YBa2Cu3O7 Films Research Articles

Electric field-induced oxygen vacancies in YBa2Cu3O7.

The microscopic doping mechanism behind the superconductor-to-insulator transition of a thin film of YBa2Cu3O7 was recently identified as due to the migration of O atoms from the CuO chains of the film. Here, we employ density-functional theory calculations to study the evolution of the electronic structure of a slab of YBa2Cu3O7 in the presence of oxygen vacancies under the influence of an external electric field. We find that, under massive electric fields, isolated O atoms are pulled out of the surface consisting of CuO chains. As vacancies accumulate at the surface, a configuration with vacancies located in the chains inside the slab becomes energetically preferred, thus providing a driving force for O migration toward the surface. Regardless of the defect configuration studied, the electric field is always fully screened near the surface, thus negligibly affecting diffusion barriers across the film.

Depression of critical temperature due to residual strain induced by PLD deposition on YBa2Cu3O7-δ thin films

We present the study of a high Tc superconductor under residual strain. We study the growth of a series of thin films of YBa2Cu3O7−δ (YBCO) using the Pulsed Laser Deposition (PLD) technique. The samples exhibit a residual in-plane compressive strain, whose degree depends on the growth conditions and the thickness of the film, and which alters the superconducting behavior. A thorough characterization of the system, correlating structural and superconducting properties is presented. Raman spectroscopy is introduced to characterize the samples and rule out oxygen loss effects. A possible explanation for the nearly linear depression of the critical temperature Tc with c-axis expansion was introduced, in terms of the mutual Coulomb screening of charge fluctuations along the c-axis, between consecutive CuO2 planes in the structure.

Improvement of the Delamination Strength of Yttrium Barium Copper Oxide (YBCO) Films by the Hamaker Method

Failure of yttrium barium copper oxide (YBCO) coated conductors (CC) tapes usually manifests as delamination occurring majorly in the YBCO films. Because the delamination strength of any material is greatly influenced by its microstructure, a good understanding of the intermolecular interactions in the YBCO films is essential to achieve the desired control of the delamination of YBCO CC tapes. Our previous works on the delamination behavior of multilayered YBCO CC tapes showed that the Hamaker based-models is viable for investigating the damage characteristics of YBCO films. Therefore, in this article, we investigated the intermolecular interactions of the constituent molecules of YBa2Cu3O7 films by Hamaker method. Then, used the deductions for the combining laws of the Hamaker coefficients for the interacting molecules to uncover and eliminate the interactions that cause the microstructural defects in the YBCO films. Our results show that increasing or decreasing the energy of the intervening medium between the interacting molecules to specific critical values eliminates the identified microstructural defects in the YBCO films. In particular, the elimination of the natural separation phenomenon among interacting molecules of the YBCO films improves its delamination strength significantly. Although based on our previous works, this technique had good agreement with the numerical, closed-form solution, and X-rays diffraction methods; further experimental validation is still under construction.

Overcoming optimization constraint for J c by hybrid pinning in YBa2Cu3O7 films containing nanorods

Critical current density (J c) in YBa2Cu3O7 films are improved by nanorods. J c increases with increasing the nanorod content up to an optimum content, and decreases after exhibiting a maximum due to degradation of the nanorod structure. To overcome this optimization constraint, hybrid pinning consisting of multiple types of pinning centers was investigated. In the present study, Y2O3 nanoparticles were additionally introduced into the YBa2Cu3O7 films containing high density BaHfO3 nanorods to increase the effective matching field. As a result, the global pinning force maximum was shifted to high magnetic field, and the J c was improved especially in high magnetic field. Thus, even in the case that the J c improvement in the YBa2Cu3O7 + BaHfO3 was difficult by increasing the nanorod content, the Y2O3 addition successfully improved the J c. This demonstrates that the hybrid pinning can overcome the optimization constraint for J c in the YBa2Cu3O7 films containing nanorods.

До кінетики руйнування надпровідного стану нелінійного копланарного хвилеводу на основі плівки високотемпературного надпровідника

Subject and Purpose. The mechanism of destruction of the S-state of a nonlinear high-temperature superconductor as part of a coplanar waveguide has not been properly elucidated as the effect of avalanche-type transition to a highly dissipative state, which was experimentally detected by the authors, takes place. The present work is concerned with the development of an appropriate approach describing kinetics of destruction of the S-state of a nonlinear high-temperature superconductor in a coplanar waveguide with allowances made for an inhomogeneous distribution of the microwave current in the superconducting film strip. Methods and Methodology. Use of I.B. and O.G. Vendiks’ reasoning [2] is made on kinetics of the destruction of the superconducting state of a wide film when a direct current governed by the time-dependent Ginzburg-Landau equation is applied. Keeping unchanged their idea as to the S–N boundary forming in the film strip with the boundary movement to the middle of the strip, the S–N boundary motion equation is obtained for a coplanar waveguide, proceeding in doing this from the motion equation of magnetic flux vortices under certain restrictions specified. Results. The time of S-state destruction has been numerically estimated: 1) for a wide superconducting film of YBa2Cu3O7–d composition, the destruction is by the direct current and 2) for a coplanar waveguide based on the same film, the destruction is by the microwave current. When the superconductivity is small (I / I c ³ 1), the destruction time values in both cases are close to each other within the order of magnitude. Conclusion. It is for the first time that the S-state destruction time in a coplanar waveguide has been expressed in terms of the microwave current distribution in the waveguide. It has been shown that this characteristic linearly depends on the ratio between the critical current and the microwave current amplitude in contrast to a quadratic dependence obtained for a superconducting strip with a direct current.

Complexes of Parallel Grain Boundaries in YBa2Cu3O7 Film for Josephson Junction Chains and Arrays

Substrates consisting of five parallel planar grain boundaries (GBs), oriented perpendicular to the surface and spaced by several micrometers, have been grown by solid-phase bonding of fianite crystals in order to obtain large complexes of closely spaced bicrystal Josephson junctions based on high-temperature superconductor (HTSC) films. The substrates had a crystallographic orientation (100) and dimensions of 1.0 × 10.0 × 10.0 mm3. All GBs were of symmetrical type, and their lattices were rotated by 12° in opposite directions around the axis perpendicular to the surface. The distance between GBs in a packet complex was 15 µm, and this value was maintained with an error of no more than 1 µm along their entire length of 10 mm. The deviation of the shape of all five GBs from an ideal geometric plane was within 1 µm along their entire length. Films of HTSC YBa2Cu3O7 with inheritance of GBs were grown on these substrates. Structures of two types were formed on the films using lithography. It is shown that the use of these fianite substrates in HTSC-based devices of cryogenic electronics increases significantly the density of bicrystal Josephson junctions; reduces several times the total length of superconducting lines connecting these junctions; and, correspondingly, decreases significantly the inductive resistance of these circuits and improves their electrical characteristics in comparison with the structures having similar functions but based on one or two parallel GBs.

Large artificial ferromagnetic dot arrays for the critical current enhancement in superconducting YBa2Cu3O thin films

In order to enhance and/or control critical current density (Jc) in superconducting YBa2Cu3O (YBCO) thin films, different arrays of 3 µm large ferromagnetic (iron) dots with differing configurations and shapes have been deposited on top of high-quality YBCO thin films post-buffered with a layer of CeO2. Some tremendous Jc enhancement of up to nearly 100% have been obtained at high temperatures and low fields. However, the Jc performance is strongly dependent on the array configurations, shape and amount of ferromagnetic iron involved. We show that it is possible to enhance Jc at high or low magnetic field ranges. The results are clearly different to similar non magnetic array structures used to previously manipulate Jc in YBCO films, which proves the magnetic origin of the changes in Jc we observed. The enhancement is likely due to the flux localization and magnetic pinning effects, rather than magnetic shielding alone, which is effective at relatively low fields only. The results also suggest that the observed Jc changes depend on rather minor variations in initial pinning and corresponding Jc levels of the films. At the same time a common trend for all of the various investigated magnetic arrays could not be established due to explained factors.

The Study of Switching Dynamics in Planar Structures Based on Epitaxial Films of YBa2Cu3O7-δ High-Temperature Superconductor

We have been studying the dynamic effects of bipolar resistive switching (BERS) in memristive planar heterostructures based on c-oriented epitaxial films of the high-temperature superconductor YBa2Cu3O7 (YBCO). We have been observing the suppression of the memristive properties of the structures under sinusoidal and pulse loads and the nucleation and the evolution of the regions of current density and electric field in the structures under study. We found that the limiting frequencies of a sinusoidal type load for observing the switching effect are frequencies of about 104 Hz. It has been shown that the percolation channel is formed by the appearance of electric field domains in which the electric field threshold is reached. The switchings are controlled by two processes, with time t < ms and a longer time of the order of a few seconds. Possible physical models of the observed phenomena are being discussed.

Simultaneous achievement of high Jc and suppressed Jc anisotropy by hybrid pinning in YBa2Cu3O7 three-phase-nanocomposite film

Nanoscale pinning centers are introduced into YBa2Cu3O7 (YBCO) films and tapes to improve vortex pinning and critical current density (Jc) for coated conductor application. While pinning with a single type of pinning center has been mainly investigated, hybrid pinning with multiple types of pinning center is expected to be more promising for simultaneously achieving high Jc values and suppressing Jc anisotropy. In the present study, a three-phase-nanocomposite film consisting of an YBCO matrix, BaHfO3 nanorods and Y-O nanoparticles was fabricated. A global pinning force maximum (Fp,max, where Fp = JcB) of 1.57 TN m−3 at 4.2 K, which is as high as the record level of Fp,max, was achieved by the hybrid pinning of BaHfO3 nanorods and Y-O nanoparticles. Furthermore, the hybrid pinning improved the angular dependence of Jc. The pinning contribution from nanoparticles increased with lowering temperature, which can explain the high Jc at low temperature. Thus, the present study successfully demonstrates a highly effective structure that can simultaneously achieve suppressed Jc anisotropy and a record level of Jc.

Transport, AC susceptibility, DC magnetization, and magnetic relaxation studies of YBa2Cu3O7 films with synergetic pinning centers grown by PLD

We have grown, by Pulsed Laser Deposition (PLD), a large number of YBa2Cu3O7 films with artificial pinning centers, with various impurities, various architectures and thickness, and various techniques of nano-scale pinning engineering: substrate decoration, BaZrO3 (BZO) nano-inclusions, and (quasi) multilayer architecture. Here we will present the results regarding vortex matter, dynamics, and pinning, in some of our best samples. Magnetic relaxation studies with magnetic field perpendicular to the film show that in both cases the splayed defects and/or nanoscale inclusions help reduce the dissipation in certain field-temperature range, by inhibiting the detrimental double vortex-kink formation. The response of the vortex system to AC excitation is rather complex but extremely useful for the characterization of the vortex dynamics. We have measured AC susceptibility in various DC fields, with various AC fields and frequencies and found that the effective vortex activation energy [Formula: see text] has a logarithmic dependence on the AC-field-induced current density [Formula: see text]. Synergetic pinning centers assured a low anisotropy of the critical current for various field orientations, a property desired in coil/solenoid applications.

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.

Dominant factors for the pinning enhancement by large artificial partial and complete antidots in superconducting films

Partially (blind) or fully perforated antidots (BADs or ADs, respectively) fabricated by laser lithography and ion beam etching in superconducting YBa2Cu3O7 (YBCO) films possess a cumulative circumference wall surface, which is found to be responsible for pinning vortices and/or magnetic flux, whereby increasing the critical current density (Jc) relative to corresponding plain (unpatterned) films. Using a variety of contrastingly shaped, relatively large 2–5 μm BADs and ADs, the Jc of YBCO thin films has been effectively increased within the relatively narrow band of wall surfaces of antidots, independent whether patterns are AD or BAD type. Independence of antidot types indicates that enhancement is insensitive whether magnetic flux is inside the ADs, or vortices are inside the BADs. Within this AD wall surface band region a clear shape dependence also emerges. This finding may also provide a guide for superconducting devices requiring maximal Jc and reduced associated vortex movement noise.

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.

High-Temperature Superconducting Multimode Dual-Ring UWB Bandpass Filter

A novel multimode dual-ring ultrawideband (UWB) bandpass filter is proposed in this article, which is constructed by loading open stubs in the horizontal and vertical directions of the dual-ring resonator. Five modes are evenly distributed in the passband, and a pair of transmission zeros are introduced to the left and right transition bands to enhance selectivity. Parallel-coupled lines ensure external coupling strength for realizing the UWB, and a cross junction suppresses spurious in high frequencies to expand the upper stopband. For demonstration, a quintuple-mode high-temperature superconducting UWB bandpass filter is designed on the 0.5 mm thick MgO substrate with double-sided YBa2Cu3O7 (YBCO) films. The test results show that the 3-dB bandwidth covers 2.56 to 11.15 GHz, the in-band return loss greater than 15 dB.

An HTS power switch using YBCO thin film controlled by AC magnetic field

This report is on the design of and results from a fast-acting, high power density high temperature superconducting switch. The switch uses thin films of YBa2Cu3O7−x on a sapphire substrate switched into the off-state through application of an AC magnetic field to the superconductor, which causes any transport current to experience a dynamic resistance. Results show reliable and repeatable switching of a 10 × 30 mm section of thin film between an on-state with Ic of 100 A and an off-state of 9 mΩ, with off-state voltage exceeding 100 mV. On-state to off-state transition time is less than 1 ms and off-state to on-state transition time is around 15 ms. These results are promising for further development of a high power, fast-acting superconducting power switching device for use in applications such as flux pumps.

Superconductive REBCO Thin Films and Their Nanocomposites: The Role of Rare-Earth Oxides in Promoting Sustainable Energy

The lossless transmission of direct electrical currents in superconductors is very often regarded as an ‘energy superhighway’ with greatly enhanced efficiency. With the discovery of high temperature superconductors (HTS) in the late eighties, the prospect of using these materials in efficient and advanced technological applications became very prominent. The elevated operating temperatures as compared to low temperature superconductors (LTS), relaxing cooling requirements and the gradual development of facile synthesis processes raised hopes for a broad breakthrough of superconductor technology. The impact of superconductor technology on the economy and energy sectors is predicted to be huge if these are utilized on a large scale. The development of superconducting tapes with high critical current density (Jc) is crucial for their use in transmission cables. Many countries these days are running projects to develop wires from these HTS materials and simultaneously field trials are being conducted to assess the feasibility of this technology. These HTS wires can carry electrical currents more than 100 times larger than their conventional counterparts with minimum loss of energy. The increased efficiency of HTS electric power products may result in greatly reduced carbon emissions compared to resulting from using the conventional alternatives. In order to use the thin films of YBa2Cu3O7- (YBCO) and REBCO [RE (rare-earth) = Sm, Gd, Eu etc.], the members of the HTS family, for future technological applications, enhancement of Jc over wide range of temperatures and applied magnetic fields is highly desired. The enhancement of Jc of YBCO and REBCO films has been successfully demonstrated by employing different techniques which include doping by rare earth atoms, incorporating nanoscale secondary phase inclusions into the REBCO film matrix, decoration of the substrate surface etc. which generate artificial pinning centers (APCs). In this review, the development of the materials engineering aspect that has been conducted over the last two decades to improve the current carrying capability of HTS thin films is presented. The effect of controlled incorporation of APCs through various methods and techniques on the superconducting properties of YBCO and REBCO thin films is presented, heading towards superior performance of such superconducting thin films.

Observation of inhomogeneous depinning in YBa2Cu3O7 composite multilayers

Composite multilayer films (CMLs) comprising YBa2Cu3O7 + BaHfO3 (4.7 vol%)/YBa2Cu3O7 + BaHfO3 (3.1 vol%) were fabricated, and vortex behavior in the CMLs was evaluated to discuss inhomogeneous depinning of vortices. Magnetic field and angular dependences of critical current density (Jc) in the CMLs were similar to those in the YBa2Cu3O7 + BaHfO3 (4.7 vol%) single layer film (SL). Variation of the CML structure shifted the matching field effect in global pinning force and irreversibility temperature. The Jc in the YBa2Cu3O7 + BaHfO3 (4.7 vol%) SL was smaller than that in the YBa2Cu3O7 + BaHfO3 (3.1 vol%) SL, suggesting that vortices preferentially moved along the low-Jc layers in the CMLs. The high-Jc layers pinned the vortices in the low-Jc layers, resulting in a shift of the matching field effect. These observations are characteristic of inhomogeneous depinning of vortices in the CMLs. The inhomogeneous depinning as well as pinned configuration should be considered for understanding Jc and for structural design of pinning centers in YBa2Cu3O7 films.

High-Tc superconducting detector for highly-sensitive microwave magnetometry

We have fabricated arrays of High-Tc Superconducting Quantum Interference Devices (SQUIDs) with randomly distributed loop sizes as sensitive detectors for Radio Frequency (RF) waves. These subwavelength size devices known as Superconducting Quantum Interference Filters (SQIFs) detect the magnetic component of the electromagnetic field. We used a scalable ion irradiation technique to pattern the circuits and engineer the Josephson junctions needed to make SQUIDs. Here, we report on a 300 SQUID series array with the loop area ranging from 6 to 60 μm2, folded in a meander line covering a 3.5 mm × 120 μm substrate area, made out of a 150 nm thick YBa2Cu3O7 film. Operating at a temperature of T = 66 K in an unshielded magnetic environment under low DC bias current (I = 60 μA) and a DC magnetic field (B = 3 μT), this SQIF can detect a magnetic field of a few picoteslas at a frequency of 1.125 GHz, which corresponds to a sensitivity of a few hundreds of fT/Hz and shows a linear response over 7 decades in RF power. This work is a promising approach for the realization of low dissipative subwavelength gigahertz magnetometers.

Enhancement of the in-field critical current density of trifluoroacetate metal organic deposition derived (Y0.77Gd0.23)Ba2Cu3Oy films by annealing of CeO2 buffered R-Al2O3 substrates

We investigate the superconducting properties of (Y0.77Gd0.23)Ba2Cu3Oy [(Y,Gd)BCO] films on as-grown and annealed (600 °C–1000 °C) CeO2 buffered R-plane sapphire (R-Al2O3) substrates using trifluoroacetate metal organic deposition (TFA-MOD). The annealing was found to improve the crystallinities of not only the CeO2 buffer layers but also the (Y,Gd)BCO films. Although the anneal had no apparent effect on the pinning centers of the (Y,Gd)BCO films, the in-field Jc of the (Y,Gd)BCO films grown on the CeO2 buffered substrates improved with increasing annealing temperature. The present results are discussed in terms of the crystallinities and Jc values of the (Y,Gd)BCO films.

All polymer cryogen free cryostat for μ-MRI application at clinical field

To improve the detection sensitivity of Micro Magnetic Resonance Imaging (μ-MRI) in humans, small animals or biological sample, it is necessary to reach higher spatial resolution. Radio Frequency (RF) YBaCuO film coils, in superconducting state, are used for that purpose, instead of copper coils. In working condition, these miniature RF coils are located in clinical MRI scanners (few Tesla) and very closed to the biological sample under investigation. A non magnetic cryostat has been designed and constructed to operate these RF coils in this particular medical environment. This cryostat is principally made of polymer materials to reduce the electromagnetic perturbations to the MRI magnet and the cryogenic scheme has been chosen to be cryogen free. In this paper, we describe the cryostat and present the experimental thermal characterizations and the first images obtained in a clinical MRI scanner.