High temperature superconductors
About: This article is published in Transition Metal Chemistry.The article was published on 1987-12-01. It has received 174 citations till now. The article focuses on the topics: Technological applications of superconductivity & Flux pumping.
Citations
More filters
TL;DR: In this paper, a transformation of normal molecular hydrogen to a conductive and metallic state at room temperature is observed above 220 GPa, which is the state of the art for molecular hydrogen.
Abstract: Molecular hydrogen is expected to display metallic properties under high pressures, but so far experiments performed at low temperatures (100 K) have showed that hydrogen remains insulating up to 300 GPa. A transformation of normal molecular hydrogen to a conductive and metallic state at room temperature is now observed above 220 GPa.
306 citations
TL;DR: In this paper, basic experimental data are presented for a new class of high-temperature superconductors, namely iron-based layered compounds of the types REOFeAs (RE = La, Ce, Nd, Pr, Sm,...), AFe2As2 (A = Ba, Sr,...).
Abstract: Basic experimental data are presented for a new class of high-temperature superconductors — iron-based layered compounds of the types REOFeAs (RE = La, Ce, Nd, Pr, Sm, ...), AFe2As2 (A = Ba, Sr, ...), AFeAs (A = Li, ...), and FeSe(Te). The structure of electronic spectra in these compounds is discussed, including the correlation effects, as is the spectrum and role of collective excitations (phonons and spin waves). Basic models for describing various types of magnetic ordering and Cooper pairing are reviewed.
235 citations
Cites background from "High temperature superconductors"
...Physics of HTSC and of a number of new and unusual superconductors was discussed in a number of individual and collective monographs [11, 12, 13, 14]....
[...]
...Nauk (Physics Uspekhi) 178, 202 (2008) [11] N....
[...]
TL;DR: A comprehensive review of structure work on high-Tc oxides as reported during the years 1987 and 1988 is given in this paper, where 13 structures are refined from X-ray single-crystal and/or neutron powder diffraction data.
Abstract: A comprehensive review of structure work on high-Tc oxides as reported during the years 1987 and 1988 is given. Thirteen structures are refined from X-ray single-crystal and/or neutron powder diffraction data:I. (Ba1−x,Kx)BiO3 (Tc=30 K),II. (La2−x, Srx)CuO4 (Tc=40 K),III. (Nd, Ce, Sr)2CuO4 (Tc=28 K),IV. (Nd2−x, Cex)CuO4 (Tc=24 K),V. YBa2Cu3O7 (Tc=90 K),VI. YBa2Cu4O8 (Tc=80 K),VII. Y2Ba4Cu7O14 (Tc=40 K),VIII. Pb2Sr2NdCu3O8 (Tc=70 K),IX. TlBa2CaCu2O7 (Tc=103 K),X. TlBa2Ca2Cu3O9 (Tc=120 K),XI. Tl2Ba2CuO6 (Tc=90 K),XII. Tl2Ba2CaCu2O8 (Tc=112 K),XIII. Tl2Ba2Ca2Cu3O10 (Tc=125 K). Except forI (perovskite type),II (K2NiF4 type) andIV (Nd2CuO4 type) they represent new structure types. Structure data, bond distances, structure drawings and calculated X-ray powder diffraction patterns are given for each compound. Structural features and correlations with superconductivity are discussed. The review contains 301 citations.
182 citations
TL;DR: In this paper, the scaling of the critical temperature Tc as a function of the Lifshitz parameter z = EΓ−EF, where EF is the chemical potential and E is the energy of the Γ critical point where the σ Fermi surface changes from the 3D to a 2D topology, is reported.
Abstract: We report experimental data showing the Feshbach shape resonance in the electron doped MgB2 where the chemical potential is tuned by Al, Sc, and C substitutions. The scaling of the critical temperature Tc as a function of the Lifshitz parameter z = EΓ−EF, where EF is the chemical potential and EΓ is the energy of the Γ critical point where the σ Fermi surface changes from the 3D to a 2D topology, is reported. The resonant amplification of Tc(z) driven by the interband pairing is assigned to a Feshbach shape resonance characterized by quantum superposition of pairs in states corresponding to different spatial location and different parity. It is centered at z = 0 where the chemical potential is tuned to a Van Hove-Lifshits feature for the change of Fermi surface dimensionality in the electronic energy spectrum in one of the subbands. In this heterostructure at atomic limit the multiband superconductivity is in the clean limit because the disparity and negligible overlap between electron wavefunctions in different subbands suppresses the single electron interband impurity scattering rate. The emerging scenario from these experimental data suggests that the Feshbach shape resonance could be the mechanism for high Tc in particular nanostructured architectures.
98 citations
TL;DR: In this article, a nonaqueous chemical etch, with Br as the active ingredient, was described which removes the insulating hydroxides and carbonates that form on high-temperature superconductor surfaces as a result of atmospheric exposure.
Abstract: A nonaqueous chemical etch, with Br as the active ingredient, is described which removes the insulating hydroxides and carbonates that form on high-temperature superconductor surfaces as a result of atmospheric exposure. X-ray photoemission spectra have been recorded before and after etching YBa2Cu3O(7-x) films. It is found that, after the etch, the high binding energy O 1s and Ba 3d peaks associated with surface contaminants are greatly reduced, the Y:Ba:Cu ratio is close to the expected 1:2:3, and the oxidation state of the Cu(2+) is not affected. The resistance of an etched film reaches zero at 78 K, compared to 81 K for a similar unetched film. The suitability of other nonaqueous halogen-based etches is discussed, as is the applicability of this etch to other high-Tc superconductors.
97 citations
References
More filters
IBM1
TL;DR: In this paper, Ba−La−Cu−O system, with the composition BaxLa5−xCu5O5(3−y) have been prepared in polycrystalline form, and samples with x=1 and 0.75,y>0, annealed below 900°C under reducing conditions, consist of three phases, one of them a perovskite-like mixed-valent copper compound.
Abstract: Metallic, oxygen-deficient compounds in the Ba−La−Cu−O system, with the composition BaxLa5−xCu5O5(3−y) have been prepared in polycrystalline form. Samples withx=1 and 0.75,y>0, annealed below 900°C under reducing conditions, consist of three phases, one of them a perovskite-like mixed-valent copper compound. Upon cooling, the samples show a linear decrease in resistivity, then an approximately logarithmic increase, interpreted as a beginning of localization. Finally an abrupt decrease by up to three orders of magnitude occurs, reminiscent of the onset of percolative superconductivity. The highest onset temperature is observed in the 30 K range. It is markedly reduced by high current densities. Thus, it results partially from the percolative nature, bute possibly also from 2D superconducting fluctuations of double perovskite layers of one of the phases present.
10,272 citations
TL;DR: A stable and reproducible superconductivity transition between 80 and 93 K has been unambiguously observed both resistively and magnetically in a new Y-Ba-Cu-O compound system at ambient pressure.
Abstract: A stable and reproducible superconductivity transition between 80 and 93 K has been unambiguously observed both resistively and magnetically in a new Y-Ba-Cu-O compound system at ambient pressure. An estimated upper critical field H c2(0) between 80 and 180 T was obtained.
5,965 citations
TL;DR: Observation de la transition supraconductrice a 91 K, sur 1,5 K and determination of the densite de courant critique, de l'effet Meissner, du champ critique, du parametre de Sommerfeld, de parametres GL.
Abstract: We have prepared and identified as a single phase the high-temperature superconducting compound in the chemical system Y-Ba-Cu-O, an orthorhombic, distorted oxygen-deficient perovskite of stoichiometry ${\mathrm{Ba}}_{2}$${\mathrm{YCu}}_{3}$${\mathrm{O}}_{9\mathrm{\ensuremath{-}}\mathrm{\ensuremath{\delta}}}$ (\ensuremath{\delta}\ensuremath{\simeq}2.1). Samples exhibit zero resistance at 91 K, with a transition width of 1.5 K. The Meissner effect attains a value of 76% of the independently measured diamagnetic susceptibility. We estimate parameters that characterize this superconductor, e.g., \ensuremath{\gamma}\ensuremath{\simeq}3--5 mJ (mole Cu${)}^{\mathrm{\ensuremath{-}}1}$ ${\mathrm{K}}^{\mathrm{\ensuremath{-}}2}$. The critical current density at 77 K and H=0 exceeds 1100 A/${\mathrm{cm}}^{2}$.
1,264 citations
TL;DR: The results of resistivity and magnetic susceptibility measurements in La/sub 2-//sub x/Sr/sub X/CuO/sub 4/ for x less than or equal to 0.3 were reported in this article.
Abstract: We report the results of resistivity and magnetic susceptibility measurements in La/sub 2-//sub x/Sr/sub x/CuO/sub 4/ for xless than or equal to0.3. The x = 0.2 sample shows a superconducting transition at 36.2 K with a width of 1.4 K. The associated dc diamagnetic susceptibility (Meissner effect) is a large fraction (60%--70%) of the ideal value. We estimate the density of states from critical-field and resistivity data and suggest, by analogy to BaPb/sub 1-//sub x/Bi/sub x/O/sub 3/, that conventional phonon-mediated superconductivity can account for the high T/sub c/ in this class of materials.
784 citations
01 Jul 1975
759 citations