Very High Critical Current Densities in Yba2Cu3O7-8/ Nd1.83Ce0.I7Cuox Superlattices

The critical current density of YBa2Cu307-8/ Ndi.83Ceo.17CuOx (Y/Nd) superlat-tices grown heteroepitaxially by hollow cathode magnetron sputtering was measured in magnetic fields perpendicular and parallel to the c-axis. The thickness dy and djvd of the individual Y and the Nd layers ranged between 50 and 400A. In superlattices with modulation periods below a critical wavelength of Ac =450A the Y layers are coherently strained, whereas in those with modulation periods above Ac 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 x 107A/cm2 were observed for multilayers with a modulation period just above Ac. For B_Lc-axis, the critical current density Jc± is almost independent of B up to a field B (B ≍ 2T for dy =100Å), which corresponds to the lower critical field of the Y layers. Jc⊥ values as high as 2 x 106A/cm2 were obtained for 5=1 T and T=77K. The angular dependence Jc(p) is determined solely by the magnetic field component parallel to the c-axis demonstrating the two-dimensional nature of the superlattices.