Penetration depth measurements on type II superconducting films

摘要: A penetration depth (λ) measurement technique, which is based upon the λ-dependence of propagation velocity electromagnetic waves in superconducting transmission lines, refined and used to accurately measure λ's Pb films containing Au, In, or Bi additions. The results are applied test two distinct predictions for London (or type II) superconductors. First, measured dependence λ low temperature electrical resistivity compared with theoretical prediction a II superconductor dilute homogeneous impurity concentration. We find that follow this simple reasonably well, irrespective species impurity, anticipated exceptions. Namely, deviations occur pure Pb, not superconductor, highest concentration, case Fermi surface may be appreciably distorted from Pb. Second, London-theory effective (λeff) film thickness (d), λeff= λ(T) coth d/λ(T), tested, d/λ range d/λ, closely approximated by 1 λ/d. Separate experiments either temperature, T, varied reveal excellent agreement above formula. To our knowledge first detailed confirmation explicit hyperbolic cotangent dependency.