Strain effect of a-axis oriented Sr_1-xLa_xCuO₂ thin films grown on LaAlO₃ substrates

Electron-doped infinite-layer compound Sr_1-xLa_xCuO₂(SLCO) is suitable for fundamental studies and device applications because of the simplest crystal structure and the highest T_c among electron-doped superconducting cuprates. The epitaxially grown c-axis oriented SLCO thin films with T_c of around 40 K were fabricated on the lattice matched substrates like DyScO₃ and KTaO₃[1]. Since the in-plane coherence length x_ab(4.5nm) of SLCO is much larger than the out-of-plane coherence length x_c(0.3nm)[2], the a-axis oriented films are favorable for junction fabrication. However, compared with c-axis oriented thin films, the resistivities of a-axis oriented thin films were thousands times larger and the properties were semiconductor-like[3]. It's reasonable to consider that the unclear strain effect from LAO substrates need to be clarified. In this paper, we report on a systematic investigation of the structure and electrical properties of c-axis oriented SLCO thin films grown on Ba_ySr_1-yTiO₃ (BSTO) buffer layers with tunability of the lattice constant from a₀=0.3905 nm (y=0, SrTiO₃) to a₀=0.4000 nm (y=1, BaTiO₃), which is favorable to obtain a quantified result of strain effect. We also report on structure and electrical properties improvement of a-axis oriented SLCO thin films on LAO substrates by strain effect control which has been quanti-ficationally studied by c-axis oriented SLCO thin films.