Thickness dependence of structural and electrical properties of electron-doped Sr_1−xLa_xCuO₂ infinite-layer thin films grown by pulsed laser deposition

As the building blocks for all of the high-T_c cuprate superconductors, infinite layer (IL) compounds have the simplest structures and the highest T_c of electron-doped superconductors. However, IL structure is one of the high-pressure forms, which makes it difficult to synthesize a single crystal. Therefore, it is highly desirable to obtain high-quality epitaxial thin films making use of epitaxial effect. Although there are many reported attempts to grow IL thin films on different substrates, no one has systematically studied the thickness dependence of structural and electrical properties of IL thin films. In this report, electron-doped Sr_1−xLa_xCuO₂ thin films of various thicknesses were deposited on (001) KTaO₃ substrate by pulsed laser deposition. It is shown that IL peak shifts to a lower angle with increase of film thickness, indicating the reduction of the tensile strain. With further increase of thickness, there emerges an impurity phase. Transport measurements showed strong influence of the sample thickness on resistivity and Tc. For a certain thickness range we have demonstrated that superconductivity will occur. The resistive superconducting transition with T_{c onset} = 14.2 K and T_{c (ρ =0)} = 10 K has been observed. A moderate thickness is required to obtain IL thin films with superconductivity.