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

Abstract

Abstract We systematically investigated the influence of columnar defects (CDs) on the flux dynamics around B ∣∣ ab in YBa 2 Cu 3 O 7- δ (YBCO) films, where two types of the crossed CD configurations with the crossing angle relative to the c -axis, θ i = ±30° and ±60°, were prepared by using 200 MeV Xe ion irradiation. The crossed CDs with θ i = ±30° induce a peak of critical current density J c centered at B ∣∣ c , which suggests a typical entanglement state of flux lines. The J c at B ∣∣ ab , by contrast, is insensitive to the crossed CDs with θ i = ±60°, which are crossing at ±30° around the ab -plane. In addition, the behaviors of the glass–liquid transition temperature T g and the dynamic critical exponent z indicate that the VG state develops at B ∣∣ ab not only for θ i = ±30° but also for θ i = ±60°. The difference in the contribution of CDs to the flux dynamics for between θ i = ±30° and ±60° also stands out at B ∣∣ CDs, where the magnetic field for θ i = ±60° is more tilted toward the ab -plane: the J c peak at B ∣∣ CDs occurs in any magnetic field for θ i = ±60°, whereas the correlated pinning state disappears in high magnetic fields for θ i = ±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.