Epitaxial strain effects on superconducting and transport properties of La2-xSrxCuO4+δ

Epitaxial strain in La2-xSrxCuO4+delta thin films (0 less than or equal to x less than or equal to 0.30) is controlled by using SrLaAlO4 buffer layers of different thicknesses on SrTiO3 substrates. We found that compressive epitaxial strain results in higher T, for all the Sr concentrations. Better oxygenation by cooling the films in ozone/molecular oxygen mixture also leads to higher T-c. In undoped and lightly-doped ultrathin films, the samples are insulating under tensile strain, but superconducting when the strain is sufficiently compressive. We suggest that the epitaxial strain affects the insertion of interstitial oxygen, which is responsible for the observed effects. Hall measurements confirm the change in carrier density in films of different strain. The Hall angle also changes with epitaxial strain. The epitaxial strain dependence of the slope in the T-2 dependence of the cotangent of the Hall angle is different for underdoped and optimally-doped samples.