Abstract
Ruddlesden Popper Sr n +1Ru n O 3n+1 ruthenates exhibit a wide variety of exceptional properties providing an ideal playground to study new forms of ordering effects such as superconductivity in Sr 2 RuO 4 . A new normal metal Sr 3 Ru 2 O 7 /superconducting Sr 2 RuO 4 eutectic system has been successfully grown. Transport and magnetic studies on the eutectic material revealed the presence of an unexpected superconducting behaviour in the Sr 3 Ru 2 O 7 domain. Several scenarios have been proposed to explain this unusual behaviour addressing the crucial need of a detailed investigation by local probe techniques. We report the nanostructural characterisation of the Sr3Ru2O7/Sr 2 RuO 4 eutectic crystals by transmission electron microscopy and high angle annular dark field scanning transmission electron microscopy. We compared the nanostructure of the Sr 3 Ru 2 O 7 region of the eutectic with that of Sr 3 Ru 2 O 7 single-phase crystals in which no superconducting behaviour has ever been observed. We found that Sr 3 Ru 2 O 7 can be grown with higher purity via eutectic solidification showing only a diluted amount of randomly dispersed Sr 2 RuO 4 layers. We also explored the Sr 3 Ru 2 O 7 /Sr 2 RuO 4 interfacial nanostructure. Two typologies of interfaces are observed within the eutectic: interfaces parallel to the growth direction are sharp and defect-free whereas interfaces perpendicular to the growth direction appear wavy and decorated with Ru precipitates. An exotic pairing between the Sr 2 RuO 4 layers finely dispersed in the Sr 3 Ru 2 O 7 matrix is suggested as possible scenario for the unusual superconductivity of the Sr 3 Ru 2 O 7 domain of the eutectic.
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