Asymmetric field profile in Bose glass phase of irradiated YBa2Cu3O7-delta: Loss of interlayer coherence around 1/3 of matching field

Magneto-optical imaging in YBa2Cu3O7-delta with tilted columnar defects (CD 's) shows an asymmetric critical-state held profile. The observed hystereti c shift of the profile ridge (trough) from the center of the sample is expl ained by in-plane magnetization originating from vortex alignment along CD' s. The extracted ratio of the in-plane to out-of-plane magnetization compon ent has a maximum at 1/5 of matching held (B-Phi) and disappears above B-ps i/3, suggesting a reduction of interlayer coherence well below B-Phi in the Bose glass phase. Implications are discussed in comparison with the vortex liquid recoupling observed in irradiated Bi2Sr2CaCu2O8+gamma.