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Flux entry fields in amorphous superconductors

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Abstract

We have measured the flux entry fields (lower critical fieldsH c1) of homogeneous and inhomogeneous extreme type II amorphous superconductors based on zirconium. Samples are prepared by melt quenching at both ambient and elevated substrate temperatures. The degree of homogeneity is classified according to the widths of both inductive and resistive transitions. TheH c1 (T) curves for “powdered” homogeneous samples with weak flux pinning are found to be in good agreement with Maki's theory. Taking into account the electron-phonon renormalization effect, we deduce the zero-temperature energy gap values 2Δo/k B T c to be BCS like. On the other hand, anomalousH c1 (T) curves are observed in “powdered” inhomogeneous samples and strips from homogeneous samples parallel to the applied field. Appreciable irreversibility effects are also observed. The latter results are discussed qualitatively in terms of bulk and surface inhomogeneity effects.

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Research supported by National Science Foundation grant DMR-82-02624.

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Poon, S.J., Dunn, P.L. Flux entry fields in amorphous superconductors. J Low Temp Phys 54, 81–95 (1984). https://doi.org/10.1007/BF00681478

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Keywords

  • Zirconium
  • Magnetic Material
  • Substrate Temperature
  • Applied Field
  • Homogeneous Sample