Superconductivity in Nonsymmetric Epitaxial YBa2Cu3O7−δ - PrBa2Cu3O7−δ Superlattices Grown by Pulsed Laser Ablation

ABSTRACTPulsed KrF (248 nm) excimer laser ablation has been used to grow nonsymmetric epitaxial YBCO/PrBCO superlattices containing 1-, 2-, 3-, 4-, and 8-unit-cell-thick YBCO layers, separated by N-cell-thick insulating PrBCO layers (N = 1–16). The 1×N and 2×N structures exhibit a rapid initial decrease of Tco with increasing PrBCO layer thickness, followed by saturation of Tco at a nonzero value, as the YBCO layers' separation is increased further. The limiting Tco values for 1-, 2-, 3-, 4-, and 8-cell-thick YBCO layers isolated in a PrBCO matrix are ∼19 K, ∼54 K, ∼71 K, ∼80 K, and ∼87 K, respectively. Single-cell-thick YBCO layers are found to be superconducting even when separated by ∼19 nm in a PrBCO matrix. These results are discussed in terms of possible Josephson and/or proximity effects coupling the YBCO layers, and the possibility that PrBCO modifies the electronic structure and depresses Tco in YBCO cells that are immediately adjacent to the PrBCO layers. Finally, high-temperature postannealing studies show that these superlattice structures are stable and that little diffusion occurs along the c-axis direction of compositional modulation.