Phase coherence along the c-axis in Bi 2Sr 2CaCu 2O 8+ y with columnar defects probed by Josephson plasma resonance

Abstract

We studied the c-axis phase coherence in Bi 2Sr 2CaCu 2O 8+ y with columnar defects using the Josephson plasma resonance as a probe. At temperatures close to T c, the Josephson plasma resonance field ( H p) shows a characteristic temperature dependence of decoupled pancake vortices similar to the pristine Bi 2Sr 2CaCu 2O 8+ y . The drastic increase in H p occurs at a frequency independent characteristic field even in the vortex liquid phase. We interpret this change as a manifestation of recoupling of decoupled vortices by the columnar defects. The increase in H p becomes larger with increasing the density of columnar defects. The temperature dependence of H p at lower temperatures but above the irreversibility line can be understood by considering two kinds of vortices, some trapped in the columnar defects and others located between them giving a decoupled liquid-like response.