The microwave surface impedance of DyBa/sub 2/Cu/sub 3/O/sub 7-x/ very thin films

Abstract

Measurements of the surface impedance of DyBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// (DyBCO) thin films have been made around 6 GHz by using the parallel plate resonator method with sapphire dielectrics. The films were deposited by RF magnetron sputtering on LaAlO/sub 3/ substrates to thicknesses between 20 and 320 nm. The change of the London penetration depth as a function of temperature is deduced from resonance frequency shifts. A generalized two fluid model is used to fit the data in terms of an effective penetration depth /spl lambda//sub eff/(0) at 0 K, taking into account the effect of grain boundary weak links. This analysis give an interpretation of the changes in /spl lambda//sub eff/(0) as a function of the film thickness and yields values for /spl lambda//sub eff/(0) around 160 nm for films thinner than 120 nm.