Enhancing superconductivity of ultrathin YBa2Cu3O7-δ films by capping non-superconducting oxides

In this study, we have explored the ways to fabricate and optimize high-quality ultrathin YBa2Cu3O7-δ (YBCO) films grown on single-crystal (001) SrTiO3 substrates. Nearly atomic-flat YBCO films are obtained by pulsed laser deposition. Our result shows that the termination of SrTiO3 has only a negligible effect on the properties of YBCO. In contrast, we found that capping a non-superconducting oxide layer can generally enhance the superconductivity of YBCO. PrBa2Cu3O7, La2CuO4, LaMnO3, SrTiO3, and LaAlO3 have been examined as capping layers, and the minimum thickness of superconducting YBCO with capping is ~2 unit cells–3 unit cells. This result might be useful in constructing good-performance YBCO-based field effect devices.