Dynamic interactions between pancake vortex stacks and Josephson vortices in Bi2Sr2CaCU2O8 single crystals:: relaxation and ratchets

We present a detailed study of the dynamic interactions between Josephson vortices and stacks of pancake vortices in a Bi2Sr2CaCu2O8 single crystal, obtained by measuring the effect of applied in-plane magnetic field pulses on the c-axis magnetization. The predominant interaction relaxes the system towards equilibrium. However, using a highly sensitive AC technique we are able to measure also the forces acting to drive the system away from equilibrium, consistent with the existence of dragging interactions between the Josephson and pancake systems. Such forces were discussed recently as the basis of possible flux ratchet devices.