FLUX MOTION IN STRAINED YBA2CU3O7-DELTA/ND1.83CE0.17CUOX SUPERLATTICES

The dissipative flux motion in artificially grown, biaxially strained YBa2Cu3O7-delta/Nd1.83Ce0.17CuOx (Y*/Nd*) superlattices in magnetic fields perpendicular to the a-b plane was studied by ac-susceptibility measurements. In superlattices with modulation periods below a critical wavelength of 450 angstrom the Y* layers are coherently strained and show a strongly reduced critical temperature and activation energy for flux motion. This behavior is mainly caused by the reduction of the hole density in the Y* layers due to the coherency strain and not by the decoupling of the Y* layers. For multilayers with a modulation wavelength above 450 angstrom the coherency strain was found to relax. In the latter multilayers the activation energy for flux motion in the Y* layers increases linearly with increasing Y* thickness and shows a logarithmic magnetic-field dependence.