Magnetic penetration depths in superconducting Nb films

Abstract

Absolute magnetic penetration depths λ in evaporated Nb films have been measured as a function of residual resistivity ρ{variant}Tc and temperature T by means of a refined two-junction junction interferometer technique. The measured λ(ρ{variant}Tc) dependence is within the local London theory with ξ0=410 A ̊ and λL(0) = 440 A ̊, and the experimental λ(T) follows the empirical approximation λ(T) = λ(0) ( 1-T4 T4c) 1 2, where Tc = 9.0 K for a film with ρTc = 5.8 μΩcm. To our knowledge, this is the first experimental test of λ(ρTc) in Nb. © 1981.