부산대학교 도서관

Measurements of microwave surface impedance of high-Tc 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 200µm 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. YBa2Cu3O7 films produced by a laser deposition technique on CaNdAlO4 substrates withTc=91 K andjc=107 A/cm2 and on NdGaO3 substrates withTc=91 K andjc=106 A/cm2 are examined, and the valuesRs=0.6 mO,?=348 nm atf=8.97 GHz andRs=0.5 mO,?=250 nm atf=10.12 GHz, respectively, are obtained at 77 K.