Suppression of superconductivity by crystallographic defects in epitaxial Sr₂RuO₄ films

Epitaxial Sr₂RuO₄ thin films grown by pulsed-laser deposition from high-purity (99.98%) Sr₂RuO₄ targets on (001) LaAlO₃ were found to be not superconducting down to 0.4 K. Structural disorder is believed to be responsible. A correlation was observed between higher resistivity ratios in electrical transport measurements and narrower x-ray diffraction rocking curve widths of the Sr₂RuO₄ films. High-resolution transmission electron microscopy revealed that the dominant structural defects, i.e., the defects leading to the observed variation in rocking curve widths in the films, are {011} planar defects, with a spacing comparable to the in-plane superconducting coherence length of Sr₂RuO₄. These results imply that minimizing structural disorder is the key remaining challenge to achieving superconducting Sr₂RuO₄ films.