MICROWAVE DISSIPATION IN YBa2Cu3O7-δ THIN FILMS WITH IRRADIATION-INDUCED COLUMNAR DEFECTS

We present measurements of the magnetic field dependent microwave dissipation in a heavy-ion irradiated thin YBa 2 Cu 3 O 7-δ film, in order to study the effects of columnar defects on the pinning of vortices. Columnar defects were produced at 45° with respect to the c axis. Measurements of the microwave dissipation at 48 GHz were taken as a function of the angle between the field and the c axis, in order to compare the response along and perpendicular to the columns. The field was in the 0.3 T range. Several temperatures near the liquid nitrogen temperature were investigated. We find a dip in the dissipation when the field is aligned to the tracks. The dip is absent when the field is aligned perpendicular to the tracks, and with the same angle with respect to the crystallographic directions. The dip is not very sharp, and shows up for angles as far as 30° from the track directions. From the measurements, we estimate the pinning frequency along the columns at 80 K to be νpc ≃ 25 GHz .