Strain Effect of a-Axis-Oriented Sr_1-xLa_xCuO₂ Thin Films Grown on LaAlO₃ Substrates

The epitaxial thin films of electron-doped infinite-layer cuprate superconductor Sr_1-xLa_xCuO₂ (SLCO; x = 0.1 ) were grown by dc magnetron sputtering, and their structural and electrical properties were systematically investigated by changing mismatch to substrate and SLCO film thickness, with a reduction annealing period under vacuum to remove the excess apex oxygen. Thin films of Ba_ySr_1-yTiO₃ (BSTO) with y = 0.55 , 0.6, and 0.7, prepared on (001) (La_0.18Sr_0.82)(Al_0.59Ta_0.41)O₃ substrates, were used as the epitaxial buffer layers to induce different levels of tensile strain in c -axis-oriented SLCO, while (001) LaAlO₃ substrates were used for the growth of a-axis-oriented SLCO. The highest T_c value of c-axis oriented SLCO was obtained on the BSTO (y = 0.6) layers and the mismatch dependence of strain relaxation thickness was clarified. The strain in a-axis SLCO films was analyzed and controlled by changing the thickness of SLCO thin films. As a result, strong thickness dependence of superconducting properties was observed, and T_c ^zero was obtained in the a-axis SLCO for the first time. Based on these results, the strain effects of the SLCO film properties are discussed.