Doping dependence of superconducting properties in pulsed-laser-deposited La2-xSrxCuO4+δ (0⩽x⩽0.30) thin films

We have studied the Sr doping dependence of the superconducting properties of La_2-xSr_xCuO_4+δ thin films grown by pulsed laser deposition over the range of 0⩽x⩽0.30. We found that the strain in the films depends on the Sr doping level. In 1000 Å La_2-xSr_xCuO_4+δ films grown on 1000 Å SrLaAlO₄ buffer layer, the strain changes from compressive to tensile when m increases. For both compressive and tensile strain, films prepared in strongly oxidizing ozone/molecular oxygen mixture are superconducting for all Sr content with x⩽0.25. When the films are cooled in pure molecular oxygen the x dependence is similar to that in the bulk, although the transition temperature depends on the strain. The results suggest that the Sr content, epitaxial strain, and oxygenation conditions are all important factors influencing the superconductivity in La_2-xSr_xCuO_4+δ thin films