Ba_ySr_{1 - Y}TiO₃ buffer layers for strain tuning of infinite-layer Sr_{1 - X}La_xCuO₂ thin films

We report on the precise tuning of lattice strain in an infinite-layer electron-doped high temperature superconductor Sr_{1 - x}La_xCuO₂ (SLCO; a_SLCO = 0.3949 nm for x = 0.1), which is a perovskite-related oxide, using perovskite BaTiO₃-SrTiO₃ (BSTO; Ba_ySr_{1 - y}TiO₃) buffer layers. The BSTO buffer layers formed on (001) (La_0.18Sr_0.82)(Al_0.59Ta_0.41)O₃ substrates by magnetron sputtering were fully relaxed with high crystalline quality due to high oxygen partial pressure deposition and post annealing at 950 °C. The lattice constants of the BSTO buffer layers could be controlled in the range of 0.3926-0.3973 nm by changing the Ba content (y = 0.2-0.7). These BSTO buffer layers allow coherent growth of SLCO thin films, and a clear dependence of the superconducting transition temperature on the lattice strain was observed. The fabrication of these BSTO/superconductor heterostructures may provide novel devices composed of functional perovskite thin films, in addition to a general approach for the precise control of lattice strain in functional perovskite thin films.