E.A. Stepantsov

Weak links and dc SQUIDS on artificial nonsymmetric grain boundaries in YBa2Cu3O7−δ

We have studied weak links and dc–SQUIDs made from pulsed laser deposited YBa2Cu3O7−δ thin films on Y–ZrO2 bicrystal substrates. The transport properties of the weak links were studied as a function of the misorientation angle (θ) between the two halves of the bicrystal and an exponential dependence of the weak link critical current density was observed for angles up to 40° at 77 K. Josephson effects with clear microwave and magnetic field responses were observed. An optimum dc–SQUID performance at 77 K was obtained for θ=32°. At this temperature, we achieved a periodic magnetic field response with a modulation depth of 12 μV.

Microstructure of an artificial grain boundary weak link in an YBa2Cu3O7−σ thin film grown on a (100)(110), [001]-tilt Y-ZrO2 bicrystal

Abstract The microstructure of an artificial grain boundary in an YBa 2 Cu 3 O 7-σ (YBCO) thin film grown on a (100)(110), [001]-tilt yttria-stabilized-zirconia (YSZ) bicrystal substrate has been studied using transmission electron microscopy (TEM). The orientation relationship between the YBCO film and the YSZ substrate was [001] YBCO ‖[001] YSZ and [110] YBCO ‖[100] YSZ for each half of the bicrystal film. However, the exact boundary geometry of the bicrystal substrate was not transferred to the film. The substrate boundary was straight while the film boundary was wavy. In several cases there was bending of the lattice confined within a distance of a few basal-plane lattice spacings from the boundary plane and microfaceting. No intergranular secondary phase was observed but about 25% of the boundary was covered by c -axis-tilted YBCO grains and a -axis-oriented grains, both of which were typically adjacent to CuO grains or surrounded by a thin Cu-rich amorphous layer.

Low 1/f noise in YBa2Cu3O7 dc SQUIDs on (Y)ZrO2 bicrystal substrates

We report low noise operation of YBa2Cu3O7 SQUIDs superconducting quantum interference devices using Josephson junctions grown on bicrystal substrates of (Y)ZrO2. Energy sensitivities measured at 10 Hz (Se=4.5×10−29 J/Hz) were to our knowledge lower than previously reported for a YBa2Cu3O7 SQUID with practical loop size (∼40 μm). The 1/f part of the voltage noise reached a maximum at 85 K where the noise spectrum was essentially white. The 1/f noise increased both at lower temperatures due to increased critical current fluctuations (∼Ibias2.2) and at higher temperatures, where the flux noise from the film produces a peak below Tc(=89 K).

Microstructure and properties of artificial grain boundaries in epitaxial YBA2Cu3O7−δ thin films grown on [001] tilt YZrO2 bicrystals

Abstract The microstructure of artificial grain boundaries in YBa2Cu3O7−δ (YBCO) thin films grown on [001] tilt YZrO2 (YSZ) bicrystal substrates has been characterized using transmission electron microscopy and atomic force microscopy. Despite a relatively straight morphology of the substrate boundaries, the film boundaries were wavy. The waviness was a result of the combined effects of grooving at the substrate boundaries prior to the film deposition and an island-growth mechanism for YBCO on YSZ substrates. The dihedral angle of the groove walls varied with the misorientation angle and depended on the symmetry of the substrate boundary. The amplitudes of the film boundary waviness compared well with the widths of the grooves. In addition, the grooves induced local bending of the YBCO lattice planes and additional tilt components perpendicular to the c-axis close to the film boundaries.

Bicrystal junctions and superconducting quantum interference devices in YBa2Cu3O7 thin films

Josephson junctions and superconducting quantum interference devices (SQUIDs) were made by depositing thin films of YBa2Cu3O7 on bicrystal substrates of Y‐ZrO2 and SrTiO3. The critical current density of the junctions at 77 K could be adjusted from 100 to 106 A/cm2 by selecting bicrystals with misorientation angles θ from 45° to 0°. Current‐voltage curves from junctions with θ≳22° followed the resistively shunted junction model with noise rounding close to the transition temperature. The response of the critical current to magnetic fields was Fraunhofer‐like and the width (w) dependence was 1/w2 due to flux focusing effects. Shapiro steps under microwave radiation were observed. SQUIDs based on these junctions had energy resolutions at 77 K down to 8.6×10−30 J/Hz and a 10 Hz flux noise level down to 1.5×10−9 Φ20/Hz at 85 K. A SQUID of the Ketchen design with a flux focusing washer had a magnetic field sensitivity of 15 pT/√Hz at 77 K. The temperature dependence of the voltage modulation depth close to TC ...

YBa2Cu3Ox Josephson junctions on a bicrystal sapphire substrate for devices in the millimeter and submillimeter wavelength ranges

High-temperature superconducting Josephson junctions on bicrystal sapphire substrates were fabricated and investigated experimentally. The critical parameters of the junctions satisfy the constraints for the design of devices in the millimeter and submillimeter wavelength ranges. The results of dynamic measurements show that in these junctions the superconducting current exhibits a sinusoidal dependence on the phase difference of the superconducting wave functions of the electrodes, and a simple resistive model is used to analyze their microwave properties. At the same time, the temperature dependence of the critical current of the junctions differs appreciably from that typical of tunnel junctions with s-superconductors and may be explained as d-type pairing of the superconducting electrodes and an SNS junction.

On the possibility of usage of crystalline composites in investigations of high-Tc superconductivity

Potentialities of Solid Phase Intergrowing (SPI) of crystals [5] in conformity with the investigations of HTSC are discussed. In particular the application of SPI for creation of dielectric crystalline substrates containing model boundaries (low- or high-angle, single or multiple) perpendicular to their surfaces is analyzed. Both HTSC film structures with a single boundary of a given crystallographic orientation and plain shape, and systems of such boundaries in parallel rows or with triple joints are constructed on a base of this type substrates.

Phase dependence of the superconducting current in YBCO Josephson junctions on a bicrystal substrate

AbstractDependences of the amplitudes of the harmonic and subharmonic Shapiro steps on an external monochromatic signal were used to study the current-phase dependence of high-temperature superconducting junctions on a bicrystal substrate. It is shown that for a symmetric definition of the transport current across the junction with an edge transparency of the order of

Properties of YBCO junctions and squids on YSZ bicrystals

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