Strain Effect of $a$ -Axis-Oriented Sr1−xLaxCuO2 Thin Films Grown on LaAlO3 Substrates

The epitaxial thin films of electron-doped infinite-layer cuprate superconductor Sr
_1-x
La
_x
CuO
₂
(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
_y
Sr
_1-y
TiO
₃
(BSTO) with y = 0.55, 0.6, and 0.7, prepared on (001) (La
_0.18
Sr
_0.82
)(Al
_0.59
Ta
_0.41
)O
₃
substrates, were used as the epitaxial buffer layers to induce different levels of tensile strain in c-axis-oriented SLCO, while (001) LaAlO
₃
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.