Showing papers in "Superconductor Science and Technology in 1999"
TL;DR: In this article, the dynamic resistance in a slab-like superconductor is calculated, taking into account a field-dependent critical current density, and the model predicts the observed dependence of dynamic resistance on field amplitude, field frequency and transport current.
Abstract: The dynamic resistance in a slab-like superconductor is calculated, taking into account a field-dependent critical current density. In superconductors carrying DC transport current in an AC external magnetic field, the dynamic resistance causes a transport loss which depends on the amplitude and frequency of this field as well as on the transport current. This resistance is calculated analytically in a critical-state model applied to a superconducting slab in a parallel field. The field has a general periodic time dependence and for the superconductor a relation between critical current and momentary magnetic field as in the Kim model is assumed. The dynamic resistance appears only at field amplitudes larger than the so-called threshold field, which depends on the transport current. The model predictions are compared with experimental results obtained with a Bi-2223/Ag tape at liquid-nitrogen temperature. At small field amplitude and at low transport current, the derived model predicts the observed dependence of dynamic resistance on field amplitude, field frequency and transport current. For a larger field amplitude and simultaneous high transport current, the resistance is found to be larger than the model predicts. This is probably due to the not completely slab-like geometry and/or to a different field dependence of the critical current density in a high AC field.
118 citations
TL;DR: In this paper, up to four biaxial oriented Sm-123 seeds were placed on the top of rectangular shaped YBCO bars (up to ), and the oriented grown single grains were joined by partially coherent grain boundaries with an improved current transport capability and high levitation forces with overall values of 55-65 N.
Abstract: YBCO bulk materials were crystallized by a multi-seeded melt growth process. Up to four biaxial oriented Sm-123 seeds were placed on the top of rectangular shaped YBCO bars (up to ). The oriented grown single grains are joined by partially coherent grain boundaries with an improved current transport capability and high levitation forces with overall values of 55-65 N. Segregation of nonsuperconducting rest melt and microcracks limit the current transport across the grain boundary.
100 citations
TL;DR: An overview of the deposition and deposition techniques of high-Tc material is presented in this article, where the major technologies are discussed and compared, and advantages and problems of various substrate materials are illustrated.
Abstract: An overview of the deposition and deposition techniques (with the emphasis on PVD techniques) of high-Tc material is presented. The major technologies are discussed and compared, and advantages and problems of various substrate materials are illustrated. The consequences connected with lattice mismatch are discussed, and film nucleation and growth modes of ceramic superconducting material are sketched. Finally, remaining areas for further research are listed.
99 citations
TL;DR: In this article, a single buffer layer architecture for YBCO (YBa2Cu3O7-y) coated conductors was developed for RE2O3 (RE = Y, and rare earths) as candidate materials.
Abstract: In an effort to develop alternative single buffer layer architectures for YBCO (YBa2Cu3O7-y) coated conductors, we have studied RE2O3 (RE = Y, and rare earths) as candidate materials. High-quality Y2O3, Gd2O3 and Yb2O3 buffer layers were grown epitaxially on biaxially textured Ni (100) substrates using reactive electron beam evaporation. Using thermodynamic considerations for the formation of metal oxides, we employed both reducing atmospheres and water vapour to oxidize the film in situ to form stoichiometric RE2O3. We have also prevented NiO formation at the substrate-film interface during this process. Detailed x-ray studies have shown that the Y2O3, Gd2O3 and Yb2O3 films were grown with a single epitaxial orientation. The lattice mismatch between YBCO and Gd2O3 was small as compared with that of YBCO with other rare earth oxides. SEM micrographs indicated that ~0.5 ?m thick Y2O3 films on rolled-Ni substrates were dense, continuous and crack free. A high Jc of 1.8 ? 106 A cm-2 at 77 K and self-field was obtained on YBCO films grown on alternative buffer layers with a layer sequence of YBCO/Yb2O3 (sputtered)/Y2O3 (e-beam)/Ni.
97 citations
TL;DR: In this article, the effect of addition of Y211 on the sample microstructure, its distribution and refinement by chemical doping are discussed in detail in detail, and the effects of adding Y211 to the Y-Ba-Cu-O material are discussed.
Abstract: High critical current density in high temperature superconducting melt-processed Y-Ba-Cu-O (YBCO), which consists of a superconducting (Y123) phase matrix containing discrete (Y211) inclusions, can be achieved by control of the grain microstructure during processing. Y123 grain growth rate, Y211 particle size, morphology, distribution and density and the chemistry of the peritectically molten liquid are key parameters in the processing of this material and effectively determine its microstructure. In addition, YBCO processed with excess Y211 generates defects at the Y123/Y211 interface which form effective flux pinning sites and hence enhance . The effect of addition of Y211 on the sample microstructure, its distribution and refinement by chemical doping are discussed in detail in this review.
90 citations
TL;DR: In this article, the present status and future perspectives of discrete Josephson junction arrays for applications as sub-mm wavelength radiation sources are discussed, and the recent experimental results are reviewed.
Abstract: This paper reviews the present status and future perspectives of discrete Josephson junction arrays for applications as sub-mm wavelength radiation sources. It is intended to cover the whole field, i.e. theory, fabrication and experimental results. The theoretical part reviews the fundamental aspects of Josephson junctions for oscillator applications and introduces the different possible array types. The recent results of analytical as well as numerical investigations are discussed. After the description of the fabrication of both low- as well as high- superconductor Josephson junctions and arrays, methods to investigate the array dynamics experimentally are mentioned. Finally, the recent experimental results are reviewed. This topic is divided into two parts, the first dealing with low- arrays, the second with high- arrays. The different possibilities to design arrays and to include them in practical applications are discussed and compared, with special emphasis on those experiments where radiation was generated successfully. The article is completed with a discussion of the most important experimental results.
85 citations
TL;DR: A numerical method for solving for the current and field distributions inside devices containing type II superconductors is described in this article, which is based on the finite element method, the method of moments and the critical state model.
Abstract: A numerical method for solving for the current and field distributions inside devices containing type II superconductors is described. The two-dimensional solution technique accommodates the effects of surrounding media including iron and can handle systems with an arbitrary number of type II superconductors and conventional materials. The technique is based on the finite element method, the method of moments and the critical state model. The impetus behind this work is the study of rotating electrical machines which contain superconducting artefacts placed alongside magnetic materials and current sources. In this paper, a reluctance machine consisting of an iron rotor flanked with two HTS pieces is chosen to demonstrate the method.
83 citations
TL;DR: In this paper, an inductance-load-biasing method was proposed to reduce power consumption of rapid single flux quantum (SFQ) logic circuits, where a current source can be made of a large inductor accompanied by a large flux.
Abstract: We propose an inductance-load-biasing method in order to reduce power consumption of rapid single flux quantum (SFQ) logic circuits. The main idea arises from the fact that a current source can be made of a large inductor accompanied by a large flux. In our proposal, the current source is composed of a large inductor Lb, a small resistor Rb and a small voltage source Vb. Computer simulations of inductance-load-biased Josephson transmission lines (JTLs) show that an SFQ pulse propagates correctly when Lb is large enough even if Rb is very small. In order to implement the inductance-load-biased JTL, we have made two different layouts: one uses a large bias inductance Lb of a typical stripline structure on a ground plane which occupies a rather large area; the other uses Lb in the shape of a coplanar stripline, which costs a smaller area.
72 citations
TL;DR: In this paper, the authors developed highly sensitive SQUID-based magnetometers and gradiometers, fabricated in a standard Nb/AlOX/Nb technology, and measured a 7.5 mm2 effective area for each loop and a field gradient resolution of 36 fT m-1 Hz-1/2 corresponding to a field resolution in the loop of 1.6 fT Hz 1/2.
Abstract: We have developed highly sensitive SQUID-based magnetometers and gradiometers, fabricated in a standard Nb/AlOX/Nb technology. The SQUID itself is designed as a current sensor having an input coil and a feedback coil. The number of turns of the input coil can be adjusted to ensure optimal coupling to the pickup loops with an inductance in the range from 5 nH to 300 nH. Several types of planar pickup loop configurations have been realized. The magnetometer has a pickup loop with a size of 1 cm × 1 cm. With a typical white noise level better than 4 µ0 Hz-1/2 and an effective area of 2.6 mm2 a field resolution of 3.2 fT Hz-1/2 results for the magnetometer. Two loops connected in series with an area of 2 cm × 2 cm each and a baseline of 4 cm were used in the gradiometer. We measured a 7.5 mm2 effective area for each loop and a field gradient resolution of 36 fT m-1 Hz-1/2 corresponding to a field resolution in the loop of 1.6 fT Hz-1/2.
64 citations
TL;DR: In this paper, the authors reported successful fabrication of 3D intrinsic Josephson junctions using c-axis YBCO thin films of 800 nm thickness and Bi-2212 single-crystal whiskers.
Abstract: We report successful fabrication of 3D intrinsic Josephson junctions (IJJs) using c-axis YBCO thin films of 800 nm thickness and Bi-2212 single-crystal whiskers. The stacks of IJJs were prepared by a lateral focused ion beam etching method. The width depending on the required junction size and the full depth of film thickness were patterned in a micro area from the normal direction etching. By tilting the sample stage up to 90°, two grooves of the bridge were etched from the lateral direction in accordance with the required junction size. The junctions did not show any degradation of critical current density (Jc) down to an in-plane area of 0.5 µm2.
58 citations
TL;DR: In this article, a hot-electron transition-edge superconducting bolometer with adjustable thermal relaxation speed is proposed, where the bolometer contacts are made from a superconductor with high critical temperature which blocks the thermal diffusion of hot carriers into the contacts.
Abstract: A hot-electron transition-edge superconducting bolometer with adjustable thermal relaxation speed is proposed. The bolometer contacts are made from a superconductor with high critical temperature which blocks the thermal diffusion of hot carriers into the contacts. Thus electron-phonon interaction is the only mechanism for heat removal. The speed of thermal relaxation for hot electrons in a nanometer-size superconducting bolometer with T(sub c) = 100-300 mK is controlled by the elastic electron mean free path l. The relaxation rate behaves as T(sup 4)l at subkelvin temperatures and can be reduced by a factor of 10-100 by decreasing 1. Then an antenna- or wave guide-coupled bolometer with a time constant approx. = 10(exp -3) to 10(exp -4) s will exhibit photon-noise limited performance at millimeter and submillimeter wavelengths. The bolometer will have a figure-of-merit NEPtau = 10(exp -22) - 10(exp -21) W/Hz at 100 mK which is 10(exp 3) to 10(exp 4) times better (ie: smaller) than that of a state-of-the-art bolometer. A tremendous increase in speed and sensitivity will have a significant impact for observational mapping applications.
TL;DR: In this paper, a review of different processes and corresponding recent results in the field of texturing high-Tc superconductors in order to align and develop the planes where the current flows easily is presented.
Abstract: Most of the potential applications of the high-temperature superconductors require large critical currents, much higher than those obtained using a classical sintering process. This paper reviews different processes and corresponding recent results in the field of texturing high-Tc superconductors in order to align and develop the planes where the current flows easily. Different melt-textured growth methods are discussed from both theoretical and practical viewpoints, and the limitations associated with the diffusion and interface phenomena are introduced. Influence of the process parameters, as well as the microstructure of the precursors and the use of additives in order to enlarge the single domain size and to optimise the superconducting characteristics is discussed. Mechanical texturing and texturing under a magnetic field, as well as combination of both processes, are also considered. Recent results, which appear to be an important breakthrough for the industrial development because of the large crystallization rates are also mentioned.
TL;DR: In this article, a review of high-gas-pressure single crystal growth studies of YBa2Cu4O8 and Y2Ba4Cu7O15-x performed in oxygen pressure up to 3000 bar and Hg1-xMxBa2Can-1CunO2n+2+ (M = Pb, Re; n = 1-7) compounds in argon pressure up 11 000 bar at temperature up to 1200 °C.
Abstract: In this paper we present a review of high-gas-pressure single crystal growth studies of YBa2Cu4O8 and Y2Ba4Cu7O15-x performed in oxygen pressure up to 3000 bar and Hg1-xMxBa2Can-1CunO2n+2+ (M = Pb, Re; n = 1-7) compounds in argon pressure up 11 000 bar at temperature up to 1200 °C. Chain compounds A1-xCuO2 (A = Sr, Ca, Ba) have been synthesized at high oxygen pressure up to 2000 bar. High-pressure phase diagram studies of the investigated systems are also discussed. Structure analyses of Y2Ba4CunO2n+x (n = 6-8), Hg1-xMxBa2Can-1CunO2n+2+ (M = Pb, Re; n = 1-8), Sr0.73CuO2 and (Sr,Ca)4Cu6O10 single crystals have been performed. The effects of substitutions and trends in bondlengths are discussed. The vortex state properties of HgBa2Ca2Cu3O8+ and YBa2Cu4O8 single crystals are compared. For Hg-based compounds, the influence of oxygen content, chemical substitutions and radiation defects on vortex pinning were determined. The quasi-one-dimensional cuprates Ca0.83CuO2 and Sr0.73CuO2 show an antiferromagnetically ordered state of long-range 3D character at T < 10 K. The spin dynamics of Sr0.73CuO2, measured by inelastic neutron scattering, indicate that this ordered state coexists with a dimerized singlet ground state.
TL;DR: In this paper, the authors describe the issues surrounding the fabrication of thin films of the thallium-based HTS materials and the importance of achieving biaxial grain alignment in optimizing the properties of the films.
Abstract: Thin films of the Tl-based high-temperature superconducting (HTS) phases are beginning to find application in a number of practical devices, especially in the field of microwave communication systems. This review describes the issues surrounding the fabrication of thin films of the thallium-based HTS materials. The influence of thermodynamics and kinetics, the various potential thalliation techniques and the selection of an appropriate substrate material are all important considerations when designing a process for the fabrication of thin films of these highly reactive materials. The properties of the resulting films are critically dependent on the microstructures developed during thalliation. Microstructural evolution during thalliation, the effect of structural defects on the properties of such films and the importance of achieving biaxial grain alignment in optimizing the properties of the films are all discussed.
TL;DR: In this paper, a target prepared from nanopowder is used for pulsed laser deposition of thin films on substrates, and atomic force microscopy is used to obtain the critical current density in zero field at 77 K, superconducting transition temperature K and transition width of K.
Abstract: A target prepared from nanopowder is used for pulsed laser deposition of thin films on substrates. Investigations by atomic force microscopy show that in this way it is possible to prepare smooth films which are free from droplets. In optimized growth conditions the critical current density in zero field at 77 K, superconducting transition temperature K and transition width of K are obtained.
TL;DR: In this paper, the precursor quality for the synthesis of the superconductor Hg-1223 was investigated and it was shown that an excessively oxygenated precursor leads to overdoped superconducting phases, presence of other members with lower n, and some unreacted precursor.
Abstract: Thanks to a novel technique (thermobaric analyser or TBA) for measuring the in situ pressure in quartz tubes, we have investigated the precursor quality for the synthesis of the superconductor Hg-1223 which is an essential parameter to control. We have made this study on the samples and we can conclude that this superconductor phase requires a ceramic precursor sintered in a low mixture gas flux. An excessively oxygenated precursor leads to overdoped superconducting phases, presence of other members with lower n, and some unreacted precursor. The precursor oxygenation degree also modifies the kinetics of formation of and the partial melting of the superconductor material may be affected.
TL;DR: A review of high-temperature superconductors and scanning probe microscopes can be found in this paper, with emphasis on scanning microscopes based on tunnelling (STM), atomic force (AFM), magnetic force (MFM), the Hall effect (SHPM), a SQUID sensor, microwaves, near-field optics, or magneto-optic techniques.
Abstract: High-temperature superconductors (HTS) and scanning probe microscopes have been developed at a rapid rate over the last decade and a half. The cross-linking between these two exciting fields has produced many beautiful results and new possibilities that are still being explored. The highlights of these results are reviewed here, with emphasis on scanning microscopes based on tunnelling (STM), atomic force (AFM), magnetic force (MFM), the Hall effect (SHPM), a SQUID sensor, microwaves, near-field optics, or magneto-optic techniques. These tools are used in the characterization of HTS from the routine evaluation of surface topography to the sophisticated elucidation of the symmetry of the order parameter. Some more recent techniques and possible new directions are also discussed.
TL;DR: In this article, it is shown that a sharp cube texture can be produced after pre-heated deformation and recrystallization of fine grained (15 µm) Ag ingots.
Abstract: A systematic study of texturing mechanisms in pure Ag is presented, the goal being to obtain a cube textured {100}001 tape that can be used as a substrate for superconducting coated conductors. It is shown that a sharp cube texture can be produced after pre-heated deformation and recrystallization. Optimal parameters are detailed. 99.99% pure Ag powder is used as starting material. Fine grained (15 µm) Ag ingots are pre-heated at 100 °C before standard cold rolling. The effect of pre-heating on deformation texture is to change the main texture from the brass orientation {110}112 to the Goss {110}001 one. The presence of a copper-type texture with relatively high values of the ODF (oriented distribution function) after the 100 °C pre-heated deformation can be understood as a slight increase of the stacking fault energy of Ag during the pre-heated deformation. The optimal annealing is achieved at 700 °C for 30 min in a primary vacuum. This leads to a sharp cube texture. The FWHM values of the three x-ray pole figures are, at no more than 10°, the smallest ever reported for cube textured Ag tapes. The formation of cube texture is interpreted in terms of orientation nucleation and orientation growth theories that play a common role during the texturing process. The stability of cube texture at high temperature up to 900 °C indicates that the tapes are suitable for epitaxial growth of superconducting oxides.
TL;DR: In this paper, a two-stage differential pumping system was used to reduce the electron path in the high-pressure oxygen atmosphere within the deposition chamber, and the specular beam intensity was sufficiently high to allow the observation of intensity oscillations during the growth of oxide materials such as SrTiO3 and La2/3Ca1/3MnO3.
Abstract: Pulsed laser deposition is a well established deposition technique for oxide thin films and heterostructures. The knowledge and control of the growth processes of oxide materials are important for the fabrication of high-quality epitaxial and heteroepitaxial thin-film structures. Because of the high oxygen pressure during the growth process standard reflection high-energy electron diffraction (RHEED) analysis is not possible. To overcome this problem we have used a two-stage differential pumping system. In this way, the electron path in the high-pressure oxygen atmosphere within the deposition chamber has been reduced considerably. The specular beam intensity of the RHEED system was sufficiently high to allow the observation of intensity oscillations during the growth of oxide materials such as SrTiO3 and La2/3Ca1/3MnO3. In addition to the RHEED investigation the surface morphology of the deposited films has been characterized in situ by ultrahigh-vacuum atomic force microscopy.
TL;DR: In this paper, the critical current density and the microwave surface resistance of YBCO films on sapphire wafers and LaAlO3 cylinders were characterized by integral and spatially resolved measurements using optical and electron microscopy and by x-ray diffraction.
Abstract: Epitaxial c-oriented YBCO films laser deposited onto 3 in diameter CeO2-buffered sapphire wafers and LaAlO3 cylinders as well as sputter deposited onto 2 in diameter LaAlO3 wafers were characterized by integral and spatially resolved measurements of the critical current density jc and the microwave surface resistance Rs, by microstructure investigations using optical and electron microscopy and by x-ray diffraction. Epitaxial misorientations of in-plane-rotated as well as of a-axis-oriented grains were found in amounts up to 10%. The in-plane rotation seriously degraded Rs while the a orientation mainly lowered jc. Moreover, a degradation of Rs and of the microwave power handling could be clearly correlated with the density of microcracks occasionally found in YBCO films on sapphire. Inhomogeneities like a-axis-oriented grains were observed to `disperse' microcracks, probably in favour of the electrical properties. The impact of further microstructure imperfections on Rs, in particular of the typical twin lamellae and their domains, is discussed in view of findings from transmission electron microscopy.
TL;DR: In this paper, the phase transformations and structural changes occurring during initial heating and annealing of an Ag-clad high-Tc superconducting tape of the (Bi, Pb)2Sr2Ca2Cu3Ox type are investigated.
Abstract: The phase transformations and structural changes occurring during initial heating and annealing of an Ag-clad high-Tc superconducting tape of the (Bi, Pb)2Sr2Ca2Cu3Ox type are investigated. The annealing takes place in air at an operating temperature of 835 °C. Using x-ray diffraction with 100 keV photons from a synchrotron source the concentration, stoichiometry and texture of the dominant phases are monitored in situ during the transformation of BiSCCO from (Bi, Pb)2Sr2CaCu2Ox (2212) to (Bi, Pb)2Sr2Ca2Cu3Ox (2223). In addition, information on grain size and residual strain is obtained. During heating the (Ca, Sr)2PbO4 additive decomposes between 700 °C and 820 °C. Simultaneously, the residual strain in the 2212 grains is relieved and the c-axis alignment of the grains is substantially improved. Moreover, the Pb content of the 2212 structure increases continuously. We interpret these results as being related to a temperature-dependent solubility limit of Pb in 2212, leading to a substantial grain growth of the phase. Above 812 °C 2212 partly decomposes to form (Ca, Sr)2CuO3 and a liquid. At the operating temperature 2212 and (Ca, Sr)2CuO3 react with the liquid to form 2223. During the conversion the 2212 lattice expands, indicating that the remaining 2212 grains contain less and less Pb. The final 2212 and 2223 textures are approximately identical, and Avrami plots of the transformation kinetics give exponents m in the range 1 < m < 2. During the annealing the 2212 linewidth is constant, implying that there is neither strain nor finite-size broadening of the 2212 peaks during the transformation. This points to a transformation mechanism where only a few 2212 grains transform at a given time. Implications of these findings are discussed in relation to intercalation and nucleation-and-growth models.
TL;DR: In this article, an Ag-sheathed 2223 multifilament tape was produced by the powder-in-tube method and various parts of the tape were heat treated at different temperatures under reduced oxygen partial pressure.
Abstract: An Ag-sheathed 2223 multifilament tape was produced by the powder-in-tube method. The various parts of the tape were heat treated at different temperatures under reduced oxygen partial pressure. The microstructure and the texture were characterized by synchrotron x-ray diffraction and SEM and correlated with Jc. In the low temperature range (<826 °C), the 2223 fraction and the c-axis alignment of 2223 grains increased with increasing temperature. A significant increase of Jc (from 1 to 41 kA cm-2) was observed in this range, indicating that the phase purity and the texture were the major controlling factors. In the medium temperature range (826-830 °C), the 2223 fraction and the grain alignment tend to saturate, and Jc remains nearly constant at a level of 40 kA cm-2. In the high temperature range (830-836 °C), the 2223 fraction and the grain alignment remained unchanged but Jc decreased with increasing temperature. The drop in Jc was related to the presence of an amorphous phase and a small amount of 2201 phase, indicating that the grain connectivity has become the major current-limiting factor. The variations in the filament shape, density and alignment within the multifilament tape were characterized. The influence of the inhomogeneous structure on Jc is discussed.
TL;DR: In this article, a two-step transition is observed if the sample exhibits also the secondary peak effect in the magnetization loops, which is observed in the case of single crystal and melt-processed YBa2-Cu3O7-δ.
Abstract: Superconducting transitions are measured in field-cooled cooling (FCC) and field-cooled warming (FCW) modes in external magnetic fields ranging between 1 mT and 7 T on various high-T c superconductors (single crystal and melt-processed YBa2-Cu3O7-δ, single crystals and melt-processed NdBa2Cu3O7-δ, and on various ternary 123-superconductors). Our measurements reveal that a two step transition is observed if the sample exhibits also the secondary peak effect in the magnetization loops.
TL;DR: In this paper, the effect of the oxygenation time on the levitation force of top-seeded melt-textured YBCO domains has been investigated and the existence of an optimal annealing time, depending on the sample volume, has been brought to the fore.
Abstract: The effect of the oxygenation time on the levitation force of top-seeded melt-textured YBCO domains has been investigated. The existence of an optimal annealing time, depending on the sample volume, has been brought to the fore. Longer annealings lead to a definitive deterioration of samples. A study of the levitation force versus thickness has been performed. The force has shown a monotonic dependence below a critical thickness as a function of the experimental conditions. When the sample thickness exceeds this critical value, the force has reached its maximal value and saturates.
TL;DR: In this paper, measurements of viscous flow for a YBa2Cu3O7 bicrystal LAGB can be applied in a statistical model that predicts the characteristic V-I response for a particular grain-to-grain dispersion of grain boundary angles.
Abstract: There is considerable interest in the dynamics of vortices in granular `coated conductors' consisting of a 2D network of low angle grain boundaries (LAGBs). The V-I characteristic of the conductor is determined by a combination of flux vortex channelling along the grain boundaries and current percolation within the grain network. In this work it is shown that measurements of viscous flow for a YBa2Cu3O7 bicrystal LAGB can be applied in a statistical model that predicts the characteristic V-I response for a particular grain-to-grain dispersion of grain boundary angles.
TL;DR: In this article, the influence of flux pinning on the vortex glass-liquid phase transition and irreversibility in HTSs has been examined on the basis of systematic measurements of electric field (E) versus current density (J) curves in a YBCO thin film.
Abstract: The influence of flux pinning on the vortex glass-liquid (GL) phase transition and irreversibility in HTSs has been examined on the basis of systematic measurements of electric field (E) versus current density (J) curves in a YBCO thin film. It has been shown that the GL transition is identical to the thermal depinning determined by the minimum value of the macroscopic pinning strength. The isothermal scaling of the E-J characteristics is directly related to the nature of the pinning. The irreversibility line can be described as an iso-J line governed by the statistical pin distribution. If we determine the criteria for the irreversibility line, we can describe the irreversibility line based on the depinning line. The essential physical quantity, therefore, can be attributed to the flux depinning.
TL;DR: In this article, a binary (Nd, Sm)-Ba-Cu-O superconductors with Tc of 96 K and a high irreversibility field up to 8 T have been fabricated in air via a newly developed technique.
Abstract: Binary (Nd, Sm)-Ba-Cu-O superconductors with Tc of 96 K and a high irreversibility field up to 8 T have been fabricated in air via a newly developed technique. The initial composition was controlled by using binary (Nd, Sm)2BaO4 as an addition. In comparison with both NdBaCuO and YBaCuO melt-textured superconductors, the present composition showed a remarkable enhancement of critical current densities in an intermediate field regime (1-3 T). Microstructural observations and compositional analysis showed that the distributions of Nd and Sm in the (Nd, Sm)-123 matrix were homogeneous while the atomic ratio between these two rare earth elements was inconsistent with that in the nominal composition. These new characteristics were thought to cohere with the different solubilities between Nd and Sm in the liquid phase. Finally, trapped magnetic field mapping showed a single-domain shape of the trapped field, which indicated the growth of a single grain in the samples.
TL;DR: The quatratran as mentioned in this paper is a superconducting electronic device which can provide either current or voltage amplification of low-level electrical signals at low temperatures, which is based on quasiparticle trapping from a superconductor into a normal metal, coupled with normal-insulator-superconductor (NIS) tunnel junctions.
Abstract: We propose a new superconducting electronic device which can provide either current or voltage amplification of low-level electrical signals at low temperatures. The device, which we call the quatratran, is based on quasiparticle trapping from a superconductor into a normal metal, coupled with normal-insulator-superconductor (NIS) tunnel junctions. Quasiparticles injected into the S electrode of a first junction are trapped in an N layer, producing excited charge carriers. This N layer is also used as the N electrode of a second NIS junction which produces an amplified signal. We explain the principles of operation and describe the electronic characteristics. Results from test devices demonstrate the soundness of the principles. We also suggest how quatratrans can be applied to the detection of particles and radiation.
TL;DR: In this article, the critical Josephson current jcJ(T) is accompanied by a small leakage current jbl(1/Rbl) and hence the rf residual losses Rres caused by weak links are small.
Abstract: In Nb2O5-x junctions the critical Josephson current jcJ(T) is accompanied by a small leakage current jbl(1/Rbl) and hence the rf residual losses Rres caused by weak links are small. HTS in-plane weak links show very much reduced jcJ(0) values compared with theory and a large leakage current jbl of the order of jcJ owing to a high density of intermediate states in disordered HTS junction material. The finite Rres(T,f,H) is due to the finite normal conducting leakage current with Rbl(T<0.9Tc) constant of weak links at separations aJ, where the Rres(T) dependence is dominated by jcJ(T) jcJ(0)(1-T/Tc). Quantitative experiment-model agreement is obtained with measured values of aJ(0.2-20 µm), of Rbn(1000-1 n cm2) and of jcJ(10-107 A cm-2) with
TL;DR: In this article, the anomalous field (H) dependence of pinning force density (F P) was deduced from magnetization measurements on the single-crystal and polycrystalline samples of CeRu 2.
Abstract: We report the anomalous field (H) dependence of pinning force density F P as deduced from our magnetization measurements on the single-crystal and polycrystalline samples of CeRu 2 . It is shown that, contrary to a single maximum in other hard type II superconductors, CeRu 2 samples exhibit two distinct peak features in their F P -H plots. Our results show that the scaling of F P with the applied magnetic field at different temperatures cannot be described by the conventional Kramer model based on crossover from a line-breaking regime to a flux-line lattice shearing regime.