Asymmetric field profile in Bose glass phase of irradiated YBa2Cu3O(7-delta): loss of interlayer coherence around 1/3 of matching field.

Magneto-optical imaging in YBa(2)Cu(3)O(7-delta) with tilted columnar defects (CD's) shows an asymmetric critical-state field profile. The observed hysteretic shift of the profile ridge (trough) from the center of the sample is explained by in-plane magnetization originating from vortex alignment along CD's. The extracted ratio of the in-plane to out-of-plane magnetization component has a maximum at 1/5 of matching field ( B(Phi)) and disappears above B(Phi)/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 Bi(2)Sr(2)CaCu(2)O(8+y).