected infrared beam when the beam comes into contact with a sample. In this work a spectral measurements using the ATR-FTIR technique will be presented. Spectral measurements of liquids and powders in the THz regime will be discussed and analyze. Furthermore, we will present ATR-FTIR spectral measurements that were carried out for commercial companies.

Improving Radar's Spatial Recognition: A Radar Scanning Method Based on Microwave Spatial Spectral Illumination

The transmission and receiving of several channels via a single antenna is a long standing problem. We have developed a multi-channel coupler in the VHF frequency range enabling to reduce the number of antennas to one third of channels number used at one time. The system is based on a meander stripline used for each coupling channel. The channels were matched simultaneously to a single antenna using a controlled capacitor banks located on each channel. The multi coupler performance shows low insertion loss and low return loss for each channel attached to the antenna.

Publisher's Note: Effect of Coulomb interactions on the disorder-driven superconductor-insulator transition [Phys. Rev. B89, 035149 (2014)]

In the present work high temperature superconducting (HTSC) technology is implemented as a microwave coupler. The technology is realized in both UHF and VHF frequency range using a quasi-dynamical communication system. The application of HTSC in RF has many advantages, such as low losses, high power transfer and high coupling. The growing demand for multichannel and multipurpose communication systems requires multichannel solutions. However, multiple channels require multiple antennas, yet the number of antennas in communication systems is limited. Increasing the number of antennas can lead to interference and mutual coupling. Therefore, we developed a multi-channel communication system in which the frequency of each channel can be dynamically tuned in the system frequency range. The system is capable of transmitting several channels simultaneously, thus a single antenna serves several channels. It is used for high power transmission and is realized by a quasi-dynamical variable-matching unit based on a HTSC coupler.