Angular behavior of flux dynamics in YBCO films with crossed columnar defects around the ab-plane

Abstract

We systematically investigated the influence of columnar defects (CDs) on the flux dynamics around B ∣∣ ab in YBa2Cu3O7-δ (YBCO) films, where two types of the crossed CD configurations with the crossing angle relative to the c-axis, θi = ±30° and ±60°, were prepared by using 200 MeV Xe ion irradiation. The crossed CDs with θi = ±30° induce a peak of critical current density Jc centered at B ∣∣ c, which suggests a typical entanglement state of flux lines. The Jc at B ∣∣ ab, by contrast, is insensitive to the crossed CDs with θi = ±60°, which are crossing at ±30° around the ab-plane. In addition, the behaviors of the glass–liquid transition temperature Tg and the dynamic critical exponent z indicate that the VG state develops at B ∣∣ ab not only for θi = ±30° but also for θi = ±60°. The difference in the contribution of CDs to the flux dynamics for between θi = ±30° and ±60° also stands out at B ∣∣ CDs, where the magnetic field for θi = ±60° is more tilted toward the ab-plane: the Jc peak at B ∣∣ CDs occurs in any magnetic field for θi = ±60°, whereas the correlated pinning state disappears in high magnetic fields for θi = ±30°. These results suggest that the pinning by CDs is angle-dependent due to the flux line structure with strong line tension around B ∣∣ ab: CDs around the ab-plane can trap flux lines along their long axis only in much narrower angular-range, in comparison with CDs around the c-axis.