Very high critical current densities in YBa/sub 2/Cu/sub 3/O/sub 7- delta //Nd/sub 1.83/Ce/sub 0.17/CuO/sub x/ superlattices

The critical current density of YBa/sub 2/Cu/sub 3/O/sub 7- delta //Nd/sub 1.83/Ce/sub 0.17/CuO/sub x/ (Y/Nd) superlattices grown heteroepitaxially by hollow cathode magnetron sputtering was measured in magnetic fields perpendicular and parallel to the c-axis. The thickness d/sub Y/ and d/sub Nd/ of the individual Y and Nd layers ranged between 50 and 400 AA. In superlattices with modulation periods below a critical wavelength Lambda /sub c/=450 AA the Y layers are coherently strained, whereas in those with modulation periods above Lambda /sub c/ the coherency strain starts to relax, resulting in the formation of a high density of misfit dislocations. Very high zero field critical current densities up to 1.1*10/sup 7/ A/cm/sup 2/ were observed for multilayers with a modulation period just above Lambda /sub c/. For B perpendicular to the c-axis, the critical current density J/sub c perpendicular to / is almost independent at B up to a certain field ( approximately=2 T for d/sub y/=100 AA) that corresponds to the lower critical field of the Y layers. J/sub c perpendicular to / values as high as 2*10/sup 6/ A/cm/sup 2/ were obtained for B=1 T and T=77 K. The angular dependence J/sub c/( phi ) is determined solely by the magnetic field component parallel to the c-axis demonstrating the two-dimensional nature of the superlattices.<>