Ultrasonic Absorption in Superconducting Single Crystals of Nb1 − xMox

  • L. L. Lacy


The measurement of ultrasonic absorption by the conduction band electrons has frequently been used to determine the superconducting energy gap Δ(T). In general, the experiments performed on many of the elemental superconductors in the clean state (i.e., ξ0/l < 1, where l is the electron mean free path and ξ0 is the BCS coherence length) tend to support the BCS1 prediction
$${{{\alpha }_{s}}}/{{{\alpha }_{n}}}\;=2{{\left( {{e}^{{\Delta }/{kT}\;}}+1 \right)}^{-1}}$$
Discrepancies from Eq. (1) have, however, been reported for a number of high-purity elements such as the type I superconductor Sn2 and the type II superconductor Nb.3–6 Only a few attenuation measurements have been made on superconducting alloys in the dirty regime(i.e.,ξ0/l > 1) due to the difficulty of measuring the electron attenuation, which is often overshadowed by the background absorption α B . Tittman7 has shown the validity of Eq. (1) for the type II superconductor V-5.6 at.% Ta in the dirty regime ξ0/l ≈ 5) assuming a BCS gap parameter A≡ 2Δ(0)/kT c ≈ 3.6. It is therefore expected that Eq. (1) should describe attenuation measurements for superconducting alloys, or at least it should apply in the dirty limit ξ0/l ≫ 1.


Attenuation Measurement Conduction Band Electron Ultrasonic Absorption Specific Heat Data Dirty Limit 
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Copyright information

© Springer Science+Business Media New York 1974

Authors and Affiliations

  • L. L. Lacy
    • 1
  1. 1.Space Sciences LaboratoryNASA Marshall Space Flight CenterUSA

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