Superconductivity in Bi2Sr2CuO6+delta(Sr, Ca)CuO2 multilayers obtained by molecular beam epitaxy

Bi-based high temperature superconduting 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 Bi2Sr2CuO6+delta (2201) is alternately stacked by an insulating layer of CaCuO2 or SrCuO2 in order to obtain 2201/CaCuO2 or 2201/SrCuO2 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/SrCuO2 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 = 4.2K. On the contrary, the 2201/CaCuO2 samples are superconducting with critical temperatures strongly depending on the CaCuO2 thickness.