Measurements of the thickness dependence of the surface resistance of laser ablated high-T/sub c/ superconducting thin films

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Abstract
The authors report on measurements of the surface resistance of thin Y/sub 1/Ba/sub 2/Cu/sub 3/O/sub 7-x/ (TBCO) films made by laser ablation on SrTiO/sub 3/. 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/sub eff/ on the thickness of the superconducting films. From the measured R/sub eff/, one can calculate the true surface resistance R/sub ST/ by an analytical approximation which takes into consideration substrate losses and multireflections within the film. Results show that within the measurement uncertainty R/sub ST/ does not change with changing film thickness. At 77 K, R/sub ST/ values of about 15 m Omega were measured; at 30 K, R/sub ST/ reached 9 m Omega .