Microwave dissipation in YBa2Cu3O7-delta thin films with irradiation-induced columnar defects

We present measurements of the magnetic field dependent microwave dissipati on in a heavy-ion irradiated thin YBa2Cu3O7-delta film, in order to study t he effects of columnar defects on the pinning of vortices. Columnar defects were produced at 45 degrees with respect to the c axis. Measurements of th e microwave dissipation at 48 GHz were taken as a function of the angle bet ween the field and the c asis, in order to compare the response along and p erpendicular to the columns. The field was in the 0.3 T range. Several temp eratures 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 degrees from the track dir ections. From the measurements, me estimate the pinning frequency along the columns at 80 K to be nu (pc) similar or equal to 25 GHz.