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  • Articles  (35)
  • Superconductivity  (35)
  • 1995-1999  (35)
  • Electrical Engineering, Measurement and Control Technology  (35)
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  • Articles  (35)
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  • 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
    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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  • 7
    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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  • 8
    Electronic Resource
    Electronic Resource
    New Research Opportunities in Superconductivity IV (1997)
    Springer
    Journal of superconductivity 10 (1997), S. 583-621 
    Details
    ISSN: 1572-9605
    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/10.1023/A:1022696328654
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  • 9
    Electronic Resource
    Electronic Resource
    The Crystal Field in Rare Earth Based High-Temperature Superconductors (1997)
    Springer
    Journal of superconductivity 10 (1997), S. 623-643 
    Details
    ISSN: 1572-9605
    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/10.1023/A:1022654312724
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  • 10
    Electronic Resource
    Electronic Resource
    Navy Programs in Superconducting Technology (1998)
    Springer
    Journal of superconductivity 11 (1998), S. 1-4 
    Details
    ISSN: 1572-9605
    Keywords: Superconductivity ; magnets ; cryogenics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract A review of U.S. Navy efforts in superconducting technology is given. Programs include development of superconducting magnets for motors in ship propulsion systems and to generate magnetic moments in mine sweeping systems. A program to develop superconducting quantum interference devices (SQUIDs) for detection of mines and buried ordnance has successfully been demonstrated. In electronic applications, superconducting filters, resonators, and antennae are being developed for radar, communication, and space systems. Concurrent with these superconductivity programs are efforts to improve the efficiency, reliability, and affordability of refrigeration systems.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1022656620516
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  • 11
    Electronic Resource
    Electronic Resource
    Resonant tunneling in normal metal-superconductor junctions: Low-voltage conductance features and excess current (1995)
    Springer
    Journal of superconductivity 8 (1995), S. 71-78 
    Details
    ISSN: 1572-9605
    Keywords: Superconductivity ; resonant tunneling ; conductance ; energy gap
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract We have studied the conductance of normal metal-superconductor junctions with a potential barrier on the interface containing localized electron states. The probabilities of the Andreev reflection and the quasiparticle transmission are calculated using a one-dimensional model with a single localized state. The conductance of the junctions with many localized states described by a uniform distribution of the bound state energies around the Fermi level is calculated in the low-temperature region. It is shown that the Andreev reflection processes assisted by the resonant tunneling result in new features of the conductance, such as a zerobias maximum, a low-energy gaplike structure, and a two-gap behavior of the conductance at applied voltages near the value corresponding to the energy gap of the superconductor. The current-voltage characteristics for high applied voltages reveal both an excess current and current deficit, depending on the parameters of the localized states and the transparency of the tunnel barrier.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00732243
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  • 12
    Electronic Resource
    Electronic Resource
    Gap states in HTSC by infrared spectroscopy (1995)
    Springer
    Journal of superconductivity 8 (1995), S. 437-440 
    Details
    ISSN: 1572-9605
    Keywords: Superconductivity ; gap ; infrared ; d-wave
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract Recent infrared reflectance spectroscopy on high quality crystals of a number of HTSC systems shows thatall have finite conductivity in the frequency region of the superconducting gap. Results on untwinned YBCO from a number of laboratories show that this absorption is not due to experimental problems or sample-to-sample variations. Other materials also show absorption features in the gap region in the form of peaks. We discuss these results in terms of recent ideas of the effect of impurities in d-wave superconductors.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00722824
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  • 13
    Electronic Resource
    Electronic Resource
    Shadow bands in models of correlated electrons (1995)
    Springer
    Journal of superconductivity 8 (1995), S. 475-478 
    Details
    ISSN: 1572-9605
    Keywords: Superconductivity ; Hubbard Model ; Shadow Bands
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract A consequence of strong antiferromagnetic correlations in models of high-Tc cuprates is the appearance in photoemission (PES) calculations of considerable more weight above the Fermi momentum PF than expected for non-interacting electrons. This effect, qualitatively discussed by Kampf and Schrieffer under the name of “shadow bands”, is here quantitatively analyzed in the two dimensional Hubbard and t-J models using Monte Carlo and exact diagonalization techniques in the realistic strong coupling regime.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00722834
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  • 14
    Electronic Resource
    Electronic Resource
    A simple theory for the cuprates: the Antiferro-magnetic van Hove scenario (1995)
    Springer
    Journal of superconductivity 8 (1995), S. 483-486 
    Details
    ISSN: 1572-9605
    Keywords: Superconductivity ; t-J and Hubbard models ; Mechanisms
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract A model of weakly interacting hole quasiparticles is proposed to describe the normal state of the high temperature superconductors. The effect of strong correlations is contained in the dispersion of the holes. Many-body effects induce anomalous quasiparticleflat bands similar to those observed in recent angle-resolved photoemission experiments. A model of weakly interacting hole quasiparticles is proposed to describe the physics of carriers in the cuprates. The model predicts superconductivity in the dx2-y2 channel, with a typical Tc ∼ 100K. The concept of “optimal doping” appears naturally in this model, as well as a large ratio 2Δ/κT c ∼ 5.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00722836
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  • 15
    Electronic Resource
    Electronic Resource
    Experimental determination of the symmetry of the order parameter in YBCO (1995)
    Springer
    Journal of superconductivity 8 (1995), S. 491-494 
    Details
    ISSN: 1572-9605
    Keywords: Superconductivity ; pairing symmetry ; YBCO ; SQUID
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract At present, the symmetry of the order parameter in the high temperature superconductor YBCO is quite controversial. Recent experiments using SQUIDs and Josephson junctions appear to support competing theories, with some experiments supporting a dx2−y2 pairing symmetry for the order parameter and others a s-wave pairing symmetry. We note that a number of factors such as trapped flux, magnetic field gradients and SQUID asymmetries could lead such measurements astray. We use a Scanning SQUID Microscope and a time-reversal invariance test to resolve these experimental problems. We find the order parameter in YBCO has a time-reversal invariant dx2−y2 symmetric component. We estimate the amplitude of anyimaginary s-wave symmetric component to be less than 4% and anyreal s-wave component to be less than 82%.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00722838
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  • 16
    Electronic Resource
    Electronic Resource
    Is the pseudogap in the high Tc cuprates evidence for dynamic van Hove Jahn-Teller effects? (1995)
    Springer
    Journal of superconductivity 8 (1995), S. 579-582 
    Details
    ISSN: 1572-9605
    Keywords: Superconductivity ; Pseudogap ; Structural Phase Transition
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract Angle-resolved photoemission has demonstrated that in optimally doped YBa2Cu3O7 (YBCO) and Bi2Sr2CaCu2O8, the van Hove singularity (vHs) is pinned close to the Fermi level. Such a pinning was predicted by the vHs scenario, due to strong electron-phonon coupling. This coupling arises for a novel Jahn-Teller (JT) effect, in which a structural distortion splits the degeneracy of the two vHs's. In the lanthanum cuprates, there appears to be a sequence ofdynamic JT phases, possibly terminating in a low-temperature static JT phase. The highest-temperature JT phase corresponds to the onset of octahedral tilts in the La cuprates (pyramidal tilts in YBCO), and can be identified with the experimentally observed pseudogap phase. Here I will summarize recent experimental evidence for such a dynamic JT effect in the cuprates.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00727430
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  • 17
    Electronic Resource
    Electronic Resource
    Hole pockets in the doped 2D Hubbard model (1995)
    Springer
    Journal of superconductivity 8 (1995), S. 617-618 
    Details
    ISSN: 1572-9605
    Keywords: Superconductivity ; Hubbard Model ; Electronic Density ; Hole Pockets
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract The electronic momentum distribution n(k) of the two dimensional Hubbard model is studied for different values of the coupling U/t, electronic density 〈n 〉, and temperature, using quantum Monte Carlo techniques. A detailed analysis of the data on 8 × 8 clusters shows that features consistent with hole pockets at momenta k=(±π/2,±π/2,) appear as the system is doped away from half-filling. Our results are consistent with recent experimental data for the cuprates discussed by Aebi et al. (Phys. Rev. Lett.72, 2757 (1994)). In the range of couplings studied, the depth of the pockets is maximum at 〈n 〉 approximately 0.9, and it increases with decreasing temperature. The apparent absence of hole pockets in previous numerical studies of this model is explained.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00727444
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  • 18
    Electronic Resource
    Electronic Resource
    Solutions of the Eliashberg equations with abnormally large values of 2Δ(0)/T C (1996)
    Springer
    Journal of superconductivity 9 (1996), S. 59-64 
    Details
    ISSN: 1572-9605
    Keywords: Superconductivity ; Eliashberg equations ; high-T c cuprates ; organic superconductors
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract We consider the Eliashberg equations with an electron-phonon matrix elementg(k, k, q) possessing a low-energy cutoffξ 1. In the superconducting state, we assume that this cutoff is bound from below by the superconducting gap 2Δ. We solve for Δ andξ 1 self-consistently, as a function of temperature, and find that the ratio 2Δ(0)/Tc is very large; for parameters that we consider realistic for the cuprates, this ratio is approximately 10. This calculation applies to materials where the mean free path is long (clean limit). We also find that a hysteretic behavior is in principle possible.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00728426
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  • 19
    Electronic Resource
    Electronic Resource
    A new series of mercury-based high-T c superconductors (Hg, W)Sr2(Y1−x Ca x )Cu2 (1996)
    Springer
    Journal of superconductivity 9 (1996), S. 93-95 
    Details
    ISSN: 1572-9605
    Keywords: Superconductivity ; mercury-based superconductors
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract A new series of superconducting mercury-based layered cuprates has been synthesized. X-ray diffraction indicates that the compounds with formula Hg0.8W0.2Sr2Y1−x Ca x Cu2O6+δ (0.3≤x≤0.6) exhibit the 1212 structure with space groupP 4/mmm . The investigation of superconductivity determined by electrical resistance measurement shows that the superconducting transition temperature (T c , onset) of Hg0.8W0.2Sr2Y0.4Ca0.6Cu2O6+δ is up to 94 K.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00728432
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  • 20
    Electronic Resource
    Electronic Resource
    Tuning of the Fermi level at the second subband of a superlattice of quantum wires in the CuO2 plane: A possible mechanism to raise the critical temperature (1996)
    Springer
    Journal of superconductivity 9 (1996), S. 343-348 
    Details
    ISSN: 1572-9605
    Keywords: Superconductivity ; EXAFS ; superstructure ; quantum wires ; nonhomogeneity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract The structure of the stripes in Bi2Sr2CaCu22O8+y superconductor has been refined by polarized CuK-edge extended X-ray absorption fine structure (EXAFS). The distribution of Cu-O (planar) distances range from 1.87 Å to 1.96 Å. The results show that the in-plane CuO2 lattice distortions in the 1D modulation are large enough to form a potential barrier of widthW between the stripes of undistorted CuO2 lattice of widthL=15±0.5 Å. The calculations show that the maximum of the density of states formed by the second subband is tuned to the Fermi level.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00727276
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  • 21
    Electronic Resource
    Electronic Resource
    Superconductivity and Critical Coupling in Non-Fermi Liquids (1998)
    Springer
    Journal of superconductivity 11 (1998), S. 339-345 
    Details
    ISSN: 1572-9605
    Keywords: Superconductivity ; non-Fermi liquid
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract The critical temperature of a superconductor with a non-Fermi liquid ground state has been calculated. The density of states has two different forms and is energy dependent. The critical values of the coupling factor λ were calculated. The constant density of states results are obtained as particular cases. These results are an extension of the work done by Grosu et al. [Phys. Rev. B 56, 8298 (1997)].
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1022694629696
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  • 22
    Electronic Resource
    Electronic Resource
    Studies on (Hg0.7Mo0.3)Sr2(Sr1−xLax)Cu2Oz with a Wide Range of Doping State (1999)
    Springer
    Journal of superconductivity 12 (1999), S. 403-408 
    Details
    ISSN: 1572-9605
    Keywords: Superconductivity ; crystal structure ; Hg-based cuprate
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract The single-phased series of Sr-bearing Hg-1212 superconducting cuprate,(Hg0.7Mo0.3)Sr2(Sr1−x La x )Cu2O z has been prepared. X-ray diffraction showed that, the obtained samples belong to the 1212-structure with tetragonal space group P4/mmm, similar to that of (Hg, Mo)Sr2(Ca, Y)Cu2Oz, and stabilized in a wide compositional range of 0.25≤x≤0.75. Refinements of the structure are carried out in which the oxygen atoms at the (Hg, Mo) layer is shifted from high-symmetry position (0.5, 0.5, 0) to (x, x, 0). Magnetization and electrical resistivity measurements show that the as-prepared samples exhibit evidence for superconductivity and their superconducting properties were improved after O2 annealing with T onset c as high as 92 K.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1007765718878
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  • 23
    Electronic Resource
    Electronic Resource
    The Effect of Nitrates on Thallium Based Oxycarbonate Superconductors (1998)
    Springer
    Journal of superconductivity 11 (1998), S. 123-124 
    Details
    ISSN: 1572-9605
    Keywords: Superconductivity ; Nitrates ; Oxycarbonates
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract We have synthesised a series of compounds in both the (PbTl)Sr4Cu2O7(CO3)1−y(NO3)y (0.1≤y≤0.5) and TlSr2Ba2Cu2O7(CO3)1−y(NO3)y (0.1≤y≤0.2) systems. We report the synthesis conditions of these materials, an X-ray diffraction analysis of their structure and the changes induced in superconducting behaviour produced by the introduction of nitrate groups into the starting composition.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1022627222759
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    Full Wafer In Situ Deposition of Thallium Lead Superconductors (1998)
    Springer
    Journal of superconductivity 11 (1998), S. 129-132 
    Details
    ISSN: 1572-9605
    Keywords: Superconductivity ; TIPbSrCaCuO ; thin films
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract Thin films of (Tl,Pb)Sr2Ca0.8Y0.2Cu2O7, and (Tl,Pb)Sr2CuO5 can be grown in a single step process which involves sputter deposition from a mixed oxide target and simultaneous thermal evaporation of Tl2O. The use of a radiant heater has allowed extension of this in situ deposition process to full LaAlO3 and NdGaO3 wafers. Variations in the composition of the deposited film is 〈 4% across a 50 mm wafer while the thickness uniformity is ≍ 8%. The highest transition temperature for a (Tl,Pb)Sr2Ca0.8Y0.2 Cu2O7 film thus far is 83 K. The RMS surface roughness of (Tl,Pb)Sr2CuO5 films is uniform across the wafer and approximately 1% of the film thickness for films 20 to 100 nm thick.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1022683307738
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    Synthesis and Structure of Hg1−xCrxSr2CuO4+δ Mercurocuprates (1998)
    Springer
    Journal of superconductivity 11 (1998), S. 141-142 
    Details
    ISSN: 1572-9605
    Keywords: Superconductivity ; mercury ; chromium ; synthesis ; structure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract We report preliminary results concerning the synthesis and structural characterisation of the chromium stabilised 1201 phases: Hg1−xCrxSr2CuO4+δ. A systematic study of the formation of phases in this system has been undertaken, together with a combined powder neutron and synchrotron x-ray diffraction study, to address the issue of chromium clustering and ordering in this system.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1022691509555
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    Superconductivity in Lithium- and Sodium-Doped Mercury-Based Cuprates (1998)
    Springer
    Journal of superconductivity 11 (1998), S. 169-171 
    Details
    ISSN: 1572-9605
    Keywords: Superconductivity ; Alkali-doping ; Hg-based Cuprates
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract The effect of Na- and Li-doping in Hg-based cuprates has been studied. It has been found that superconductivity can be achieved in samples containing small amount of Na or Li. While little change is found in the crystalline structure, the formed superconducting phase have the onset Tc typically above 140 K and zero-resistance Tc up to 136K. More interestingly, the processing temperature for the doped Hg-1223 can be reduced significantly to near 700 °C which is promising for thin films growth on many technologically compatible substrates.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1022608113189
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  • 27
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    Mixed-State Hall Effect in HgBa2CaCu2O6+δ Thin Films with Columnar Defects (1998)
    Springer
    Journal of superconductivity 11 (1998), S. 163-167 
    Details
    ISSN: 1572-9605
    Keywords: Superconductivity ; thin film ; columnar defect ; pinning
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract The mixed state Hall effect has been studied in high quality HgBa2CaCu2O6+δ thin films while the pinning strength is modified by the irraddition of columnar defects. It has been shown that the pinning strength can be significantly improved by columnar defects. The sign reversal in Hall resistivity is found to be nearly independent of pinning while the scaling behavior between Hall resistivity (ρxy) and longitudinal resistivity (ρxx) is influenced by pinning. The exponent β in the scaling law β xy ∼ β xy β decrease from 1.8 ± 0.1 to 1.5 ± 0.1 as pinning is enhanced. This results suggest that the sign reversal and the scaling are unrelated, and pinning is not the mechanism of the sign reversal.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1022656029119
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    Influence of hole filling by Ti on the superconductivity of YBa2Cu3O7−δ (1995)
    Springer
    Journal of superconductivity 8 (1995), S. 373-375 
    Details
    ISSN: 1572-9605
    Keywords: Superconductivity ; oxygen content ; hole filling ; suppression ofT c
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract The structural and superconducting properties of YBa2(CU1−x Ti x )3Oz samples are investigated using X-ray diffraction, ac susceptibility, and oxygen content measurements. The effect of increasing Ti concentration in YBa2(Cu1−x Ti x )3Oz lowers the oxygen content and decreasesT c, which is attributed to hole filling by Ti.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00728174
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    Sign reversal of the Hall effect in YBa2(Cu1−x )3O7−δ single crystals (1995)
    Springer
    Journal of superconductivity 8 (1995), S. 383-389 
    Details
    ISSN: 1572-9605
    Keywords: Superconductivity ; YBa2(Cu1−x Co x )3O7−δ ; Hall effect ; Single crystals
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract We have measured the in-plane Hall effect and in-plane resistivity of cobalt-doped YBa2Cu3O7−δ (YBCO) single-crystal samples. The concentration of cobalt ranged from 1 to 3%. As the applied field was varied, a sign reversal of the Hall resistivity was seen for 1 and 2% Co-doped samples, but not for the 3% sample. Our results are expressed in terms of conductivities, as recently recommended by the work of Dorseyet al. and Kopninet al. In the mixed state just below the superconducting transition temperatureT c, the Hall conductivityσ xy is the sum of two terms,C 1/H andC 2H, whereC 1 andC 2 are field-independent but temperature-dependent. As previously observed by Ginsberg and Manson for undoped YBCO, the coefficientC 1 is approximately proportional toτ 2 andC 2 is approximately linear inτ, whereτ = 1−(T/T c ). The values ofC 1 andC 2 are presented for each cobalt concentration.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00728176
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    Chemical potential pinning near a van Hove singularity in the cuprates (1995)
    Springer
    Journal of superconductivity 8 (1995), S. 659-660 
    Details
    ISSN: 1572-9605
    Keywords: Superconductivity ; van Hove Singularity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract The Fermi energy is shown to be pinned near a van Hove singularity for an extended doping range in the one-band and three-band Hubbard models as a consequence of filling dependent band renormalizations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00727465
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    Influence of long-range interactions on superconductivity and phase separation (1995)
    Springer
    Journal of superconductivity 8 (1995), S. 657-658 
    Details
    ISSN: 1572-9605
    Keywords: Superconductivity ; Charge Density Wave ; t-J Model
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract The t-J model is studied including a long-range 1/r repulsive interaction. It is observed that charge-density-wave states become stable as the strength of the 1/r term, Vcoul, is increased. Due to this effect, the domain of stability of the superconducting phase that appears near phase separation at Vcoul=0 is not enlarged by a 1/r interaction as naively expected. Nevertheless, superconductivity exists in a finite region of parameter space, even if phase separation is suppressed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00727464
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    Effect of gold doping on the superconducting critical temperature and transition width in single-crystal YBa2Cu3Oδ (YBCO) (1996)
    Springer
    Journal of superconductivity 9 (1996), S. 259-261 
    Details
    ISSN: 1572-9605
    Keywords: Superconductivity ; gold-doped YBa2Cu3O−δ ; transition temperature ; transition width
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract Single-crystal YBa2Cu3O−δ (YBCO) has been made with some of the copper atoms in the copper-oxygen chains replaced by gold. The samples were made by a flux method. The gold concentration was determined by EDX (energy-dispersive X-ray spectroscopy) as a function of the nominal (i.e., flux) composition. Up to about 4.8% of all the copper atoms can be replaced by gold. The effect of the gold doping on the superconducting transition temperature (T c ) and the transition width (ΔT c ) were determined.
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    URL: http://dx.doi.org/10.1007/BF00728312
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    Metastable states of the 2223 phase in the Bi(Pb)SrCaCuO system (1996)
    Springer
    Journal of superconductivity 9 (1996), S. 277-280 
    Details
    ISSN: 1572-9605
    Keywords: Superconductivity ; Bi2Sr2Ca2Cu3O y ; microwave absorption ; critical temperature
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract By the magnetically modulated microwave absorption method (MAMMA) we observed the modifications induced by different calcination temperatures (between 830°C and 870°C) on the 2223 phase formed in a system sintered at (855±5)°C with the starting composition Bi1.7Pb0.3Sr2Ca2Cu3O y . The presence of the 2223 phase in almost distinct states (consequently, multiple 2223 phases) in the same sample was observed. As the calcination temperature was increased up to 850°C, the highest temperature state of the 2223 phase intensified. Higher calcination temperatures resulted in the enhancement of other lower-temperature states. The homogeneity of the 2223 phase was greatly improved by annealing the samples at, 800°C for 5 min in a flowing nitrogen atmosphere. We labeled as “metastable” the lower-temperature states having excess oxygen, which, by easily losing the supplementary oxygen under the above annealing procedure, were shifted to higher temperatures.
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    URL: http://dx.doi.org/10.1007/BF00727548
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    Superconductivity in the cuprates as a consequence of antiferromagnetism and a large hole density of states (1996)
    Springer
    Journal of superconductivity 9 (1996), S. 379-387 
    Details
    ISSN: 1572-9605
    Keywords: Superconductivity ; t-J and Hubbard models ; mechanisms
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract We briefly review a theory for the cuprates that has been recently proposed based on the movement and interaction of holes in antiferromagnetic (AF) backgrounds. A robust peak in the hole density of states (DOS) is crucial to produce a large critical temperature once a source of hole attraction is identified. The predictions of this scenario are compared with experiments. The stability of the calculations after modifying some of the original assumptions is addressed. We find that if the dispersion is changed from an antiferromagnetic band at half-filling to a tight-binding cosk x+cosk y narrow band at 〈n〉=0.87, the main conclusions of the approach remain basically the same i.e., superconductivity appears in the $$d_{x^2 - y^2 } $$ -channel andT c is enhanced by a large DOS. The main features distinguishing these ideas from more standard theories based on antiferromagnetic correlations are here discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00727282
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    Charge-transfer in YBa2Cu3O x (1996)
    Springer
    Journal of superconductivity 9 (1996), S. 563-570 
    Details
    ISSN: 1572-9605
    Keywords: Superconductivity ; charge transfer ; YBa2Cu3Ox
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract The charge-transfer hypothesis is shown to be inconsistent with data for YBa2Cu3Ox: (i) The two-step behavior ofT c(x) (with jumps from zero to ≈60 K and then to ≈90 K) is not reflected as a similar, statistically significant two-step behavior in the bond-valence-sum charge of cuprate-plane Cu ions (as once believed), (ii) as a consequence of the law of conservation of charge, the derivatives of the layer charges with respect to oxygen contentx for both the Ba-O layers and the charge-reservoir Cu-O chains have the opposite signs to those predicted, and (iii) the charge-transfer observed for superconducting YBa2Cu3Ox is not sufficient to produce superconductivity, as demonstrated by insulating PrBa2Cu3Ox, which has virtually the same layer charges.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00728235
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