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  • 1980-1984  (15)
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Year
  • 1
    Electronic Resource
    Electronic Resource
    On the critical temperature of anisotropic superconductors (1982)
    Springer
    Journal of low temperature physics 47 (1982), S. 157-167 
    Details
    ISSN: 1573-7357
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract An approximate analytic formula for the increase in the superconducting critical temperature caused by anisotropy is derived and compared with both the results of exact numerical solutions of the Eliashberg equations and with a previous approximate formula due to Allen and Butler. In all the cases considered our new formula is found to be more accurate than the previous one and to agree reasonably well with the exact results for the intermediate and weak coupling superconductors considered.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00682025
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    On the effective spectral densities for a superconductor with paramagnons (1984)
    Springer
    Journal of low temperature physics 57 (1984), S. 291-305 
    Details
    ISSN: 1573-7357
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Solutions of generalized Eliashberg equations containing an explicit paramagnon contribution are generated and used to obtain tunneling characteristics, which are then inverted in order to recover an effective spectral density. We consider several shapes for the paramagnon spectral density and vary the characteristic paramagnon energy. We invert the information on the gap using both the generalized and conventional Eliashberg equations and compare the effective spectral functions obtained by these methods with each other and with the actual kernels for the electron paramagnon and electron phonon spectral density. Scaling laws relating approximately the inverted and actual kernels are established and limitations on these laws described.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00681194
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    Thermodynamics of superconducting lanthanum (1983)
    Springer
    Journal of low temperature physics 51 (1983), S. 135-148 
    Details
    ISSN: 1573-7357
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We have calculated the thermodynamics of superconducting lanthanum from numerical solutions of the finite-temperature Eliashberg equations, written on the imaginary frequency axis, with electron-phonon kernel taken from the available tunneling data. We compare the theory with a recent specific heat determination of the thermodynamics. Also, we study several possible changes in the spectral density chosen to improve agreement with experiment. Our favored spectrum is obtained by a constant scaling of the tunneling spectral density chosen to increase the mass enhancement parameter from 0.79 to approximately 1.0.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00683418
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    Paper (German National Licenses)
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  • 4
    Electronic Resource
    Electronic Resource
    Detailed study of the thermodynamics of a superconductor with paramagnons (1981)
    Springer
    Journal of low temperature physics 42 (1981), S. 585-600 
    Details
    ISSN: 1573-7357
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: The effect of paramagnons on the thermodynamics of a superconductor has been studied within Eliashberg theory. For model microscopic parameters approximating those characteristic of Nb we compare results for finite and zero paramagnon mass enhancement parameter, λspin. The change obtained in the thermodynamics is significant, but because of present uncertainties in the experimental data and in the value of the calculated electron-phonon interaction, an accurate value of λspin cannot be determined. The effect of spin fluctuations on the quasiparticle density of states in the region of phonon energies is also investigated. Our results have implications for tunneling inversion.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00117432
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  • 5
    Electronic Resource
    Electronic Resource
    A comparative study of the thermodynamics of superconducting Nb0.75Zr0.25 and Nb (1981)
    Springer
    Journal of low temperature physics 43 (1981), S. 131-138 
    Details
    ISSN: 1573-7357
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: From the microscopic parameters derived from tunneling for Nb0.75Zr0.25 and Nb we compute and compare their thermodynamic properties using the imaginary frequency axis formulation of Eliashberg theory. While these two materials have similar critical temperatures, Nb0.75Zr0.25 is found to show much larger strong coupling corrections than does Nb. The substantial increase in the gap to critical temperature ratio observed experimentally can easily be understood by functional derivative techniques.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00118626
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    Paper (German National Licenses)
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  • 6
    Electronic Resource
    Electronic Resource
    Effect of normal impurities on anisotropic superconductors with variable density of states (1982)
    Springer
    Journal of low temperature physics 47 (1982), S. 411-426 
    Details
    ISSN: 1573-7357
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We develop a generalized BCS theory of impure superconductors with an anisotropic electron-electron interaction represented by the factorizable model introduced by Markowitz and Kadanoff, and a variable electronic density of statesN(ε), assumed to peak at the Fermi energy, which is modeled by a Lorentzian superimposed on a uniform background. As the impurity scattering is increased, the enhancement ofT c by both the anisotropy and the peak inN(ε) is washed out. The reduction is investigated for different values of the anisotropy and different peak heights and widths. It is concluded that the effects of anisotropy and the peak are reduced together in such a way that any effect due to anisotropy is not easily distinguishable from that due to the peak.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00683982
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  • 7
    Electronic Resource
    Electronic Resource
    Impure anisotropic superconductors with variable density of states peaked away from the Fermi energy (1983)
    Springer
    Journal of low temperature physics 50 (1983), S. 113-122 
    Details
    ISSN: 1573-7357
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract A generalized BCS-type theory of impure superconductors with an anisotropic electron-electron interaction and variable electronic density of states is extended to the case in which the Fermi energy εF falls at an arbitrary position within the peak. It is found that when εF is well away from the center of the peak, then the reduction in the transition temperature due to the washing out of the anisotropy can in some cases be distinguished from that due to the density of states.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00681842
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    Paper (German National Licenses)
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  • 8
    Electronic Resource
    Electronic Resource
    Gap anisotropy in superconductors with paramagnetic impurities (1981)
    Springer
    Journal of low temperature physics 42 (1981), S. 69-80 
    Details
    ISSN: 1573-7357
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: The effect of magnetic impurities with localized moments on the anisotropy in the gap and, hence, of the critical temperature is studied by numerical solution of the Eliashberg equations with a simple model for the anisotropy in the interaction. Quantitative results are given for lead for the transition temperature as a function of normal and spin-flip lifetimes. A significantly higher critical concentration of spin-flip scatterers is needed to suppress superconductivity in the anisotropic system than in the isotropic one with the same mean electron-phonon interaction; for concentrations between that critical for the anisotropic and that critical for the isotropic system superconductivity persists because the anisotropy is found to have increased above that in the pure material. This anisotropy increase is studied in detail.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00116696
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  • 9
    Electronic Resource
    Electronic Resource
    On the BCS theory of paramagnetic impurities in anisotropic superconductors (1981)
    Springer
    Journal of low temperature physics 42 (1981), S. 81-99 
    Details
    ISSN: 1573-7357
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: We develop a theory based on BCS theory which treats the effect of paramagnetic impurities in an anisotropic superconductor. It is found that in a separable model for the order parameter its anisotropy is expected to increase with increasing concentration of paramagnetic impurities. The critical temperature, the order parameter, and the quasiparticle density of states are computed numerically from our theoretical results. We find that there exists a regime which is superconducting by virtue of the fact that the paramagnetic impurities make the material highly anisotropic. In this regime the critical temperature can be reduced rapidly to zero by adding dilute concentrations of normal scattering impurities.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00116697
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    Paper (German National Licenses)
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  • 10
    Electronic Resource
    Electronic Resource
    Anisotropy effects on the specific heat jump of a superconductor with normal and paramagnetic impurities (1984)
    Springer
    Journal of low temperature physics 55 (1984), S. 67-81 
    Details
    ISSN: 1573-7357
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We present analytical calculations of the specific heat jump of an anisotropic superconductor with normal and paramagnetic impurities. We solve the imaginary-axis Eliashberg equations with a square-well model for the electron-phonon interaction and obtain additional terms not present in BCS theory. For low concentrations of paramagnetic impurities, anisotropy decreases the specific heat jump normalized to the normal state specific heat, while this quantity is larger in the anisotropic superconductor than in the isotropic one for large enough concentrations of paramagnetic impurities.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00683652
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    Paper (German National Licenses)
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