Angular behaviour of critical current density in YBa2Cu3Oy thin films with crossed columnar defects

Abstract

Columnar defects (CDs) were installed into YBa2Cu3Oy thin films at the crossing angle ±θi relative to the c-axis using 200 MeV Xe ions, in order to clarify the influence of ±θi on the angular behaviours of critical current density Jc. The width of a Jc peak occuring at B || c linearly increases with broadening CD-crossing angle, where its shape maintains a single peak in the range of θi ≤ ±25°. The CDs crossing at ±45°, on the other hand, drastically change the angular behaviour of Jc around B || c: the Jc is equally elevated over the angular region from −45° to 45° in the lower magnetic field, whereas the rapid reduction of the Jc occurs at B || c with increasing magnetic field, leading to the appearance of double peaks near the irradiation angles, ±45°. This crossover phenomenon is attributed to the difference in the pinned states of flux lines between B || c and at the irradiation angles: the CDs crossing at ±45° cannot provide the correlated flux pinning along the c-axis, resulting in the uncorrelated pinned state at B || c.