Preparation and superconducting properties of ultrathin YBa2Cu3O7−x films

Ultrathin films of YBa2Cu3O7−x with thicknesses down to 2 nm were grown on(100)SrTiO3 and (100)MgO by inverted cylindrical magnetron sputtering. Metallic behavior and zero resistance temperatures above 4.2 K were obtained in 3-nm-thick films on SrTiO3. Thinner films revealed temperature-activated conductivity and only partial transitions to superconductivity due to inhomogeneities in the film morphology. On MgO, the critical film thickness leading to deteriorations of the transport properties was 6 nm. An analysis of the fluctuation-enhanced conductivity near Tc in terms of the Aslamazov–Larkin theory [Phys. Lett. A 26, 238 (1968)] revealed three-dimensional behavior even in the thinnest fully superconducting films.