High-T-c superconductor insulator superconductor heterostructures with highly resistive insulator layers

Trilayers in which a dielectric or ferroelectric film such as SrTiO3, BaTiO3 or BaxSr1-xTiO3 separates two layers of a high-T-c superconductor are required for many device applications of high-T-c materials. To clarify the mechanism limiting the insulation properties of the insulating layer, the microstructure of such samples was analyzed using transmission electron microscopy. These studies suggest that diffusion along threading dislocations or along grain boundaries in the insulating layer lowers its resistivity. Substitution of the insulating monolayer with a bilayer increases the resistivity from similar or equal to 10(11) to 3 x 10(13) Omega . cm (at 2 x 10(5) V/cm, below 100 K). To our knowledge, this is by far the highest resistivity achieved in such heterostructures.