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Journal of Low Temperature Physics

, Volume 66, Issue 3–4, pp 191–208 | Cite as

Anisotropy effects in tantalum, niobium, and vanadium down to the millikelvin temperature range

  • F. M. Sauerzopf
  • E. Moser
  • H. W. Weber
  • F. A. Schmidt
Article

Abstract

Experiments on the transition fields to the normal conducting state were made on single crystals of Ta, Nb, and V in the temperature range between 40 mK and the transition temperature. In tantalum results are presented on the thermodynamic quantitiesTc, μ0Hc(T),D(t), and γ in the clean limit and as a function of impurity concentration at low impurity levels (<0.15 at %). Special attention is paid to the phase transition between type I and type II superconductivity, which occurs at a certain conversion temperatureT*<Tc in materials with κ(Tc)<1/√2. This transition is found to be strongly anisotropic because of theHc2 anisotropy effect appearing in the type II superconducting state. It is shown that atT=0 no signs of type II superconductivity will appear for κ(Tc)⩽0.44, whereas type II superconductivity will be found in every crystal direction for κ(Tc)⩾0.50. The analysis ofHc2 anisotropy in Ta in terms of cubic harmonic functions demonstrates that the first anisotropic expansion coefficienta4 remains finite atT*, whereas the second,a6, vanishes when type II superconductivity disappears. No significant values of any higher order coefficient could be detected in Ta. For Nb and V the temperature dependence of the anisotropy coefficientsa4,a6,a8, anda10 was established in the entire temperature range. The diversity of results clearly indicates that different microscopic mechanisms contribute to the observedHc2 anisotropy effect in these materials.

Keywords

Vanadium Niobium Harmonic Function Tantalum Superconducting State 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

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Copyright information

© Plenum Publishing Corporation 1987

Authors and Affiliations

  • F. M. Sauerzopf
    • 1
  • E. Moser
    • 1
  • H. W. Weber
    • 1
  • F. A. Schmidt
    • 2
  1. 1.Atominstitut der Österreichischen UniversitätenViennaAustria
  2. 2.Materials Preparation CenterAmes LaboratoryAmes

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