Interaction between columnar defects and pancake vortices in Bi₂Sr₂CaCu₂O_8+y studied by Josephson plasma resonance

Interlayer pancake vortex arrangement is studied by Josephson plasma resonance in Bi2Sr2CaCu2O8+y with columnar defects in a wide range of matching field Bθ (5 G ∼ 40 kG). The c-axis coherence is found to be drastically enhanced above a characteristic field H* in the vortex liquid state, which we interpreted as recoupling of pancake vortices by columnar defects. The recoupling field H* scales as (0.2-0.3)Bθ at high doses (Bθ > 500 G), but at lower doses it is almost constant (H* ∼ 60 Oe), suggesting that the recoupling occurs when vortex-vortex interactions are significant at low doses. At high doses we found that (1) H* does not depend on oxygen content of the crystal and (2) when columnar defects are introduced at an angle θ from the c axis, H* is scaled as (0.2-0.3) Bθ cos θ. These results indicate that the recoupling at high doses is controlled only by the density of defects in each CuO2 layers. © 2000 Elsevier Science B.V. All rights reserved.