Parallel-plate resonator of variable spacer thickness for accurate measurements of surface impedance of high-T c superconductive films

Abstract

Measurements of microwave surface impedance of high-T{sub c} films at gigahertz frequencies and nitrogen temperature are performed. A simple technique employing a parallel-plate resonator with liquid nitrogen as a dielectric spaces is suggested. The use of a precise mechanical device provides smooth changing of distance between films from 200 {mu}m down to zero. Coupling to the resonator is accomplished by means of two small antennas - half-wave vibrators for frequency 10 GHz. The method for determining resistivity and magnetic field penetration depth was based on the analysis of spacer thickness dependences of the resonator quality factor and frequency. YBa{sub 2}Cu{sub 3}O{sub 7} films produced by a laser deposition technique on CaNdAlO{sub 4} substrates with T{sub c} = 91 K and j{sub c} = 10{sup 7} A/cm{sup 2} and on NdGaO{sub 3} substrates with T{sub c} = 91 K and j{sub c} = 10{sup 6} A/cm{sup 2} are examined, and the values R{sub s} 0.6 m{Omega}, {lambda} = 348 nm at f = 8.97 GHz and R{sub s} = 0.5 m{Omega}, {lambda} = 250 nm at f = 10.12 GHz respectively, are obtained at 77 K. 9 refs., 4 figs.