Radiofrequency impedance measurements at 2 MHz on YBa2Cu3O7 epitaxial films

Measurements of the temperature dependence of the rf electrical impedance o f YBa2Cu3O7 epitaxial films of 0.25, 0.5 and 1.0 mum thickness are reported . The contactless 2 MHz ac measurements yield both the real and the imagina ry parts of the impedance. The temperature dependence of the real part of t he impedance shows a peak in the resistance just below T-c for all the samp le thicknesses, and we interpret this as being due to a Kosterlitz-Thouless (K-T) transition. The imaginary part gives the change in the kinetic induc tance. From an analysis of the data near the K-T transition temperature an effective superconducting thickness of the sample is determined.