Atomic-level engineering of cuprates and manganites

Using ALL-MBE, we have engineered a novel, artificial (metastable) cuprate superconductor, BiSr₂Ca₇-_xDy_xCu₈O_{19 + y}, in which only the central Ca layer is doped by Dy. This provides, within a single unit cell, the bottom superconducting electrode, an insulating barrier layer (only few Å thick), and the top superconducting electrode, thus constituting an artificial intra-cell Josephson junction. In this way, we have fabricated the first high-T_C tunnel (SIS) junctions. They exhibit significant Josephson supercurrents and very sharp quasiparticle tunneling I-V characteristics. Next, single-crystal thin films of manganites grown by ALL-MBE have shown remarkable anisotropy of colossal magnetoresistance (CMR). We have also fabricated lateral superlattices with alternating stripes (nano-wires) of La_1-xCa_xMnO₃ and La_1-xSr_xMnO₃, few tens of nanometers wide. They show substantial in-plane anisotropy in transport properties, and a fivefold increase in low-field sensitivity. Our most recent results include successful growth of La_1-xSr_xMnO₃ on top of Bi₂Sr₂CaCu₂O₈, and vice versa.