Showing papers on "High-temperature superconductivity published in 1987"
TL;DR: The oxide superconductors, particularly those recently discovered that are based on La2CuO4, have a set of peculiarities that suggest a common, unique mechanism: they tend in every case to occur near a metal-insulator transition into an odd-electron insulator with peculiar magnetic properties.
Abstract: The oxide superconductors, particularly those recently discovered that are based on La2CuO4have a set of peculiarities that suggest a common, unique mechanism: they tend in every case to occur near a metal-insulator transition into an odd-electron insulator with peculiar magnetic properties. This insulating phase is proposed to be the long-sought “resonating-valence-bond” state or “quantum spin liquid” hypothesized in 1973. This insulating magnetic phase is favored by low spin, low dimensionality, and magnetic frustration. The preexisting magnetic singlet pairs of the insulating state become charged superconducting pairs when the insulator is doped sufficiently strongly. The mechanism for superconductivity is hence predominantly electronic and magnetic, although weak phonon interactions may favor the state. Many unusual properties are predicted, especially of the insulating state.
5,409 citations
TL;DR: In this article, it was shown that the properties of high-mathrm{T}$ oxide superconductors are consistent with a model in which the charge carriers are holes in the O(2p) states and the pairing is mediated by strong coupling to local spin configurations on the Cu sites.
Abstract: It is shown that the properties of high-${\mathrm{T}}_{\mathrm{c}}$ oxide superconductors are consistent with a model in which the charge carriers are holes in the O(2p) states and the pairing is mediated by strong coupling to local spin configurations on the Cu sites.
1,525 citations
TL;DR: In this paper, the first successful preparation of thin films of Y-Ba-Cu-O superconductors using pulsed excimer laser evaporation of a single bulk material target in vacuum was reported.
Abstract: We report the first successful preparation of thin films of Y‐Ba‐Cu‐O superconductors using pulsed excimer laser evaporation of a single bulk material target in vacuum. Rutherford backscattering spectrometry showed the composition of these films to be close to that of the bulk material. Growth rates were typically 0.1 nm per laser shot. After an annealing treatment in oxygen the films exhibited superconductivity with an onset at 95 K and zero resistance at 85 and 75 K on SrTiO3 and Al2O3 substrates, respectively. This new deposition method is relatively simple, very versatile, and does not require the use of ultrahigh vacuum techniques.
1,122 citations
TL;DR: In this article, a new process was proposed to make films of Y1Ba2Cu3O7 using coevaporation of Y, Cu, and BaF2 on SrTiO3 substrates.
Abstract: We report on a new process to make films of Y1Ba2Cu3O7 using coevaporation of Y, Cu, and BaF2 on SrTiO3 substrates. The films have high transition temperatures (up to 91 K for a full resistive transition), high critical current densities (106 A/cm2 at 81 K), and a reduced sensitivity to fabrication and environmental conditions. Because of the lower reactivity of the films, we have been able to pattern them in both the pre‐annealed and post‐annealed states using conventional positive photoresist technology.
411 citations
TL;DR: The accomplishment of high-tem temperature superconductivity is of immense scientific and technological importance and several critical transition-temperature barriers have recently been breached since the long-standing record temperature of 23.2 K for Nb3Ge was exceeded.
Abstract: The accomplishment of high-temperature superconductivity is of immense scientific and technological importance. Several critical transition-temperature barriers have recently been breached since the long-standing record temperature of 23.2 K for Nb3Ge was exceeded. The most important milestones were the announcement of T c ≈ 30 K in lanthanum barium copper oxide by Bed-norz and Muller,1 whose work was based upon materials developed by Michel and Raveau,2 and the work of Chu, Wu, and others,3 based upon the replacement of lanthanum by yttrium, which resulted in superconductivity at temperatures of approximately 95 K.
384 citations
TL;DR: In this article, a superconducting transition with an onset temperature near 8 K was observed for the BiSr-Cu-O system through electrical resistivity and magnetic susceptibility measurements.
Abstract: A superconducting transition with an onset temperature near 8 K was observed for the Bi-Sr-Cu-O system through electrical resistivity and magnetic susceptibility measurements. The superconductivity is of a bulk nature and reproducible.
370 citations
TL;DR: In this article, a two-dimensional (2D) band structure calculation for alcaline-earth-substituted La2CuO4 in the tetragonal phase was proposed.
Abstract: We propose a two-dimensional (2D) band structure calculation for alcaline-earth-substituted La2CuO4 in the tetragonal phase. We find a degenerate logarithmic singularity in the electronic density of states, as usual in 2D systems. This leads to an orthorhombic-to-tetragonal structural phase transition (SPT). Using the BCS theory, we calculate the superconducting critical temperature Tc as a function of the position of the Fermi level (i.e. Cu+++/Cu++ ratio). This model explains the high Tc's observed experimentally and the relation between superconductivity and SPT.
275 citations
TL;DR: Structural, magnetic, and electronic properties of compounds in the series La2-xSrx CuO4-y for 0.05 ≤ x ≤ 1.1, with δx = 0.025, revealed superconductivity among several members of the series.
Abstract: Structural, magnetic, and electronic properties of compounds in the series La 2- x Sr x CuO 4- y for 0.05 ≤ x ≤ 1.1, with δ x = 0.025, were studied. Resistance, susceptibility, Meissner, and shielding measurements have revealed superconductivity among several members of the series. For x = 0.15, the transition temperature T c , measured at the midpoint of the resistive transition, is a maximum at 39.3 K with a width of 2 K. At other compositions the transition is broader and occurs at a lower temperature. Annealing the x = 0.15 sample in oxygen at 500°C increases T c to 40.3 K, while annealing at the same temperature under vacuum suppresses the superconductivity. These changes in oxygen content and T c are reversible.
270 citations
TL;DR: In this article, the authors reported the growth of single crystals as large as 4 mm of YBa2Cu3O7 and DyBa2C 3O 7 and confirmed superconductivity in them by magnetic and electrical measurements.
Abstract: Increased understanding of fundamental properties of the new cuprate superconductors depends on advances in the preparation of quality materials for study. Early work focused on the study of sintered polycrystalline samples. In some cases, grain growth during sintering yielded individual grains large enough (˜80 μm) for single crystal X-ray determination1. Larger single crystals allow measurements of physical properties including measurements of anisotropic behaviour. The anisotropy of upper critical fields in YBa2Cu3O7 single crystals has been reported by lye et al.2 who found critical fields characteristic of a quasi-two-dimensional superconductor, which are highest when the field is orientated perpendicular to the c-axis. Dinger et al.3 have measured critical fields and critical currents of single crystals and find anisotropies of 10 and greater3. These studies contain little detail on the crystal growth of YBa2Cu3O7. Here we report the growth of single crystals as large as 4 mm of YBa2Cu3O7 and DyBa2Cu3O7 and confirm superconductivity in them by magnetic and electrical measurements. Single crystals of other rare earth barium cuprates are also obtained although we have yet to optimize growth conditions for these phases.
265 citations
TL;DR: In this paper, a broad superconducting transition with an onset near 30 K was observed for La-Ba-Cu oxides in the measurement of magnetic susceptibility, which is of bulk nature and reproducible after several heat cycles.
Abstract: A broad superconducting transition with an onset near 30 K is observed for La-Ba-Cu oxides in the measurement of magnetic susceptibility. The superconductivity is of bulk nature and reproducible after several heat cycles.
257 citations
TL;DR: In this paper, the authors report preliminary success in the fabrication of fine-wire, composite superconductors consisting of a high-conductivity normal metal shell such as Ag or Cu/Ni/Au and a superconducting core of Ba2YCu3O7 oxide.
Abstract: Commercially useful, bulk superconductors typically require stabilization using a normal metal cladding for reasons of electrical, thermal, and mechanical protection and, in general, need to be drawn into fine fibers and wound into a magnet configuration. The recent discovery of high‐TC superconductor materials such as Ba2YCu3O7 stimulated worldwide interest in the subject, however, with much concern about fabricability of such brittle ceramic materials into desirable fine wire geometry. In this letter, we report preliminary success in the fabrication of fine‐wire, composite superconductors consisting of a high‐conductivity normal metal shell such as Ag or Cu/Ni/Au and a superconducting core of Ba2YCu3O7 oxide. The wire is would into a coil, and then heat treated to produce the desired chemistry in a dense structure. The resistivity of the composite wire is measured to be zero at ≊90 K (in zero field) with a zero‐field critical density of ≊175 A/cm2. Microscopy and x‐ray analysis show that the superconduc...
TL;DR: In this article, thin films of Y•Ba•Cu•O superconductors on (100)µSrTiO3 were prepared using the pulsed excimer laser evaporation technique.
Abstract: Thin films of Y‐Ba‐Cu‐O superconductors on (100) SrTiO3 were prepared using the pulsed excimer laser evaporation technique. After an annealing treatment in oxygen the films exhibited superconductivity with zero resistance at 85 K with transition widths (90%–10%) as narrow as a 2 K. A considerable amount of orientation of the films with respect to the substrates was observed by x‐ray diffraction and ion channeling techniques. Interface reaction revealed by Rutherford backscattering and Auger electron spectrometry resulted in a thickness dependence of the superconducting properties of the films.
TL;DR: The magnetic susceptibility of ceramic samples in the metallic BaLaCuO system has been measured as a function of temperature as discussed by the authors, and it is found that, for small magnetic fields of less than 0.1 T, the samples become diamagnetic at somewhat lower temperatures than the resistivity drop.
Abstract: The magnetic susceptibility of ceramic samples in the metallic BaLaCuO system has been measured as a function of temperature. This system had earlier shown characteristic sharp drops in resistivity at low temperatures. It is found that, for small magnetic fields of less than 0.1 T, the samples become diamagnetic at somewhat lower temperatures than the resistivity drop. The highest-temperature diamagnetic shift occurs at (33 ± 2) K, and may be related to shielding currents at the onset of percolative superconductivity. The diamagnetic susceptibility can be suppressed with external fields of 1 to 5 T.
TL;DR: In this paper, high Tc superconductivity with Tc near 30 K was observed for the single phase of (La Ba)2CuO4-y by both magnetic susceptibility and resistivity measurements.
Abstract: Occurrence of high-Tc superconductivity with Tc near 30 K is observed for the single phase of (La Ba)2CuO4-y by both magnetic susceptibility and resistivity measurements. This indicates that high- Tc superconductivity in La-Ba-Cu oxide is realized in the K2NiF4-type structure, (La Ba)2CuO4-y.
AT&T1
TL;DR: In this paper, multiple metal-target dc magnetron sputter deposition of a metallic YBa2Cu3 alloy in pure Ar followed by ex situ oxygen annealing was used to prepare superconducting films on various substrates.
Abstract: Multiple metal‐target dc magnetron sputter deposition of a metallic YBa2Cu3 alloy in pure Ar followed by ex situ oxygen annealing was used to prepare superconducting films on various substrates. This work particularly examines film‐substrate reactions which are degrading to superconductivity. Better superconductors were obtained using predeposited buffer layers, notably on cubic zirconia and MgO substrates covered with Ag and Nb. Best films have Tc=80 K, metallic resistivities with resistance ratio≳2, and critical current density ≲10 kA cm−2 at 4.2 K. Normal‐state resistivity measurements were made for O2 furnace temperatures up to 850 °C. Procedures for lithographically patterning these films are also described.
TL;DR: In this article, a detailed high temperature X-ray diffraction was performed to study the structural phase of YBa 2 Cu 3 O 7−δ, and the results indicated the existence of a reversible orthorhombic to tetragonal phase transition at a temperature close to 750°C.
TL;DR: A superconducting transition with an onset temperature of 52.5 K has been observed under hydrostatic pressure in compounds with nominal compositions given by (La0.9Ba0.1)2 CuO4-Y.
Abstract: The electrical properties of the (La/0/9/Ba/0.1/)CuO/4-y/ system are examined under ambient and hydrostatic pressures. The resistance, ac magnetic susceptibility, and superconductivity onset, midpoint, and intercept temperatures are measured. It is observed that at ambient pressure the resistance decreases with temperature decreases, and the ac susceptibility shows diamagnetic shifts starting at about 32 K. Under hydrostatic pressure a superconducting transition with an onset temperature of 52.5 K is observed, and the resistance increases at lower temperatures. The data reveal that the electrical properties of the La-Ba-Cu-O system are dependent on samples and preparation conditions. Various causes for the high temperature superconductivity of the system are proposed.
IBM1
TL;DR: The structural, transport, and magnetic properties of the principal phase responsible for superconductivity in the recently discovered Y-Ba-Cu-O compounds with transition temperatures greater than 90 K are reported.
Abstract: We report the structural, transport, and magnetic properties of the principal phase responsible for superconductivity in the recently discovered Y-Ba-Cu-O compounds with transition temperatures greater than 90 K.
TL;DR: In this paper, the authors measured the Cu−2p3/2-core level spectra of NaCuO2 in which the copper ion was in a 3+ state and compared it with the core line position in pure CuO and to superconducting oxides.
Abstract: A number of theoretical models have been developed to explain the unexpected high temperature superconductivity in La-Me-Cu-oxides (Me=Ba, Sr) and Y-Ba-Cu-oxides. Some of these models invoke charge fluctuations on the copper ions in the superconductors between a 2+ and a 3+ state. In order to test these possibilities we have measured the Cu−2p
3/2-core level spectra of NaCuO2 in which the copper ion is in a 3+ state and compared it with the core line position in pure CuO and to superconducting oxides. The data strongly suggest, that there is, if any very little Cu3+ in the superconducting compounds present. However, we notice, that in comparison to trivalent and monovalent copper oxides the Cu−2p
3/2 line in CuO and the superconducting oxides is unexpectedly broad. The cause of this large linewidths remains so far unexplained.
TL;DR: In this article, a scaling theory is developed which allows a consistent treatment of the coupled ln2(T)-singularities arising from density wave and Cooper pairing fluctuations in the weak coupling limit.
Abstract: In order to investigate possible nonphonon mechanisms for superconductivity in the copper oxide compounds, the two-dimensional Hubbard model is studied in the weak-coupling limit. A scaling theory is developed which allows a consistent treatment of the coupled ln2(T)-singularities arising from density wave and Cooper pairing fluctuations. For a half-filled band a spin-density-wave (antiferromagnetic) phase transition occurs, whereas for small deviations from half-filling spin fluctuations lead to a d-type superconducting phase. The method generalizes straightforwardly to finite-range interactions. The possible relevance to oxide superconductors and experimental tests are briefly discussed.
TL;DR: In this article, it was shown that the superconducting phase is a disordered isomorph of the orthorhom-bic YBa2Cu3O7−δ structure.
Abstract: The observation of superconductivity above 90 K in the Y–Ba–Cu–O system1,2 has prompted a search for other structures that display high-temperature superconductivity. The discovery of superconductivity above 70 K in La3−xBa3+xCu6Ol4+y3 raises some questions concerning its relationship to the YBa2Cu3O7−δ structure and the origins of the high-temperature superconductivity. The original X-ray diffraction study of La3Ba3Cu6O14+y, indicated a tetragonal structure4,5, on the basis of which it has been proposed that La3−xBa3+xCu6O14+y is a new class of high-temperature superconductor which, in contrast to YBa2Cu3O7−δ, contains no Cu–O chains3. More recently, a neutron diffraction study of non-superconducting La3Ba3Cu6O14+y6has indicated that the correct structure of this compound is simply the tetragonal YBa2Cu3O7−δ structure with partial substitution of lanthanum on the barium site7–12. In the present neutron powder diffraction study of a series of La(Ba2−xLax)Cu3O7+δ compounds, we show that the superconducting phase is a similarly disordered isomorph of the orthorhom-bic YBa2Cu3O7−δ structure13–19. The region of solid solubility for this compound extends from x = 0.5 (La:Ba:Cu ratios of 3:3:6) to x≈ 0.25 and does not include the stoichiometric compound x = 0 (LaBa2Cu3O7−δ). The presence of Cu–O chains, and not just a formal copper charge state of ≥2, is vital for the occurrence of superconductivity.
TL;DR: A brief review of the current proposals to explain the observation of superconductivity with high transition temperatures in the copper oxides is given in this paper, where a brief review is given.
Abstract: A brief review is given of the current proposals to explain the observation of superconductivity with high transition temperatures in the copper oxides.
TL;DR: In this paper, the phase diagram of a single-phase compound with a stoichiometry YBa2Cu3Oy was determined for the high-temperature superconductivity (92.5 K).
Abstract: We have determined the phase diagram of the Y‐Ba‐Cu‐O system through structural, superconducting critical temperature and critical current density characterization. Our results show that a single‐phase compound with a stoichiometry YBa2Cu3Oy is responsible for the high‐temperature superconductivity (92.5 K) in this system.
TL;DR: A two-step resistive transition, one beginning at 240 K and the other at 90 K, has been observed in Y-Ba-Cu-O compounds and the superconductivity, possibly in granular form, at both temperatures has been verified by means of the rf-to-dc conversion associated with the ac Josephson effect.
Abstract: A two-step resistive transition, one beginning at 240 K and the other at 90 K, has been observed in Y-Ba-Cu-O compounds. The superconductivity, possibly in granular form, at both temperatures has been verified by means of the rf-to-dc conversion associated with the ac Josephson effect.
TL;DR: In this paper, the series of rare-earth (R)-barium copper oxides with nominal composition (RBa2)Cu3O9−σ and the prototype compound (YBa2)cu3O 9−σ have been prepared from the R (except Pm), Y, and Cu oxides and Ba carbonate by sintering, followed by arc-melting and annealing in pure oxygen.
TL;DR: In this article, the authors reported the isolation of the pure oxide phase responsible for high Tc superconductivity, which has the composition Y0.33Ba 0.33±δ, with an oxygen defect perovskite structure.
Abstract: The discovery of La–Ba(Sr)–Cu oxides of K2NiF4 structure exhibiting superconductivity in the 30–40 K region was reported early this year1. The recent announcement of superconductivity above the temperature of liquid nitrogen in Y–Ba–Cu oxides2 has belied all expectations. Unfortunately, all the Y–Ba–Cu oxide compositions exhibiting this remarkable feature were biphasic or multiphasic. We have studied various compositions of the Y3–xBa3+xCu6O14 and now report the isolation of the pure oxide phase responsible for high Tc superconductivity. This oxide has the composition Y0.33Ba0.67CuO2.33±δ, with an oxygen defect perovskite structure. The pure oxide shows the onset of superconductivity at 120 K, attaining zero resistance at 87 K. It also exhibits the highest Meissner effect of all the high-Tc oxide superconductors.
TL;DR: Optical transmission and reflection spectra and Raman spectra of superior-quality 90, 180, 400, and 1000-nm-thick superconducting Y-Ba-Cu-O films suggest that it seems unlikely that the high-quality superconductivity in cuprates could arise from exciton-mediated electron pairing.
Abstract: Optical transmission and reflection spectra (mid IR through uv) and Raman spectra of superior-quality 90-, 180-, 400-, and 1000-nm-thick superconducting Y-Ba-Cu-O films are reported. Characteristic excitonic bands, and in particular the absorption band at \ensuremath{\simeq}0.37 eV reported earlier, are not observed. It therefore seems unlikely that the high-${T}_{c}$ superconductivity in cuprates could arise from exciton-mediated electron pairing.
TL;DR: In this paper, the preparation of thin-film superconductors by metalorganic deposition (MOD) is described. Butts et al. used Rutherford backscattering spectrometry to determine film compositions and thicknesses.
Abstract: Metalorganic deposition (MOD) is a nonvacuum method of thin‐film deposition which allows easy alteration of chemical components and is compatible with thin‐film processing. We report the preparation of thin‐film superconductors by MOD. Rutherford backscattering spectrometry was used to determine film compositions and thicknesses. Films, approximately 500 nm thick, of YBa2Cu4Oz (z undetermined) were deposited on 〈100〉 single‐crystal SrTiO3. A superconducting onset temperature of 90 K was measured with 37 K the zero resistance temperature. Scanning electron microscopy revealed grain sizes approximately 250 nm in diameter.