Effect of DC and AC Currents on the Surface Sheath Conductivity of Niobium Single Crystals

  • R. C. Callarotti


We have measured resistive transitions of niobium single crystals in a dc magnetic field H at 4°K. The transitions were measured for different values of dc current I dc flowing along the cylindrical samples, and also in the presence of a small alternating field h=h0 cos(ωt),H≫h. The presence of the ac field increases the resistance of the samples in the surface sheath region (H C2 <H<H C3 ). We have interpreted our results in terms of a model proposed by Callarotti et al., 1 according to which the ratio of the sheath conductivity a s to the normal conductivity a N is
$${{\sigma }_{s}}/{{\sigma }_{N}}=1+\left\{ A\left[ \left( {{H}_{C3}}-\left.H \right)/\left( {{H}_{C3}}-{{H}_{C2}}{{\left.) \right]}^{2}}/\left[ {{I}_{dc}}+\left. B{{h}_{o}} \right] \right. \right. \right. \right. \right\}$$
where A and B are constants.


Magnetic Permeability Cylindrical Sample Resistive Transition Resistivity Ratio Surface Sheath 


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  1. 1.
    R.C. Callarotti, J.J. Engelhardt, and M. Vecchi, to be published.Google Scholar
  2. 2.
    R.C. Callarotti, Ph.D. Thesis, The Massachusetts Institute of Technology, May 1967.Google Scholar
  3. 3.
    H.J. Fink and R.D. Kessinger, Phys. Rev. 140, A1937 (1965).MathSciNetADSCrossRefGoogle Scholar

Copyright information

© Springer Science+Business Media New York 1974

Authors and Affiliations

  • R. C. Callarotti
    • 1
  1. 1.Instituto Venezolano de Investigaciones CientíficasCaracasVenezuela

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