Flux Pinning by Columnar Defects Along a-axis in a-axis Oriented YBCO Thin Films

Abstract

Columnar defects (CDs) along a -axis were installed into an in-plane aligned a -axis-oriented $\text{YBa}_{2}\text{Cu}_{3}\text{O}_{y}$ film by using heavy-ion irradiation, in order to clarify the influence of CDs on flux pinning properties around B || ab . The critical current density J c at B || c significantly decreases after the irradiation, since the CDs act as a channel for flux creep along their length. The magnetic field dependence of J c at B || ab , on the other hand, is weakened by the introduction of CDs. This means that the CDs can trap flux lines at B || ab , whereas naturally growth defects working as effective ab -correlated PCs exist. The trapping angle of CDs along the a -axis is extremely narrow (∼5.8°) in comparison with CDs along the c -axis and is roughly coincides with other ab -correlated PCs. The small trapping angle of CDs along the a -axis is attributed to strong line tension energy of flux lines with elliptical core around B || ab .