Angular dependence ofc-axis magnetoresistance inBi2Sr2CaCu2O8+δsingle crystals with columnar defects

We measured the angular dependence of the c-axis magnetoresistance ${\ensuremath{\rho}}_{c}(\mathbf{B})$ of ${\mathrm{Bi}}_{2}{\mathrm{Sr}}_{2}{\mathrm{CaCu}}_{2}{\mathrm{O}}_{8+\mathrm{\ensuremath{\delta}}}$ irradiated with heavy ions. At temperatures near 69 K the scaling of ${\ensuremath{\rho}}_{c}(\mathbf{B})$ with the c-axis magnetic field component ${B}_{\ensuremath{\perp}}$ is broken and the in-plane field, ${B}_{\ensuremath{\parallel}},$ affects ${\ensuremath{\rho}}_{c}.$ At this temperature, at a specific field ${B}_{\mathrm{cr}}\ensuremath{\approx}{B}_{\ensuremath{\Phi}}/2,$ magnetoresistance becomes independent of field orientation. This crossing point allows us to estimate the correlation length L of pancake positions along the c axis. We find $L/s\ensuremath{\sim}100$ at ${B=B}_{\mathrm{cr}},$ where s is the interlayer spacing. This provides evidence of strong enhancement of pancake alignment in the vortex liquid in crystals with columnar defects.