YBa2Cu3O7 Films Research Articles

High-temperature superconductor quantum flux parametron for energy efficient logic

We report the fabrication and measurement of quantum flux parametron logic from high-transition-temperature Josephson junctions operating at 25 K, above the temperature of liquid helium. The circuits are written directly into the plane of a single-layer thin film of YBa2Cu3O7 using a focused helium ion beam. A single-cell quantum flux parametron was constructed and correct logic operation was verified by using an on-chip superconducting quantum interference device for readout. A three-cell shift register was also fabricated and tested using a three-phase clock cycle. We estimate the average bit energy to be about 1×10−20 J at 1 GHz.

Arrays of nano-high-transition temperature superconductor quantum interference devices

We report the fabrication and testing of arrays of nanoscale superconducting quantum interference devices (SQUIDs) directly written into a thin film of the high-transition temperature superconductor YBa2Cu-3O7−δ with a focused helium ion beam. We compare three array configurations with 400 nm by 400 nm nanoSQUIDs connected in series and parallel and a two-dimensional (2D) combination of both. Our electrical transport measurements show that series arrays of three nanoSQUIDs exhibit modulation voltages greater than 1 mV and that combining the devices in parallel greatly enhances the slope of the voltage–magnetic field characteristic. A 2D array with 3 SQUIDS in series and 7 in parallel exhibited a transfer function of 5.51 mV/mT.

Exceptional behavior of a high-temperature superconductor in proximity to a ferromagnet in a bilayer film, La0.67Sr0.33MnO3/YBa2Cu3O7.

We studied the electronic properties of a high-temperature superconductor in proximity to a ferromagnetic material in a bilayer film of La0.67Sr0.33MnO3 (LSMO)/YBa2Cu3O7 (YBCO). High-quality single-crystalline films of YBCO and LSMO/YBCO were grown epitaxially on an SrTiO3 (001) surface. Magnetization data of the LSMO/YBCO bilayer exhibit ferromagnetic transition at about 255 K, which is much smaller than the Curie temperature of bulk LSMO. Experimental data show the emergence of magnetic anisotropy with cooling, which becomes significantly stronger in the superconducting phase. The onset temperature of diamagnetism is observed at 86 K in the YBCO sample for the out-of-plane magnetization and at 89 K in the in-plane data. Interestingly, the diamagnetism sets in at about 86 K for both magnetization directions in the LSMO/YBCO film despite the presence of the ferromagnetic LSMO layer underneath. Ba 4d and Y 3d core-level spectra show different surface and bulk electronic structures. Surface contribution is reduced significantly in the LSMO/YBCO sample, suggesting enhanced bulk-like behavior due to an enhancement of electron density near the surface arising from charge transfer across the interface. These results reveal an outstanding platform for on-demand tuning of properties without affecting the superconductivity of the system for the exploration of fundamental science and applications in advanced technology.

Defining optimal thickness for maximal self-field in YBCO/CeO2 multilayers grown on buffered metal

The effect of multilayering YBa2Cu3O (YBCO) thin films with sequentially deposited CeO2 layers between YBCO layers grown on buffered metallic template is investigated to optimize the self-field critical current density . We have obtained that the improvement in clearly depends on the YBCO layer thickness and temperature, where at high temperature can be increased even 50% when compared with the single layer YBCO films. Based on our experimental results and theoretical approach to the growth mechanism during multilayer deposition, we have defined a critical thickness for the YBCO layer, where the maximal self-field is strongly related to the competing issues between the uniform and nonuniform strain relaxation and the formation of dislocations and other defects during the film growth. Our results can be directly utilized in the future coated conductor technology, when maximizing the overall in-field by combining both the optimal crystalline quality and flux pinning properties typically in bilayer film structures.

Modulation of vortex pinning by matrix defects in YBa2Cu3O7 nanocomposite film

Nanorods are a very effective pinning center in YBa2Cu3O7 films, and the vortex pinning mechanism should be understood to further improve the critical current density (J c) in the nanocomposite films. Matrix defects are naturally formed during nanocomposite growth, and in this study the effect of matrix defects on the J c in the YBa2Cu3O7 films containing nanorods is discussed. YBa2Cu3O7 + BaHfO3 and YBa2Cu3O7 + BaSnO3 films were prepared by varying the laser repetition frequency to control the matrix defects. All the films contained the nanorods. The YBa2Cu3O7 + BaHfO3 film of 2 Hz exhibits high J c for magnetic field parallel to the c-axis (B//c) due to the nanorods and the isolated random point defects. In the YBa2Cu3O7 + BaHfO3 film of 10 Hz, while the short stacking faults and networked random point defects decreased the J c for B//c, the short stacking faults improved the J c for tilted magnetic field. In the YBa2Cu3O7 + BaSnO3 film of 10 Hz, the isolated random point defects improved J c regardless of the magnetic field direction. While the ab-plane correlated defects are analyzed by the structural observation, the network or isolated nature of the random point defects can be discussed by the normal state resistivity. The matrix defects of YBa2Cu3O7 nanocomposite films should be designed considering the correlated/network/isolated nature which is determined by the morphology and defect concentration.

Nonreciprocal critical current in an obliquely ion-irradiated YBa2Cu3O7 film

We observed a superconducting diode effect (SDE) at 77 K in a YBa2Cu3O7 (YBCO) film irradiated with 75-MeV-Au ions directed 30°-off normal to the film surface. Up to 3% asymmetry in dc critical-current appeared remarkably in out-of-plane magnetic fields. In this field orientation, a conventional SDE does not emerge due to an asymmetric barrier to vortex entry between the film surface and the film–substrate interface. We also observed a sudden reversal of the diode polarity when the magnetic-field-angle was rotated across the ion-incident-angle. Our results indicate an unconventional SDE in YBCO films that include tilted 1D defects.

Detailed look into the unstable S-N border during propagation of the N-zone into the thin YBaCuO film

The focus is on the initial processes which change the shape of the bending S-N border during pulsed electrical S-N switching of thin YBaCuO films. These processes were noted on the SEM images of damaged films. The YBaCuO strip samples of high critical current densities were damaged by overcritical current pulses of nanosecond duration. The processes obtain different properties depending on the effective penetration length that the films have. During the N-zone propagation by the channel, led by the top unstable S-N border, an iterative transformation of the S-N border shape takes place. Two sets of the processes at the single transformation step, demonstrating weak and strong coherent jets action, are visualized and described. The origin of coherent jet formation, which is the driving force of the processes, is discussed. A peculiar interpretation of the moving top of the N-zone as a band in the state of Richtmayer-Meshkov instability is also proposed. It appears that devices with elements of the micro-scale dimensions should manifest the ultra-high speed of the S-N switching.

Properties of percolation channels in planar memristive structures base on epitaxial films of oxide perovskite compounds YBa<sub>2</sub>Cu<sub>3</sub>O<sub>7 – δ</sub> and La<sub>1 – <i>x</i></sub>Sr<sub><i>x</i></sub>MnO<sub>3 – δ</sub>

The choice of base materials and the use of their functional properties in the development of the structure and elucidation of the mechanism of resistive switching has been analyzed. Mesoscopic heterostructures based on epitaxial oriented 〈001〉 films of high-temperature superconductor YBa2Cu3O7 – δ and doped manganite La1 – xSrxMnO3 – δ, were obtained, and the properties of percolation channels of structures based on these compounds were studied. The effects of “self-adapting electroforming” in microcontact heterostructures based on epitaxial films of manganite are observed. Numerical calculations using the critical electric field model have shown that “self-electroforming” occurs in strong electric fields and a gap structure is formed in the contact zone. This structure provides reproducibility of resistive switching.

Terahertz Resonators Based on YBa2Cu3O7 High-Tc Superconductor

Superconducting split-ring resonator arrays allow to overcome two main limitations affecting metallic metamaterial resonating in the terahertz (THz) range: ohmic losses and tunability of their optical response. In this work, we design and experimentally realize direct and complementary square arrays of superconducting YBa2Cu3O7 (YBCO) split-ring resonators working in the THz spectral range. The main purpose of this paper is to show how the metamaterial resonances can be tuned by temperature (T) when crossing the superconducting transition temperature Tc of YBCO. The tuning property can be quantified by describing the THz transmittance of the patterned YBCO films vs. T through a model of coupled resonators. This model allows us to estimate the THz resonances of split-ring arrays and their interaction, showing how the kinetic inductance Lk in the superconducting state is the main parameter affecting the metamaterial properties.

The influence of BaSnO3 and BaZrO3 nanoinclusions on the critical current and local structure of HTS coated conductors

We studied the effect of artificial pinning centers in the form of nanoinclusions of stannate BaSnO3 (BSO) and zirconate BaZrO3 (BZO) barium on the critical current of high-temperature superconducting tapes of the second generation (2G) based on YBa2Cu3O films (YBCO). It has been found that the introduction of BaZrO3 nanoinclusions increases the critical current at 77 K for the magnetic field direction parallel and normal to the tape surface, while the introduction of BaSnO3 nanoinclusions decreases the critical current in both cases. To elucidate the origin of a different impact of nanoinclusions we examined the local structure of the YBCO-matrix using x-ray absorption spectroscopy (EXAFS and XANES). The spectra were collected at K-edges of Cu, Sn, and Zr at the European Synchrotron (ESRF). It was revealed that the introduction of BaZrO3 nanoinclusions increases the stiffness of copper–oxygen bonds in superconducting CuO2 plane and minimizes their static disorder in the YBCO matrix, while the introduction of BaSnO3 nanoinclusions leads to a significant increase in static disorder with a relatively weak effect on the stiffness of Cu–O bonds. These changes in the local structure become decisive for changing the macroscopic properties of high-temperature superconductor-tapes.

Flux focused series arrays of long Josephson junctions for high-dynamic range magnetic field sensing

Series arrays of closely spaced, planar long Josephson junctions were demonstrated to be transducers of magnetic flux featuring high-dynamic range, wide-bandwidth, and the capability to operate at cryogenic nitrogen temperatures. By tuning and scaling the geometry of these devices, it is possible to improve their sensitivity to an applied magnetic field and to generate higher voltage responses. Moreover, these devices feature linear voltage responses allowing for the potential of unlocked operation. Herein, we study the flux focusing effect in series arrays of planar Josephson junctions, which are well-suited to fabrication in thin films of the high-transition temperature superconductor YBa2Cu3O7−δ via helium focused ion beam irradiation. We present efforts to characterize the array geometry and properties for magnetic field sensing, with investigations of single Josephson junction behavior and demonstrations of small and large series arrays of Josephson junctions. Furthermore, two-tone spectroscopy is performed to quantify the practical linearity of the voltage response. In this work, a series array of 2640 long Josephson junctions is demonstrated, achieving a sensitivity of 1.7 mV/μT and a linear response over a region of 10.6 μT resulting in a dynamic range of 117 dB while operating at 40 K.

Investigation of diethanolamine (DEA) as a chelating agent in the fabrication of fluorine-free propionate route YBa2Cu3O7 (YBCO) thin films

The role of diethanolamine (DEA) as a chelating agent was investigated in a fluorine-free precursor solution for the growth of superconducting YBa2Cu3O7 (YBCO) thin films via chemical solution deposition. Infrared spectroscopy and thermal analyses were employed to elucidate the interactions between the chelating agent and propionate-based coating solution. The physical properties of the as-obtained YBCO films were investigated to assess the effect of DEA addition on film growth. Special emphasis was placed on the determination of superconducting transport properties. These have been investigated in wide magnetic field (0–18 T) and temperature (4.5–77 K) ranges to account for various possible application scenarios. The 100 nm thick YBCO film deposited on a (001) SrTiO3 single-crystal substrate exhibited a critical current density of 4 MA cm−2 at 77 K in self-field.

High critical current solution derived YBa2Cu3O7 films grown on sapphire

Superconducting fault current limiters (SFCLs) are very attractive devices which require to increase its robustness against the destructive hot spots. The use of sapphire substrates to grow YBa2Cu3O7 (YBCO) films is a very attractive approach due to its high thermal conductivity. This article reports the growth of microcrack-free, epitaxial YBCO layers by chemical solution deposition (CSD) on Ce1−x Zr x O2 (CZO)/yttrium-stabilized zirconia/r-cut barely polished sapphire (BPS) substrates which can be produced in long lengths at low cost. The surface quality of the r-cut sapphire and its role on the epitaxy of CZO and YBCO layers is discussed. The issue of the microcrack generation in YBCO layers is investigated in relation to the film thickness, the growth process and the oxygenation annealing step. We demonstrate that microcracks formation is related to the in-plane tensile stress generated during the oxygenation step instead of the differential thermal expansion effects and thus it can be minimized through an adapted oxygenation process. We have shown that CSD growth of YBCO films with thicknesses up to 400 nm and attractive superconducting properties (J C ∼ 1.9 MA cm−2 at 77 K) can be achieved on BPS substrates which can be used at moderate cost for SFCL devices.

Enhancement of self-field critical current density by several-tens-MeV ion irradiation in YBa2Cu3O7 films prepared by fluorine-free metal-organic deposition

An up to 63% enhancement in critical current density (J c) was achieved for 1 μm thick YBa2Cu3O7 (YBCO) films at self-field at 77 K by irradiation with 24–84 MeV Au ions. This enhancement is highly unusual, since in YBCO films, J c at self-field (J c sf) is generally insensitive to ion irradiation, unlike J c in magnetic fields. Our observed film-thickness dependence of the irradiation effect and our microstructure imaging indicate that this rare observation is attributed to an extremely “clean” (i.e. less-disordered) microstructure in the top 700 nm of the layer of our 1 μm thick films prepared via fluorine-free metal-organic deposition. Our results directly indicate that discontinuous 1D vortex-pinning centers (pins) that have the following features effectively enhance MA cm−2-order J c sf at 77 K of YBCO films; namely, 5–10 nm in diameter, ∼20 nm in size along a pin track, have a ∼20 nm gap between the pins in a pin track, and are directed in the c-axis.

Growth of YBa2Cu3O7 Films with a Packet of Parallel Grain Boundaries Spaced by Nanometer Distances

Growth of YBa2Cu3O7 Films with a Packet of Parallel Grain Boundaries Spaced by Nanometer Distances

Descriptive model of the transition from superconducting to normal state in thin high quality YBaCuO films by nanosecond electrical pulses

A descriptive model of normal zone (N-zone) propagation during the pulsed transition from superconducting to normal state (S-N switching) in the YBaCuO thin films is proposed. The model should explain the unexpected film damage. An ideal propagation of the N-zone was simulated using a combination of sinus-like functions, representing an unstable border between superconducting and normal states (S-N border). Plane geometry of the S film causes the concentration of current and expelled magnetic field at the film edges, which allows us to consider the S-N border as a separate object. Three cases, when the S-N border has effective penetration depth (λeff) of 2.45, 1.64, and 1.155 μm widths with accordingly different critical current densities and impact of coherent jets, are considered. To define numerical values of the S-N switching parameters, earlier obtained experimental parameters were taken. It was shown that the ideal propagation is insufficient to explain the damaging process. Based on the scanning electron microscope (SEM) images of damaged films, it is concluded that coherent jets and other magnetic hydrodynamics phenomena exist in the real N-zone propagation. During the propagation, closed S and N areas form and then are contracted, resulting in round dark spots visible in the SEM images. The conservation of the trapped magnetic flux is manifested during this contraction. Numerical calculations of contracting processes show that circular currents at λeff reach the Ginzburg-Landau de-pairing current densities. This explains the unexpected irreversible damage of the high quality thin YBaCuO films after the flash S-N switching.

Predicting the superconducting transition temperature and relative resistance ratio in YBa[formula omitted]Cu[formula omitted]O[formula omitted] films

The increase in critical temperature, Tc, of high-temperature superconductors fulfills the needs of practical applications with liquid-helium-free refrigeration and a delay in magnet failure. The YBa2Cu3O7 (YBCO) superconductor exhibits Tc of greater than 90 K and an upper critical field of greater than 100 T, which is a promising candidate in high-field magnet design. Due to their large anisotropy in current transportation, YBCO superconductors are usually processed as thin films by pulsed-laser deposition. But the research requires significant manpower for materials synthesis, analysis, and quench detection, as well as costly equipment and facilities. In this work, we develop the multiple linear regression model to shed light on the relationship between pulsed laser deposition parameters and the superconducting transition temperature (Tc) and relative resistance ratio (rR) in the laser deposition of YBa2Cu3O7 films. The model is straightforward and simple and demonstrates a high degree of accuracy and stability, contributing to fast low-cost estimations of Tc and rR.

Nonmonotonous temperature dependence of Shapiro steps in YBCO grain boundary junctions.

The amplitudes of the first Shapiro steps for an external signal with frequencies of 72 and 265 GHz are measured as function of the temperature from 20 to 80 K for a 6 μm Josephson grain boundary junction fabricated by YBaCuO film deposition on an yttria-stabilized zirconia bicrystal substrate. Non-monotonic dependences of step heights for different external signal frequencies were found in the limit of a weak driving signal, with the maxima occurring at different points as function of the temperature. The step heights are in agreement with the calculations based on the resistively–capacitively shunted junction model and Bessel theory. The emergence of the receiving optima is explained by the mutual influence of the varying critical current and the characteristic frequency.

YBa2Cu3O7 films grown onto SrTiO3 and YSZ substrates by chemical solution deposition of trifluoroacetates

We report the preparation and characterization of YBa2Cu3O7 (YBCO) films grown onto SrTiO3 and YSZ substrates by the trifluoroacetates chemical solution deposition method and following sintering with oxygen atmosphere at 860 °C. The X-ray diffraction (XRD) reveals (00ℓ) – oriented crystallites indicating epitaxial growth of the films in the c-direction. Despite granular morphology and the presence of Y2BaCuO5 and CuO as minor secondary phases, the technique shows the successful formation of the superconducting YBCO and preventing the formation of the unwanted BaCO3 phase. Rocking curve measurements of the (005) reflection for the YBCO/SrTiO3 was fitted with one Gaussian function with full width at the half maximum (FWHM) of 0.44° confirming that it consists of YBCO crystallites with different texture. For the sample grown on YSZ, the rocking curve was fitted with two Gaussian functions, one corresponding to the YBCO layer (FWHM = 0.4°) and another to the substrate (FWHM = 0.3°). The magnetic measurements taken in zero field cooling and field cooling modes confirm the formation of the superconducting YBCO with critical temperatures (TC) 91.8 and 85.7 K for the samples grown onto YSZ and SrTiO3, respectively. The critical current density (JC) curves indirectly calculated by using the Bean´s model from the M(T) loops were JC ~ 109 A/cm2 for the sample deposited onto YSZ and JC ~ 107A/cm2 for the YBCO deposited onto SrTiO3. Overall, the difference in TC and JC values between both samples could be related to their difference in oxygen content, porosity, hole concentration per Cu ion and the presence of secondary phases.

Angular vortex phase diagram in YBa2Cu3O7 films with c-axis correlated pinning centers

High temperature superconductors (HTSCs) exhibit rich vortex phases under the influence of nanoscale pinning centers, and complicated configurations and behavior of vortices are realized by anisotropic vortex pinning, vortex interaction, and line tension. To understand the behavior and configurations of vortices, YBa2Cu3O7 films containing self-organized nanorods (BaSnO3, BaZrO3, BaHfO3) were prepared, and the critical current density and the resistivity were measured for varying angles between the nanorods (//c-axis) and the magnetic field (θ) in the temperatures of 65–90 K. The trapping angle of the strong nanorod (θ ts) determines the vortex phase boundary in the magnetic field lower than the matching field (B< B ϕ). While the large c-axis J c peak and the resistivity dip are observed for θ< θ ts due to the vortex accommodation on the nanorods, the vortices for θ> θ ts are pinned by the matrix uncorrelated defects and/or the ab-plane pinning centers. In the magnetic field higher than B ϕ(B> B ϕ), the weak matrix c-axis correlated defects such as twin boundaries accommodate vortices at the angles smaller than the trapping angle of the matrix c-axis correlated defect. Although the matrix c-axis correlated defects do not pin the matrix-vortices for the larger angles, the matrix-vortices are pinned by the vacant nanorod portions that appear due to the magnetic field tilt. This vortex retrapping results in the off-axis J c peak and the off-axis resistivity dip. Thus, the weak pinning by matrix defects, the cage potential, and the vortex retrapping as well as the strong nanorod pinning determine the angular vortex phase of the HTSCs containing c-axis correlated pinning centers.