Epitaxial thin films to 2): Structure, strain, and superconductivity

We have grown (001)-oriented thin films of (Formula presented) with strontium composition (Formula presented) by reactive coevaporation and characterized them by x-ray-diffraction and resistivity measurements. A systematical change in the c-axis length indicates that single-phase films were obtained for the whole compositional range. The films with the oxygen composition (Formula presented) showed superconductivity for x between 0.06 and 0.30. For (Formula presented) the superconducting transition temperature (Formula presented) was maximized to 44 K, due to a strain effect caused by the lattice mismatch between films and substrates. Around this composition, it is found that (Formula presented) for the films shows a good correlation with the c-axis length. For (Formula presented) for the films strongly depends on the residual resistivity (Formula presented) higher (Formula presented) for lower (Formula presented) The depression of (Formula presented) around (Formula presented) is smaller than that for the bulk samples, suggesting that the strain suppresses the “1/8 anomaly.” The films with (Formula presented) attained by cooling in ozone showed (Formula presented) between 40 and 48 K for (Formula presented) For (Formula presented) the compositional dependence of the resistivity is explained by both oxygen defects and a structural phase transition at (Formula presented).