Determination of surface resistance and magnetic penetration depth of superconducting YBa/sub 2/Cu/sub 3/O/sub 7- delta / thin films by microwave power transmission measurements

Abstract

A novel waveguide power transmission measurement technique has been developed to extract the complex conductivity ( sigma *= sigma /sub 1/-j sigma /sub 2/) of superconducting thin films at microwave frequencies. The microwave conductivity of two laser-ablated YBa/sub 2/Cu/sub 3/O/sub 7- delta / thin films on LaAlO/sub 3/ with transition temperatures (T/sub c/) of approximately 86.3 and 82 K, respectively, in the temperature range 25 to 300 K was determined. From the conductivity values, the authors calculated the penetration depth ( lambda ) to be approximately 0.54 and 0.43 mu m and the surface resistance (R/sub s/) to be approximately 24 and 36 m Omega at 36 GHz and 76 K for the two films under consideration. The R/sub s/ values were then compared to those obtained from the change in the Q-factor of a 36-GHz TE/sub 011/-mode oxygen-free, high-conductivity (OFHC) copper cavity by replacing one of its end walls with the superconducting sample. It was found that this technique allows noninvasive characterization of high-T/sub c/ superconducting thin films at microwave frequencies.