Search

In this study, the prediction of n-value (index-value) surfaces—a key indicator of the field and temperature dependence of critical current density in superconductors—across various high-temperature superconducting materials is addressed using a deep learning modeling approach. As superconductors play a crucial role in advanced technological applications in aerospace and fusion energy sectors, improving their performance model is essential for both practical and academic research purposes. The feed-forward deep learning network technique is employed for the predictive modeling of n-value surfaces, utilizing a comprehensive dataset that includes experimental data on material properties and operational conditions affecting superconductors' behavior. The model demonstrates enhanced accuracy in predicting n-value surfaces when compared to traditional regression methods by a 99.62% goodness of fit to the experimental data for unseen data points. In this paper, we have demonstrated both the interpolation and extrapolation capabilities of our proposed DFFNN technique. This research advances intelligent modeling in the field of superconductivity and provides a foundation for further exploration into deep learning predictive models for different superconducting devices. [ABSTRACT FROM AUTHOR]

In this paper, we have extracted transport critical current density ( J c ) of BaZrO3 (BZO) added YBa2Cu3O 7 − δ (YBCO) by using several low electric field (E)-based criteria. By varying E-based criteria in order of magnitude, we have extracted J c (T) and granular critical current density, J c G (T) by using JE (IV) characteristics. The temperature (T) dependence of J c and J c G is found to be affected strongly as a result of the choice of E as criterion. The sensitiveness of J c and J c G becomes prominent with the lowering of T. The Ambegaokar–Baratoff (AB) and the Ginzburg–Landau (GL) descriptions of J c (T) and J c G (T) have been studied to understand how varying criteria may change the extraction of several associated coefficients. Extrapolated J c (T = 0) and J c G (T = 0) is also highly sensitive to criteria used. [ABSTRACT FROM AUTHOR]

A system of two equations based on one of the classical electricity laws was used to determine the sizes and temperatures of ohmic areas formed under action of overcritical nanosecond electrical pulses. Calculations were performed at five points for three experimentally obtained voltage–current (V-I) dependences for samples with the same geometry but different critical current density values. The system included two additional conditions to satisfy the known descriptive model of transition from superconducting (SC) to a normal (N) state—S-N switching—and to obtain physically acceptable solutions over the entire current range of V-I dependence. The solution for each point takes the form of a function, since the initial temperature increase of the primary channel across the film is entered as a parameter. Two modes of concentrated energy release in the channel were disclosed. Their random appearance leads to an unexpected degradation of the sample. As such, the obtained results correspond to the situations occurring during the experiments. The validity of applying additional conditions to the system is discussed. In the discussion, it is also explained at which moments the moving S-N border acquires the velocity of the order of ~106 m/s, comparable to the Fermi velocity. Consideration to describe the moving unstable S-N border as being constantly in a state of Richtmyer–Meshkov instability is presented. [ABSTRACT FROM AUTHOR]

Current-voltage characteristics have been calculated for a high-temperature superconductor containing triangular and square periodic arrays of pinning centers with various disorder rates. Non-monotonic dependences of critical current density on the disorder rate have been obtained for the triangular lattice, showing that a perfectly ordered lattice provides smaller critical currents than that with minor distortions, especially at high magnetic fields. For the square lattice, the critical current was mostly declining, with minor peaks at small disorder rates. A thorough analysis of the vortex dynamics has been done, showing the differences in the way vortices move through the disordered lattice and how their paths affect the critical current density. [ABSTRACT FROM AUTHOR]

Emergent inhomogeneous electronic phases in metallic quantum systems are crucial for understanding high‐Tc superconductivity and other novel quantum states. In particular, spin droplets introduced by nonmagnetic dopants in quantum‐critical superconductors (QCSs) can lead to a novel magnetic state in superconducting phases. However, the role of disorders caused by nonmagnetic dopants in quantum‐critical regimes and their precise relation with superconductivity remain unclear. Here, the systematic evolution of a strong correlation between superconductive intertwined electronic phases and antiferromagnetism in Cd‐doped CeCoIn5 is presented by measuring current–voltage characteristics under an external pressure. In the low‐pressure coexisting regime where antiferromagnetic (AFM) and superconducting (SC) orders coexist, the critical current (Ic) is gradually suppressed by the increasing magnetic field, as in conventional type‐II superconductors. At pressures higher than the critical pressure where the AFM order disappears, Ic remarkably shows a sudden spike near the irreversible magnetic field. In addition, at high pressures far from the critical pressure point, the peak effect is not suppressed, but remains robust over the whole superconducting region. These results indicate that magnetic islands are protected around dopant sites despite being suppressed by the increasingly correlated effects under pressure, providing a new perspective on the role of quenched disorders in QCSs. [ABSTRACT FROM AUTHOR]

Emergent inhomogeneous electronic phases in metallic quantum systems are crucial for understanding high‐Tc superconductivity and other novel quantum states. In particular, spin droplets introduced by nonmagnetic dopants in quantum‐critical superconductors (QCSs) can lead to a novel magnetic state in superconducting phases. However, the role of disorders caused by nonmagnetic dopants in quantum‐critical regimes and their precise relation with superconductivity remain unclear. Here, the systematic evolution of a strong correlation between superconductive intertwined electronic phases and antiferromagnetism in Cd‐doped CeCoIn5 is presented by measuring current–voltage characteristics under an external pressure. In the low‐pressure coexisting regime where antiferromagnetic (AFM) and superconducting (SC) orders coexist, the critical current (Ic) is gradually suppressed by the increasing magnetic field, as in conventional type‐II superconductors. At pressures higher than the critical pressure where the AFM order disappears, Ic remarkably shows a sudden spike near the irreversible magnetic field. In addition, at high pressures far from the critical pressure point, the peak effect is not suppressed, but remains robust over the whole superconducting region. These results indicate that magnetic islands are protected around dopant sites despite being suppressed by the increasingly correlated effects under pressure, providing a new perspective on the role of quenched disorders in QCSs. [ABSTRACT FROM AUTHOR]

This article discusses characteristic features of energy dissipation from the eigenfield of transport current upon its stable penetration into a technical superconductor. The regimes of partial and complete penetration are considered. Analysis of dissipative states of a superconductor is compared with the results following from the theory based on the critical state model. It is demonstrated that the critical state model, according to which there is no electric voltage in superconductors at currents lower than critical one, underestimates heat release from the eigenfield of transport current and does not allow calculating correctly the energy losses in superconductors with actual current–voltage characteristics in the range of subcritical currents that can exist upon complete current penetration into superconductor. The error of the critical state model depends on the pattern of increase in current–voltage characteristic, the rate of current input, the transverse size of superconductor, and the critical current density. At the same time the self-similar and the zero-dimensional approximations make it possible to determine the energy losses in superconductors with actual current–voltage characteristic from varying eigenfield of transport current with sufficient accuracy upon both its partial and complete penetration. [ABSTRACT FROM AUTHOR]

The critical current density (Jc) of a superconductor with a high transition temperature is a fundamental quantity that determines the scope of the application of new superconductors in practice. Reports show that the critical transport current density of thin films of yttrium-based superconductors grown by different methods can range from the value106A/cm2' in temperature77k° to a value of the 107A/cm²order of4 ko. These values of current density provide the use of superconductors on a small scale in the electronic industry In this work, the dependence of the critical transfer current density of type II flat superconductor with a rectangular cross-section that is mixed in three magnetic fields that are applied perpendicular to the surface of the superconducting strip is investigated. The results of these calculations clearly show that (a)- as the thickness of the superconducting sample increases, the critical current density decreases (b)- the comparison of the results of the calculations of the application of three different fields indicates that with the increase of the field, it decreases. [ABSTRACT FROM AUTHOR]

The relaxation phenomena of a FeSe0.5Te0.5 single crystal sample, with twinned morphology, exhibiting a second magnetization peak effect have been analyzed by means of dc magnetization measurements as a function of magnetic field (H). Using different magnetic field sweep rates for performing the superconducting hysteresis loops m(H), a change in the width of these curves has been observed together with a shift of the second peak field position. A consequent and significant variation of critical current density Jc has been extracted from the superconducting m(H) curves within the Bean critical state model. In this framework, the ratio between the critical current densities Jc calculated at 200 Oe/s and 5 Oe/s has been calculated showing interesting results in terms of transport capabilities. From the Jc(H) curves at T = 10 K for different sweep rates, the irreversibility field has been obtained for T = 10 K and fitted with a power law. The increasing trend of the irreversibility field as a function of sweep rate could suggest the use of this material for power applications where overheating due to vortices movement inside the superconductor has to be limited. [ABSTRACT FROM AUTHOR]

The photo-induced superconducting phase transition is widely used in probing the physical properties of correlated electronic systems and to realize broadband photodetection with extremely high responsivity. However, such photoresponse is usually insensitive to electrostatic doping due to the high carrier density of the superconductor, restricting its applications in tunable optoelectronic devices. In this work, we demonstrate the gate voltage modulation to the photoresponsivity in a two-dimensional NbSe2-graphene heterojunction. The superconducting critical current of the NbSe2 relies on the gate-dependent hot carrier generation in graphene via the Joule heating effect, leading to the observed shift of both the magnitude and peak position of the photoresponsivity spectra as the gate voltage changes. This heating effect is further confirmed by the temperature and laser-power-dependent characterization of the photoresponse. In addition, we investigate the spatially-resolved photocurrent, finding that the superconductivity is inhomogeneous across the junction area. Our results provide a new platform for designing tunable superconducting photodetector and indicate that the photoresponse could be a powerful tool in studying the local electronic properties and phase transitions in low-dimensional superconducting systems. [ABSTRACT FROM AUTHOR]

The aim of this work was to study the effect of compaction pressure on the growth of the crystalline structure of the Bi-2212 phase and on the current density of the material. Ceramic samples were prepared by conventional solid-state reaction method, sintered at 840 ∘ C after compacting at five different pressures that were 300, 450, 600, 750, and 900 MPa. The obtained samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), resistivity vs. temperature (ρ vs. T ) by the four-point probe method, critical current density vs. magnetic field ( J c vs. H ) at 4 K, and by mass density vs. pressure ( ρ m vs. P ). The XRD patterns show the main reflections of the Bi-2212 and Bi-2223 phases for all samples, varying slightly in intensity and with the presence of approximately 95.77% and 4.23% of each phase. The highest critical temperature values, at the beginning of the superconductor transition, T c , o n 1 , and for R = 0 , T c , 0 , are noted to be about 111.63 K and 101.20 K, respectively. For the calculations of critical current density, we used the Bean model, obtaining 6.84 x 10 7 A m - 2 (the highest for 600 MPa) and 9.71 x 10 6 A m - 2 (the lowest for 300 MPa). The optimal conditions that improve the electrical, physical, and morphological behavior of the Bi-2212 superconducting material occur when the compaction pressure is 600 MPa and the lattice parameter c of the crystal structure is increased. [ABSTRACT FROM AUTHOR]

In this work, the Generalized Hubbard Model on a square lattice is applied to evaluate the electrical current density of high critical temperature d-wave superconductors with a set of Hamiltonian parameters allowing them to reach critical temperatures close to 100 K. The appropriate set of Hamiltonian parameters permits us to apply our model to real materials, finding a good quantitative fit with important macroscopic superconducting properties such as the critical superconducting temperature ( T c ) and the critical current density (J c) . We propose that much as in a dispersive medium, in which the velocity of electrons can be estimated by the gradient of the dispersion relation ∇ ε (k) , the electron velocity is proportional to ∇ E (k) in the superconducting state (where E (k) = (ε (k) − μ) 2 + Δ 2 (k) is the dispersion relation of the quasiparticles, and k is the electron wave vector). This considers the change of ε (k) with respect to the chemical potential (μ) and the formation of pairs that gives rise to an excitation energy gap Δ (k) in the electron density of states across the Fermi level. When ε (k) = μ at the Fermi surface (FS), only the term for the energy gap remains, whose magnitude reflects the strength of the pairing interaction. Under these conditions, we have found that the d-wave symmetry of the pairing interaction leads to a maximum critical current density in the vicinity of the antinodal k-space direction (π , 0) of approximately 1.407236 × 10 8 A/cm2, with a much greater current density along the nodal direction (π 2 , π 2) of 2.214702 × 10 9 A/cm2. These results allow for the establishment of a maximum limit for the critical current density that could be attained by a d-wave superconductor. [ABSTRACT FROM AUTHOR]

We have investigated the pinning potential of high-quality single crystals of superconducting material CaKFe4As4 having high critical current density and very high upper critical field using both magnetization relaxation measurements and frequency-dependent AC susceptibility. Preliminary studies of the superconducting transition and of the isothermal magnetization loops confirmed the high quality of the samples, while temperature dependence of the AC susceptibility in high magnetic fields show absolutely no dependence on the cooling conditions, hence, no magnetic history. From magnetization relaxation measurements were extracted the values of the normalized pinning potential U*, which reveals a clear crossover between elastic creep and plastic creep. The extremely high values of U*, up to 1200 K around the temperature of 20 K lead to a nearly zero value of the probability of thermally-activated flux jumps at temperatures of interest for high-field applications. The values of the creep exponents in the two creep regimes resulted from the analysis of the magnetization relaxation data are in complete agreement with theoretical models. Pinning potentials were also estimated, near the critical temperature, from AC susceptibility measurements, their values being close to those resulted (at the same temperature and DC field) from the magnetization relaxation data. [ABSTRACT FROM AUTHOR]

Although consensus about the mechanism responsible for the recently discovered superconductivity in H2S characterized by Tc ≈ 200 K at a pressure of ≈ 150 GPa is yet to emerge, the flurry of activity it triggered has already resulted in a variety of insights and results. Taken up in this paper in the light of the insights provided by Gordon et al. (Angew. Chem. Int. Ed. 55, 3682 (2016)) and by Gor'kov and Kresin (Rev. Mod. Phys. 90, 011001 (2018)) is a detailed study of the role that the chemical potential and the effective mass of the charge carriers play in the results reported by Talantsev and co-authors (Annalen der Physics 529, 1600390 and 1700197 (2017)) for the critical current density of compressed H2S. Our framework comprises the pairing equation for moving Cooper pairs derived via the Bethe–Salpeter equation generalized to include chemical potential, temperature and an applied magnetic field, and the number equation generalized to include temperature and the applied magnetic field. We are thus led to make contact with Marel's (Physica C 165, 35 (1990)) work of about 30 years ago that was concerned with the duality in the behavior of the chemical potential in high-Tc superconductors as a function of temperature. [ABSTRACT FROM AUTHOR]

The addition of artificial pinning centers has led to an impressive increase in the critical current density (Jc) of superconductors, enabling record-breaking all-superconducting magnets and other applications. The Jc of superconductors has reached ~0.2–0.3 Jd, where Jd is the depairing current density, and the numerical factor depends on the pinning optimization. By modifying λ and/or ξ, the penetration depth and coherence length, respectively, we can increase Jd. For (Y0.77Gd0.23)Ba2Cu3Oy ((Y,Gd)123), we can achieve this by controlling the carrier density, which is related to λ and ξ. We can also tune λ and ξ by controlling the chemical pressure in Fe-based superconductors, i.e., BaFe2(As1−xPx)2 films. The variation in λ and ξ leads to an intrinsic improvement in Jc via Jd, allowing extremely high values of Jc of 130 MA/cm2 and 8.0 MA/cm2 at 4.2 K, consistent with an enhancement in Jd of a factor of 2 for both incoherent nanoparticle-doped (Y,Gd)123 coated conductors (CCs) and BaFe2(As1−xPx)2 films, showing that this new material design is useful for achieving high critical current densities in a wide array of superconductors. The remarkably high vortex-pinning force in combination with this thermodynamic and pinning optimization route for the (Y,Gd)123 CCs reached ~3.17 TN/m3 at 4.2 K and 18 T (H||c), the highest values ever reported for any superconductor. A very active research area in superconductivity is the performance improvementofthe current carrying capability (Jc). Here, we show that the depairing current (Jd) can beincreased by controlling the penetration depth (λ) and coherence length (ξ) in the two most representative materials: in REBa2Cu3Oy we increased the carrier density to decrease λ and ξ, and in BaFe2(As1-xPx)2 we tuned the chemical pressure. The combination ofthese thermodynamic and flux-pinning optimization routes leads to a dramatic increase of Jc to Jc ~150 MA/cm2 at 4.2 K (32.4% of Jd) for REBa2Cu3Oy, the highest value ever reported for any superconductor. [ABSTRACT FROM AUTHOR]

In this work, we compared Bi2Sr2CaCu2O8+θ (BSCCO) superconducting nanofibers prepared by electrospinning (ES) and solution blowing spinning (SBS) techniques for the first time. The differences in microstructure and magnetic properties of BSCCO superconducting fibers prepared by ES and SBS were investigated. The thickness of the ES-BSCCO nanofibers was more uniform than that of the SBS-BSCCO nanofibers. In addition, the superconducting transition temperature of superconducting SBS-BSCCO nanofibers was only 73.5 K due to the weak connection of grains, which was lower than 82.5 K of the ES-BSCCO sample. Further studies showed the area enclosed by the hysteresis loop, the critical current density, and the intensity of the pinning force of SBS-BSCCO fibers were all smaller than those of the ES-BSCCO sample. Finally, we found that the pinning mechanism of these two BSCCO samples could be ascribed to the activation of the point-pinning mechanism and surface-pinning mechanism. [ABSTRACT FROM AUTHOR]

This paper proposes a way to represent the anisotropic nonlinear superconducting properties using a discrete model for magnetization with the corresponding critical parameters, equivalent to the Power Law model for currents. This simplified model makes it possible to analyze magnetic systems with superconducting elements in a stationary mode, which reduces the calculation time. Using of proposed model is demonstrated by the calculation of force interactions between high-temperature superconducting (HTS) samples and permanent magnet in zero-field-cooling (ZFC) and field-cooling (FC) modes. HTS bulks in the form of a prism and stack made of HTS tape are considered. The calculation of the electromagnetic field was carried out using the method of integral equations for field sources. The data of calculations are compared with the results of experimental studies. [ABSTRACT FROM AUTHOR]

In this study, pure and Mo/W co-doped Bi-based superconducting samples were prepared by conventional solid-state reaction method. The effects of co-doping Mo and W were investigated by magneto-resistivity measurements (ρ-T) under various magnetic fields. The critical current density (Jc) was determined from the width of the hysteresis (M-H) curves using the Bean model and it was found that the pure sample showed the best value with a value of 1.53 × 104 A/cm2 at 10 K. The pinning force was calculated using the Jc values and it was found that the pure sample with the highest Jc value naturally had the maximum pinning force which is directly proportional to Jc. The flux pinning energies (i.e., activation energies) were determined using Arrhenius plots. A thermally activated flux flow (TAFF) model was used to calculate these energies. The activation energy ranged from 0.52302 to 0.286005 eV under 0 T. In addition, resistivity measurements (ρ-T) were used to calculate the coherence length (ξ(0)) at 10 K. [ABSTRACT FROM AUTHOR]

High-entropy alloy (HEA) superconductors—a new class of functional materials—can be utilized stably under extreme conditions, such as in space environments, owing to their high mechanical hardness and excellent irradiation tolerance. However, the feasibility of practical applications of HEA superconductors has not yet been demonstrated because the critical current density (Jc) for HEA superconductors has not yet been adequately characterized. Here, we report the fabrication of high-quality superconducting (SC) thin films of Ta–Nb–Hf–Zr–Ti HEAs via a pulsed laser deposition. The thin films exhibit a large Jc of >1 MA cm−2 at 4.2 K and are therefore favorable for SC devices as well as large-scale applications. In addition, they show extremely robust superconductivity to irradiation-induced disorder controlled by the dose of Kr-ion irradiation. The superconductivity of the HEA films is more than 1000 times more resistant to displacement damage than that of other promising superconductors with technological applications, such as MgB2, Nb3Sn, Fe-based superconductors, and high-Tc cuprate superconductors. These results demonstrate that HEA superconductors have considerable potential for use under extreme conditions, such as in aerospace applications, nuclear fusion reactors, and high-field SC magnets. Thin-film high-entropy alloy (HEA) superconductors have recently attracted a lot of attention, but their critical current density and potential usefulness in engineering applications has remained unclear. Here, the authors fabricate HEA films with remarkably high critical current density and resistance to radiation damage. [ABSTRACT FROM AUTHOR]

The structural and magnetic properties of a niobium nitride (NbN) film prepared by reactive sputtering onto a quartz substrate are investigated. It is shown using scanning electron microscopy that the film has a columnar structure with a diameter of crystallite columns of about 50 nm. The film magnetization loops are measured for the field orientation parallel and perpendicular to its surface. Based on the experimental data, the critical current densities of the film are estimated in both cases. For the field parallel to the film surface, the estimate is 6.5 × 104 A/cm2 at the liquid helium temperature. For the field perpendicular to the surface, the critical current density is close to the depairing current density (107 A/cm2). Analysis of the results based on different models of magnetic vortex pinning in superconductors shows that in the former case, pinning occurs at the boundaries of columns in the bulk of the sample, while in the latter case, it is determined by the influence of the surface barrier. [ABSTRACT FROM AUTHOR]

The preparation of YBCO superconducting films by using metal organic chemical deposition (MOD) involves low-temperature pyrolysis and high-temperature treatment. The former process generally requires the introduction of water vapor and other gases. The study on pyrolysis in a low vacuum environment and non-carrier gas atmosphere has never been reported. In this work, we explored a low vacuum pyrolysis scheme with simple Argon gas decompression and a carrier-free atmosphere. The effects of heating rate on the microstructure of pyrolysis films were investigated, and the high-temperature treatment temperature (Th) was also optimized. Compared with conventional pyrolysis, the present low-vacuum pyrolysis does not employ the flowing dry or wet gases, facilitating the internal gas release during film decomposition. More importantly, the efficiency was greatly improved with reduced pyrolysis time. The obtained film surface is free of CuO particle, which leads to a lower roughness. We also investigated the effect of Th on the final YBCO film texture and superconductivity. As Th increased from 810 °C to 815 °C, the BaCuO2 phase decreased with enhanced c-axis orientation being evident by XRD and Raman spectra. As a result, the critical current density (Jc) increased from 0.38 MA/cm2 to 1.2 MA/cm2 (77 K, self-field). [ABSTRACT FROM AUTHOR]

Superconducting devices are an interesting technological option for improvement of efficiency of energy systems. High-temperature superconducting tapes are among the best choices for power applications. Because of their high non-linearity, the design of devices with superconducting tape requires specific simulation models and methods to correctly represent the superconducting behavior. The J-A formulation has been investigated as an efficient tool to represent the electromagnetic behavior of such devices. It is based on the current density (J) and magnetic vector potential (A), and able to represent both superconducting materials and ferromagnetic materials. With regards to the tapes, the use of thin-film approximation can be successful with the J-A formulation. Usually, only representations considering the superconducting layer of tapes have been investigated. This becomes a problem for operations where the current in the superconductor surpasses the critical current, for example in transient analysis. This paper presents an analysis of the effects the inclusion of all of the tapes' layers have on simulations with the J-A formulation with thin-film approximations. By considering all layers of the tape, one represents the transition between superconducting and high-loss states of the tape. A simple system, consisting of a single tape with applied current, has been studied as benchmark and simulated with J-A and the more established T-A formulation in two cases: considering all layers; and only the superconducting layers. Results show that results for the J-A and T-A formulations are compatible and the inclusion of all layers improves the stability of the simulation and provides correct assessment of the electric field in the tapes. • J-A formulation. • HTS tape second generation. [ABSTRACT FROM AUTHOR]

AeA Fe 4 As 4 (Ae = Ca, A = K; 1144) having a transition temperature of 35 K is a stoichiometric family of iron-based superconductors (FBS). Here, we present a detailed study of a high-pressure synthesis of CaKFe 4 As 4 bulks to investigate the impact of these conditions on the superconducting properties of the 1144 family. Additionally, these samples are also prepared by conventional synthesis method at ambient pressure (CSP) and studied the influence of impurities on the superconducting properties of CaKFe 4 As 4. Structural, microstructural, transport and magnetization measurements have been performed to reach the final conclusions. Interestingly, the high-pressure synthesis of the parent CaKFe 4 As 4 compound enhances the transition temperature (T c) by 2 K and the critical current density (J c) by one order of magnitude in the whole magnetic field range of 9 T than that of the 1144 bulks prepared by CSP. It suggests the improvement of the pinning centers and grain connections by the high-pressure synthesis approach. Interestingly, our results depict the superconducting onset transition temperature (T c onset ) of this stoichiometric 1144 family is robust with the presence of the common 122 (CaFe 2 As 2 or KFe 2 As 2) impurity phases, which is a different behavior compared to other FBS families. However, these impurity phases reduce the grain connections and lead to the phase separation during the formation of the superconducting (1144) phase. • Stoichiometric CaKFe 4 As 4 (1144) superconductor was prepared by high pressure synthesis method. • This novel approach has enhanced the superconducting properties and quality of the 1144 samples. • The onset superconducting transition is robust with the common impurity phases unlike other iron based superconductors. [ABSTRACT FROM AUTHOR]

For high-field power applications of high-temperature superconductors, it became obvious in recent years that nano-engineered artificial pinning centers are needed for increasing the critical current and pinning potential. As opposed to the artificial pinning centers obtained by irradiation with various particles, which is a quite expensive approach, we have studied superconducting samples having self-assembled defects, created during the sample fabrication, that act as effective pinning centers. We introduced a simple, straight-forward method of estimating the frequency-dependent critical current density by using frequency-dependent AC susceptibility measurements, in fixed temperatures and DC magnetic fields, from the positions of the maxima in the dependence of the out-of-phase susceptibility on the amplitude of AC excitation magnetic field. The results are compatible with a model that stipulates a logarithmic dependence of the pinning potential on the probing current. A mathematical derivation allowed us to estimate from the experimental data the pinning potentials in various samples, and in various DC magnetic fields. The resulted values indicate large pinning potentials, leading to very small probability of magnetic flux escaping the pinning wells, hence, leading to very high critical currents in high magnetic fields. [ABSTRACT FROM AUTHOR]

When compared with rare-earth coated conductors, magnesium diboride superconducting cables are known to show significant advantages by cost and easy production. However, the inherent difficulty for achieving a significant reduction of their magnetization losses in multifilamentary wires, without degrading the high critical current density that is so characteristic of the monowire, is considered as one of the major drawbacks for their practical use in high power density applications. Being this one of the major markets for superconducting cables, from fundamental principles and computational optimization techniques, in this paper we demonstrate how the embedding of the superconducting filaments into soft-ferromagnetic metastructures can render to their full magnetic decoupling, and therefore, to the maximum reduction of the energy losses that can be achieved without deteriorate the critical current density of the cable. The designed multifilamentary metastructure is made of NbTi coated MgB2 superconducting filaments in a Cu-matrix, serving as a reference for validating our model with actual experimental measurements in monowires and multifilamentary wires. The novelty in our computationally aided multifilamentary wires, is that each one of the filaments is embedded within a thin metastructure made of a soft-ferromagnetic layer and a resistive layer. We have found that for soft-ferromagnetic layers with magnetic permeabilities in the range of μ r = 20–100, nearly a full magnetic decoupling between the superconducting filaments can be achieved, leading to efficiencies higher than 92 % , and an overall reduction of the AC-losses (including eddy currents at the Cu-matrix) higher than 50 % . [ABSTRACT FROM AUTHOR]

In this study, the role of gamma irradiation on lanthanum-added Bi1.85Pb0.35Sr2Ca2LaxCu3Oδ (BSCCO) bulk ceramic superconductors prepared by conventional solid state sintering method was examined. For this purpose, microstructure, critical current densities (Jc), and condensation properties of samples were characterized in detail before and after the application of gamma irradiation. These characteristics were analyzed by Scanning Electron Microscopy (SEM), Magnetic Hysteresis (M-H) curves, and density measurements, respectively. It was observed from SEM images that many samples had a layered and porous grain structure, characteristic of high temperature superconductors. It was found that the critical current densities calculated from the width of the M-H curves do not behave proportionally to the increasing gamma radiation intensity. It was found that the density values of the samples determined by Archimedes method were in the range of approximately 71–84% of the theoretical value. [ABSTRACT FROM AUTHOR]

The oxygen concentration and distribution in the microstructure of MgB2- and YBa2Cu3O7-δ-based materials affect the formation of nanostructural defects and thus influence the critical current density, upper critical magnetic field and irreversibility field. For MgB2 oxygen containing additions (Dy-O, Ti-O) in the form of nanograins occurred not to be very effective for an increase of critical current density, jc. Sn-O additions to MgB2 can provoke even a significant decrease of jc due to a chemical interaction of Sn with MgB2. The processing pressure and temperature influence the defect density of the relevant pinning centers and the regularity of their distribution in doped and undoped MgB2 as well as in MT-YBCO. [ABSTRACT FROM AUTHOR]

Since the 1970’s the effect of the increase of the critical current of superconductors in the longitudinal external magnetic field has been known. The critical current density of a Nb-Ti wire at low longitudinal magnetic fields demonstrated several times the larger value compared with that in a transverse magnetic field. The same phenomenon has been observed for 2G HTS tapes. It is natural to try to use this phenomenon to increase the critical current in DC HTS power cables. In this paper, we present the analysis of feasibility to use the longitudinal magnetic field effect to increase critical currents in practical HTS power cables. The experimental model of the HTS DC cable has been developed, produced, and tested in liquid nitrogen. The increase of the critical current observed when the longitudinal magnetic field generated. This increase coincides with the calculations. [ABSTRACT FROM AUTHOR]

Spin–orbit torque induced ferromagnetic magnetization switching brought by injecting a charge current into strong spin–orbit-coupling materials is an energy-efficient writing method in emerging magnetic memories and spin logic devices. However, because of the short spin coherence length in ferromagnetic layers, the interfacial effective spin–orbit torque typically leads to high critical current density for switching thick ferromagnet, which goes against low-power and high-density requirements. Here, we experimentally demonstrate efficient bulk spin–orbit torque-driven perpendicular magnetization switching under relatively low critical current density in thick Pt/Co multilayers with gradient-induced symmetry breaking. Through tuning the thickness gradient of Pt, the spin–orbit torque efficiency and switching chirality can be highly controlled, which also indicates that net spin current arises from gradient. Meanwhile, x-ray absorption spectroscopy results reveal that the atomic intermixing can significantly enhance the spin–orbit torque efficiency through improving the strength of spin–orbit-coupling of Pt. We also establish a micromagnetic model by taking both gradient-induced and intermixing-enhanced spin–orbit torque into account to well describe the experimental observations. This work would blaze a promising avenue to develop novel spin–orbit torque devices for high-performance spintronic memory and computation systems. [ABSTRACT FROM AUTHOR]

We investigated the effect of the thickness of superconducting layer on the competition between ferromagnetism and superconductivity. The epitaxial bilayer systems consisting of GdBa 2 Cu 3 O 7-x (GdBCO) with varying thickness and La 0.7 Sr 0.3 MnO 3 (LSMO) were grown on (001) SrTiO 3 (STO) substrate. From the spectroscopic measurements, we observed an existence of a possible structural coupling between the GdBCO and the LSMO layers. The structural coupling is found to depend on the GdBCO thickness and to induce different types of strain on both layers, leading to the competition between the ferromagnetic and the superconducting orders. With respect to the flux pinning, an additional pinning contribution besides magnetic pinning induced by LSMO is emerged by the structural coupling, which is attributed to local atomic disorder. Controlling the thickness of GdBCO modifies the structural coupling and consequently, the degree of additional pinning contribution aroused by disorder on the CuO 2 plane can be adjusted. An appropriate structure with a certain thickness amplifies the hybrid effect of magnetic pinning and additional pinning, resulting in an enhancement of the critical current density at high magnetic fields. Our findings suggest a possibility of controlling complex flux pinning through an optimization of structural coupling between the GdBCO and the LSMO layers. [ABSTRACT FROM AUTHOR]

The particle size dependence of the isothermal magnetization loops, critical current density, and the irreversibility field were determined for a superconducting sample of SmFeAsO0.91F0.09 in a low field range. The central peak position in the ascending branch of the magnetization is shifted to lower field values as the particle size rg decreases. In agreement with the collective flux creep theory, this peak follows a logarithmic law as a function of rg. In all the samples with different particle size, the critical current density (Jc) shows a peak associated to a high concentration of weak bulk pinning center. In the low field range, the particles with a small size present higher Jc values than the particles with a bigger size. In this region, and far from Tc, we found that Jc ~ rg−1/2 for all the particles sizes, in agreement with the collective flux theory for small particles with a 2D pinning character. At these temperatures, it was estimated a value of ~ 840 nm for the pinning correlation length L. Nevertheless, as the temperature is increased, a change to a Jc ~ 1/rg dependence is observed, that cannot be explained by the flux creep theory; nevertheless, the experimental data allows to estimate a value of ~ 275 nm for L. At higher fields, the Jc values are higher in the bigger particles than in the smaller ones. The irreversibility field determined at 50 K also depends on rg, following a power law (Hirr1/3 ~ rg) as indicated by the flux creep theory. [ABSTRACT FROM AUTHOR]

This paper presents an approach for deriving the continuum sensitivity of superconducting systems operating at critical current densities and an optimization method based on the continuum sensitivity. In the sensitivity problem, the superconducting systems is represented by a variational state equation, wherein the magnetic permeability depends on the magnetic field, which is transformed from a state equation with a field-dependent source. The design sensitivity is derived using the material derivative concept of continuum mechanics and the adjoint variable method. The adjoint system has a material property represented as a symmetric tensor that contains the sensitivity of the current density with respect to the magnetic field. The design sensitivity is represented in the analytical form of a surface integral on the interface between the superconducting material and its surroundings, which depends on the sensitivity of the current density. The optimization scheme is constructed based on the continuum design sensitivity. In the design optimization, the level set method is used to express the shape variation of the superconducting materials. The numerical example of infinite solenoids demonstrates that the design sensitivity provides an accurate design solution considering the critical current condition. In addition, the design example of a magnetic resonance imaging solenoid shows that the derived design sensitivity has the inherent ability for attaining the compact design by treating the input current of a superconducting system as a critical condition. [ABSTRACT FROM AUTHOR]

Based on existing quasi-isotropic strand (QIS) conductor and twisted stacked tape cable–cable in conduit conductor (TSTC-CICC), this paper proposed a novel QIS-CICC. The conductor was numerically modeled and the anisotropy of critical currents was analyzed. The simulations showed that although the critical currents of the QIS-CICC were worse than those of the TSTC-CICC for the self-field condition, the current decay of the QIS-CICC was far less than that of the TSTC-CICC under a 1 T external field, and the anisotropies of the two conductors were almost the same. [ABSTRACT FROM AUTHOR]

In this work, I shall summarize different phenomenological approaches of vortex trapping as well in conventional superconductors that serve as a basis for experimental fact interpretations in new superconductors as in massive and nanometric high critical temperature superconductors, and I shall present our experimental studies on vortex trapping in single crystals of La1.85Sr0.15CuO and YBa2Cu3O7-δ but also in nanoparticles of YBa2Cu3O7-δ. Particular attention should be paid to the study of high-TC superconducting nanoparticles of YBa2Cu3O7-δ system doped with magnetic nanoparticles of Y3Fe5O12. The reduction in the size of grains of these two compounds by mechanical grinding led to the size disparities of these grains, confirmed by an analysis by means of an atomic force microscope. These disparities are inherent in mechanical grinding. The average sizes of the obtained nanoparticles were estimated to be in the range of 80 nm by means of XRD reflection using the Scherrer equation. The nanometric size of the obtained grains revealed new phenomena considered in the past as contradictory like the coexistence of ferromagnetism and superconductivity and the trapping of vortices by spins which were studied here in detail and allowed us highlighting this coexistence and interpreting the variations in field and temperature of the critical current density JC in this system. [ABSTRACT FROM AUTHOR]

High temperature superconducting (HTS) magnets usually work in closed-loop mode to generate a stable magnetic field by carrying persistent currents, such as Maglev trains, machines and some projects of magnetic resonance imaging. In these applications, the HTS magnets can usually be operated under external AC fields that possibly come from harmonic fields and electromagnetic vibration. Thereby, AC current is induced and circulating in the closed-loop HTS coil. However, a systematic study of the effect of induced current on the electromagnetic properties, especially the current decay/demagnetization of HTS magnets, has not been performed. In this work, experimentally, the measurement of the shielding factor indicates that the HTS magnet is capable of carrying induced AC current with an amplitude as large as its self-field critical current. In addition, the instantaneous current in HTS magnets (including the original direct current and induced current) under axial AC fields are measured, showing that a larger induced current would lead to quicker demagnetization. Numerically, a distinct simulation model for closed-loop HTS coil is established based on the H-formulation. Good agreement is found between the simulation and experimental results of the waveform of induced current, but less consistency is observed for the decay curves of direct current. Based on the numerical and experimental results, the physical mechanism of induced current on accelerating the current decay of HTS magnets is studied, i.e., a net flux motion is induced across an AC cycle in the region flowing direct current, leading to the generation of a net DC electric field. [ABSTRACT FROM AUTHOR]

The gate-tunable Josephson junction, generally achieved in planar Josephson field-effect transistors (JoFETs), is a key element for the applications of superconducting devices. At present, the performance of these systems with planar JoFETs is often impeded by the large channel length, which, at best, lies in the range of tens of nanometers. In contrast, the channel length in vertical junctions can be easily scaled down to nano-scale to realize the strong Josephson coupling. However, the vertical junctions are believed to be insensitive to the field-effect due to the atomic screening of electric fields in metals. Here, we report on a novel realization of few-layer black phosphorus (BP)-based vertical JoFETs using an electric-double-layer configuration. In transport experiments, using junctions of different shape, superconducting quantum interference device-like magnetic diffraction patterns of the junction critical current and anomalous Shapiro steps on current voltage characteristics are observed, strongly indicating that the critical current density in the junctions is highly inhomogeneous and peaked at the edges or even near the junction corners. The electric-field tunability of the Josephson coupling could be attributed to the edge- or corner-dominated supercurrent density profile combining with the carrier diffusivity in the few-layer BP. The ability to control the vertical Josephson coupling provides us with new opportunities to study high-performance and high-temperature superconducting Josephson field-effect transistors operating on an atomic-scale channel length. [ABSTRACT FROM AUTHOR]

In the future, superconducting magnetic energy storage (SMES) technology will be developed toward large capacity. Among them, a single magnet is expensive and technically challenging. The integration of multiple SMES (M-SMES) is a feasible technical route. But there is coordination among multimodule energy storage magnets, so the formulation of its control strategy is very important. In this article, based on the toroidal magnet, a state evaluation method of toroidal magnet considering the withstand voltage and temperature of the magnet is proposed. To solve the problem of power distribution caused by the difference in initial capacity, initial temperature, and maximum output power during the cooperative control of multiple SMES, a temperature equilibrium control strategy for energy storage magnets combined with state assessment is proposed. System simulation results showed that this strategy could effectively balance the working state of each module and maximize the power output capability of the energy storage magnet by ensuring the safety of the magnet. [ABSTRACT FROM AUTHOR]

Grain boundaries (GBs), as extremely anisotropic pinning defects, have a strong impact on vortex motion in type-II superconductors, and further on the macro level dominates the superconductivity for example the critical current density. Many previous studies indicated that mostly GB plays the role of a strong barrier for vortex motion, while an easy-flow channel just under some certain conditions. In order to thoroughly make clear of the questions of what is exactly the role of GB on vortex motion and how it works, in this article we developed a large scale molecular dynamic model and revealed the action of GB on vortex motion in type-II superconductors. The most significant finding is that the role of GB on vortex motion can be changeable from a barrier to an easy-flow channel, and which is intrinsically determined by the competition effect correlated with its action on vortex between in the GB and no-GB regions. Such the competition effect essentially depends on the attributes of both the GB (described by the GB strength and angle θ) and no-GB pining regions (by the relative disorder strength αp/αv). Specifically, for a YBa2Cu3O7 – x (YBCO) sample, to obtain a clear knowledge of vortex motion in GB region, we visualized the three typical trajectories of vortices during the three vortex movement stages. Further, in order to understand how GB results in the macro current-carrying property, corresponding to the current–voltage relation of the YBCO conductor, we obtained the average velocity vy of vortices varying with their driving force, which is nearly identical with the previous observations. [ABSTRACT FROM AUTHOR]

We present a detailed study of Ta/Ru-based buffers and their influence on features crucial from the point of view of applications of Magnetic Tunnel Junctions (MTJs) such as critical switching current and thermal stability. We study buffer/FeCoB/MgO/Ta/Ru and buffer/MgO/FeCoB/Ta/Ru layers, investigating the crystallographic texture, the roughness of the buffers, the magnetic domain pattern, the magnetic dead layer thickness, and the perpendicular magnetic anisotropy fields for each sample. Additionally, we examine the effect of the current induced magnetization switching for complete nanopillar MTJs with lateral dimensions of 270 × 180 nm. Buffer Ta 5/Ru 10/Ta 3 (thicknesses in nm), which has the thickest dead layer, exhibits a much larger thermal stability factor (63 compared to 32.5) while featuring a slightly lower critical current density value (1.25 MA/cm2 compared to 1.5 MA/cm2) than the buffer with the thinnest dead layer Ta 5/Ru 20/Ta 5. We can account for these results by considering the difference in damping which compensates for the difference in the switching barrier heights. [ABSTRACT FROM AUTHOR]

In the present paper, the possibility of magnetization of HTSC tape by means of pumping by a local magnetic field is considered. Within the framework of the critical state model, the calculation of the density of the induced currents and the magnetization of a square (12 × 12 mm) fragment of a second-generation HTS tape (YBCO) was made. The model considers real dependence of the critical current density on the magnetic field and has been successfully tested previously. In the sample, the currents were induced by the impact of a local magnetic field. The size of the localized area of the external magnetic field to be considered was much smaller than the size of the HTS sample. It is showed that the repeated cyclical impact of the local outer field leads to the accumulation of the total magnetic moment in the sample up to a magnitude of 94% of the theoretical magnetization limit for this sample. The results obtained make it possible to optimize the mode of magnetization of a square fragment of a tape (or a stack of tapes) when implementing a magnetic flux pump. The experimental studies showed results comprisable well with theoretical ones. [ABSTRACT FROM AUTHOR]

We show a systematic correlation between temperature, critical current density (CCD), and ASR. The ASR declines while the CCD increases with temperature. The behavior is consistent with a void nucleation model for cell failure. Void nucleation is driven by the cell voltage: a lower ASR reduces the voltage which helps to raise the critical current density. The voids are postulated to be precipitated by local concentrations of electrochemical currents which pull lithium into the electrolyte leaving behind a void in the lithium layer across from the interface. We also report on a possible method for reducing the non-uniformity of current flow across the interface by introducing a layer of silver at the interface. It has the effect of increasing the CCD to 3.5 mA cm−2 at elevated temperature. [ABSTRACT FROM AUTHOR]

Conductor on round core (CORC) cables with the features of flexibility and a high engineering current density have been a potential candidate for high magnetic field magnets and accelerator magnets. In these applications, reducing the magnetization loss generated in superconductors is essential in the process of design. CORC cables fabricated by multifilament-coated conductor (CC) tapes have been proved to have a low magnetization loss. However, the degradation of the critical current (Ic) and additional coupling losses significantly affects the performance of CORC cables. In this article, ultraviolet laser cutting technology is used to scribe both the superconducting layer and copper stabilization layers into narrow filaments. First, the magnetization loss of a single tape with different numbers of filaments was measured by a calibration-free method. Then, based on the testing results of a single tape, two typical CORC cables are wound by 10-mm-wide and 4-mm-wide CC tapes. The magnetization loss of cables made of striated tapes was discussed by both experimental and numerical methods. It is found that the magnetization loss significantly decreases with an increasing number of filaments under a high background magnetic field. The magnetization losses decrease in CORC cables made of striated CC tape. Due to the reduced coupling loss and attenuated shielding effect, there is not much difference between the two values of the magnetization loss reduction rates in CORC cables and single tapes. The conclusions obtained in this article will be instructive for the future design of CORC cables. [ABSTRACT FROM AUTHOR]

We compare the potential of SQUID arrays and Josephson junction arrays as magnetic field detectors in an open-loop configuration, accounting for such limitations as technological parameter fluctuations, current density distribution and self-field effects originating from the bias current. Because of the simplicity of its single layer process, the ion-damaged barrier technology is used to fabricate the Josephson junctions (JJ) and to make the evaluations by extrapolation to larger area detectors. From preliminary experimental results on series arrays of Josephson junctions, we expect a less detrimental effect of self-flux and parameter dispersion, which is particularly important with high critical temperature technologies. [ABSTRACT FROM AUTHOR]

The intra-layer no-insulation (LNI) method is effective for protecting a layer-wound REBCO coil from a quench. However, a recently reported hoop stress modification (both increase and decrease) due to screening currents is a potential problem causing conductor degradation during charging. Epoxy impregnation can suppress the hoop stress modification and in this work, we develop prototypes of epoxy-impregnated LNI-REBCO coils to be charged at 77 K. Degradation of the coil performance due to cooling down can be prevented by mechanically isolating each layer. The coil shows a reasonably short field delay and current bypassing behavior, which are major technical benefits of the LNI-REBCO coil. A structural analysis with screening current-induced electromagnetic forces qualitatively suggests that the epoxy-impregnated LNI-REBCO coil can support a compressive hoop stress which causes conductor degradation due to buckling. The tensile hoop stress, however, is still very high at the upper and lower ends of each layer, causing fracture of a superconducting layer; i.e., additional reinforcement is required. [ABSTRACT FROM AUTHOR]

Superconducting coils may suffer from electromagnetic vibration due to changing electromagnetic fields under AC conditions. In the long term, this vibration may cause performance degradation of superconducting tapes. In order to study the influence of electromagnetic vibration between superconducting tapes on their performance, the study can be started from the simplest form of electromagnetic vibration, that is, the electromagnetic vibration between two superconducting tapes. The degree of electromagnetic vibration under different AC currents were analyzed by simulation, and the variation of critical current (Ic) and the n-value of Y-Ba-Cu-O (YBCO) tapes after undergoing long-term electromagnetic vibration through experiments were measured. The results show that two YBCO tapes does not show obvious performance degradation under tens of hours the electromagnetic vibration caused by the AC current amplitude of 1.2 to 1.4 times Ic. [ABSTRACT FROM AUTHOR]

The superconducting joint between Bi2223 tapes has been developed with a method of joint by incongruent melting (JIM) in our Laboratory. The multi-junction method used to increase the contact area yielded a demonstrated increase in critical current. In previous studies, a simple boundary shape with lap-joint was chosen to connect several filaments in the tape, and this method is not suitable for connecting all about 100 filaments. Of course, more filaments are necessary to be joined with superconducting boundary, in order to increase the critical current of joint. However, due to the thin tape structure, there is difficult to use of butt joint between two cross-sections of tapes. In this study, we proposed a multi-junction method by using multiple boundaries with stepped structure. In experiments, joint samples with increasing of junction number to three from one were prepared, and the critical current for each unction number were measured at 77 K (self-magnetic field). In result, the critical current is increased with increasing of the junction number, and a highest critical current of 51.8 A was obtained in three-junction sample. in particular, the critical current at first junction (end of tapes) is highest, indicating that critical current at the end is important in total critical current of joint. Therefore, single junction at end of tapes was prepared and evaluated by using X-ray diffraction and critical current measurement. From X-ray diffraction patterns, the joint area is estimated to be about 1 cm. The critical current was 36.5 A at 77 K. [ABSTRACT FROM AUTHOR]

BaMO3 (M = Zr, Hf) pinning centers introduced in REBa2Cu3O7-x (REBCO and RE = rare earth) coated conductors yield superior performance in high magnetic fields. We present the critical current density Jc over a temperature range of 4.2–77 K and magnetic fields of 0–14 T (B || c-axis), of 5-15 mol.% Zr- and Hf- added REBCO 4+ μm thick film tapes fabricated by advanced metal organic chemical vapor deposition (A-MOCVD). The morphology of self-assembled BMO nanorods aligned along c-axis is found to be dependent on the Zr/Hf content. We also observe a correlation between the density of RE2O3 in-plane nanoprecipitates and the continuity and concentration of BMO nanorods in films of different Ba content. It is found that the (Ba + M)/Cu (M = Zr, Hf) content in REBa2Cu3O7-x affects the shape of pinning force density curves over a wide magnetic field range and temperatures below 20 K. Another remarkable observation is the similarity in the critical current properties of Hf and Zr- added REBCO films as function of (Ba + M)/Cu content at intermediate to high range of (Ba + M)/Cu content. A quantitative analysis of pinning efficiency and correlation with the microstructure of Zr and Hf- added REBCO coated conductors is discussed. [ABSTRACT FROM AUTHOR]

With excellent mechanical properties and electromagnetic properties, compact superconducting cables are considered as potential candidates for large capacity power applications and fusion magnets. In this paper, the concept of a novel compact cable, conductors in tube (CIT) cable is introduced from the aspect of design, fabrication, and performance evaluation, respectively. The principal advantages of CIT cables are that the cable can release the residual stress created from the fabrication process, and the outer former of the cable can be used as both the supporter as well as the container of refrigerant liquid. Firstly, the topological structure and the detailed fabrication process of a CIT cable are presented. Then, a typical CIT cable is manufactured. The feasibility of this new structure is verified by its critical current test. Moreover, bending characteristics of CIT cables are evaluated and compared with Conductors on Round Core (CORC) cables from the aspect of both simulation and experiments. The superior bending performance enables it to be potential in the future compact magnet application. [ABSTRACT FROM AUTHOR]

We developed a fabrication process to establish large arrays of up to 5-stacked Josephson junctions for the Josephson Arbitrary Waveform Synthesizer (JAWS). SNS-type Josephson junctions with NbxSi1-x barriers are used for this application. By modifying our standard window process, e.g. to add a CMP (chemical mechanical polishing) and an ALD (atomic layer deposition) step, the yield of this process was increased. An output voltage of 1 V RMS could be achieved by using 4 JAWS arrays in series with a total number of 60,000 5-stacked junctions. The investigation of the current-voltage characteristics (IVC) showed an interesting and potentially useful feature. The required pulse amplitude per junction for getting the maximum Shapiro step width reduces for higher junction stacks. We found that the pulse power linearly reduces with the square of the junction number in the array. The origin of this effect might be a strong neighbour-neighbour interaction of the junctions, which are closely arranged within the stacked configuration. This might generate a strong self-synchronization of the junctions. [ABSTRACT FROM AUTHOR]

Advanced metal organic chemical vapor deposition technique (A-MOCVD) was used to grow 4-5 μm thick REBa2Cu3O7−δ (REBCO, RE = rare earth) films, doped with 5% and 15% Hf. Thick REBCO films doped with 5% Hf exhibit self-field critical current density (Jc) over 1.8 MA/cm2 at 77 K and 3 MA/cm2 at 65 K, 1.5 T. Increasing the Hf content to 15% resulted in Jc above 9 MA/cm2 at 20 K, 9 T. The effect of (Ba+Hf)/Cu content in Hf-added (5 and 15 mol.%) REBCO films on the critical current density at 77 K, 0 T, c-axis lattice parameter and out-of- plane texture has been studied. In addition to growth of thick film REBCO tapes with superior performance, the A-MOCVD reactor has been used to quadruple the precursor-to-film conversion efficiency above 45%. This achievement has a first order impact in lowering the cost of REBCO tapes made by A-MOCVD. [ABSTRACT FROM AUTHOR]