Investigations of coupled DyBa2Cu3O7-(Y1-xPrx)Ba2Cu3O7 multilayer structures

The authors report on the behavior of high Tc superconductor coupled multilayer structures in magnetic field perpendicular to the ab plane. In these structures the number N of superconducting layers in the sample has been systematically varied. They extract the activation energy for flux motion from resistive measurements of the superconducting transition. For samples containing N 24 angstrom thick DyBa2Cu3O7 layers, each separated from the next by 96 angstrom of an (0.45Pr0.55)Ba2Cu3O7 alloy, they find that the activation energy U increases linearly with the number N of layers for N < 3--4, and then saturates. The linear increase of U is taken as evidence that coupling through (0.45Pr0.55)Ba2Cu3O7 increases the correlated volume involved in the flux motion and thus U. For N < 3 stacked pancake vortices move rigidly and the vortex lattice is 2-D. For N > 3--4 shear of the vortex lattice becomes important, the vortex lattice dimensionality crosses-over to 3-D, and the activation energy saturates. 58 refs