Superconductivity in Bi/sub 2/Sr/sub 2/CuO/sub 6+/spl delta///(Sr,Ca)CuO/sub 2/ multilayers obtained by molecular beam epitaxy

Bi-based high temperature superconducting multilayers have been obtained by Molecular Beam Epitaxy (MBE) using a deposition method which consists of both co-deposition and growth interruption techniques. We have studied two kinds of structures in which a layer of Bi/sub 2/Sr/sub 2/CuO/sub 6+/spl delta// (2201) is alternately stacked by an insulating layer of CaCuO/sub 2/ or SrCuO/sub 2/ in order to obtain 2201/CaCuO/sub 2/ or 2201/SrCuO/sub 2/ multilayers. Reflection High Energy Electron Diffraction (RHEED), used to control the quality of the interfaces and the two-dimensional growth mode, gives evidence of an increase in the surface roughness increasing the number of periods. The layered structure has been confirmed comparing experimental and simulated X-ray spectra. The R vs. T curves of the 2201/SrCuO/sub 2/ multilayers present an onset and behave differently from those of the single phase samples with the same stoichiometry but they are not superconducting down to T=4.2 K. On the contrary, the 2201/CaCuO/sub 2/ samples are superconducting with critical temperatures strongly depending on the CaCuO/sub 2/ thickness.