Penetration Depths of High-T sub c Films Measured by 2-Coil Mutual Inductances.

A fundamental parameter of sample quality in epitaxial films of high T sub c oxides is the effective penetration depth lambda sub || of the superconducting sheet. We describe our contactless audio-frequency method, an arrangement in which a YBa sub 2 Cu sub 3 O sub 7 film on SrTiO sub 3(100) is sandwiched between sets of stacked coils, and the procedure for computing the complex sheet impedance and hence lambda sub || from the change in mutual inductance produced by screening currents in the film. Data for the temperature dependence is presented.