Angular Dependence of C-Axis Magnetoresistance in Bi-2212 Single   Crystals With Columnar Defects
  We measured the angular dependence of the c-axis magnetoresistance rho_c(B) of Bi-2212 irradiated with heavy ions. At temperatures near 68 K the scaling of rho_c(B) with the c-axis magnetic field component B_perp is broken and the in-plane field, B_parallel, affects rho_c. At this temperature, at a specific field B_cr \approx B_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 is about 100 at B=B_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. 
N. Morozov, L.N. Bulaevskii, M.P. Maley, J.Y. Coulter, A.E. Koshelev   and T.-W. Li