Surface resistance of thin Perovskite films - High-temperature superconductors and giant magnetoresistance manganites

We present a systematic study of the surface resistance of perovskite thin films and bulk samples at microwave frequencies. The d.c. resistivity p of the various samples spans three orders of magnitude. For bulk samples, we obtain the usual ρ1/2 dependence of Rs. For ρ < 1 μΩ cm, Rs displays conventional behavior, i.e. Rs α ρ. However, for ρ > 1 μΩ cm, Rs is not proportional to ρ but to the conductivity σ. Using this fact, we have made the first direct observation of a peak in σ1, just below Tc in a-axis films of YBa2Cu3O7.