Asymmetric Field Profile in Bose Glass Phase of Irradiated YBa2Cu3O7-d: Loss of Interlayer Coherence around 1/3 of Matching Field

Magneto-optical imaging in YBa2Cu3O7-d 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 originated 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 ($B_Φ$) and disappears above $B_Φ/3$, suggesting a reduction of interlayer coherence well bellow $B_Φ$ in the Bose glass phase. Implications are discussed in comparison with the vortex liquid recoupling observed in irradiated Bi2Sr2CaCu2O8+y.