Multiple superconducting transitions in the Sr3Ru2O7 region of Sr3Ru2O7-Sr2RuO4 eutectic crystals

TL;DR

This study reveals multiple superconducting transitions in Sr3Ru2O7 regions of eutectic crystals, suggesting superconductivity arises from stacking faults rather than bulk properties, which is a novel finding for this material.

Contribution

It demonstrates superconductivity in Sr3Ru2O7 regions of eutectic crystals and proposes stacking faults as the origin, a new insight into the material's properties.

Findings

Multiple superconducting transitions observed in Sr3Ru2O7 region.

Superconductivity is not a bulk property but likely due to stacking faults.

Critical field curves show positive curvature near zero fields.

Abstract

We report superconducting properties of Sr3Ru2O7-Sr2RuO4 eutectic crystals, consisting of the spin-triplet superconductor Sr2RuO4 with a monolayer stacking of RuO2 planes and the metamagnetic normal metal Sr3Ru2O7 with a bilayer stacking. Although Sr3Ru2O7 has not been reported to exhibit superconductivity so far, our AC susceptibility measurements revealed multiple superconducting transitions occurring in the Sr3Ru2O7 region of the eutectic crystals. The diamagnetic shielding essentially reached the full fraction at low AC fields parallel to the c axis. However, both the shielding fraction and the onset temperature are easily suppressed by AC fields of larger than 0.1 mT-rms and no anomaly was observed in the specific heat. Moreover, the critical field curves of these transitions have a positive curvature near zero fields, which is different from the upper critical field curve of the bulk Sr2RuO4. These facts suggest that the superconductivity observed in the Sr3Ru2O7 region is not a bulk property. To explain these experimental results, we propose the scenario that stacking RuO2 planes, the building block of superconducting Sr2RuO4, are contained in the Sr3Ru2O7 region as stacking faults.