Showing papers on "High-temperature superconductivity published in 1988"
TL;DR: The single-phase perovskite Ba0.6K0.4BiO3 has a magnetically determined onset temperature of 29.8 K, a Tc considerably higher than that of conventional superconductors and surpassed only by copper-containing compounds.
Abstract: It is well known that the breakthrough of Bednorz and Muller1 in discovering superconductivity in (La, Ba)2CuO4 was inspired in part by their knowledge of the superconducting properties of Ba(Pb, Bi)O3 (ref. 2). With a transition temperature, Tc, of ∼12 K, that compound was not generally considered anomalous despite the fact that its Tcis 3–5 times higher than that of traditional superconductors with comparable density of states3–5. The increases in Tc for copper-oxide-based materials continue to generate worldwide excitement, but from both a chemical and theoretical point of view it would also be exciting if high-Tcsuperconductivity were observed in another class of materials. Here we report the results of experiments leading us to the single-phase perovskite Ba0.6K0.4BiO3, which has a magnetically determined onset temperature of 29.8 K—a Tc considerably higher than that of conventional superconductors and surpassed only by copper-containing compounds. Superconductivity in this compound occurs within the framework of a three dimensionally connected bismuth-oxygen array. These results suggest that further research toward exploring the limiting Tcs for bismuth-oxide-based, high-temperature superconductors might be fruitful.
972 citations
TL;DR: In this paper, stable and reproducible bulk superconductivity with an onset at 120 K and zero resistance above 100 K in the Tl-Ca/Ba-Cu-O system was reported.
Abstract: The discovery of 30-K superconductivity in the La–Ba–Cu–O system1 and 90-K superconductivity in the Y–Ba–Cu–O system2 stimulated a worldwide search for even higher-temperature superconductors. Unfortunately, most of the higher-temperature transitions reported in the past year have proved to be unstable, irreproducible, or not due to bulk superconductivity3–7. Recently, we and co-workers8,9 reported superconductivity above 90 K in a new Tl–Ba–Cu–O system, and pointed out that elemental substitutions in this system may lead to even higher-temperature superconductivity. Here we report stable and reproducible bulk superconductivity with an onset at 120 K and zero resistance above 100 K in the Tl–Ca/Ba–Cu–O system. This transition temperature is much higher than those observed for typical rare-earth-containing superconductors, and the onset temperatures are comparable to that in the Bi–Ca/Sr–Cu–O system, as reported in refs 10 and 11 (received after submission of this paper).
910 citations
TL;DR: The model proposed recently by Yeshurun and Malozemoff to explain the ''irreversibility line'' in high-temperature superconductors is extended to account for the experimentally measured width and shape of the resistive transition in a magnetic field.
Abstract: The model proposed recently by Yeshurun and Malozemoff to explain the "irreversibility line" in high-temperature superconductors is extended to account for the experimentally measured width and shape of the resistive transition in a magnetic field, without invoking material inhomogeneity. It is argues that high ${T}_{c}$ and ${H}_{c2}$ are necessary, but not sufficient, conditions for such materials to show zero resistance at room temperature in substantial magnetic fields.
867 citations
TL;DR: In this paper, the authors reported superconductivity in the rare earth-free TI-Ba-Cu-O system with a resistance starting at 90 K with zero resistance at 81 K.
Abstract: The initial discovery by Bednorz and Muller1 of 35-K superconductivity in the La-Ba-Cu-O system has stimulated worldwide activity in searching for higher-temperature superconductors. Elemental substitution has proved to be most effective in raising transition temperature. Substitution of Sr for Ba has produced 40-K superconductivity2–5and substitution of Y for La has produced a new high-temperature superconductor with transition temperature above liquid-nitrogen temperature6. A class of superconducting compounds of the form RBa2Cu307-x has been explored by further substitutions of other rare earths (Y is considered in the rare-earth [RI category here) for Y7-13. To date, a rare earth, an alkaline earth, copper and oxygen have been required for all high-temperature superconductors14,15. (Zhanget al 14reported 90-K superconductivity in the Th-Ba-Pb(Zr)-Cu-O system. Panetal15reported 50-K superconductivity in the Y-Ba-Ag-O system. As Th is a member of the actinide series which belongs to the same Group 3B in the periodic table as the lanthanide series and Ag belongs to the same Group 1B as Cu, high-temperature supercon-ductors are still thought to be closed in the Group 3B—Group 2A-Group 1B—oxygen system. ) Only partial substitutions ha. e led to superconductors, but with no significant rise of transition tem-perature (the only exception is 40-K superconductivity in La2CuO4-x , refs 16, 17). Here we report superconductivity in the rare-earth-free TI-Ba-Cu-O system. We have obsened sharp drops of resistance starting above 90 K with zero resistance at 81 K in this system. Magnetic measurements have confirmed that these sharp drops of resistance in the TI-Ba-Cu-O samples origi-nate from superconductivity. The samples are stable in air for at least two months, and their preparation is easily reproduced.
645 citations
TL;DR: In this article, a simple theoretical model for the granularity is introduced and then used to discuss a number of electrodynamic properties (hysteretic magnetization versus magnetic field, zero-field-cooled and field cooled magnetisation versus temperature, ac susceptibility, and flux creep with logarithmic time dependence).
Abstract: The microstructure of bulk samples of the copper-oxide high-temperature superconductors commonly is describable in terms of anisotropic grains of stoichiometric material separated by layers of nonstoichiometric interface material. The granularity strongly influences the electromagnetic properties, especially the transport critical-current density and the magnetization. In this paper, a simple theoretical model for the granularity is introduced and then used to discuss a number of electrodynamic properties (hysteretic magnetization versus magnetic field, zero-field-cooled and field-cooled magnetization versus temperature, ac susceptibility, and flux creep with logarithmic time dependence). Special attention is drawn to the importance of distinguishing between intragranular and intergranular effects.
539 citations
TL;DR: Those oxides that superconduct at the highest temperatures contain copper-oxygen sheets; however, other elements such as bismuth and thallium play a key role in this new class of superconductors.
Abstract: Spectacular advances in superconductors have taken place in the past two years. The upper temperature for superconductivity has risen from 23 K to 122 K, and there is reason to believe that the ascent is still ongoing. The materials causing this excitement are oxides. Those oxides that superconduct at the highest temperatures contain copper-oxygen sheets; however, other elements such as bismuth and thallium play a key role in this new class of superconductors. These superconductors are attracting attention because of the possibility of a wide range of applications and because the science is fascinating. A material that passes an electrical current with virtually no loss is more remarkable when this occurs at 120 K instead of 20 K.
532 citations
TL;DR: In this article, the authors reported the growth of small single crystals of this phase, with composition (Ca 0.86Sr0.14)CuO2, and their characterization by single-crystal X-ray diffraction.
Abstract: Oxide superconductors in the system Tl2Ba2Can–1CunO4+2n (ref. 1) have transition temperatures (Tc) above 100 K, increasing with n. So far, stacking sequences up to n = 3 have been found in small crystals, and sequences with n > 3 have been seen in electron microscopy studies1. For large n, the stoichiometry of Tl2Ba2Can–1CunO4+2n approaches CaCuO2, a structure expected to consist only of CuO2 planes separated by Ca atoms. By analogy with Tl2Ba2Can–1CunO4+2n, the unit cell of this hypothetical phase is expected to be tetragonal with a = 3.86 A. Such a compound is not known in the Ca–Cu–O system, but Roth2 recently reported that small amounts of Sr on the Ca site can stabilize this simple structure. Here we report the growth of small single crystals of this phase, with composition (Ca0.86Sr0.14)CuO2, and their characterization by single-crystal X-ray diffraction. The crystals are tetragonal with space group P4/mmm, and the structure contains planar [CuO2]∞ layers separated by Ca and Sr atoms. The structure is a simple defect perovskite with ordered oxygen vacancies and can be regarded as the n = ∞ parent of the A2B2Can–1CunO4+2n (A = Bi, Tl; B = Sr, Ba) superconductors.
514 citations
TL;DR: In this paper, a trilayer Cu perovskitelike units separated by bilayer TI-O units were found in T12Ca2 Ba2 Cu3 Ox with a transition to zero resistance at ≃ 125 K.
Abstract: Bulk superconductivity is reported in T12Ca2 Ba2 Cu3 Ox with a transition to zero resistance at ≃ 125 K, the highest transition temperature (Tc) yet found. Transmission electron spectroscopy shows that the unit cell is body-centered tetragonal and contains trilayer Cu perovskitelike units separated by bilayer TI-O units. (T c in this material varies from 118 to 125 K depending on preparation conditions. A high density of perovskitelike bilayer intergrowths are observed in the 118-K material, which we speculate result in the decreased (T c. A second structure containing only bilayer perovskitelike units—TI2 Ca1 Ba2Cu2Ox—is a bulk superconductor with Tv ranging from 95 to 108 K.
441 citations
TL;DR: In this article, a new family of high-temperature superconductors with the general formula Pb2Sr2ACu3O8+δ is described.
Abstract: A new family of high-temperature superconductors is described, with the general formula Pb2Sr2ACu3O8+δ. Although they have the planes of CuO5 square pyramids characteristic of the other copper-oxide superconductors, the new compounds belong to a distinct structural series, with wide scope for elemental substitution. Their unusual electronic configuration also gives new insight into the role of charge distribution among the structural building blocks in controlling superconductivity.
430 citations
TL;DR: This paper shows that the development of resonating valence bond correlations and the subsequent superconducting order in the high-T/sub c/ oxide superconductors are described by an U(1) lattice gauge theory.
Abstract: In this paper we show that the development of resonating-valence-bond correlations and the subsequent superconducting order in the high-${T}_{c}$ oxide superconductors are described by an U(1) lattice-gauge theory. The insulating state has an almost-local gauge symmetry and doping changes this to a global symmetry, which is spontaneously broken at low temperatures, resulting in superconductivity. New topological excitations associated with the singlet field are found.
412 citations
01 Jan 1988
TL;DR: In the years following the discovery of superconductivity in doped lanthanum copper oxide in late 1986, there has been a large multinational effort in the study of what are now called high Tc superconductors as discussed by the authors.
Abstract: In the years following the discovery of superconductivity in doped lanthanum copper oxide in late 1986 there has been a large, multinational effort in the study of what are now called high Tc superconductors. As a result of this work at least ten discrete phases of superconducting oxides have been identified. The authors felt it would be useful to have a symposium whose focus was to identify and discuss the common structural features of these oxide superconductors. These proceedings hopefully represent a state of the art view of the correlations between crystal chemistry and superconductivity in metal oxide systems.
TL;DR: In oxide superconductors the local suppression of antiferromagnetic correlations in the vicinity of a hole lowers the energy of the system, leading to a quasi two-dimensional bag of weakened spin order that follows the hole in its motion.
Abstract: In oxide superconductors the local suppression of antiferromagnetic correlations in the vicinity of a hole lowers the energy of the system. This quasi two-dimensional bag of weakened spin order follows the hole in its motion. In addition, holes prefer to share a bag, leading to a strong pairing attraction and a high T c superconductivity. There are many experimental consequences of this mechanism for both the superconducting and normal phases.
TL;DR: Stable superconductivity up to 114 K has been reproducibly detected in Bi-Al-Ca-Sr-Cu-O multiphase systems without any rare-earth elements, providing an extra material base for the study of the mechanism of high-temperaturesuperconductivity and also the prospect of reduced material cost for future applications of superconductor.
Abstract: Stable superconductivity up to 114 K has been reproducibly detected in Bi-Al-Ca-Sr-Cu-O multiphase systems without any rare-earth elements. Pressure has only a slight positive effect on T(c). These observations provide an extra material base for the study of the mechanism of high-temperature superconductivity and also the prospect of reduced material cost for future applications of superconductivity.
TL;DR: Stable and reproducible superconductivity has been unambiguously observed in a new Tl-Ba-Cu-O system containing no group-IIIB elements and further substitutions of elements for this system may lead to even higher-temperature superconductors.
Abstract: Stable and reproducible superconductivity has been unambiguously observed in a new Tl-Ba-Cu-O system containing no group-IIIB elements. Resistance in these rare-earth--free oxides starts to drop sharply above 90 K and reaches zero at 81 K. Meissner flux expulsion and diamagnetic shielding show bulk superconductivity. Further substitutions of elements for this system may lead to even higher-temperature superconductors.
TL;DR: A perovskite-like single-crystal substrate material has been investigated that simultaneously permits epitaxial growth of 1 2 3 superconductor films and possesses desirable rf properties of low dielectric constant and loss tangent as mentioned in this paper.
Abstract: A perovskite‐like single‐crystal substrate material has been investigated that simultaneously permits epitaxial growth of 1‐2‐3 superconductor films and possesses desirable rf properties of low dielectric constant and loss tangent. The lattice constant of 3.792 A provides a lattice match to within 1% of the a axis of 1‐2‐3. Sputtered films of erbium‐barium‐copper‐oxide have been produced on (100) LaAlO3 substrates that exhibit sharp resistive transitions at 90 K (ΔT=1K), bulk superconductivity as determined by ac susceptibility measurements, and nearly single‐crystal growth as evidenced by x‐ray diffraction and high‐resolution scanning electron microscopy. The high‐frequency dielectric properties of LaAlO3 were experimentally investigated at several temperatures. The low‐frequency dielectric constant was measured to be 15 and the microwave loss tangent ranged from 6×10−4 at room temperature to 5×10−6 at 4 K.
TL;DR: In this paper, a two-step synthesis technique was described, starting with a stoichiometric oxide composition, which yields single-phase samples suitable for transport measurements, and showed that superconductivity in Ba1−xKxBiO3−y occurs only in a cubic perovskite phase which is stable at ≲600°C and which forms only for x > 0.25.
Abstract: The recent discovery of superconductivity near 30 K in Ba1−xKxBiO3−y (x≈0.4)1,2 is remarkable for two reasons. It is the first copper-free oxide superconductor that has a transition temperature (Tc) above that for the best intermetallic superconductor; and the structure is reported to be cubic, which excludes a two-dimensional metal–oxygen sublattice analogous to the CuO2 planes believed to be responsible for superconductivity in the copper-oxide-based superconductors. Cava et al.1 described a synthesis technique which involved starting with a 100% excess of KO2. At least part of the excess potassium was found to be present in the final sample (in a form not detectable by X-ray diffraction), resulting in samples that were not suitable for resistivity measurements and making a precise determination of the potassium and oxygen content in the superconducting phase impossible. Here we describe a two-step synthesis technique starting with a stoichiometric oxide composition, which yields single-phase samples suitable for transport measurements. Neutron powder diffraction studies of samples with varying potassium concentration show that superconductivity in Ba1−xKxBiO3−y, occurs only in a cubic perovskite phase which is stable at ≲600°C and which forms only for x > 0.25. Within this cubic phase, Tc is highest for compositions near the structural phase transition (x ≈ 0.25) and decreases with increasing x.
TL;DR: In this article, thin superconducting films of Y•Ba•Cu•O were prepared at 650°C using the pulsed laser deposition technique and they exhibited superconductivity with zero resistance at temperatures as high as 83 K.
Abstract: Thin superconducting films of Y‐Ba‐Cu‐O were prepared at 650 °C using the pulsed laser deposition technique. The as‐deposited films were fully superconducting at low temperature (30 K). After annealing in oxygen at 450 °C for 3 h, the films exhibited superconductivity with zero resistance at temperatures as high as 83 K. Film‐substrate interface reaction was minimal as revealed by Rutherford backscattering and Auger electron spectrometry. These films processed at such low temperatures are also found to have excellent planar surface morphology and high critical current density.
TL;DR: In this article, the resistivity and magnetic susceptibility measurements on sintered Bi4Sr3Ca2Cu4O16+x containing 20% by weight of Au, Ag, or Pt-group metals indicate that Au and the Ptgroup metals significantly suppress or eliminate the superconducting transition in BiSr•Ca•Cu•O.
Abstract: The Bi‐Sr‐Ca‐Cu‐O superconductors have been doped with various noble metals and their superconducting properties have been investigated. The resistivity and magnetic susceptibility measurements on sintered Bi4Sr3Ca2Cu4O16+x containing 20% by weight of Au, Ag, or Pt‐group metals indicate that Au and the Pt‐group metals significantly suppress or eliminate the superconducting transition in Bi‐Sr‐Ca‐Cu‐O. Only Ag is found to be benign, maintaining both the 115 and 85 K transitions in the compound. This nonpoisoning behavior of silver is of significant technical importance because of the need for a proper stabilizing normal metal for composite superconductor wire, nonreactive crucible materials for melt processing or crystal growth, and suitable nonpoisonous substrates or barriers for thin‐ or thick‐film superconducting devices.
TL;DR: In this article, the dominant oxygen-2p nature of the Fermi-liquid state in the high-Tc superconductor was obtained using the technique of angle-resolved resonant photoemission.
Abstract: It has been generally accepted that a strong on-site Coulomb repulsion of the Cu 3d electrons dominates the electronic structure of the high-transition-temperature (high-Tc) superconductors. The on-site Coulomb repulsion has been evaluated as 6–7 eV, comparable with the valence-band width1,2. This strong correlation is thought to cause the Cu 3d electrons to be localized as in a Mott insulator, and doped holes may be transferred to oxygen sites, as the charge transfer energy is small compared with the correlation energy. These doped holes yield a substantial density of states at the Fermi level, characteristic of metals. There has been great effort to find and characterize the electronic states at the Fermi level, because these states relate directly to the mechanism of the high-Tc superconductivity by providing Cooper pairs below Tc. Here we report the first direct evidence for the dominant oxygen-2p nature of the Fermi-liquid state in the high-Tc superconductor, obtained using the technique of angle-resolved resonant photoemission.
TL;DR: The electronic structure of the new Bi-based high-temperature superconductor, with T/sub c/ onsets above 110 K, is shown to be altered considerably from that of the other cuprate superconductors by the presence of Bi.
Abstract: The electronic structure of the new Bi-based high-temperature superconductor, with ${T}_{c}$ onsets above 110 K, is shown to be altered considerably from that of the other cuprate superconductors by the presence of Bi. There are Bi-O bands which cross the Fermi level, and the two-dimensional character of the bands is even greater than that of previous cuprates. Like the other cuprates, band critical points occur at the Fermi level.
TL;DR: In this paper, a model for flux creep in high Tc superconductors is developed, which predicts that associated with the flux creep regime is a resistance which shows a linear variation with applied magnetic field.
TL;DR: In this paper, a model of Josephson coupling between grains is proposed to explain the millimeter-wave surface impedance of oriented, polycrystalline thin films of high Tc superconductors.
Abstract: We propose a model of Josephson coupling between grains to explain the millimeter‐wave surface impedance of oriented, polycrystalline thin films of high Tc superconductors. An effective junction IcR product and effective grain size are calculated based on recent measurements of the surface impedance. We suggest a criterion on film quality for the observation of losses intrinsic in the superconductor. The effects of crystalline orientation on surface impedance are considered.
TL;DR: In this article, a crossover between different contributions of magnetoresistance is investigated for high temperature superconductors above the critical point and the phase relaxation time and the theoretical formula of the crossover are discussed.
Abstract: Magnetoresistance for high temperature superconductors is investigated above the critical point. Near transition temperature, there is a crossover from two dimensions to three dimensions. According to superconducting fluctuation, a crossover between different contributions of magnetoresistance appears. The phase relaxation time and the theoretical formula of the crossover in the magnetoresistance are discussed.
TL;DR: In this article, the magnetic field induced microwave absorption in sintered high-Tc copper oxide superconductors is found to be proportional to the surface area of samples and not to their volume, establishing that absorption takes place near the sample surface.
Abstract: Magnetic-field-induced microwave absorption in sintered high-Tc copper oxide superconductors is found to be proportional to the surface area of samples and not to their volume, establishing that absorption takes place near the sample surface. The surface resistance and reactance increase with magnetic field as a result of energy loss through fluxons driven by superconducting currents. When the magnetic field is modulated, absorptive and dispersive signals arise from modulation of the complex surface impedance through processes induced by the changing magnetic fields.
TL;DR: By depositing YBaCuO films at low substrate holder temperatures (600°C) using a pulsed laser, films with the orthorhombic phase exhibiting superconductivity with high zero resistance temperatures (Tc0) were produced as mentioned in this paper.
Abstract: By depositing YBaCuO films at low substrate holder temperatures (600 °C) using a pulsed laser, films with the orthorhombic phase exhibiting superconductivity with high zero resistance temperatures (Tc0) were produced. Tc0 values as high as 50 and 80 K were seen on films deposited directly on Si and on Si with only a 50 nm ZrO2 buffer layer, respectively. The key to the successful film deposition is the low processing temperatures involved, which minimized the interface reactions as observed by Auger electron spectrometry.
TL;DR: In this paper, the structural changes that accompany Zn and Ga substitution, as deduced from X-ray and neutron diffraction, correlate these changes with the superconducting properties.
Abstract: One of the outstanding questions concerning the high-temperature superconductor YBa2Cu3O7 is the relative importance of the CuO2 planes (Cu(2) site) and the CuO chains (Cu(1) site). Many theories1,2 have stressed the importance of the 3d holes at the Cu sites, which provide an antiferromagnetic correlated background necessary for the coupling of the superconducting electrons. We have substituted Zn(3d104s2) and Ga(3d104s24p1) in the Cu(2) and Cu(1) sites, respectively, while maintaining the oxygen stoichiometry at 7. In the valence states of 2 + and 3 + respectively, the 3d bands of both elements are completely full, without the complication of a magnetic moment. Here we discuss the structural changes that accompany Zn and Ga substitution, as deduced from X-ray and neutron diffraction, and correlate these changes with the superconducting properties. We show that the integrity of the planes is much more important than that of the chains in sustaining high-Tc superconductivity.
TL;DR: In this article, positive-muon spin-rotation and relaxation measurements of the oxygen-deficient perovskite YBa2Cu3O(x) have revealed local antiferromagnetic order for x = 6.0-6.4 with a Neel temperature TN that decreases rapidly with increasing oxygen content.
Abstract: Positive-muon spin-rotation and -relaxation measurements of the oxygen-deficient perovskite YBa2Cu3O(x) have revealed local antiferromagnetic order for x = 6.0-6.4 with a Neel temperature TN that decreases rapidly with increasing oxygen content x. For slowly annealed samples with x = 6.35-6.5 the superconducting transition temperature Tc increases smoothly with x from 25 K at x = 6.348 to 60 K at x = 6.507. Two such samples with x = 6.348 and x = 6.400 appear to 'switch' from superconductivity to antiferromagnetic order at lower temperatures.
TL;DR: Les mesures sont menees sur des superconducteurs d'oxyde de cuivre qui explicitent le regime experimental dans lequel les effets extrinseques sont negligeables and confirment l'existence of the tension intrinseque prevue.
Abstract: The torque on a superconductor in a magnetic field H has been thought to be dominated by trapped flux or sample shape effects, but it has recently been suggested that an anisotropic type-II material should experience an intrinsic torque for H(c1) much less than H, which in turn is less than H(c2). The predicted phenomenon results from transverse magnetization of the Abrikosov lattice. Measurements are presented on copper-oxide superconductors which delineate the experimental regime in which extrinsic effects are negligible and confirm the existence of the predicted intrinsic torque.
TL;DR: In this paper, it is shown how these effects follow from the hysteretic magnetization curves and how the energy is dissipated, and how they are dissipated in a magnet of low symmetry.
Abstract: A type I superconductor levitated above a magnet of low symmetry has a unique equilibrium position about which it may oscillate freely. In contrast, a type II superconductor has a continuous range of stable equilibrium positions and orientations where it floats rigidly without swinging or orbiting as if it were stuck in sand. A strong internal friction conspicuously indicates the existence and unpinning of flux lines in oxide superconductors levitated above liquid nitrogen. It is shown how these effects follow from the hysteretic magnetization curves and how the energy is dissipated.