Effect of inclined magnetic field on pinning parameters in YBaCuO thin films with columnar defects

The effect of inclined magnetic field on pinning parameters in YBCO thin films with columnar defects was investigated. The columnar defects were produced by the heavy-ion irradiation with 200 MeV Xe ions parallel to c-axis. The magnetic field was applied inclined to c-axis with angle θB which was 0°, 10°, and 20°. One of the pinning parameters z, which is also called the dynamic critical exponent, extremely increased near the certain field related to the density of columnar defects in the case of θB = 0°, that is, a peak in the magnetic field dependence of z appeared near B/Bϕ = 1/3, while such peak was not observed before irradiation. On the other hand, the peak did not appear and the values of z decreased with the tilting angle θB. According to the percolation model, the appearance of the peak of z near B/Bϕ = 1/3 for θB = 0° originates from the matching effect. When the magnetic field is inclined away from columnar defects, the vortices are not pinned along those defects so that the matching effect is not achieved and the columnar defects take the various values of pinning force to flux lines.