Interlayer coherence in Bi₂Sr₂CaCu₂O_8+y with splayed columnar defects

Abstract

By using the Josephson plasma resonance, we investigate the interlayer phase coherence (IPC) in the vortex states of GeV-proton-irradiated Bi2Sr2CaCu2O8+y crystals containing splayed columnar defects, which are introduced by Bi fission. At high temperatures in the vortex liquid state, we observe an enhancement of IPC in a field range beginning well below the matching field BΦ, in close correspondence with the recoupling crossover observed near BΦ/3 in the heavy-ion irradiated Bi2Sr2CaCu2O8+y. At low temperatures in the vortex solid state, a reentrant behavior of the resonance field is found in the zero-field-cooling condition, which has not been observed in pristine samples. This behavior suggests strongly suppressed IPC in this system, which may be explained by the vortex entanglement induced by the columnar defects in the splayed glass state. © 2007 Elsevier B.V. All rights reserved.