Measurements of the thickness dependence of the surface resistance of laser ablated high-Tc superconducting thin films

The authors report on measurements of the surface resistance of thin Y₁Ba₂Cu₃O_7-x (TBCO) films made by laser ablation on SrTiO₃. Several films were prepared with thicknesses ranging from 100 nm to 400 nm. The surface resistance of these films was measured automatically in a temperature range from 20 K to 90 K using a copper cavity at 66.8 GHz. The measured values quantitatively show the expected temperature dependence of the effective surface resistance R_eff on the thickness of the superconducting films. From the measured R_eff, one can calculate the true surface resistance R_ST by an analytical approximation which takes into consideration substrate losses and multireflections within the film. Results show that within the measurement uncertainty R_ST does not change with changing film thickness. At 77 K, R_ST values of about 15 mΩ were measured; at 30 K, R_ST reached 9 mΩ