Critical current measurements in superconductor - ferromagnet - superconductor junctions of $YB{a}_{2}C{u}_3{O}_y$-$SrRu{O}_3$-$YB{a}_{2}C{u}_3{O}_y$: No evidence for a dominant proximity induced triplet superconductivity in the ferromagnetic barrier

Abstract

Transport measurements in ramp-type junctions of $YB{a}_{2}C{u}_3{O}_y-SrRu{O}_3-YB{a}_{2}C{u}_3{O}_y$ with $T_c$ values of either 80-90 K or 60-70 K are reported. In both type of junctions but without a barrier ("shorts"), the supercurrent densities at 4.2 K reached 7.5 and 3.5 MA/cm${}^2$, respectively, indicating the high quality of the fabrication process. Plots of the critical current versus thickness of the ferromagnetic barrier at 4.2 K show exponential decays with decay lengths of 1.1 nm for the 90 K phase and 1.4 nm for the 60 K phase, which are much shorter than the relevant coherence lengths ${\xi }_F\sim 5-6$ nm or ${\xi }_N\sim$16 nm of $SrRu{O}_3$. We thus conclude that there is no dominant proximity induced triplet superconductivity in the ferromagnet in our junctions.

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