Strain engineering using La0.7Sr0.3MnO3 buffer layer for enhancing superconductivity in GdBa2Cu3O7−x films

Substrate-induced epitaxial strain plays a crucial role in the physical properties of cuprate thin films; therefore, it is essential to control the epitaxial strain. In this work, we studied the effect of a La0.7Sr0.3MnO3 (LSMO) buffer layer on the epitaxial strain experienced by GdBa2Cu3O7−x (GdBCO) thin films deposited on a LaAlO3 (LAO) substrate. This was accomplished by varying the thickness of the LSMO buffer layer, which was inserted between the GdBCO and LAO to control the substrate-induced epitaxial strain, from 20 to 80 nm. It was found that the direction of MnO6 octahedral distortion in the LSMO layer was changed by the substrate-induced strain and it causes a difference on the local structure and the superconducting properties of the GdBCO/LSMO bilayer, confirming local structural coupling between the LSMO buffer and the GdBCO. The superconducting transition temperature (Tc) of GdBCO can be enhanced by adequately relaxing the strain state of the CuO2 plane. This finding suggests the possibility of actively enhancing the superconductivity by controlling the substrate-induced strain state by suitably adjusting the LSMO layer.