Showing papers on "Flux pinning published in 2007"
TL;DR: Angle-dependent critical-current measurements demonstrate that a strong and isotropic flux-pinning mechanism is extremely effective at high temperatures and high magnetic fields leading to high-temperature superconductors with record values of pinning force.
Abstract: Strong isotropic flux pinning in solution-derived YBa 2 Cu 3 O 7− x nanocomposite superconductor films
566 citations
TL;DR: In this paper, a review of the superconducting properties of MgB2 that are relevant for power applications is presented, focusing on the reversible mixed state parameters, which define the limiting conditions for loss-free currents: the transition temperature, the upper critical field and the depairing current.
Abstract: This review focuses on the superconducting properties of MgB2 that are relevant for power applications. The reversible mixed state parameters are the most important, since they define the limiting conditions for loss-free currents: the transition temperature, the upper critical field and the depairing current. They also determine the flux pinning energy, the pinning force and the elastic properties of the flux line lattice and, therefore, strongly influence the critical current densities. The magnetic properties of magnesium diboride are anisotropic and influenced by the two different energy gaps of the σ- and π-bands. Whereas the transition temperature could not be enhanced significantly during the past five years, the upper critical field was considerably increased by impurity scattering or doping. Flux pinning is very weak in MgB2 single crystals and was only improved by irradiation techniques so far. In polycrystalline samples, grain boundary pinning seems to play the dominant role. High critical currents close to the theoretical limit were found in c-axis oriented thin films. The anisotropy of the upper critical field strongly reduces the critical currents in untextured MgB2 at high magnetic fields, where the supercurrents become highly percolative, since not all grains are superconducting anymore. The performance of polycrystalline wires and tapes was significantly improved during the past few years by increasing the upper critical field and by reducing its anisotropy. Pinning seems to be nearly optimized in many forms of this material, but the connectivity between the grains might be further improved.
291 citations
TL;DR: In this paper, the effects of grain connectivity, flux-creep phenomena, and grain size on critical current density and flux pinning curves have been analyzed and compared with the predictions of theoretical models accounting for the effect of the grain size.
Abstract: We report temperature and magnetic-field dependence of flux pinning force in bulk $\mathrm{Mg}{\mathrm{B}}_{2}$ with variable grain size. The samples are prepared by advanced methods, allowing minimizing effects of porosity, impurities, and inclusions of secondary phases. The effects of grain connectivity, flux-creep phenomena, and grain size on critical current density and flux pinning curves are analyzed. We have compared the field dependence of the pinning force for a range of samples with the predictions of theoretical models accounting for the effect of the grain size. There is qualitative agreement between grain-boundary pinning mechanism proposed by Hampshire and Jones [J. Phys. C 21, 419 (1987)] and the experimentally observed grain-size dependence of pinning force in bulk $\mathrm{Mg}{\mathrm{B}}_{2}$.
139 citations
TL;DR: In this paper, a trifluoroacetic acid process was used to prepare nanosized BaHfO3 particles inside a YBa2Cu3O7 film matrix.
Abstract: Both a high critical current density and a cost-competitive, easily upscalable procedure are among the most critical requirements for coated conductors. In this work, a low-cost method based on the trifluoroacetic acid process was used to prepare nanosized BaHfO3 particles inside a YBa2Cu3O7 film matrix. The inclusions have a perovskite structure and grow epitaxially in a cube-on-cube relationship. A drastically improved pinning force density and high irreversibility fields in the YBa2Cu3O7 layers were found and are discussed in respect to the Hf doping level in the precursor solutions, which resulted in an increased nanoinclusion content.
113 citations
TL;DR: It is demonstrated that the field dependence of the critical current crosses over from the well-known Fraunhofer pattern in wide junctions to a monotonic decay when the width of the normal wire is smaller than the magnetic length xi(H)=square root Phi(0)/H, where H is the magnetic field and Phi( 0) the flux quantum.
Abstract: We study theoretically the electronic and transport properties of a diffusive superconductor-normal metal-superconductor junction in the presence of a perpendicular magnetic field. We show that the field dependence of the critical current crosses over from the well-known Fraunhofer pattern in wide junctions to a monotonic decay when the width of the normal wire is smaller than the magnetic length ${\ensuremath{\xi}}_{H}=\sqrt{{\ensuremath{\Phi}}_{0}/H}$, where $H$ is the magnetic field and ${\ensuremath{\Phi}}_{0}$ the flux quantum. We demonstrate that this behavior is a direct consequence of the magnetic vortex structure appearing in the normal region and predict how this structure is manifested in the local density of states.
87 citations
TL;DR: A high-resolution magneto-optical technique was used to analyze flux patterns in the intermediate state of bulk Pb samples of various shapes - cones, hemispheres, and discs and concluded that flux tubes represent the equilibrium topology of the Intermediate state.
Abstract: A high-resolution magneto-optical technique was used to analyze flux patterns in the intermediate state of bulk Pb samples of various shapes---cones, hemispheres, and discs. Combined with the measurements of macroscopic magnetization, these results allowed studying the effect of bulk pinning and geometric barrier on the equilibrium structure of the intermediate state. Zero-bulk pinning discs and slabs show hysteretic behavior due to topological hysteresis---flux tubes on penetration and lamellae on flux exit. (Hemi)spheres and cones do not have a geometric barrier and show no hysteresis with flux tubes dominating the intermediate field region in both regimes. It is concluded that flux tubes represent the equilibrium topology of the intermediate state. Real-time video is available in the EPAPS Document No. ..
82 citations
TL;DR: YBa2Cu3O7?x+Y2O3 (YBCO+YO3) mixed films were prepared on SrTiO3/MgO substrates by pulsed-laser deposition from a YBCO target with a thin Y 2O3 sector on the top as mentioned in this paper.
Abstract: YBa2Cu3O7?x+Y2O3 (YBCO+Y2O3) mixed films were prepared on SrTiO3/MgO substrates by pulsed-laser deposition from a YBCO target with a thin Y2O3 sector on the top. The pinning properties for the mixed YBCO+Y2O3 thin film were strongly enhanced, especially at the temperatures lower than 77?K: the maximum global pinning forces FP for the Y2O3 doped sample are 7.8?GN?m?3 near 2?T at 77?K, 54.5?GN?m?3 near 4?T at 65?K, and 189?GN?m?3 near 9?T at 40?K. In the Y2O3-added samples, except for the plane configuration, the angular dependence of Jc showed a plateau, due to the flux pinning by isotropic pinning centres. Y2O3 nanoparticles randomly dispersed inside the YBCO matrix were consistently observed in the cross-sectional TEM images.
70 citations
TL;DR: In this article, an experimental powerful methodology is proposed to evaluate and quantify the anisotropy and strength of the different pinning contributions of YBa2Cu3O7−x coated conductors by combining angular dependent in-field critical current measurements in the whole temperature range.
Abstract: An experimental powerful methodology is proposed to evaluate and quantify the anisotropy and strength of the different pinning contributions of YBa2Cu3O7−x coated conductors by combining angular dependent in-field critical current measurements in the whole temperature range. A clear separation between isotropic and anisotropic pinning centers and a further classification into weak and strong pinning centers are performed. These analyses envision to establish a correlation between defect microstructure and critical currents which is essential for artificial engineering high-performance nanostructured coated conductors.
58 citations
TL;DR: In this paper, an abnormal loss peak was found in the multilayer cuprate supercondutor CuxBa2Ca2Cu3Oy (Cu-1223), where two components couple with each other through the intercomponent Josephson interaction.
Abstract: An AC magnetic field can rotate a vortex-molecule composed of two fractional vortices in a multiband type of multicomponent superconductor, where two components couple with each other through the intercomponent Josephson interaction. It may directly relate to an abnormal AC loss peak, which we have found recently in the multilayer cuprate supercondutor CuxBa2Ca2Cu3Oy (Cu-1223).
55 citations
TL;DR: In this paper, the authors reported a systematic study of Ag admixing in MgB2 prepared by solid-state reaction at ambient pressure, which revealed the formation of MgAg nanoparticles in Ag admixed samples.
Abstract: In the present investigation, we report a systematic study of Ag admixing in MgB2 prepared by solid-state reaction at ambient pressure. All the samples in the present investigation have been subjected to structural∕ microstructural characterization employing x-ray diffraction and transmission electron microscopic (TEM) techniques. The magnetization measurements were performed by physical property measurement system. The TEM investigations reveal the formation of MgAg nanoparticles in Ag admixed samples. These nanoparticles may enhance critical current density due to their size (∼5–20nm) which is compatible with the coherence length of MgB2 (∼5–6nm). In order to study the flux pinning effect of Ag admixing in MgB2, the evaluation of intragrain critical current density (Jc) has been carried out through magnetic measurements on the fine powdered version of the as synthesized samples. The optimum result on intragrain Jc is obtained for 10at.% Ag admixed sample at 5K. This corresponds to ∼9.23×107A∕cm2 in self...
52 citations
TL;DR: The observation of hysteresis in the vortex pinning in a superconductor-ferromagnetic epitaxial nanocomposite consisting of fcc Gd particles incorporated in a Nb matrix is reported.
Abstract: This Letter reports the observation of hysteresis in the vortex pinning in a superconductor-ferromagnetic epitaxial nanocomposite consisting of fcc Gd particles incorporated in a Nb matrix. We show that this hysteretic pinning is associated with magnetic reversal losses in the Gd particles and is fundamentally different in origin to pinning interactions previously observed for ferromagnetic particles or other microstructural features.
TL;DR: In this paper, the critical current density (Jc) as a function of applied magnetic field (H) magnitude and orientation for ∼ 1-μm-thick YBa2Cu3O7−x films grown by pulsed laser deposition at growth temperatures (Tg) from 730to870°C.
Abstract: We have studied the critical current density (Jc) as a function of applied magnetic field (H) magnitude and orientation for ∼1-μm-thick YBa2Cu3O7−x films grown by pulsed laser deposition at growth temperatures (Tg) from 730to870°C. With changing Tg, alternately a high density of planar defects (YBa2Cu4Ox intergrowths) or columnar defects (Y–Cu–O nanocolumns) are introduced. These defects produce a maximum for Jc(H∼1T) parallel to the plane of the film or the film normal, respectively. For Tg⩾830°C, we present evidence of a Ba–Cu–O liquid phase during growth, which results in a dramatic change in both the microstructure of the films and magnetic field orientation dependence of Jc.
TL;DR: In this paper, the authors reported a systematic study of Ag admixing in MgB2 prepared by solid-state reaction at ambient pressure, and the results showed that MgAg nanoparticles may enhance critical current density due to their size.
Abstract: In the present investigation, we report a systematic study of Ag admixing in MgB2 prepared by solid-state reaction at ambient pressure. All the samples in the present investigation have been subjected to structural/ microstructural characterization employing x-rays diffraction (XRD) and transmission electron microscopic (TEM) techniques. The magnetization measurements were performed by physical property measurement system (PPMS). The TEM investigations reveal the formation of MgAg nanoparticles in Ag admixed samples. These nanoparticles may enhance critical current density due to their size (~5-20 nm) compatible with coherence length of MgB2 (~5-6 nm). In order to study the flux pinning effect of Ag admixing in MgB2, the evaluation of intragrain critical current density (Jc) has been carried out through magnetic measurements on the fine powdered version of the as synthesized samples. The optimum result on intragrain Jc is obtained for 10 at.% Ag admixed sample at 5K. This corresponds to 9.23x10^7 A/cm^2 in self-field,5.82x10^7 A/cm^2 at 1T,4.24 x10^6 A/cm^2 at 3.6T and 1.52x10^5 A/cm^2 at 5T. However, intragrain Jc values for MgB2 sample without Ag admixing are 2.59x10^6 A/cm^2,1.09x10^6A/cm^2,4.53x10^4 A/cm^2 and 2.91x10^3A/cm^2 at 5 K in self field, 1T, 3.6T and 5T respectively.. The high value of intragrain Jc for Ag admixed MgB2 superconductor has been attributed to the inclusion of MgAg nanoparticles into the crystal matrix of MgB2, which are capable of providing effective flux pinning centres. A feasible correlation between microstructural features and superconducting properties has been put forward.
TL;DR: In this paper, the effect of nano-diamond and carbon nanotubes (CNTs) on the critical current density of bulk MgB2 was studied and it was found that CNTs are prone to form second-phase inclusions in the matrix, leading to a more significant improvement of Jc(H) by doping by nanodiamond than by CNT, while nano-Diamond is more prone to be doped into the Mb2 lattice.
Abstract: Doping effects of nano-diamond and carbon nanotubes (CNTs) on critical current density of bulk MgB2 have been studied. CNTs are found prone to be doped into the MgB2 lattice whereas nano-diamond tends to form second-phase inclusions in the MgB2 matrix, leading to a more significant improvement of Jc(H) by doping by nano-diamond than by CNTs in MgB2. TEM reveals tightly packed MgB2 nanograins (50–100 nm) with a dense distribution of diamond nanoparticles (10–20 nm) inside MgB2 grains in nano-diamond-doped samples. Such a unique microstructure leads to a flux pinning behaviour different from that in CNTs-doped MgB2.
TL;DR: In this paper, a series of YBa2Cu3Oy (YBCO) samples with small amounts of nanosized alumina particles (50nm) are synthesized in air by solid state reaction.
Abstract: A series of YBa2Cu3Oy (YBCO) samples with small amounts (0–0.6 wt.%) of nanosized alumina particles (50 nm) are synthesized in air by solid state reaction. The microstructure has been characterized by transmission electron microscopy (TEM) and the critical current density Jc has been measured by the standard four-probe method in the applied magnetic field at 77 K. TEM and energy dispersive X-ray spectroscopy (EDS) analysis have shown that alumina reacts with the YBCO matrix to form nanometric aluminium-rich inhomogeneities intergrown within the YBCO superconducting matrix. These inhomogeneities reduce the onset transition temperature T c onset and the zero resistance temperature Tc. In spite of the monotonic decrease of the superconducting temperature Tc with increasing alumina addition, the Jc(H) behaviour is remarkably improved. The characteristic behaviour of Jc can be explained in terms of the counterbalance of two effects simultaneously caused by the nanometric alumina addition in the system. One effect is the formation of the Al-rich nanometric inhomogeneities relevant for the flux pinning, and the other effect is the reduction of matrix superconducting volume, which is reflected by a decrease of the critical current density Jc at zero applied magnetic field.
TL;DR: In this article, a peak effect in the magnetization and the magnetocaloric coefficient in a single crystal of the superconductor was investigated and it was shown that the peak effect is associated with the metastability of an underlying first-order vortex melting transition.
Abstract: We report a pronounced peak effect in the magnetization and the magnetocaloric coefficient in a single crystal of the superconductor ${\mathrm{Nb}}_{3}\mathrm{Sn}$. As the origin of the magnetization peak effect in classical type-II superconductors is still strongly debated, we performed an investigation of its underlying thermodynamics. Calorimetric experiments performed during field sweeps at constant temperatures reveal that the sharp increase in the current density occurs concurrently with additional degrees of freedom in the specific heat due to thermal fluctuations and a liquid vortex phase. No latent heat due to a direct first-order melting of a Bragg glass phase into the liquid phase is found, which we take as evidence for an intermediate glass phase with enhanced flux pinning. The Bragg glass phase can, however, be restored by a small ac field. In this case, a first-order vortex melting transition with a clear hysteresis is found. In the absence of an ac field, the intermediate glass phase is located within the field range of this hysteresis. This indicates that the peak effect is associated with the metastability of an underlying first-order vortex melting transition.
TL;DR: In this article, the synthesis and characterization of a carbon (C) doped polycrystalline MgB2 superconductor is reported with tartaric acid (C4H6O6) used as the C source.
Abstract: The synthesis and characterization of a carbon (C) doped polycrystalline MgB2 superconductor is reported with tartaric acid (C4H6O6) used as the C source. The amount of C4H6O6 is varied between 5 and 30 wt%. Relationships between microstructures, critical current density (Jc), critical temperature (Tc), upper critical field (Hc2), and irreversibility field (Hirr) for MgB2 doped with 0–30 wt% C4H6O6 are systematically studied. A reduction in Tc from 37.65 to 34.45 K and in lattice parameter a due to the C substitution occurs with C4H6O6 doping. Jc, Hc2, and Hirr are significantly enhanced with an increasing amount of C4H6O6. All the samples exhibit a Jc above 104 A cm−2 at 5 K and 8 T. This value is higher than for un-doped MgB2 by a factor of 6. The significant improvement in the superconducting properties is attributed to the lattice distortion due to the C substitution for boron, with the C coming from the C4H6O6. These findings suggest that C4H6O6 is a promising C source for MgB2 with excellent Jc properties under high field.
TL;DR: In this article, the influence of the starting powders on the superconducting properties of the final conductors of the MgB2 tapes has been studied, and they tried to improve their behavior in magnetic field by mastering their grain size and by inserting appropriate doping.
Abstract: MgB2 tapes have been synthesized through the ex-situ powder-in-tube (PIT) method. This technique involves the cold working of tubes of various metals-in this case Ni-previously filled by suitably reacted MgB powders, followed by proper heat treatments. In particular, it allows the use of different starting powders and the control over their properties. We studied the influence of the starting powders on the superconducting properties of the final conductors, and we tried to improve their behavior in magnetic field by mastering their grain size and by inserting appropriate doping. In order to improve the pinning properties of the tapes, the granulometry has been varied through ball-milling of MgB, and different dopants-such as carbon or SiC nanoparticles-have been introduced either on the precursors or on MgB. Critical current measurements on the tapes are presented, both magnetic from the SQUID and transport in high magnetic field. In particular, IV characteristics have been measured up to 13 Tesla at GHMFL (Grenoble) in order to extract the critical current in two directions, i.e. with the field perpendicular and parallel to the tape surface.
TL;DR: In this article, a magnetic levitation system (SupraTrans) with a permanent magnetic rail and YBCO superconducting bulks in the vehicle has been developed and further investigations in the static and dynamic behavior have been accomplished and are reported.
Abstract: The technical progress in the manufacture of high temperature superconducting bulk material (HTS) provides various possible applications. These include non-contact linear transport systems and frictionless rotating bearings using the pinning effect in Type-II superconductors. During the last five years, a group of industrial and research partners have developed an innovative magnetic levitation system (SupraTrans) with a permanent magnetic rail and YBCO superconducting bulks in the vehicle. To optimize the levitation and guidance system, further investigations in the static and dynamic behavior have been accomplished and are reported. Comparisons between the statics and the dynamics show a very good agreement in all comparable parameters.
TL;DR: In this paper, the influence of dysprosium (Dy) additions on flux pinning was investigated by transmission electron microscopy (TEM) in metal-organic deposited YBa2Cu3O7−δ with and without Dy.
Abstract: The microstructure of metal-organic deposited YBa2Cu3O7−δ with dysprosium (Dy) additions has been investigated by transmission electron microscopy (TEM). Dy additions which increase the density of normal-state nanoparticles in the YBCO have been demonstrated to enhance the critical current densities in moderate magnetic fields. The influence of nanoparticles, stacking faults and other planar defects on flux pinning is discussed. We observed a high density of nanoparticles in the size range of 10–50 nm, which may act as flux pinning centres to enhance the critical current density of the material. Stacking faults and planar defects are observed which may also be effective flux pinning centres in YBCO samples with and without Dy addition.
TL;DR: In this article, a high temperature superconducting (HTS) motor was designed to power a Cessna 172 with a high power of 200 HP at 2700 RPM.
Abstract: A high temperature superconducting (HTS) motor has been designed to power a general aviation aircraft. The propulsion requirements of the Cessna 172 have been chosen as baseline for the study: 200 HP at 2700 RPM. The designed motor is based on flux trapping in bulk YBCO plates and concentration of the flux generated by Bi-2223 coils and an ironless air-cooled resistive armature. The eight-pole machine would exhibit high power density comparable to that of small gas turbines around 4 HP/lb. Details of this HTS motor concept have been presented in a previous paper. However, the scaling up of such a configuration is not straightforward, as single domain YBCO elements cannot exceed a few centimeters in diameter. This paper presents the design of a motor based on the same configuration but with a much higher power rating, in the range of several MW, to power high altitude long endurance (HALE) aircraft or small jets. Due to the size limitation of the YBCO plates, two solutions can be used to increase the power: the radius and the number of poles can be increased, or the motor can be lengthened to accommodate more coil-plate pairs. The motor is able to reach more than 2 T in the air gap thus leading to high power density. The design optimization is done with respect to several objectives as a trade-off between amount of superconductor, efficiency, weight and volume. The cooling system is assumed to be provided by liquid hydrogen available onboard the aircraft as fuel for the fuel cells or turbo-generators.
TL;DR: In this paper, multilayer structures with columns of self-assembled BaZrO3 (BZO) nanodots with interlayers of CeO2 or pure YBa2Cu3O7−δ were grown on rolling-assisted biaxially textured substrates using pulsed laser deposition.
Abstract: Multilayer structures comprising YBa2Cu3O7−δ (YBCO) films with columns of self-assembled BaZrO3 (BZO) nanodots with interlayers of CeO2 or pure YBa2Cu3O7−δ were grown on rolling-assisted biaxially textured substrates (RABiTSs) using pulsed laser deposition. A significant enhancement of the critical current density (Jc) was observed for the multilayers compared with a single layer of YBCO + BZO. Jc varies as Jc~H−α with α of 0.27 for single layer of YBCO + BZO and 0.34 for both multilayered films. Enhancement of pinning in the multilayers is attributed to the presence of columnar defects comprised of self-assembled nanodots of BZO as well as planar CuO-type stacking defects arising as a result of interfacial reactions in the multilayers.
TL;DR: In this article, the authors investigated the origin of the matching effect observed in superconducting Nb films containing regular arrays of holes near the zero-field critical temperature and found that hole-induced suppression of the critical temperature rather than the widely assumed flux pinning enhancement was responsible.
Abstract: We investigate the origin of the matching effect observed in superconducting Nb films containing regular arrays of holes near the zero-field critical temperature We find ``dips'' in the resistance vs magnetic field curves at matching fields where the magnitude of the magnetic flux threading each unit cell is an integer number of the flux quantum By comparing the magnetic field dependences of the resistance and critical temperature in perpendicular and parallel magnetic field directions, we find that the matching effect in Nb films containing triangular hole arrays originates from hole-induced suppression of the critical temperature rather than the widely assumed flux pinning enhancement
TL;DR: In this paper, the carbon substitution effects of MgB2+10-wt% C4H6O5 (malic acid) on the lattice parameters, critical temperature (Tc), upper critical field (Hc2), and irreversibility fields (Hirr) as a function of sintering temperature in the range from 600 to 900
Abstract: We report the carbon (C) substitution effects of MgB2+10 wt% C4H6O5 (malic acid) on the lattice parameters, critical temperature (Tc), upper critical field (Hc2), and irreversibility field (Hirr) as a function of sintering temperature in the range from 600 to 900 °C. The additive C4H6O5 as the C source resulted in a small depression in Tc, but significantly increased the C substitution level, and hence improved the Hc2 and Hirr performance at a low sintering temperature of 600 °C in conjunction with a short sintering period of 4 h. In addition, the low-temperature sintering process resulted in small grain size and higher impurity scattering compared to a pure MgB2 superconductor. These effects promote flux pinning.
TL;DR: In this paper, two defect structures have been identified to be responsible for the enhanced pinning in metal organic deposited YBCO films, which form laminar structures parallel to the ab-plane and are responsible for large current enhancement when the magnetic field is oriented in the abplane.
Abstract: Two different types of defect structures have been identified to be responsible for the enhanced pinning in metal organic deposited YBCO films. Rare earth additions result in the formation of nanodots in the YBCO matrix, which form uncorrelated pinning centers, increasing pinning in all magnetic field orientations. 124-type intergrowths, which form as laminar structures parallel to the ab-plane, are responsible for the large current enhancement when the magnetic field is oriented in the ab-plane. TEM studies showed that the intergrowths emanate from cuprous containing secondary phase particles, whose density is partially controlled by the rare earth doping level. Critical process parameters have been identified to control this phase formation, and therefore, control the f 24 intergrowth formation. This work has shown that through process control and proper conductor design, either by adjusting the composition or by multiple coatings of different functional layers, the desired angular dependence can be achieved.
01 Jan 2007
TL;DR: In this article, the synthesis and characterization of a carbon (C) doped polycrystalline MgB2 superconductor is reported with tartaric acid (C4H6O6) used as the C source.
Abstract: The synthesis and characterization of a carbon (C) doped polycrystalline MgB2 superconductor is reported with tartaric acid (C4H6O6) used as the C source. The amount of C4H6O6 is varied between 5 and 30 wt%. Relationships between microstructures, critical current density (Jc), critical temperature (Tc), upper critical field (Hc2), and irreversibility field (Hirr) for MgB2 doped with 0–30 wt% C4H6O6 are systematically studied. A reduction in Tc from 37.65 to 34.45 K and in lattice parameter a due to the C substitution occurs with C4H6O6 doping. Jc, Hc2, and Hirr are significantly enhanced with an increasing amount of C4H6O6. All the samples exhibit a Jc above 104 A cm−2 at 5 K and 8 T. This value is higher than for un-doped MgB2 by a factor of 6. The significant improvement in the superconducting properties is attributed to the lattice distortion due to the C substitution for boron, with the C coming from the C4H6O6. These findings suggest that C4H6O6 is a promising C source for MgB2 with excellent Jc properties under high field.
TL;DR: This paper describes the experimental technique, which allows measurements to be carried out in real environments, for example, in a closed-cycle refrigerator or transport Dewar, and finds that the effects of microscopic fabrication imperfections could be as important as layout optimization.
Abstract: It is widely accepted that flux trapping is one of the most serious problems that could create an integration limit for superconductor integrated circuits. The ultimate goal of our project is to reduce the problem to a set of routine technical recommendations for SFQ circuit design. To achieve the goal, we review known theories and recommendations for the reduction of flux trapping. Another important part of the project is an experimental verification of our suggestions. In this paper, we describe our experimental technique, which allows measurements to be carried out in real environments, for example, in a closed-cycle refrigerator or transport Dewar. To illustrate the advantages of our technique we discuss in detail the measured flux trapping properties of one test circuit: a 16-bit shift register. We found that the flux trapping properties of apparently similar cells vary dramatically from cell to cell. In other words, the effects of microscopic fabrication imperfections could be as important as layout optimization.
TL;DR: In this paper, the effects of La addition on the structural and superconducting properties of (Bi,Pb)-2212 bulk superconductor prepared by solid state synthesis in the polycrystalline form were studied.
TL;DR: In this paper, the effects of heating on the magnetic flux moving in superconductors with a periodic array of pinning sites (PAPS) were studied. And the effect of the pinning site positional disorder on the voltage-current characteristic (VI curve) was analyzed.
Abstract: We study theoretically the effects of heating on the magnetic flux moving in superconductors with a periodic array of pinning sites (PAPS). The voltage-current characteristic (VI curve) of superconductors with a PAPS includes a region with negative differential resistivity (NDR) of $S$ type (i.e., S-shaped VI curve), while the heating of the superconductor by moving flux lines produces NDR of $N$ type (i.e., with an N-shaped VI curve). We analyze the instability of the uniform flux flow corresponding to different parts of the VI curve with NDR. Especially, we focus on the appearance of the filamentary instability that corresponds to an $S$-type NDR, which is extremely unusual for superconductors. We argue that the simultaneous existence of NDR of both $N$- and $S$-type gives rise to the appearance of self-organized two-dimensional dynamical structures in the flux-flow mode. We study the effect of the pinning site positional disorder on the NDR and show that moderate disorder does not change the predicted results, while strong disorder completely suppresses the $S$-type NDR.
TL;DR: In this article, the authors studied the thickness dependence of the critical current density Jc(H) of a single crystal 1μm thick YBa2Cu3O7−x thin film containing ∼5vol% of insulating Y2BaCuO5 (Y211) nanoparticles in order to better understand how to obtain high critical currents in thick films.
Abstract: Using sequential ion milling the authors have studied the thickness dependence of the critical current density Jc(H) of a single crystal 1μm thick YBa2Cu3O7−x thin film containing ∼5vol% of insulating Y2BaCuO5 (Y211) nanoparticles in order to better understand how to obtain high critical currents in thick films. Except very near the interface where the defect density was enhanced, Jc(H) in the body of the film was uniform and independent of thickness with a high maximum pinning force of 8.8GN∕m3 at 77K. The authors conclude that the nanoscale Y211 precipitates result in strong, three-dimensional pinning characterized by a pin spacing of ∼30nm, much smaller than the film thickness.