Superconducting YBa2Cu3O7 Films Research Articles

Large tunable lateral shift in prism coupling system containing a superconducting slab

A large and tunable lateral shift in a prism coupling system with a superconducting YBa2Cu3O7 film is theoretically analyzed. The dip of the reflectivity and magnitude of the lateral shift can be controlled by the temperature of the superconducting film. The sign of the lateral shift can be determined by the thickness of the superconducting film. The position of the minimum reflection and maximum Goos–Hanchen shift can be conveniently adjusted by the thickness of the dielectric layer and incident light frequency. The largest shift, as high as 1550 times the free space wavelength, is achieved for the incident light frequency $$\omega = 98$$ THz. The numerical calculation results from the Gaussian beam are in accordance with the theoretical results.

Pyrolysis study of solution-derived superconducting YBa2Cu3O7films: disentangling the physico-chemical transformations

Pyrolysis transformations, wrinkling and cracking, of thick solution-derived epitaxial superconducting YBa2Cu3O7films are disclosed throughin situanalytical studies.

Goos-Hänchen shift at the reflection of light from the complex structures composed of superconducting and dielectric layers

The Goos-Hänchen effect of light reflected from sandwich (three-layered) structures composed of a superconducting YBa2Cu3O7 film and two different dielectric films is investigated theoretically. It has been shown that optical anisotropy of YBa2Cu3O7 film, as well as its positions in the three-layer specimen, strongly effects on the lateral shift values. We have shown that, for all positions of the superconducting film in the three-layered structure, variation of temperature makes possible to control the values of the lateral shift of TE-polarized light at the incidence angles close to pseudo-Brewster angles, whereas for TM-polarized light the lateral shift is only significant at grazing incidence.

Dendritic instability in YBa2Cu3O7–δ films triggered by transient magnetic fields

Superconducting films of YBa2Cu3O7–δ are shown to become thermomagnetically unstable when experiencing a time-varying perpendicular magnetic field. Using magneto-optical imaging and ramping the applied field at rates up to 3000 T/s, dendritic flux avalanches were observed in two different films, one grown by evaporation on sapphire and one by laser ablation on SrTiO3. The unstable behavior occurs over a wide temperature range limited by an upper threshold value of 40 K for the film on sapphire, and 20 K for the one on SrTiO3. At 7 K for the same films, the threshold ramping rates are 1000 T/s and 3000 T/s, respectively. The avalanches are causing permanent damage by leaving a micron wide track where the superconductor melted during the thermomagnetic runaway.

Constrains of Super-Current Flow in YBCO Coated Conductors

High temperature superconducting YBa2Cu3O7 films have been prepared by pulsed laser deposition on top of single crystal substrates and metallic templates. Films have been investigated in order to determine the influence of microstructural peculiarities on the critical current density. It has been found that there is an inherent mechanism limiting the superconductive current flow in YBa2Cu3O7 film deposited on metallic template. This mechanism is associated with YBa2Cu3O7 film architecture, fabrication procedure and following low temperature usage.

Extended dislocation-based pinning mechanism in superconducting YBa2Cu3O7 films

To describe the critical current density (Jc) as the function of applied magnetic field (Ba) in high quality YBa2Cu3O7 (YBCO) superconducting films, the vortex pinning mechanism along the structural domain boundaries of the films is developed. The boundaries, assumed to have low misorientation angles, are quantitatively considered to consist of individual edge dislocations acting as pinning wells, rather than a continuous boundary. This extended model accurately describes the experimental Jc(Ba) over the wide field and temperature ranges. Marginal deviations of the model from the experimental Jc(Ba) curves are observed at high fields and temperatures where thermally activated depinning is significant. This pinning model is verified to provide precise structural properties of the films which can be obtained by other considerations.

Epitaxial (La, Sr)TiO3 on textured Ni–W as a conductive buffer architecture for high temperature superconducting coated conductor

The formation of epitaxial (La,Sr)TiO3 on biaxially-textured Ni–W metal alloy tape was examined as a conductive buffer layer for YBa2Cu3O7 film growth. A TiN epitaxial nucleation layer served as an effective template layer for subsequent (La,Sr)TiO3 film growth on the Ni–W tape. The TiN/(La,Sr)TiO3 multilayer was epitaxial on the Ni–W substrate as confirmed via four-circle X-ray diffraction. A high temperature superconducting YBa2Cu3O7 film was deposited epitaxially on the (La,Sr)TiO3/TiN/Ni–W tape. The YBa2Cu3O7 film exhibited a superconducting transition temperature of 86K and critical current density of 0.42×106A/cm2 at 77K.

Faceting of (001) CeO2 Films: The Road to High Quality TFA-YBa2Cu3O7 Multilayers

CeO2 films are technologically important as a buffer layer for the integration of superconducting YBa2Cu3O7 films on biaxially textured Ni substrates. The growth of YBa2Cu3O7 layers on the CeO2 cap layers by the trifluoroacetate (TFA) route remains a critical issue. To improve the accommodation of YBa2Cu3O7 on CeO2, surface conditioning or CeO2 is required. In this work we have applied ex-situ post-processes at different atmospheres to the CeO2 layers deposited on YSZ single crystals using rf sputtering. XPS analysis showed that post-annealing CeO2 layer in Ar/H2/H2O catalyses in an unexpected way the growth of (001)- terraces. We also report on the growth conditions of YBa2Cu3O7-TFA on CeO2 buffered YSZ single crystal grown by chemical solution deposition and we compare them with those leading to optimized YBa2Cu3O7-TFA films on LaAlO3 single crystals. Critical currents up to 1.6 MA/cm2 at 77 K have been demonstrated in 300 nm thick YBa2Cu3O7 layers on CeO2/YSZ system. The optimized processing conditions have then been applied to grow YBa2Cu3O7-TFA films on Ni substrates having vacuum deposited cap layers of CeO2.

High-power-density fault-current limiting devices using superconducting YBa2Cu3O7 films and high-resistivity alloy shunt layers

Switching of superconducting thin-film resistive fault-current limiting devices with alloy shunt layers was studied. Au–Ag alloy thin films, whose room-temperature resistivity is about six times higher than that of pure gold, were sputter deposited on YBa2Cu3O7 films on sapphire substrates with high critical current density of Jc=3.05±0.05MA∕cm2. A small sample, 5mm wide and 40mm long, had the capacity of a rated current of 32Arms in normal operation and withstood a high voltage of 107Vrms for 0.1s after switching, resulting in a very high switching power density of ∼1.7kVA∕cm2, which is more than four times higher than conventional devices using gold shunt layers.

Microstructures of YBa2Cu3O7 films prepared by magnetron sputtering onAl2O3 substratewith a CeO2 buffer layer

High-Tc superconducting YBa2Cu3O7 films with a CeO2 buffer layer, deposited onto sapphire substrates, were prepared by off-axis rf-magnetronsputtering. It is found that the microstructure of the buffer layer can be controlled by thesubstrate temperature, and is connected with the formation of the discontinuities in thefilm, which are the origin of micropores. The microstructural peculiarities of theYBa2Cu3O7/CeO2/Al2O3 films are studied and discussed.

Epitaxial growth of yttria-stabilised zirconia buffer layers on X-cut LiNbO3 for superconducting electrodes

We report on the epitaxial growth of yttria-stabilised zirconia (YSZ) buffer layers on X-cut LiNbO3 (LNO) single crystals by pulsed laser deposition. Despite the low chemical stability of the substrates at high temperature, high quality fully reproducible films were obtained over a relatively broad range of processing conditions. The films were (00h) out-of-plane single oriented and the in-plane edge of the YSZ unit cell was aligned with the polar axis of the LNO. However, the YSZ deposition also promoted the formation of the compound LiNb3O8. This compound is epitaxial and located at the interface. The homogeneous YSZ film presents a uniform surface, free of outgrowths and with a low roughness. These characteristics are suitable for the epitaxial growth of other oxides, as has been demonstrated with the preparation of YBa2Cu3O7/CeO2/YSZ/LNO heterostructures. The superconducting YBa2Cu3O7 films were epitaxial, with the c axis perpendicular to the surface and single in-plane orientation, and presented good transport properties (critical temperatures around 86 K and critical current densities close to 106 A/cm2 at 77 K).

PbZr0.52Ti0.48O3 and SrBi2Nb2O9 ferroelectric oxides integrated with YBa2Cu3O7 superconductor in multilayers epitaxially grown by pulsed laser deposition

Multilayers of PbZr 0.52 Ti 0.48 O 3 (PZT) or SrBi2Nb 2 O 9 (SBN) ferroelectrics (F) and YBa 2 Cu 3 O 7 (YBaCuO) superconductor (S) have been grown by pulsed laser deposition. F/S or S/F bilayers as well as S/F/S trilayers deposited on SrTiO 3 and MgO were epitaxially grown, as evidenced by x-ray diffraction (XRD) in θ-2θ and (p-scans modes, reflection high energy electron diffraction (RHEED) or electron channeling patterns (ECP). Superconducting YBaCuO films deposited on PZT exhibit a critical temperature, T c , of about 86 K slightly below the value routinely obtained in the same deposition conditions on bare (100)SrTiO 3 substrate (typically 88-89 K). By contrast, the T c of YBaCuO films on SBN, either on (100)SrTiO 3 or on (100)MgO is close to 88-89 K suggesting that SBN can be a good candidate as ferroelectric buffer layer for the growth of YBaCuO, especially on MgO for which a graphoepitaxial mechanism tends to limit the YBaCuO growth quality. In the case of F/S layers, hysteresis loops of PZT on YBaCuO show a saturated polarization larger than 30 μC/cm 2 and a coercive field of about 70 kV/cm. Secondary ion mass spectrometry (SIMS) experiments have been performed in order to correlate interdiffusion mechanisms with both structural data and physical properties.

Enhanced pinning in a magnetic-superconducting bilayer

Pinning of vortices in a high-temperature superconductor by the magnetic domain structure of a highly anisotropic ferromagnet is investigated by means of magnetic measurements in nanoscale period superconductor/ferromagnet (SC/FM) heterostructures. Two different samples consisting of highly epitaxial films of YBa2Cu3O7(SC) and BaFe12O19(FM) are analyzed relative to a pure superconducting YBa2Cu3O7 film. The irreversibility line obtained in the magnetic-field-reduced-temperature phase diagram for each heterostructure is found to shift upwards when compared to the line corresponding to the pure superconducting sample. This effect is interpreted as an evidence for the enhancement of pinning of vortices in the SC layer by the magnetic domain structure in the FM layer.

Nucleation of epitaxial yttria-stabilized zirconia on biaxially textured (001) Ni for deposited conductors

The nucleation of (001)-oriented yttria-stabilized zirconia (YSZ) directly on the (001) Ni surface is realized via nucleation on an oxygen-terminated nickel surface using pulsed-laser deposition. Under conditions where the nickel surface is either oxygen free or substantially covered with NiO, a mixed orientation of YSZ occurs. The epitaxial YSZ layer grown on a biaxially textured Ni(001) surface was used as a single buffer layer for a high temperature superconducting coated conductor architecture, yielding superconducting YBa2Cu3O7 films with high critical current densities, Jc. This architecture eliminates the necessity for a multilayer buffer architecture, since high Jc superconducting films are achieved with no intermediate buffer layer between the (001) YSZ and the biaxially textured metal.

Fabrication process and noise properties of antenna-coupled microbolometers based on superconducting YBCO films

An analysis of how the detectivity and lifetime depend on the fabrication process of superconducting antenna-coupled microbolometers has been carried out. The temperature dependences of responsivity and noise equivalent power (NEP) have been estimated in terms of the thermal model. To reveal the main degradation mechanism, 1/f-noise characterization has been used. Monte-Carlo simulation of the annealing procedure of YBa2Cu3O7 (YBCO) films for the operating ranges of frequency and temperature has shown that prevailing sources of flicker noise in superconducting microstrips are associated with transitions of oxygen atoms situated close to low-angle boundaries of the film blocks. The magnetron sputtering technique has been optimized to reduce the Hooge parameter for flicker noise to a record-breaking low value for YBCO films of about 10-4 at 93 K. Comparative analysis of chemical, ion and laser etching techniques by low-temperature scanning electron microscopy and magneto-optics allowed the fabrication of microstrips with uniform current distribution characterized by critical current density higher than 106 A cm-2 at 77 K and long-time stability. The process of low-energy ion milling of YBCO films with an Ar+ beam generated in a duopigatron ion source was used to reach a width resolution at the topology edge better than 0.2 µm. The antenna-coupled bolometers fabricated from the superconducting microstrips were used to register microwave radiation at a frequency of 70.3 GHz and temperature of 93 K. It is demonstrated that the developed technology makes possible the fabrication of long-lived YBCO-based antenna microbolometers with electrical NEPe = 1.5 × 10-12 W Hz-1/2. The calculated response time of the antenna is about 30-150 ns. Further development is associated with fabrication of coupling microbolometers with immersed lens, with predicted optical detectivity D* = (4 × 109 - 4 × 1010) cm Hz1/2 W-1 in the wavelength range 100-1000 µm.

Line impedance and propagation coefficient of narrow superconducting coplanar lines made of YBaCuO

The microwave properties of coplanar waveguides with line widths from 1 /spl mu/m to 40 /spl mu/m made of superconducting YBaCuO films with a thickness t=180 nm on LaAlO/sub 3/ are investigated. The line impedance Z/sub L/ and the normalized propagation coefficient /spl beta///spl beta//sub 0/ of these waveguides are measured between 45 MHz and 26.5 GHz at temperatures between 77.4 K and 92 K. The ratio of the line width w to the distance of the ground layers d is constant with w/d=0.2. Therefore, Z/sub L/ and /spl beta///spl beta//sub 0/ are independent of w for perfectly conducting waveguides. For superconducting waveguides it is found that Z/sub L/ and /spl beta///spl beta//sub 0/ differ from the values of perfectly conducting waveguides. They increase for smaller line widths at a constant temperature. At w=1 /spl mu/m and T=80 K, Z/sub L/ and /spl beta///spl beta//sub 0/ are nearly twice as high as calculated for perfect conductors. Furthermore, Z/sub L/ and /spl beta///spl beta//sub 0/ increase with the temperature. It is shown that these effects are attributed to an increase of the inductance per unit length L' due to the superconducting material, whereas the capacitance per unit length C' behaves like C' of perfectly conducting waveguides. Using these results, the dimensions of the superconducting waveguides, which are necessary to obtain a desired Z/sub L/ at a given line width w, are calculated.

Microwave characterization of YBa2Cu3O7−x thin films grownin situ by Off-axis magnetron sputtering

Superconducting films of YBa2Cu3O7−x were depositedin situ on LaAlO3 substrates using single-target 90° off-axis sputtering. The obtained films have tipicalT c values of 91K. Surface resistance measurements on as-grown films reach 1.1 mΩ at 77K and 10GHz; whilst on ion-etched patterned resonant linesR s (77K, 10GHz) it is about 10mΩ.

Bolometric properties of YBaCuO films on mica substrates

The structural, noise and bolometric properties superconducting YBaCuO films on mica substrates are reported. The bolometer based on that film had the detectivity D ∗=2,8·10 8 W -1· Hz 1 2 ·cm at modulation frequency 10 Hz.

Y-Ba-Cu-O/PZT Current Controllable Distributed RC-Element

ABSTRACTA superconducting, current controllable, distributed RC-component was designed and fabricated. The component consisted of YBa2Cu3O7 (YBCO) thin film resistor, which was covered with a dielectric layer and an electrode to form a capacitor. The YBCO thin film was deposited by pulsed laser ablation on a SiTiO3 (100) substrate. It was patterned by photolithography and wet etched to form a tapered strip. This YBCO strip was covered with a lead zirconate titanate layer made by laser ablation and, finally, the dielectric layer was covered with a gold electrode by vacuum evaporation. The electrical characteristics of the superconducting YBCO film and the -element were measured.Using the constructed component, high-pass and notch filter circuits were demonstrated. It was possible to control the electrical properties of these filters by a dc-current applied through the YBCO strip which causes the superconducting film to be come partly resistive.

Microwave surface impedance at 10 GHz and quasiparticle scattering in YBa2Cu3O7 films

The surface impedance of superconducting YBa2Cu3O7 films as a function of temperature at 10 GHz has been measured in a parallel plate resonator geometry. The penetration depth λ(T), complex microwave conductivity σ(T), and quasiparticle scattering rate 1/τ(T) were also determined. After a rapid fall as T is lowered below Tc, the surface resistance Rs exhibits a linear dependence from 65 K down to 6 K. As T drops below Tc, the real part of the conductivity σ1 has a rapid rise, which is attributed to the observed dramatic increase in τ. The normal-fluid density shows a linear behavior at low temperatures, which is inconsistent with s-wave BCS superconductivity.