YBa2Cu3O7-δ Thin Films Research Articles

Variations of the elemental composition distribution over the thickness of YBa2Cu3O7-δ thin films obtained by pulsed laser deposition from one target

Epitaxial YBa2Cu3O7‒δ (YBCO) films 150-200 and 300 nm thick, respectively, were deposited on SrTiO3 (100) substrates by pulsed laser deposition at different conditions: with and without using the velocity filtration technique. The films have T(R=0) in the range of 77.4 - 87 R(T) depending on the conditions of deposition from one target with YBa2Cu3O6.8 composition. The films contain Zn, Sr, Pd, Ag and Ti impurity elements obtained from the target (a total of no more than 2 at. % ). Data of the film resistance temperature dependences, X-ray phase analysis, analysis of X-ray fluorescence (XRF) spectra and study of the surface relief by SEM methods revealed the nonuniform distributions of impurity and matrix Y, Ba, Cu elements over the film depth. Impurity concentrations near the surface lead to the formation of faceted spiral pyramids on the surface, which probably evolve into large elongated particles according to the Ostwald mechanism. This knowledge is practically important for optimizing pulsed laser deposition technologies and creating 2D instruments and devices for studying physical phenomena.

Study on rapid growth and improved performance of superconducting YBa2Cu3O7-δ coated conductors assisted by transient liquid phase

This study employs a fluorine-free metal organic deposition method (FF-MOD), with transient liquid phase assistance, to expedite the growth (TLAG) of superconducting YBa2Cu3O7-δ (YBCO) thin films on LaMnO3 metal substrates. The research evaluates the phase formation and performance of YBCO films with varying proportions of preformed BaZrO3 (BZO) nanocrystals. The experimental results indicate that the optimal proportion for incorporating BZO nanocrystals is 5 %, leading to the YBCO film displaying critical current density at 77 K under zero-field conditions. This achievement marks a significant advancement in the rapid growth of YBCO films on metal substrates with enhanced current-carrying capacity. Additionally, the research assesses the changes in overall uniformity and microstrain of YBCO films after the addition of BZO nanocrystals, shedding light on the key factors contributing to performance enhancement and offering insights for future improvements. This investigation offers valuable insights for attaining high-speed, high-performance growth of superconducting YBCO coating conductors.

Temporal Evolution of Defects and Related Electric Properties in He-Irradiated YBa2Cu3O7-δ Thin Films.

Thin films of the superconductor YBa2Cu3O7-δ (YBCO) were modified by low-energy light-ion irradiation employing collimated or focused He+ beams, and the long-term stability of irradiation-induced defects was investigated. For films irradiated with collimated beams, the resistance was measured in situ during and after irradiation and analyzed using a phenomenological model. The formation and stability of irradiation-induced defects are highly influenced by temperature. Thermal annealing experiments conducted in an Ar atmosphere at various temperatures demonstrated a decrease in resistivity and allowed us to determine diffusion coefficients and the activation energy ΔE=(0.31±0.03) eV for diffusive oxygen rearrangement within the YBCO unit cell basal plane. Additionally, thin YBCO films, nanostructured by focused He+-beam irradiation into vortex pinning arrays, displayed significant commensurability effects in magnetic fields. Despite the strong modulation of defect densities in these pinning arrays, oxygen diffusion during room-temperature annealing over almost six years did not compromise the signatures of vortex matching, which remained precisely at their magnetic fields predicted by the pattern geometry. Moreover, the critical current increased substantially within the entire magnetic field range after long-term storage in dry air. These findings underscore the potential of ion irradiation in tailoring the superconducting properties of thin YBCO films.

Ultra-High-Sensitivity and -Stability Thin-Film Heat Flux Sensor Based on Transverse Thermoelectric Effect

In this study, we investigate the sensitivity properties of YBa2Cu3O7-δ thin films with a 15° tilting angle in relation to heat flux density. The films were prepared using the laser pulsed deposition (PLD) technique, and their characteristics were evaluated using various techniques, including X-ray diffraction (XRD), transmission electron microscopy (TEM), atomic force microscopy (AFM), and infrared steady-state and laser transient calibration systems. The YBa2Cu3O7-δ films prepared in this study were found to be of good quality, exhibiting a single-phase structure with strict (001) orientation. Both the substrate and film diffraction peaks were sharp and consistent with the step-flow growth mode, indicating high crystalline quality. Ultra-high sensitivity in the range of 0 to 100 kW/m2, the maximum sensitivity is 230 μV/(kW/m2), and an uncertainty is only 3%. According to the infrared steady-state heat flux calibration system test, when the single output power of the quartz lamp array is 0.2 kW, 0.3 kW, 0.4 kW and 0.5 kW, the maximum output voltage is 0.19 mV, 0.41 mV, 0.63 mV and 0.94 mV, respectively, indicating that the output voltage of the sensor increases with the increase in heat flux, showing a good linear characteristic, and the fitting linearity is 0.99. Through the test of the laser transient thermal current calibration system, the sensors are found to have excellent response–recovery characteristics at 500 kHz and 1000 kHz fiber laser frequencies, and the maximum voltage output is 8.83 mV and 9.09 mV, respectively. Moreover, the component has excellent repeatability, and the maximum measurement error is only 1.94%. Our findings demonstrate the potential of YBa2Cu3O7-δ thin films for use in heat flux sensing applications.

Angle-dependent Magnetoresistance of an Ordered Bose Glass of Vortices in YBa2Cu3O7-δ Thin Films with a Periodic Pinning Lattice

The competition between intrinsic disorder in superconducting YBa2Cu3O7−δ (YBCO) thin films and an ultradense triangular lattice of cylindrical pinning centers spaced at 30 nm intervals results in an ordered Bose glass phase of vortices. The samples were created by scanning the focused beam of a helium-ion microscope over the surface of the YBCO thin film to form columns of point defects where superconductivity was locally suppressed. The voltage–current isotherms reveal critical behavior and scale in the vicinity of the second-order glass transition. The latter exhibits a distinct peak in melting temperature (Tg) vs. applied magnetic field (Ba) at the magnetic commensurability field, along with a sharp rise in the lifetimes of glassy fluctuations. Angle-dependent magnetoresistance measurements in constant-Lorentz-force geometry unveil a strong increase in anisotropy compared to a pristine reference film where the density of vortices matches that of the columnar defects. The pinning is therefore, dominated by the magnetic-field component parallel to the columnar defects, exposing its one-dimensional character. These results support the idea of an ordered Bose glass phase.

Growth of YBa2Cu3O7-δ superconducting films under different atmospheres by pulsed laser deposition

This paper aims to explore the epitaxial growth process for high-temperature superconducting YBa2Cu3O7-δ (YBCO) thin films by pulsed laser deposition (PLD) under different deposition atmospheres. The possibility of depositing YBCO superconducting thin films, under an oxygen-free environment, that was different from the oxygen atmosphere for most deposition processes of YBCO superconducting thin films was studied. Three different atmospheres, with oxygen, nitrous oxide, and nitrogen, were used in the experiment. The influence of atmospheric pressure on the formation and superconductivity of the YBCO phase were studied in detail. The characterization of structure and electrical properties of the thin films showed that YBCO thin films showed highly preferentially growth along the c-axis, had good superconductivity, and could be prepared under all three atmospheres. The formation of the YBCO phase at high temperatures did not need oxygen, and subsequent low-pressure oxygen-annealing process was only required at low temperatures of about 350 ℃. Our findings are of great significance for the preparation and application of YBCO thin films on substrates that were easy to oxidize at high temperatures, such as nickel strips or some electronic printed circuit boards.

Utilizing the Transverse Thermoelectric Effect of Thin Films for Pulse Laser Detection

In this work, pulse laser detectors based on the transverse thermoelectric effect of YBa2Cu3O7-δ thin films on vicinal cut LaAlO3 (001) substrates have been fabricated. The anisotropic Seebeck coefficients between ab-plane (Sab) and c-axis (Sc) of thin films are utilized to generate the output voltage signal in such kind of detectors. Fast response has been determined in these sensors, including both the rise time and the decay time. Under the irradiation of pulse laser with the pulse duration of 5–7 ns, the output voltage of these detectors shows the rise time and the decay time of 6 and 42 ns, respectively, which are much smaller than those from other materials. The small rise time in YBa2Cu3O7-δ-based detectors may be due to its low resistivity. While the high thermal conductivity and the large contribution of electronic thermal conductivity to the thermal conductivity of YBa2Cu3O7-δ are thought to be responsible for the small decay time. In addition, these detectors show good response under the irradiation of pulse lasers with a repetition rate of 4 kHz, including the precise determinations of amplitude and time. These results may pave a simple and convenient approach to manufacture the pulse laser detectors with a fast response.

Study of fluctuation conductivity in YBa2Cu3O7−δ films in strong magnetic fields

We report the effect of the ab-plane magnetic field B up to 8 T on the resistivity ρ(T) and fluctuation conductivity σ′'(T) in YBa2Cu3O7-δ thin films. As expected, up to ∼ 2.5 T the magnetic field monotonously increases ρ, the width of the resistive transition, ΔTc, and coherence length along the c axis, ξC(0), but decreases both Tc and the range of superconducting (SC) fluctuations ΔTfl. The fluctuation conductivity exhibits a crossover at characteristic temperature T0 from the 3D Aslamasov-Larkin (AL) theory near Tc to the 2D fluctuation theory of Maki-Thompson (MT). However, at B = 3 T, the MT term is completely suppressed, and above T0 σ′'(T) is unexpectedly described by the fluctuation contribution of 2D AL, suggesting the formation of a 2D vortex lattice in the film under the action of a magnetic field. At the same time, ΔTf sharply increases by a factor of about 7, and ξC(0) demonstrates a very unusual dependence on Tc when B increases above 3 T. Our results demonstrate the possibility of the formation of a vortex state in YBCO and its evolution with increasing B.

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.

Anisotropy of the In-Plane and Out-of-Plane Resistivity and the Hall Effect in the Normal State of Vicinal-Grown YBa2Cu3O7-δ Thin Films.

The resistivity and the Hall effect in the copper-oxide high-temperature superconductor YBaCuO (YBCO) are remarkably anisotropic. Using a thin film of YBCO grown on an off-axis cut SrTiO substrate allows one to investigate these anisotropic transport properties in a planar and well-defined sample geometry employing a homogeneous current density. In the normal state, the Hall voltage probed parallel to the copper-oxide layers is positive and strongly temperature dependent, whereas the out-of-plane Hall voltage is negative and almost temperature independent. The results confirm previous measurements on single crystals by an entirely different measurement method and demonstrate that vicinal thin films might be also useful for investigations of other layered nanomaterials.

Fluctuation Conductivity in MOD-Derived YBCO Thin Films

Normal-state properties of some epitaxial YBa2Cu3O7-δ thin films which were derived from the metal-organic deposition route were studied through the context of Aslamazov and Larkin theory of fluctuation conductivity. Six samples with various superconducting properties were selected for this purpose. Resistivity vs. temperature analysis showed that the general normal-state behavior of the samples can be described by 3D, 2D, and 1D Aslamazov and Larkin model of fluctuation conductivity. Samples with the higher superconducting transition temperatures showed the higher Josephson interlayer coupling. Moreover, a linear behavior has been found between Josephson interlayer coupling constant and critical current density. In addition, fitting excess conductivity with Lawrence-Doniach (LD) and Maki-Thompson (MT) models revealed that the LD term dominates in 3D region near the superconducting transition. However, the MT term gains an important role in 2D region far away superconducting transition.

Fabrication of YBCO Thin Films by Fluorine-Free MOCSD Method: Influence of Sintering Near the Melting Point

YBa 2 Cu 3 O 7-δ thin films were deposited by a fluorine-free metal-organic chemical solution deposition method using metal acetates as the starting materials. In this article, influence of different sintering temperatures (770-800 °C) on structural and superconducting properties of the films was investigated. Using a mixture of argon with 100 ppm oxygen as the atmosphere of the sintering process, some grain melting was observed at this temperature range, which favors to obtain a more c-axis epitaxial films with a higher critical current density. The decomposition mechanism of organic components of precursor powder was studied by Thermal Gravimetric Analysis (TGA)/Differential Scanning Calorimetry (DSC) analysis. The structural and morphological properties of the films were investigated by X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM), and Atomic Force Microscopy (AFM) analysis. Four-point probe and inductive third-harmonic voltage measurements were carried out to determine transition temperature and critical current density, respectively. The film sintered at 790 °C showed a superconducting transition temperature at 91.5 K with a width of 1.2 K and a critical current density of 2 MA/cm 2 .

Estimation of Electricity Storage Density of Compact SMESs Composed of Si-wafer Stacks Loaded with Superconducting Thin Film Coils in Spiral Trenches under the Constraints of the Critical Magnetic Flux Density

Numerical estimations of electricity storage volume density: W for a proposed compact superconducting magnetic energy storage system composed of 4 stacks of 20 to 1800 Si-wafers loaded with superconducting YBa2Cu3O7-δ thin film coils in spiral trenches formed by MEMS process were performed in conjunction with estimations of magnetic flux density and electromagnetic hoop stress applied to the coil. Changing the design parameters such as trench depth, trench width, trench wall thickness, number of stacked Si wafers, the inner-radius of the spiral coil under the fixed outer-radius of 47.45 mm, the maximum W was obtained to be 13.6 Wh/l under the constraint of the maximum magnetic flux density applied to the coil: Bmax < 20 T. The maximum hoop stress applied to the coil was estimated to be much lower than the mechanical strength limit of the Si wafer :4 GPa, indicating that other substrate materials such as typical engineering ceramics can be used in place of Si wafer if microfabrication of spiral trenches is feasible.

Atomic-scale imaging of interfacial polarization in cuprate-titanate heterostructures

The interfaces in oxide heterostructures that bring novel physical phenomena and functionalities have attracted great attention in fundamental research and device applications. For uncovering structure–property relationships of oxide heterostructures, direct evidence of the atomic-scale structure of heterointerfaces is highly desired. Here, we report on studying the structure of interfaces between YBa2Cu3O7-δ thin films and SrTiO3 substrates by means of aberration-corrected ultrahigh-resolution electron microscopy. Employing advanced imaging and spectroscopic techniques, shifts of atoms at the interface away from the regular lattice sites are measured, leading to the interfacial polarity. The local polarization induced by the atomic shifts directs toward the cuprate films and is estimated to be about 36.1 μC/cm2. The observed interfacial polar layer is understood by the special atomic configuration across the interface, which could modulate the electrical properties in superconducting devices that are based on the ferroelectric/superconductor heterosystems.

Interaction between untreated SrTiO3 substrates and solution-derived YBa2Cu3O7-δ films

In this work it is shown how SrTiO3 substrates interact with YBa2Cu3O7-δ thin films during film processing. The effect of this interdiffusion on morphology and transport properties is analyzed. The films were deposited by low fluorine Metal Organic Decomposition (MOD) on SrTiO3 (0 0 1) single crystals. In general, a sharp c-axis oriented growth and high critical temperature (Tc) were observed in all samples; however, the surface of the otherwise good-quality films is spoiled by the presence of inhomogeneous circular areas of seemingly different appearance and texture. In order to understand the nature of these defects, the substrates and the films were deeply investigated by optical microscopy, scanning and transmission electron microscopy (SEM, TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), contact-stylus surface profilometry (SSP), Atomic Force Microscopy (AFM) and time of flight secondary ion mass spectrometry (ToF-SIMS). The round spots are the manifestation, on the film surface, of ion interdiffusion from the substrate into the YBCO film Spot-free samples can be obtained with different pre-treatments of the SrTiO3 substrates. Although these defects are detrimental for the film local structure, Jc values are not significantly affected, although the defects' influence might become substantial while working on smaller scales.

Suppression of superconductivity at the nanoscale in chemical solution derived YBa2Cu3O7-δ thin films with defective Y2Ba4Cu8O16 intergrowths.

The analysis of the microstructure and superconducting behavior of chemical solution deposited epitaxial YBa2Cu3O7−δ films, with thickness going down to 5 nm has been carried out with the purpose to disclose the behavior of the most common intergrowth in these films, the Y2Ba4Cu8O16. The analysis of ultrathin films is a unique opportunity to investigate the superconducting behavior of these nanoscale defects because of the high concentration created as a consequence of the elastic energy associated to the misfit strain. Magnetic susceptibility and X-ray diffraction measurements evidence a strong decrease of the superconducting volume correlated with an increase of the intergrowth volume fraction. We demonstrate that these intergrowths are non-superconducting nanoscale regions where Cooper pair formation is disrupted, in agreement with their key role as artificial pinning centers for vortices in YBa2Cu3O7−δ films and coated conductors.

Measurements of phase shifts in YBCO transmission lines for evaluation of kinetic inductance change

We fabricated a coplanar waveguide (CPW) using high temperature superconductor YBa2Cu3O7-δ (YBCO) and evaluated its characteristics for the realization of a superconducting parametric amplifier. A YBCO thin film with a film thickness of 200 nm was formed by the PLD method using a YAG laser on a 10 × 10 mm MgO substrate. The YBCO thin films were processed into the CPW shape with a line width of 8 μm, a gap width of 8 μm and a line length of 5 mm by photolithography and sputter etching. Using a network analyzer, phase differences of microwave were measured at dc current bias from 0 mA to 14 mA. From the measurement results, it was found that the phase difference decreased with increasing temperature. In addition, it was found that the phase shifts greatly varied near the superconducting transition temperature at each current bias. We observed a maximum phase difference Δθ of -0.08 rad at a bias current of 14.0 mA, which is the closest to the transition temperature. A parametric gain was estimated to be 0.15 dB from the measured maximum phase difference.

Effect of colossal magnetoresistance material La0.67Ca0.33MnO3 on superconducting properties of YBa2Cu3O7-δ thin films

Abstract By specific design of the sample, in which SrTiO3 substrate is fully covered by a thin layer of the colossal magnetoresistive material La0.67Ca0.33MnO3 (LCMO) and the latter is partially covered by high-temperature superconductor YBa2Cu3O7-δ (YBCO), and by using multiple current and voltage contacts, direct evidence of the strong effect of LCMO on YBCO is obtained. It is found that LCMO strongly influences not only superconducting, but also normal state of YBCO, and it is argued that this is a consequence of the spin injection from the former to the latter. The effect of the deposition conditions and crystal orientation of YBCO layer on this effect is clarified. A surprising peak in the temperature dependence of resistance seen in ex-situ ab-plane oriented sample is explained as a combination of two effects: influence of spin-polarized electrons on superconductor below its critical temperature and the interface-controlled shift of Curie temperature of LCMO to low temperatures. Considering expected use of LCMO and YBCO in composite quantum computation circuits, their combination with another advanced quantum material, graphene, is explored.

Electrochemical Tuning of Metal Insulator Transition and Nonvolatile Resistive Switching in Superconducting Films.

Modulation of carrier concentration in strongly correlated oxides offers the unique opportunity to induce different phases in the same material, which dramatically change their physical properties, providing novel concepts in oxide electronic devices with engineered functionalities. This work reports on the electric manipulation of the superconducting to insulator phase transition in YBa2Cu3O7−δ thin films by electrochemical oxygen doping. Both normal state resistance and the superconducting critical temperature can be reversibly manipulated in confined active volumes of the film by gate-tunable oxygen diffusion. Vertical and lateral oxygen mobility may be finely modulated, at the micro- and nano-scale, by tuning the applied bias voltage and operating temperature thus providing the basis for the design of homogeneous and flexible transistor-like devices with loss-less superconducting drain–source channels. We analyze the experimental results in light of a theoretical model, which incorporates thermally activated and electrically driven volume oxygen diffusion.

Preparation of YBa2Cu3O7-δ and La1.85Sr0.15 CuO4 Bilayer Structure for Superconducting Connection

To connect superconducting wires through a different superconductor, it is essential to evaluate a range of characteristics of the various superconducting materials. In this study, a combination of YBa 2 Cu 3 O 7-δ (YBCO) and La 1.85 Sr 0.15 CuO 4 (LSCO), which are typical high-temperature superconductors, was investigated. An LSCO/YBCO layered thin film (LSCO/YBCO bilayer) was prepared and its crystallinity, surface morphology, and electrical properties were evaluated. The LSCO thin film grew epitaxially, oriented to the (00l) plane on the (00l)-oriented YBCO thin film due to the small lattice mismatch between YBCO and LSCO. The surface flatness of the LSCO/YBCO bilayer was almost the same as that of the LSCO thin film, because the LSCO thin film grew without roughening the surface of the YBCO thin film. The electrical resistivity of the LSCO/YBCO bilayer decreased at the individual superconducting-transition temperatures of YBCO and LSCO, and eventually became superconducting at 20 K. The superconducting properties of YBCO and LSCO were almost preserved, with the result that a superconducting connection between YBCO and LSCO was achieved.