Showing papers on "High-temperature superconductivity published in 1992"
TL;DR: A new scaling approach is presented which allows one to map results obtained for isotropic superconductors to anisotropic materials in a simple and direct way.
Abstract: We present a new scaling approach which allows one to map results obtained for isotropic superconductors to anisotropic materials in a simple and direct way. The scaling rules are obtained on the level of Ginzburg-Landau-- or London--type equations and applied directly to the desired phenomenological quantity. We illustrate the method by calculating the elasticity moduli, the depinning and melting temperatures, the critical current densities, and the activation barriers for classical and quantum creep in anisotropic superconductors for an arbitrary angle between the magnetic field and the axes of anisotropy.
495 citations
TL;DR: The physics of flux lines in the cuprate superconductors pinned by columnar defects is mapped onto boson localization in two dimensions, and a scaling theory for the irreversibility line which separates them is proposed.
Abstract: The physics of flux lines in the cuprate superconductors pinned by columnar defects is mapped onto boson localization in two dimensions. The theory predicts a Bose glass phase with an infinite tilt modulus and zero linear resistivity, as well as an entangled flux liquid. We describe correlations and transport in these phases, and propose a scaling theory for the irreversibility line which separates them.
373 citations
TL;DR: In this article, the authors reported the isolation of an alkaline-earth-deficient infinite-layer phase, (Ca1-xSrx)1-yCuO2 (y~Ol), with Tc up to 110 K.
Abstract: THE 'infinite-layer' parent structure1 of the copper oxide superconductors (Fig 1) is the simplest structure containing the CuO2 sheets that are apparently essential to high-transition-temperature (high-Tc) superconductivity At ambient pressure only Ca1-x SrxCuO2 with x≈Ol can be stabilized in this structure1,2but at high pressures and temperatures compounds ranging from Ba1/3Sr2/3CuO2 to Ca2/3Sr1/3CuO2 through SrCuO2 can be synthesized3 We have previously reported superconductivity with Tc = 40–100 K in the Ba–Sr–Cu–O system4,5 but have not until now been able to isolate a superconducting phase Here we report the isolation of an alkaline-earth-deficient infinite-layer phase, (Ca1-xSrx)1-yCuO2 (y~Ol), with Tc up to 110 K In contrast to Sr1-xRxCuO2 (with R a rare-earth element and Tc⩽43 K), which from the composition dependence of the lattice constants is thought to be an n-type superconductor6,7 our data suggest that the present superconductor is of p-type, with the carriers arising from calcium and strontium vacancies High-resolution electron micrographs reveal defect layers, which we suggest are where the calcium and strontium vacancies are concentrated
344 citations
TL;DR: In this article, the paramagnetic effect found experimentally in some granular high temperature superconductors is explained by a model of a Josephson network of d-wave superconductions.
Abstract: The paramagnetic effect found experimentally in some granular high temperature superconductors is explained by a model of a Josephson network of d -wave superconductors. The unusual microwave absorption characteristics of these systems is also explained in a consistent way. Finally, a new experiment is proposed to give a decisive test for d -wave superconductivity in high T c superconductors.
321 citations
TL;DR: In this article, the authors summarized processing of bulk YBa2Cu3Ox superconductors with an emphasis placed on the relationship between microstructure and critical currents, and some possible applications of melt processed superconductor in bulk form are also introduced.
Abstract: The author summarizes processing of bulk YBa2Cu3Ox superconductors with an emphasis placed on the relationship between microstructure and critical currents. Sintering is commonly used in ceramic processing but has been unsuccessful in producing high-Jc materials, primarily due to the weak links at grain boundaries. Melt processes have been found to be effective in increasing Jc values through a combination of grain alignment and the introduction of pinning centres. Some possible applications of melt processed superconductors in bulk form are also introduced in this review. Although many attempts have been made to fabricate long conductors, Jc values are still very small for long conductors, while the length is limited for high-Jc materials.
311 citations
TL;DR: For certain ceramic samples of the Bi-based high-temperature superconductors, the dc field-cooling signal becomes paramagnetic in fields below a few 100 mOe, consistent with orbital paramagnetic moments due to the appearance of spontaneous supercurrents in fields smaller than the lower critical field H c1a parallel to the CuO planes.
Abstract: For certain ceramic samples of the Bi-based high-temperture superconductors, the dc-field-cooling signal becomes paramagnetic in fields below a few 100 mOe This effect correlates with an anomaly in the low-field microwave absorption The data are consistent with orbital paramagnetic moments due to the appearance of spontaneous supercurrents in fields smaller than the lower critical field ${\mathit{H}}_{\mathit{c}1\mathit{a}}$ parallel to the CuO planes
241 citations
TL;DR: In this article, the parity-invariant model of two-species fermions coupled with opposite sign to an abelian gauge field is investigated. But the model is not suitable for high-T c superconductors.
166 citations
TL;DR: In this paper, the irreversible strain limit for the onset of permanent axial strain damage to Ag-sheathed Bi2Sr2Ca1Cu2O8+x and Bi 2Sr 2Ca2Cu3O10+x superconductors has been measured to be in the range of 0.2% −0.35%.
Abstract: The irreversible strain limit eirrev for the onset of permanent axial strain damage to Ag‐sheathed Bi2Sr2Ca1Cu2O8+x and Bi2Sr2Ca2Cu3O10+x superconductors has been measured to be in the range of 0.2%–0.35%. This strain damage onset is about an order of magnitude higher than for bulk sintered Y‐, Bi‐, or Tl‐based superconductors and is approaching practical values for magnet design. The measurements show that the value of eirrev is not dependent on magnetic field, nor does the critical current depend on strain below eirrev at least up to 25 T at 4.2 K. Both of these factors indicate that the observed strain effect in Ag‐sheathed Bi‐based superconductors is not intrinsic to the superconductor material. Rather, the effect is extrinsic and arises from superconductor fracture. Thus, the damage onset is amenable to further enhancement. Indeed, the data suggest that subdividing the superconductor into fine filaments or adding Ag to the superconductor powder prior to processing significantly enhances the damage th...
159 citations
TL;DR: The unidirectional solidification of the zone melt method was performed in order to clarify the growth mechanism on Y-system superconductors as mentioned in this paper, and a sharp faceted interface of YBa2Cu3Oy (123) crystals was obtained in the sample grown at the low growth rate of 1 mm/h.
Abstract: The unidirectional solidification of the zone melt method was performed in order to clarify the growth mechanism on Y-system superconductors A sharp faceted interface of YBa2Cu3Oy (123) crystals was obtained in the sample grown at the low growth rate of 1 mm/h The volume of the 211 phase changed drastically from liquid to 123 crystal These results lead to the idea that the necessary solute for peritectic reaction is provided through a liquid Based on this idea, we developed a simple solidification model that is in good agreement with the experimental results
148 citations
TL;DR: Results of these experiments argue in favor of the existence of a true phase transition in the high-field vortex state from a low-temperature superconducting vortex glass phase into a disordered high-tem temperature vortex fluid phase.
Abstract: A variety of recent experiments on both the static and the dynamic properties of vortices and flux-line lattices in the mixed state of the copper oxide superconductors are discussed. The experiments are of two basic types: (i) experiments that image the magnetic flux patterns either with magnetic decoration or neutrons and give information about static structures, and (ii) experiments that explore the dynamics of vortices either through the resistivity or other electrodynamic responses of the material. Results of these experiments argue in favor of the existence of a true phase transition in the high-field vortex state from a low-temperature superconducting vortex glass phase into a disordered high-temperature vortex fluid phase. The vortex glass phase transition model does a good job of explaining high-precision measurements of the dynamics at the transition. At low fields and temperatures, very long range hexatic order in the flux-line lattice is observed.
TL;DR: In this article, the crystal structure, superconductivity and magnetic properties of the title compounds have been investigated and the results revealed that with the concentration of Pr being constant, the transition temperatureTc of this system decreases with the increasing of La, or rather with an increasing of effective ionic radii of rare earth elements and disappears at aboutx=0.6.
Abstract: The crystal structure, superconductivity and magnetic properties of the title compounds have been investigated. The results revealed that with the concentration of Pr being constant, the transition temperatureTc of this system decreases with the increasing of La, or rather with the increasing of effective ionic radii of rare earth elements and the superconductivity disappears at aboutx=0.6. The coefficient of electron specific heat and the density statesN (0) which were infered from the magnetic measurements also decrease with the increasing of the effective radii. The relation between the radii of rare earth elements and hybridization is briefly discussed.
TL;DR: The most striking difference between the behavior of the copper oxide high-temperature superconductors and previous lowtemperature type II supercondors is the much more gradual decrease in electrical resistance with temperature in the latter, in the presence of a magnetic field as discussed by the authors.
Abstract: The most striking difference between the behaviour of the copper oxide high-temperature superconductors and previous low-temperature type II superconductors is the much more gradual decrease in electrical resistance with temperature in the latter, in the presence of a magnetic field. This raises the question of whether a type II superconductor has strictly zero resistivity, when cooled in a magnetic field. Theoretical and experimental evidence now suggests that as the temperature is lowered, there is a sharp phase transition to a truly superconducting, impurity-dominated phase containing a disordered, frozen arrangement of magnetic flux vortices.
TL;DR: In this paper, various properties of the flux-line lattice (FLL) in high-T c superconductors are compiled, derived, and discussed, and useful general and updated expressions for the energy and magnetic field of arbitrary flux line arrangements in anisotropic and layered supercondors are presented.
Abstract: Various properties of the flux-line lattice (FLL) in high- T c superconductors are compiled, derived, and discussed. Useful general and updated expressions for the energy and magnetic field of arbitrary flux-line arrangements in anisotropic and layered superconductors are presented. From these follow the nonlocal elastic moduli of the FLL which are then applied to the intricate problems of thermal fluctuations and thermal depinning of the FLL and to the linear response of the FLL to applied AC fields. Explicit expressions are derived for the complex AC penetration depth, surface impedance, AC resistivity and for the AC susceptibility of films and cylinders, taking full account of elastic pinning and viscous drag of vortices, and of thermally activated linear flux creep or tunneling. These AC properties are then applied to vibrating superconductors and to thermally activated flux diffusion, which gives a quantitative explanation of the depinning lines observed in various experiments. Finally, the shear-limited critical current density is estimated and FLL decoration experiments are discussed.
TL;DR: The character of the low energy excitations ("quasiparticles"), which interact strongly with atomic motions, with magnetic fluctuations, and possibly with charge fluctuations, must be sorted out before the superconducting pairing mechanism can be given a microscopic basis.
Abstract: Recent experimental results are beginning to limit seriously the theories that can be considered to explain high-temperature superconductivity. The unmistakable observations of a Fermi surface, by several groups and methods, make it the focus of realistic theories of the metallic phases. Data from angle-resolved photoemission, positron annihilaton, and de Haas-van Alphen experiments are in agreement with band theory predictions, implying that the metallic phases cannot be pictured as doped insulators. The character of the low energy excitations ("quasiparticles"), which interact strongly with atomic motions, with magnetic fluctuations, and possibly with charge fluctuations, must be sorted out before the superconducting pairing mechanism can be given a microscopic basis.
TL;DR: In this paper, the authors show clear and conclusive experimental evidence for the enhancement of superconductivity in GdBa2Cu3Ox and YBa2cu3Ox thin films by photoexcitation.
Abstract: We show clear and conclusive experimental evidence for the enhancement of superconductivity in GdBa2Cu3Ox and YBa2Cu3Ox thin films by photoexcitation. Upon laser illumination the critical temperature increases while the resistivity of the material decreases. The relaxation back to the original state is very slow, of the order of days at room temperature. The existence of this effect opens the possibility of fabricating weak‐link devices with in situ tunable superconducting characteristics.
TL;DR: In this paper, non-superconducting Y 2 BaCuO 5 (211) inclusions can act as pinning centres in melt-processed YBaCuO superconductorrs even when their size is orders of magnitude larger than the coherence length.
TL;DR: This work discusses a state of an orbital glass which may exist in granular superconductors and is characterized by broken fundamental symmetries (C and P).
Abstract: We discuss a state of an orbital glass which may exist in granular superconductors. The orbital glass is related to the existence of the special loops of Josephson junctions with positive and negative Josephson couplings. With an odd number of negative couplings on the loop, a spontaneous orbital moment is created. Similar to anyon superconductivity, the new state with orbital moments is characterized by broken fundamental symmetries (C and P). There the orbital paramagnetism coexists with the superconductivity and at small magnetic field and low temperatures the Meissner effect may disappear.
TL;DR: The authors have successfully grown single crystals of La 2-x-y Nd y Dr x CuO 4 by the traveling-solvent floating-zone method and enable us to investigate the anisotropic transport properties of the LTT phase.
Abstract: We have successfully grown single crystals of La 2-x-y Nd y Dr x CuO 4 (x=0,0.12,0.20;y∼0.4) by the traveling-solvent floating-zone method. All of these crystals show a tlattice instability to the low-temperature tetragonal (LTT) phase and enable us to investigate the anisotropic transport properties of the LTT phase. For x=0.12, various transport coefficient show a discontinuous jump at the phase transition (evidence for a first-order transition), and superconductivity is suppressed almost completely, while the effects are much reduced for x=0.20, which show a bulk superconductivity with reduced T c
AT&T1
TL;DR: In this paper, the authors demonstrate a technique for real-time, spatially resolved imaging of flux dynamics in superconductors with a wide variety of sample morphologies using a doped garnet film.
Abstract: THE magnetic response of the high-transition-temperature oxide superconductors to an applied field is related to two technologically important issues in these materials: their finite resistivities well below the superconducting transition and their critical currents In addition, the scientifically interesting issues of pinning, melting, vortex glass behaviour and vortex liquids1 can be probed by studying the time dependence of the magnetization Most techniques used to probe the magnetization of superconductors represent averages over the entire volume of the sample This precludes the study of defects, and also raises the question of whether the observed behaviour is intrinsic or is dominated by defects On the other hand, spatially resolved techniques such as magnetic decoration or scanned probe microscopy are usually too slow to allow studies of the dynamics of these systems Here we demonstrate a technique for real-time, spatially resolved imaging of flux dynamics in superconductors with a wide variety of sample morphologies Following earlier work2–6, we place a wafer of a magneto-optical material—in this case, a doped garnet film—in contact with a superconducting sample in a polarizing light microscope The spatial and temporal resolution afforded by the high-quality garnet film allows us to investigate the effect of defects (specifically, twin planes) on the magnetic response of the superconductor
NEC1
TL;DR: In this article, the authors show that the transition temperature of C60 superconductors decreases as the 13C content increases, as expected within the context of BCS-like phonon-mediated pairing.
Abstract: THE surprisingly high transition temperatures (Tc) for superconductivity in alkali-meta-doped C60 has spurred wide interest in understanding its mechanism1–6. Recently the increase in Tc with lattice constant was demonstrated for these materials6, and was interpreted as resulting from the corresponding increase in the density of states at the Fermi level. According to the standard (BCS) theory of superconductivity, the other important factor controlling Tc is the phonon that mediates electron pairing. To test whether this factor plays a part for the C60 superconductors, we prepared C60 containing various amounts of 13C, which we then doped with rubidium to give Rb3C60. Measurements of diamagnetic shielding and Meissner effect show that Tc decreases as the 13C content increases, as expected within the context of BCS-like phonon-mediated pairing; but the dependence on the mass is stronger than for most electron-phonon superconductors where Tcm−α with α ≤0.5. Instead, the exponent a has the remarkably large value of 1.4±0.5. Regardless of the interpretation of this value, it is clear that phonons have an important role in the origin of superconductivity in doped C60.
TL;DR: In this article, high-resolution angle-resolved photoemission measurements are reported for YBa{sub 2}Cu{sub 3}O{sub {ital x} was varied between 6.3 and 6.9, where the material is metallic.
Abstract: High-resolution angle-resolved photoemission measurements are reported for YBa{sub 2}Cu{sub 3}O{sub {ital x}} when oxygen stoichiometry {ital x} was varied between 6.3 and 6.9. Fermi surfaces were measured and their dependence on oxygen stoichiometry was monitored by observing the dispersing behavior of spectral features, scanning the entire first Brillouin zone. For {ital x}=6.9, measured Fermi surfaces correspond very well with the plane-related Fermi surfaces calculated from band theory. Relatively small changes in Fermi surfaces were observed when oxygen stoiochiometry was varied in the range 6.5{le}{ital x}{le}6.9, where the material is metallic. However, significant changes in the spectral behavior were observed when the material becomes insulating.
TL;DR: In this paper, large critical currents with a relatively weak magnetic field dependence are obtained in thick films of TlBa2Ca2Cu3Oz, and the observed behavior is attributed to a large degree of uniaxial alignment of platelike grains, and to superior intragranular flux pinning.
Abstract: Large critical currents with a relatively weak magnetic field dependence are obtained in thick films of TlBa2Ca2Cu3Oz. Transport measurements indicate Jc ≳105 A/cm2 at 77 K, zero field, and Jc≳104 at 60 K in a 2 T field applied along the c‐axis. The observed behavior is attributed to a large degree of uniaxial alignment of platelike grains, and to superior intragranular flux pinning. These results are consistent with recent theories concerning the nature of vortices in highly anisotropic (layered) superconductors and ‘‘brick wall’’models of intergranular current transport.
TL;DR: Application to cuprate superconductors shows that this mechanism along with a conventional electron-phonon interaction can explain the high T c 's and the anomalous behavior of the isotope shift as a function of doping.
Abstract: It is shown that the interactions in a strongly correlated quasi-two-dimensional electron gas with the Fermi level lying at a saddle point (Van Hove singularity) in e k can give rise to superconductivity by exchange of excitations with a characteristic low electronic energy scale E ∗ . Application to cuprate superconductors shows that this mechanism along with a conventional electron-phonon interaction can explain the high T c 's and the anomalous behavior of the isotope shift as a function of doping.
01 Jan 1992
TL;DR: In this article, Pan et al. proposed a method to achieve high in-field Jc at 77 K in Bi-Sr-Ca-Cu-O. The Violation of the BCS Theory and the Extensions Required to include the effects of a Nearby Phase Transition are discussed.
Abstract: Preface. Part I: Physics and Theory. Abrikosov Vortices Behavior in Different Pinning Potential for Moderately Anisotropic High-Tc Superconductors V.M. Pan, et al. Microwave Dissipation and the Structure of the Vortex Lattice in Bi2Sr2CaCu2O8+delta Single Crystals N. Bontemps, H. Enriquez. The Flux Line Lattice States in Single-Crystalline Superconductors with Weak Pinning V.F. Solovjov, V.M. Pan. Can we Achieve High In-Field Jc at 77 K in Bi-Sr-Ca-Cu-O? D. Shi. The Violation of the BCS Theory and the Extensions Required to Include the Effects of a Nearby Phase Transition E.L. Haase. Correlations Between Magnetostriction Jumps and Flux Instabilities in La1.85Sr0.15CuO4 Single Crystal A. Nabialek. Spin-Phonon Correlations and Optical Excitations in Oxides Y.G. Pashkevich, A.V. Yeremenko. Anisotropic Josephson Junctions on Stepped Surfaces of Bi2Sr2CaCu2O8 Crystals: Evidence for the Symmetry of the Pair Wave Function H.Z. Durusoy, M.R. Beasley. Part II: Processing and Properties - Crystals. Material Science Aspects of HTS Technical Superconductors A.D. Nikulin. Studies of Infinite-Layer, T'-Phase, and 1-D-Ladder Copper-Oxide Compounds J.T. Markert, et al. Low-Temperature H-T Phase Diagram of Nd1.85Ce0.15CuO4+-delta J. Herrmann, et al. Superconductivity in the La2CuO4.03 Single Crystal System Y. Obukhov, et al. Residual Microstresses, a-b Microcracking and Twin Structure in Oxygen Controlled Melt Grown NdBaCuO Superconductors P. Diko, et al. Microstructure and Superconducting Characteristics ofHgmPbnBa2Ca2Cu3O8+-d I. Sargankova, et al. Problems of Searching for Copper-Free HTS Compositions S.A. Nedilko, V.A. Drozd. Part III: Processing and Properties -- Thin Films. Pulsed Laser Deposition of Thin Films M. Jelinek, et al. Study of a-Axis Oriented YB2a2Cu3Ox Superconducting Thin Films on Y2O3/YSZ/Si Substrates S. Chromik, et al. Structural Disorder Investigations of YBCO Thin Films Using Raman Microscopy G. Gibson, et al. Penetration Depth Measurements in Epitaxiel YBCO Thin Films by the ESR Technique B. Akta, H.Z. Duriosoy. Part IV: Applications. HTS Multilayer Process Development for Digital Circuits M.G. Forrester, et al. Evaluation of the Magnetic Properties of Nd-Based Superconductors V. Ottoboni, et al. Noise Properties of HTSC Films for Bolometers on Si Membranes I.A. Khrebtov, et al. Application of Ion Beam Etching to Investigate the Electrical Behaviour of Josephson Junctions H. Schneidewind, et al. Synthesis of Bi-Sr-Ca-Cu-O Wires for Perspective Applications A. ul Haq, M.N. Khan. Late Submission. Electron-Density Distribution and Valence-Bond Structure in Copper-Oxygen Linkage in YB2Cu3O6.9 and CuGeO3 T. Ida, et al. Index. List of Participants.
TL;DR: In this paper, the typical features of temperature dependences of such magnetic properties as spin susceptibility and nuclear magnetic relaxation rate in various Cu oxides together with the doping dependence of the critical temperatures can be understood by a phase diagram deduced from the mean field theory for the t-J model.
Abstract: It is discussed that typical features of temperature dependences of such magnetic properties as spin susceptibility and nuclear magnetic relaxation rate in various Cu oxides together with the doping dependence of the critical temperatures can be understood by a phase diagram deduced from the mean field theory for the t-J model
TL;DR: In this article, a series of high-quality superlattices in which ultrathin slabs (one-half unit cell thick) of the high-Tc superconductor Bi2Sr2CaCu2O8 alternate with up to five such layers of the low Tc Bi2sr2Cu1O6 phase were synthesized.
Abstract: Utilizing atomic layer-by-layer molecular beam epitaxy (ALL-MBE), we have synthesized a series of high-quality superlattices in which ultrathin slabs (one-half unit cell thick) of the high-Tc superconductor Bi2Sr2CaCu2O8 alternate with up to five such layers of the low-Tc Bi2Sr2Cu1O6 phase. In all these superlattices we foundTc to be essentially equal to that of the high-Tc Bi2Sr2CaCu2O8 phase itself, which indicates that this cuprate is a 2D superconductor insofar as the interslab coupling plays at best a secondary role. Furthermore, it is demonstrated thatTc need not be reduced at heterostructure interfaces.
TL;DR: Calculations of the quasiparticle-lifetime broadening 1/{tau}, both for idealized and realistic models of the band structure, show a large lifetime broadening from electron-electron scattering, with the characteristic linear dependence on energy from the Fermi energy seen in high-temperature superconductors.
Abstract: Calculations of the quasiparticle-lifetime broadening 1/{tau}, both for idealized and realistic models of the band structure, show a large lifetime broadening from electron-electron scattering, with the characteristic linear dependence on energy from the Fermi energy seen in high-temperature superconductors, provided that the Fermi level lies near the van Hove singularity in the quasi-two-dimensional band structure. The effect comes from intra--van Hove--singularity scattering {ital without} the intervention of nesting.