Stripline resonator measurements of Z/sub s/ versus H/sub rf/ in YBa/sub 2/Cu/sub 3/O/sub 7-x/ thin films

A report is presented on measurements of the surface impedance, Z/sub S/, of YBa/sub 2/Cu/sub 3/O/sub 7-x/ thin films using a stripline resonator. The films were deposited on LaAlO/sub 3/ substrates by off-axis magnetron sputtering. The authors obtained Z/sub S/ as a function of frequency from 1.5 to 20 GHz, as a function of temperature from 4 K to the transition temperature ( approximately 90 K), and as a function of the RF magnetic field from zero to 300 Oe. At low temperatures the surface resistance, R/sub S/, of the films shows a very weak dependence on the magnetic field up to 225 to 250 Oe. At 77 K, R/sub S/ is proportional to the square of the field. The penetration depth shows a much weaker dependence on the field than does R/sub S/. The origins of the magnetic field dependence of Z/sub S/ are also discussed.<>