SUPERCONDUCTIVITY IN ULTRATHIN FILMS CONSISTING OF BI2SR2CACU2O8+DELTA BI2SR2CUO6+DELTA HETEROSTRUCTURES

Superconductivity of a one-primitive-cell-thick Bi2Sr2CaCu2O8+delta la yer was investigated in ultrathin films consisting of Bi2Sr2CaCu2O8+de lta/Bi2Sr2CuO6+delta heterostructures. Films were prepared directly on substrates of SrTiO3(001) with a molecular beam epitaxy technique. Th e number Of CuO2 planes is fixed at six in all films, in which the one -primitive-cell-thick Bi2Sr2CaCu2O8+delta layer is located at various positions with respect to the Bi2Sr2CuO6+delta layers, from the surfac e of films to the interface between films and substrates. We observed that the one-primitive-cell-thick Bi2Sr2CaCu2O8+delta layer shows supe rconductivity when it is surrounded by Bi2Sr2CuO6+delta layers. Superc onductivity of the Bi2Sr2CaCu2O8+delta layers is, however, destroyed i f it is located at the surface or at the interface between films and s ubstrates.