Field-induced pinning in the vortex liquid phase of heavy-ion irradiated Bi2Sr2CaCu2O8 thin films and multilayers

In-plane dissipation, R(H), in the vortex liquid phase is investigated in h eavy-ion irradiated anisotropic Bi2Sr2CaCu2O8 epitaxial thin films and a hi ghly anisotropic Bi2Sr2CaCu2O8/Bi2Sr2CuO6 multilayer. In a well-defined reg ion of the (H,T) phase diagram we observe a dip in the R(H) curves due to t he pinning of vortices by the columnar defects created by irradiation. This decrease of dissipation is attributed to a field-driven confinement of vor tices within the columnar defects. Our major conclusion from R(theta) curve s is that the 2D angular scaling behaviour is valid in the entire (H,T) liq uid region. These results indicate that in these systems the dissipation is always due to mobile 2D vortices, even in the presence of columnar defects .