Penetration depths of high T c films measured by two-coil mutual inductances

Abstract
A fundamental parameter of sample quality in epitaxial films of high Tc oxides is the effective penetration depth λ of the superconducting sheet. A contactless audio‐frequency method is described, in which an epitaxial YBa2Cu3O7 film is sandwiched between sets of stacked coils, and the procedure is given for computing the complex sheet impedance and hence λ from the change in mutual inductance produced by screening currents in the film. Temperature dependence of the complex impedance is presented.