ANALYSIS OF THE LOCK-IN TRANSITION IN BI2SR2CACU2O8-CRYSTALS THROUGH MICROWAVE DISSIPATION(DELTA SINGLE)

We observe the lock-in transition in Bi2Sr2CaCu2O8+delta single crysta ls, for various orientations of the magnetic field with respect to the ab plane (0-15 degrees), by measuring the dissipation at 10 GHz as a function of the field magnitude (0-1 T), in the range 45-75 K. The loc k-in transition is revealed by the dissipation switching from a regime controlled by Josephson vortices parallel to the layers to a high-fie ld regime, controlled by the perpendicular component of the field, whi ch we associate with tilted vortices. The transition from the Josephso n to the tilted lattice is shown to occur through the formation of two -dimensional vortices connected by Josephson strings. From the first p enetration field of Josephson vortices, we deduce the anisotropy param eter gamma=70(-20)(+30).