ASIRACT Experiments on the screening attenuation of YBa2Cu3O7'p thin films on different substrates have been performed in the frequency range 28-33 GHz. From these measurements, the superconductor penetration depth can be deduced, which indicates the quality of a superconducting thin film. Measured values are compared to theory and literature.
flDCIQThe losses of superconducting tiin films have been investigated extensively by the microwave resonator technique [1][2][3][4][5][6]. This reveals information about the losses of these films and is well suited for the optimizaton for microwave applications. The results are, however, influenced not only by the intrinsic properties of the superconductor but also by grain boundaries and by surface impurities including normal-conducting CuO droplets. To distinguish between these influences, it is useful to introduce a measurement which is affected by a smaller variety ofeffects. The measurement ofthe screening attenuation presented in this paper is not influenced by impurities on the surface of the sample because these do not alter the attenuation to a noticeable effect. -However, the measurement is not capable to distinguish between intrinsic effects and effects due to grain boundaries because the result is averaged over the sampled area.
IN33UNSIC HIQ1I FRQUENCY PROPE&TMS OF S]UffECQNDUCT,0RSThe high frequency properties of superconductors can be described by a notation which is based on the coexistence ofnormal-conducting charge cariers (electrons) and superconducting charge carriers (cooper pairs). Knowing that the latter do not cause any losses, we have 0=01 I0-j2 (1) From London's equations on the magnetic penetration depth k(T) of superconductors [7], we further have 02(2) w wrtok(T )2 Superconductors show a conductivity which depends on frequency (and temperature, of course), whereas the penetration depth is independent of frequency and also applies to static magnetic fields. Therefore, it is advisable to confine to a discussion on the penetration depth when comparing measurements carried out at different frequencies.It is instructive to compare the results to theoretical models. One of the most basic approaches to describe the temperature dependence of the conductivity is the two-fluid model by Gorter and Casimir [7]. Though it is based on thermodynamical considerations, it is what one would call a "semi-empirical" model which is justified by experiments. We have