HIGH-TEMPERATURE SUPERCONDUCTING MULTILAYERS AND HETEROSTRUCTURES GROWN BY ATOMIC LAYER-BY-LAYER MOLECULAR-BEAM EPITAXY

Atomic layer-by-layer molecular beam epitaxy (ALL-MBE) of high-tempera ture superconductors (HTSC) and other complex oxides has been develope d. Thin films with atomically flat surfaces and abrupt interfaces can be produced an atomic layer at a time. Samples are engineered by stack ing molecular layers of different compounds, by adding or omitting ato mic monolayers, and by doping within specified monolayers. Novel artif icial HTSC compounds such as Bi2Sr2Ca7Cu8Ox (2278), as well as various heterostructures, have been synthesized in this way. This unique synt hetic capability has allowed several fundamental physics issues, such as the dimensionality of the HTSC state, long-range proximity effects, resonant tunneling with a specified number of hops, etc, to be addres sed. Trilayer Josephson junctions with uniform and reproducible proper ties have been fabricated; phase-locked operation of two junctions has also been demonstrated. Finally, titanate slabs only 4-Angstrom thick have been grown without pin-holes and shown to provide tunneling barr iers for c-axis transport.