Induced Superconductivity in Hybrid Au/YBa2Cu3O7-x Electrodes on Vicinal Substrates

Superconducting electrodes are an integral part of hybrid Josephson junctions used in many applications including quantum technologies. We report on the fabrication and characterization of superconducting hybrid Au/YBa2Cu3O7-x (YBCO) electrodes on vicinal substrates. In these structures, superconducting CuO2-planes face the gold film, resulting in a higher value and smaller variation of the induced energy gap compared to the conventional Au/YBCO electrodes based on films with the c-axis normal to the substrate surface. Using scanning tunneling microscopy, we observe an energy gap of about 10-17 meV at the surface of the 15- nm-thick gold layer deposited in situ atop the YBCO film. To study the origin of this gap, we fabricate nanoconstrictions from the Au/YBCO heterostructure and measure their electrical transport characteristics. The conductance of the nanoconstrictions shows a series of dips due to multiple Andreev reflections in YBCO and gold providing clear evidence of the superconducting nature of the gap in gold. We consider the Au/YBCO electrodes to be a versatile platform for hybrid Josephson devices with a high operating temperature

Ultra-thin YBa2_{2}Cu3_{3}O7−x_{7-x} films with high critical current density

Despite impressive progress in the development of superconducting nanowire single-photon detectors (SNSPD), the main obstacle for the widespread use of such detectors is the low operating temperature required for low-temperature superconductors. The very attractive idea of increasing the operating temperature using high-temperature superconductors for SNSPD fabrication is problematic due to the insufficient quality of ultra-thin films from high-temperature superconductors, which is one of the key requirements for the single-photon detection by superconducting nanowires. In this work, we demonstrate the possibility of fabricating ultra-thin YBa2Cu3O7−x films on SrTiO3 substrates with a surface flatness of ±1 unit cell and a high critical current density up to 14 MA cm−2 at T = 78 K. The critical current density of ultra-thin films had very low value in the first three unit cell layers adjacent to the substrate and reached nearly the bulk value at the fifth layer. 97% of the superconducting current is carried by only two upper layers of a 5-unit-cell thick YBa2Cu3O7−x film. Due to such superconducting current distribution over the film thickness and good surface flatness 5-unit-cell thick YBa2Cu3O7−x films could be promising for the fabrication of single-photon detectors

Testing of Josephson Spectrometer with Waveguide Coupling

One of the challenges in public security is the quick and reliable identification ofthreat liquids in bottles, when vapour analysis is not possible. Recently, we demonstrated that itis possible to rapidly identify liquids by EM measurements of their dielectric functions in thesub-THz range with a high-Tc Josephson spectrometer. Following this approach, we havedeveloped a Josephson spectrometer with a new radiation coupling system, based on dielectricwaveguides. In this paper, we present the results of spectroscopic measurements on liquidsamples of various purities including 30% H2O2/H2O, performed using our Josephsonspectrometer with waveguide coupling. Also, the signal and noise characteristics of a classicalJosephson detector used in our liquid identifier were numerically simulated and the powerdynamic range was estimated for a wide spread of junction parameters

Identification of Liqiuds by High-Tc Josephson THz Detectors

AbstractFast and reliable detection of liquids will be required for future checkpoint screening techniques. Recently, a new electromagnetic-wave concept based on our high-Tc Josephson detectors and Hilbert spectroscopy has been suggested to distinguish between liquids. This technology covers a spectral range of main dispersions of liquids, from a few GHz to a few THz, and thus significantly enhances reliability of identification. The high-Tc detectors, due to a power dynamic range of more than five orders, might guarantee short identification times. Several demonstration set-ups of liquid identifiers, consisting of high-Tc Josephson detectors, integrated in Stirling coolers, and polychromatic radiation sources, have been developed and characterized. Reflection polychromatic spectra of various liquids in plastic containers have been measured at the spectral range of 15-500GHz with total scanning time down to 0.2 second. Reliable identification of liquids, both benign and threat, within an accuracy of 0.3% was demonstrated using water as a reflectance reference. The reflectance values for 30%H2O2/H2O solution at frequencies of 30 and 100GHz were practically undistinguishable from that of for pure water, but an increase of the relative reflectance from 1.017 at 282GHz to 1.033 at 434GHz has been found. Last circumstance will be used for optimization of the identifiers

Terahertz Applications of Hilbert-Transform Spectral Analysis

Bridging of the terahertz gap in the electromagnetic spectrum between the microwave and infrared ranges requires a variety of new technological developments from basic elements, such as emitters and detectors, to complete systems, such as spectrum analyzers and imagers. As an example of these developments, Hilbert-transform spectral analysis of terahertz radiation sources has been demonstrated. A spectrum analyzer based on a high- Tc square-law Josephson detector has been developed and characterized in the frequency range from 50 to 1800 GHz. Spectra of output terahertz radiation from optically-pumped lasers and frequency multipliers have been studied, and their regimes were optimized for a single-frequency operation. Starting from the optimized multipliers, a polychromatic source has been synthesized and characterized with Hilbert-transform spectrum analyze