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  • Articles  (59)
  • Superconductivity  (59)
  • Electrical Engineering, Measurement and Control Technology  (59)
  • 1
    Electronic Resource
    Electronic Resource
    New research opportunities in superconductivity IV (1997)
    Springer
    Journal of superconductivity and novel magnetism 10 (1997), S. 583-621 
    Details
    ISSN: 1557-1947
    Keywords: Superconductivity ; research opportunities ; state of the art
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract This report surveys the considerable progress made over the last five years—such as the marketing of superconducting quantum interference devices (SQUIDs), cellular wireless filter systems, and high current leads—and assesses needs and opportunities in the areas of fundamental science, materials development, thin film and device applications, and wire and bulk applications. It examines the challenges facing high-temperature superconductivity: from the need to understand the mechanism of high-temperature superconductivity and the unusual “normal” state to the need for new instrumentation for material characterization. Advances in thin film and bulk materials are reviewed, and obstacles impeding the commercialization of HTS materials are examined.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02471924
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  • 2
    Electronic Resource
    Electronic Resource
    The crystal field in rare earth based high-temperature superconductors (1997)
    Springer
    Journal of superconductivity and novel magnetism 10 (1997), S. 623-643 
    Details
    ISSN: 1557-1947
    Keywords: Superconductivity ; crystal field ; rare earth ; relaxation ; gap symmetry
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract Neutron spectroscopy is a powerful tool to determine unambiguously the crystal-field (CF) potential in rare-earth (R) based high-T c superconducting materials. This technique provides detailed information on the electronic ground state of the R ions which is important to understand the thermodynamic magnetic properties as well as the observed coexistence between superconductivity and long-range magnetic ordering of the R ion sublattice at low temperatures. Moreover, the decay of the antiferromagnetic state of the parent compound as well as the evolution of the superconducting state upon doping can be directly and quantitatively monitored. It is found that the observed CF spectra separate into different local components whose spectral weights distinctly depend on the doping level, i.e., there is clear experimental evidence for cluster formation. The onset of superconductivity can be shown to result from percolation which means that the superconductivity is an inhomogeneous materials property. Since the linewidths of CF transitions directly probe the static electronic susceptibility, we discuss temperature-dependent experiments of the relaxation rate of CF excitations in both optimally doped and underdoped regimes. It is shown that there is clear evidence for the opening of an electronic gap in the normal state of underdoped superconductors. Furthermore, the relaxation behavior appears to be extremely dependent upon the energy at which the static susceptibility is being probed. The main observed features can be reproduced by considering a strongly anisotropic gap function.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02471925
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  • 3
    Electronic Resource
    Electronic Resource
    DC Electrical Resistivity Study of Granularity in YBa2CU3O7/Ag Composites (1998)
    Springer
    Journal of superconductivity 11 (1998), S. 641-648 
    Details
    ISSN: 1572-9605
    Keywords: Superconductivity ; Ag composites ; percolation ; granularity ; weak-link resistivity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract Temperature-dependent electrical resistivity in a set of YBa2Cu3O7−x /Ag composites, all prepared under an identical sintering schedule, is analyzed to extract granularity information. The weak-link resistivity ρ wl across the grain boundaries and the percolation factor α arising due to current frustration caused by misalignment of anisotropic grains and sample defects such as voids and cracks are estimated from the residual resistivity ρ0 and the temperature coefficient of resistivity dρ/dT. Variation of these parameters with Ag vol.% quantifying the extent of granularity indicates that granularity in the composites decreases and their electrical characteristics tend to be identical to that of Ag-free YBa2Cu3O7−x single crystals and epitaxial thin films as Ag vol.% approaches a value where onset of current percolation occurs through Ag channels. The increased α and decreased ρ wl observed at higher Ag vol.% explains the larger grains in the composites with narrow size distribution.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1022609432697
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  • 4
    Electronic Resource
    Electronic Resource
    Effect of Ca Substitution on the Superconductivity of La2.5Y0.5CaBa3(Cu0.88Fe0.12)7O z (1998)
    Springer
    Journal of superconductivity 11 (1998), S. 673-676 
    Details
    ISSN: 1572-9605
    Keywords: Superconductivity ; La2.5Y0.5CaBa3(Cu0.88Fe0.12)7O z ; compensated oxide ; magnetic pair breaking
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract The structural and superconducting properties of single-phase La2.5−y Y0.5Ca1+y Ba3 (Cu0.88Fe0.12)7O z (LYCaBCuFe) (y= 0.0−1.0) compounds with triple perovskite structure are investigated using X-ray diffraction, resistivity, a.c. susceptibility, and oxygen content measurements. Increasing Ca substitution for La resulted in a decrease in unit cell axes and volume. T c R=0 shows a marginal increase from 31 K to 37 K for y = 0.0−0.21 and thereafter it decreases with increasing y leading to zero T c R=0 at y ≥ 0.84. This shows that the suppression of T c from 80 K to 31 K by Fe doping at x = 0.12 La2.5Y0.5CaBa3(Cu1−x Fe x )7O z cannot be compensated by appropriate hole doping with Ca in LaYCaBCuFe.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1022620518584
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  • 5
    Electronic Resource
    Electronic Resource
    Superconductivity and Antiferromagnetic Order in ErNi2B2C Thin Films (1998)
    Springer
    Journal of superconductivity 11 (1998), S. 707-712 
    Details
    ISSN: 1572-9605
    Keywords: Superconductivity ; antiferromagnetic order ; ErNi2Bi2C
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract Upper critical field and penetration depth of superconducting ErNi2B2C borocarbide thin films have been investigated and compared with the same properties of SmRh4B4 films. The coexistence of superconductivity and antiferromagnetic order is described through Machida's theory. A fairly satisfactory description of the experimental results is obtained.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1022632921310
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  • 6
    Electronic Resource
    Electronic Resource
    Photoinduced enhancement of superconductivity (1994)
    Springer
    Journal of superconductivity 7 (1994), S. 127-130 
    Details
    ISSN: 1572-9605
    Keywords: Superconductivity ; thin films ; photoconduction
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract The photoinduced enhancement of superconductivity in RBa2Cu3O x (R=rare earth or yttrium) and Pr y R1−y Ba2Cu3O x was explored through temperature-dependent resistivity, Hall coefficient and mobility, and x-ray diffraction measurements. The increases inT c are enhanced near the metal-insulator transition, although photoinduced changes always exist in oxygendeficient samples. Several explanations, including intergrain Josephson coupling, photoassisted oxygen ordering, and the trapping of photogenerated electrons in oxygen vacancies, are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00730382
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  • 7
    Electronic Resource
    Electronic Resource
    Acid-base equilibrium—A thermodynamic study of formation and stability of the Bi-2223 phase (1993)
    Springer
    Journal of superconductivity 6 (1993), S. 55-57 
    Details
    ISSN: 1572-9605
    Keywords: Superconductivity ; Bi-2223 ; stability
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract A general acid-base equilibrium theory was proposed to explain the formation and stability of the Bi-2223 phase based on the Lewis acid-base theory, and principle of metallurgical physical chemistry. The acid-base nature of oxide was defined according to the electrostatic force between cation and oxygen anion. A series of experimental facts were systematically explained based on the theory: substitution of Bi for Ca in. the Pb-free 2223 phase, and the effect of substitution of the high-valent cation for Bi3+; oxygen-pressure atmosphere, and the heat-schocking technique on the formation and stability of the 2223 phase.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00618506
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  • 8
    Electronic Resource
    Electronic Resource
    Anharmonicity and electron-phonon coupling in cuprate superconductors studied by inelastic neutron scattering (1994)
    Springer
    Journal of superconductivity 7 (1994), S. 399-407 
    Details
    ISSN: 1572-9605
    Keywords: Superconductivity ; phonon anharmonicity ; electron-phonon interaction
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract An overview is given on anharmonic lattice vibrations originating from structural instabilities. The transverse vibrations of the chain oxygens in YBa2Cu3O7 are found to be only moderately anharmonic. Measurements of the phonon linewidths in the Cu-O bond stretching vibrations strongly support recent calculations of the electron-phonon coupling. Results are presented on superconductivity-induced frequency shifts at short wavelengths.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00724577
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  • 9
    Electronic Resource
    Electronic Resource
    Rare-Earths as Probes of High-Temperature Superconductivity (1998)
    Springer
    Journal of superconductivity 11 (1998), S. 615-639 
    Details
    ISSN: 1572-9605
    Keywords: Superconductivity ; rare-earths
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract Using only two principles: (i) high-temperature superconductivity requires hypercharged oxygen, and (ii) the superconducting condensates are located in those parts of the crystal structures where they are unaffected by magnetic pair breaking, we are able to explain why certain rare-earth ions R are compatible with superconductivity and others are not, in the compounds RBa2Cu3O7, RBa2Cu4O8, RBa2Cu2NbO8, R2 − z Ce z CuO4, and R2 − z Ce z Sr2Cu2NbO10. Various defects are proposed as having central roles in the superconductivity or the suppression of superconductivity in these compounds. Many experiments for testing this physical picture are suggested.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1022643531034
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  • 10
    Electronic Resource
    Electronic Resource
    Quantum Transition to Supersolid Phase (1999)
    Springer
    Journal of superconductivity 12 (1999), S. 231-232 
    Details
    ISSN: 1572-9605
    Keywords: Superconductivity ; CDW ; supersolid ; coexistence ; Hubbard model
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract We study a possible coexistence of superconducting state and charge density waves which, in a broad sense, might be called a supersolid phase. We investigate the infinite dimensional (d=∞) attractive Hubbard model by applying a sublattice dependent Gutzwiller wave function $$g_{\text{A}}^{D_{\text{A}} } g_{\text{B}}^{D_{\text{B}} } |{\text{BCS}}$$ |BCS〉 as a variational wave function describing the ground state. One may naively expect that the BCS superconducting state evolves continuously to the Bose–Einstein condensed state of bipolarons as the attractive interaction increases, as far as the system is dilute. However, we show that our variational wave function has lower energy than the simple BCS wave function for all electron densities and the interaction strengths. Our variational parameters increase (g A,B→∞) as we increase the interaction strength (U→∞). The energy gap turns out to be a mixture of s and extended-s waves. In the vicinity of half-filling, we find a quantum transition from a simple superconducting phase to a supersolid phase with increase of the electron density and/or the interaction strength.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1007747720269
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