2-DIMENSIONAL AND 3-DIMENSIONAL VORTEX LATTICE-DYNAMICS IN DYBA2CU3O7-(Y1-XPRX)BA2CU3O7 COUPLED HETEROSTRUCTURES

Vortex dynamics is studied in coupled multilayer structures, containin g N 24-angstrom-thick DyBa2Cu3O7 layers, each separated from the next by 96 angstrom of (Y1-xPrx)Ba2Cu3O7 (x = 0. 4, 0.55). When the magneti c field is parallel to the c axis, we find that the activation energy U for flux motion increases linearly with the number of superconductin g layers N in the structure for N < 3. This linear increase is the res ult of the coupled motion of pancake vortices belonging to different D yBa2Cu3O7 layers. For larger N samples the activation energy saturates meaning that the vortex lattice is turning three dimensional. In cont rast to samples whose vortex lattice is purely two dimensional and for which we find the activation energy for flux motion proportional to l og10B, samples in these series show a crossover to a power-law behavio r, U almost-equal-to B-0.5, at a magnetic field H which decreases as N increases.