Showing papers on "High-temperature superconductivity published in 1996"
TL;DR: In this article, experimental studies of the time decay of the nonequilibrium magnetization in high-temperature superconductors, a phenomenon known as magnetic relaxation, are reviewed from a purely experimental perspective and discussed in the context of present phenomenological theories.
Abstract: We review experimental studies of the time decay of the nonequilibrium magnetization in high-temperature superconductors, a phenomenon known as magnetic relaxation. This effect has its origin in motion of flux lines out of their pinning sites due to thermal activation or quantum tunneling. The combination of relatively weak flux pinning and high temperatures leads to rich properties that are unconventional in the context of low temperature superconductivity and that have been the subject to intense studies. The results are assessed from a purely experimental perspective and discussed in the context of present phenomenological theories. [S0034-6861(96)00403-5]
590 citations
TL;DR: In this paper, a high density of columnar defects is created with orientations perpendicular and parallel to the copper oxide planes in a nanorod-HTSC composites.
Abstract: Most large-scale applications of the high-temperature copper oxide superconductors (HTSCs) require high critical current densities (Jc9s) at temperatures near the boiling point of liquid nitrogen to be technologically useful, although thermally activated flux flow reduces Jc dramatically at these temperatures. This intrinsic limitation can be overcome by introducing nanometer-sized columnar defects into an HTSC. Nanorods of magnesium oxide were grown and incorporated into HTSCs to form nanorod-HTSC composites. In this way, a high density of nanorod columnar defects can be created with orientations perpendicular and parallel to the copper oxide planes. The Jc9s of the nanorod-HTSC composites are enhanced dramatically at high temperatures and magnetic fields as compared with reference samples; these composites may thus represent a technologically viable strategy for overcoming thermally activated flux flow in large-scale applications.
521 citations
09 Jul 1996
TL;DR: In this article, the discovery and progress in Bi-based oxide high Tc superconductors are discussed. But the main focus of this paper is the development and progress of Bi-base oxides.
Abstract: Overview: discovery and progress in Bi-based oxide high Tc superconductors. Physics and chemistry: crystal structure thermal and magnetic properties tunnelling phases and their relationships in the Bi-Pb-Sr-Ca-Cu-O System phase equilibria and crystal chemistry of the high-temperature superconducting compounds of the system Bi2O3-SrO-CaO-CuO intrinsic pinning radiation effects preparation of precursor powders preparation of single crystals diffusion reaction in Bi-base oxides. Bulk, wire/tape and applications: Bi-based superconductor fabricated by the floating zone method Bi-based bulk current leads and their applications power-in-tube Bi2223 Ag-sheathed tape: basic process, microstructure and critical current density thermodynamics, microstructure and critical current density in Bi, Pb(2223) tapes manufacture and properties of Bi-2212-based Ag sheathed wires Bi-2212 Ag sheathed wire properties of Bi-2212 silver-sheathed tape and its application to magnets Bi-2212/Ag composite tapes processed by Doctor Blade or dip-coating process coils, power leads, busbars and cables fabrication and characterization of HYSC coils made from Bi-2223 conductors. Thin films and applications: MOCVD growth of high-quality B12223 superconducting films layer-by-layer growth of Bi-based superlattices by molecular beam epitaxy basic properties for BSCCO devices. Outlook: future prospects. (Part contents.)
98 citations
TL;DR: In this paper, a nonoptimized design of a ferrite phase shifter that employs niobium or YBCO meanderlines has produced over 1000 degrees of differential phase shift with a figure of merit exceeding 1000 degrees/dB at X band.
Abstract: Microwave devices comprising magnetized ferrite in contact with superconductor circuits designed to eliminate magnetic field penetration of the superconductor have demonstrated phase shift without significant conduction losses. The device structures are adaptable to low- or high-T/sub c/ superconductors. A nonoptimized design of a ferrite phase shifter that employs niobium or YBCO meanderlines has produced over 1000 degrees of differential phase shift with a figure of merit exceeding 1000 degrees/dB at X band. By combining superconductor meanderline sections with alternating T junctions on a ferrite substrate in a configuration with three-fold symmetry, a low-loss three-port switching circulator has been demonstrated.
68 citations
TL;DR: In this article, the frequency-dependent complex conductivity σ 1+iσ2 was obtained for pure YBa2Cu3O7-δ and the related alloy Y1-xPrxBa2cu3O 7-ε over a temperature range from 300 K down to 10 K using coherent terahertz pulse spectroscopy.
Abstract: Recent experimental investigations of the electrodynamic properties of high-temperature superconductors in the terahertz regime are reviewed. Transmission measurements were performed with use of coherent terahertz pulse spectroscopy, which enables us to extract directly the frequency-dependent complex conductivity σ1+iσ2. Investigations of both pure YBa2Cu3O7-δ and the related alloy Y1-xPrxBa2Cu3O7-δ were conducted over a temperature range from 300 K down to 10 K. From these measurements we can extract the temperature-dependent London penetration depth λL(T), the plasma frequency ωp, and the quasi-particle scattering time τ(T). The implications of our measurements for contemporary theories of high-Tc superconductivity are discussed.
53 citations
TL;DR: In this article, the authors reviewed the progress in the quest to understand the electronic basis for high-temperature superconductors with emphasis on theories that make contact with experimental realities in copper oxides.
Abstract: Progress in the quest to understand the electronic basis for high-temperature superconductors is reviewed with emphasis on theories that make contact with experimental realities in copper oxides. Key anomalies, such as the unconventional strong damping of the electrons (or holes), are examined at a level suitable for non-specialists. Correlations of superconducting temperatures with the damping are drawn, in contrast to the insensitivity of to the electron density of states. Infrared conductivity, the Hall effect, spin susceptibility, Raman spectra, NMR relaxation, the Knight shift and the microwave surface resistance of cuprates are considered, together with possible theoretical explanations. The nested Fermi liquid theory is compared to typical experimental data on cuprates. Mechanisms for high-temperature superconductivity are discused in the context of growing evidence for an energy gap with d-wave symmetry in the high- materials, whose magnitude is much larger than conventional theories predict. Relevant spin fluctuation concepts for d-wave pairing are reviewed. Other oxides are related to more traditional theories, including the BCS model of electron - phonon coupling and polarons. Novel states, such as holons and spinons, spin bags and anyons are discussed and guides to calculations for t - J models and Monte Carlo simulations are presented. Future challenges for field theory, as well as experimental probes at high pressure, are suggested.
44 citations
11 Nov 1996-Nuclear Instruments & Methods in Physics Research Section A-accelerators Spectrometers Detectors and Associated Equipment
TL;DR: In this paper, the effect of columnar defects in high temperature superconductors was investigated and it was observed that below the threshold, electronic stopping power (Se) can even provide annealing effects.
Abstract: Fast ions moving through condensed matter produce a track of excitations and ionizations that can have lasting effects depending on the properties of the medium. Latent tracks or columnar defects are always produced in insulators. These columnar defects have been used to modify the properties of high temperature superconductors by pinning the vortices. The effect of pinning is also observed in the microwave frequency regime. With the use of higher energy heavy ions electronic loss induced effects are now observed even for metals. There seems to exist a threshold electronic stopping power for each material above which latent tracks can be produced. Creation and annealing of defects due to the heavy ion energy locked into electronic excitations needs to be understood. It is observed that below the threshold, electronic stopping power (Se) can even provide annealing effects. The nuclear stopping power (Sn) is predominant at lower energies, i.e. towards the end of the range of the high energy ions. The extent of lattice deformation in the spatially separated electronic and nuclear loss region has been examined in Si crystal with a 100 MeV Ti beam using X-ray topography. An attempt is made to study the transient behavior of the defects produced by Se in cuprate superconductors. The microstructure changes associated with 85 MeV Ni ion irradiation have been studied along with the hydrogen concentration variations in diamond-like carbon films.
Book•
01 Jan 1996
TL;DR: The discovery of high temperature superconductivity was described in this paper, where the superconducting state was shown to be superfluidity. But this was not the case in the classical superconductors.
Abstract: The Discovery of High Temperature Superconductivity. Conductivity and Magnetism. The Superconducting State. Superfluidity. Explanations of Superconductivity. The Classical Superconductors. Fullerenes. The New High Temperature Superconductors. Magnets and Their Uses. Wires and Films. Further Applications. Future Prospects. Appendix A: Units and Conversion Factors. Appendix B: Symbols and Abbreviations. Appendix C: Elements and Their Symbols. Appendix D: Glossary of Terms. Index.
TL;DR: In this article, the first bulk applications of high-temperature superconductors are discussed, including current leads, fault current limiters, and wire for power transmission cables, with a transition temperature higher than that of liquid nitrogen.
Abstract: Ten years after Georg Bed‐norz and Alex Muller discovered the first high‐temperature superconductors, and nine years after superconductivity was found with a transition temperature higher than that of liquid nitrogen, considerable progress is being made in bulk applications of high‐temperature superconductors. Electronics applications and thin‐film technology are even more advanced. (See PHYSICS TODAY, March 1995, page 20.) Among the first bulk applications are: current leads, fault current limiters, and wire for power transmission cables.
TL;DR: In this article, the surface resistance of perovskite thin films and bulk samples at microwave frequencies was studied and the d.c. resistivity of the various samples spans three orders of magnitude.
TL;DR: This work analyzes in detail how the scattering by nonmagnetic impurities affects the shape and amplitude of the order parameter (OP) and the density of states in anisotropic superconductors in the framework of BCS theory.
Abstract: We analyze in detail how the scattering by nonmagnetic impurities affects the shape and amplitude of the order parameter (OP) and the density of states in anisotropic superconductors in the framework of BCS theory. Special attention is paid to the case when the OP is a mixture of {ital d} and {ital s} waves changing its sign on the Fermi surface. The critical temperature is shown to decay with the increase of the residual resistance according to the power law. At zero temperature impurity scattering gives rise to a peculiar phase transition from a gapless regime to a state with a finite gap in the quasiparticle spectrum. {copyright} {ital 1996 The American Physical Society.}
TL;DR: In this article, the behavior of electromagnetic fields in high-T/sub c/superconductors (HTSs) is studied in order to examine their effects in classical electromagnetic boundary value problems.
Abstract: The behavior of electromagnetic fields in high-T/sub c/ superconductors (HTSs) is studied in order to examine their effects in classical electromagnetic boundary value problems. It is shown that an HTS can not be simply treated as a low loss conductor and boundary conditions of HTSs cannot be considered as perfect conducting boundaries like conventional treatments. The electromagnetics of HTS are investigated in terms of complex conductivity, surface impedance with applied magnetic fields, and computational electrodynamics using the proposed model.
TL;DR: In this paper, computer simulations were performed to determine the most probable grain boundary misorientation distribution (GBMD) in model polycrystalline superconductors, and the results were important in correlating the macroscopic transport Jc with the measured grain orientation texture as determined by x-ray diffraction.
Abstract: Computer simulations were performed to determine the most probable grain boundary misorientation distribution (GBMD) in model polycrystalline superconductors. GBMDs in polycrystalline superconductors can be expected to dictate the macroscopic transport critical current density, Jc. Calculations were performed by simulating model polycrystals and then determining the GBMD. Such distributions were calculated for random materials having cubic, tetragonal, and orthorhombic crystal symmetry. In addition, since most high temperature superconductors are tetragonal or pseudotetragonal, the effect of macroscopic uniaxial and biaxial grain orientation texture on the GBMD was determined for tetragonal materials. It is found that macroscopic texture drastically alters the grain boundary misorientation distribution. The fraction of low angle boundaries increases significantly with uniaxial and biaxial texture. The results of this study are important in correlating the macroscopic transport Jc with the measured grain orientation texture as determined by x‐ray diffractionComputer simulations were performed to determine the most probable grain boundary misorientation distribution (GBMD) in model polycrystalline superconductors. GBMDs in polycrystalline superconductors can be expected to dictate the macroscopic transport critical current density, Jc. Calculations were performed by simulating model polycrystals and then determining the GBMD. Such distributions were calculated for random materials having cubic, tetragonal, and orthorhombic crystal symmetry. In addition, since most high temperature superconductors are tetragonal or pseudotetragonal, the effect of macroscopic uniaxial and biaxial grain orientation texture on the GBMD was determined for tetragonal materials. It is found that macroscopic texture drastically alters the grain boundary misorientation distribution. The fraction of low angle boundaries increases significantly with uniaxial and biaxial texture. The results of this study are important in correlating the macroscopic transport Jc with the measured grain o...
TL;DR: In this article, the rate at which electrons quantum mechanically tunnel from a metal probe tip into the surface of a superconductor reveals crucial information about fundamental mechanism of superconductivity.
Abstract: The rate at which electrons quantum mechanically tunnel from a metal probe tip into the surface of a superconductor reveals crucial information about fundamental mechanism of superconductivity. High transition temperature superconductors have been difficult to study with this technique, but as Kitazawa discusses in his Perspective, recent improvements in tunneling microscopy are overcoming the obstacles.
TL;DR: In this paper, the authors reported that the addition of fluorine has little effect on the transition temperature, but remarkably increases the width of the hysteresis loops (which is proportional to Jc).
Abstract: (Tl0.5, Pb0.5)Sr1.6Ba0.4Ca2Cu3Oy/Fx high temperature superconductors are reported with transition temperatures above 125 K. Samples with different fluorine contents (0 ≤ x ≤ 3) have been prepared. The addition of fluorine has little effect on the transition temperature, but remarkably increases the width of the hysteresis loops (which is proportional to Jc). The width of the hysteresis loops at 4.2 K was found to increase with x reaching an optimum value at x = 2.2. The. maximum width of the hysteresis loops is about 3 times larger than that for fluorine free material. Upon further increases in fluorine content the width of the hysteresis loops starts decreasing.
TL;DR: Melt processed YBa/sub 2/Cu/sub 3/O/sub x/ thick films display low surface resistance, moderate performance in fields and can be applied to three-dimensional (3-D) substrates with ease as discussed by the authors.
Abstract: Melt processed YBa/sub 2/Cu/sub 3/O/sub x/ thick films display low surface resistance, moderate performance in fields and can be applied to three-dimensional (3-D) substrates with ease. The processing and properties of such films are described. Possible applications are examined and prototype devices are described. These include high Q, low frequency resonators for cellular communications filters, low phase noise oscillators, magnetic resonance imaging receiver coils, low noise magnetic shields, coils, flux transformers, and antennas.
TL;DR: In this article, the reasons for the formation of ordered or fluctuating charge stripes and antiphase spin domains in high-temperature superconductors are surveyed, and some of the consequences for the physical properties of high temperature supercondors and the mechanism of superconductivity are presented.
Abstract: The reasons for expecting the formation of ordered or fluctuating charge stripes and antiphase spin domains in high-temperature superconductors are surveyed. Evidence for such behavior is described, and some of the consequences for the physical properties of high-temperature superconductors and the mechanism of superconductivity are presented.
TL;DR: In this article, the authors present theoretical arguments and experimental support for the idea that high-Tc superconductivity can occur with s-wave, d-wave or mixed-wave pairing in the context of a magnetic mechanism.
Abstract: We present theoretical arguments and experimental support for the idea that high-Tc superconductivity can occur with s-wave, d-wave, or mixed-wave pairing in the context of a magnetic mechanism. The size and shape of the gap is different for different materials. The theoretical arguments are based on the t-J model as derived from the Hubbard model so that it necessarily includes three-site terms. We argue that this should be the basic minimal model for high-Tc systems. We analyze this model starting with the dilute limit which can be solved exactly, passing then to the Cooper problem which is numerically tractable, then ending with a mean field approach. It is found that the relative stability of s-wave and d-wave depends on the size and the shape of the Fermi surface. We identify three striking trends. First, materials with large next-nearest-neighbor hopping (such as YBa(2)Cu(3)O(7-x)) are nearly pure d-wave, whereas nearest-neighbor materials (such as La(2-x)Sr(x)CuO(4)) tend to be more s-wave-like. Second, low hole doping materials tend to be pure d-wave, but high hole doping leads to s-wave. Finally, the optimum hole doping level increases as the next-nearest-neighbor hopping increases. We examine the experimental evidence and find support for this idea that gap function in the high-temperature superconductors is material-specific.
TL;DR: In this paper, the interaction of alternating magnetic fields with granular high temperature superconductors (HTSC) with a magnetization distribution in the HTSC volume was studied.
Abstract: We have studied the interaction of alternating magnetic fields with granular high temperature superconductors (HTSC) with a magnetization distribution in the HTSC volume. The expressions for resonance frequencies of a permanent magnet levitated above a HTSC sample were found for five oscillation modes. An original method for determination of the superconducting grains’ volume fraction is proposed.
TL;DR: In this paper, a two-zone technique was used to synthesize high temperature superconductors of the HgBaCaCuO family, where the powder-in-tube (PIT) method was used for the preparation of the composites.
Abstract: HgBaCaCuO superconductors exhibit superior superconducting properties especially at temperatures above 77K. Irradiation studies have proven that there is a great potential even for further enhancements. Progress in the synthesis of Hg-based superconductors has been achieved by the development of a two-zone technique, which has opened the window for applying a variety of materials processing techniques successfully used in other high temperature superconductors. HgBaCuO—silver composites have been prepared by the powder in tube method and reacted in the two-zone assembly. Silver, which has successfully been used as sheath material for most other high- T c superconductors, appears to be compatible with superconductors of the HgBaCaCuO family.
01 Jan 1996
TL;DR: The discovery of superconductivity at 93 °K in early 1987 represents one of the most exciting developments in modern physics as mentioned in this paper, and it is the state-of-the-art in high temperature HTS.
Abstract: The discovery of superconductivity at 93 °K in early 1987 represents one of the most exciting developments in modern physics. I shall first describe some events in the long search for superconductors with a high transition temperature (Tc) before 1986 that are important to later progress in high temperature superconductivity (HTS). I recall crucial steps taken surrounding 1986 — the critical year of HTS when George Bednorz and Alex Muller made their seminal observation of superconductivity at 35 °K in a nonconventional oxide, that preceded the exciting discovery in 1987. I also recount some episodes from 1987 — the exciting year of HTS when the 93 °K superconductors were discovered and studied. Finally, several major compound systems that were responsible for the solid advancement of Tc and better understanding of HTS in the period of 1988–1994 are summarized. At present, I know of neither experimental nor theoretical reasons for not being able to achieve superconductivity at temperature higher than the present record of 134 °K and 164 °K at ambient and high pressures, respectively.
TL;DR: In this paper, the precursor films for BiSr-Ca-Cu superconductors were prepared by employing a reproducible electrochemical technique, and the as-deposited films were analyzed using energy dispersive spectroscopy (EDS) and scanning electron microscopy (SEM).
TL;DR: In this paper, a phenomenological approach is applied to explore signatures of disordered charge stripes and antiphase spin domains in single-particle properties of the high-temperature superconductors.
Abstract: A phenomenological approach is applied to explore signatures of disordered charge stripes and antiphase spin domains in single-particle properties of the high-temperature superconductors. Stripe phases are shown to explain many experimentally observed unusual features measured in angle-resolved photoemission and optical spectroscopy. It is argued that disordered and fluctuating stripe phases are a common feature of high-temperature superconductors, supported by the additional evidence from neutron scattering and NMR.