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 bo th co-deposition and growth interruption techniques. We have studied two ki nds of structures in which a layer of Bi2Sr2CuO6+delta (2201) is alternatel y stacked by an insulating layer of CaCuO2 or SrCuO2 in order to obtain 220 1/CaCuO2 or 2201/SrCuO2 multilayers. Reflection High Energy Electron Diffra ction (RHEED), used to control the quality of the interfaces and the two-di mensional growth mode, gives evidence of an increase in the surface roughne ss increasing the number of periods. The layered structure has been confirm ed comparing experimental and simulated X-ray spectra. The R vs. T curves o f 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 samp les are superconducting with critical temperatures strongly depending on th e CaCuO2 thickness.