Critical current measurements in superconductor - ferromagnet - superconductor junctions of $YBa_2Cu_3O_y$-$SrRuO_3$-$YBa_2Cu_3O_y$: No evidence for a dominant proximity induced triplet superconductivity in the ferromagnetic barrier

TL;DR

This study investigates superconductor-ferromagnet-superconductor junctions with $YBa_2Cu_3O_y$ and $SrRuO_3$, finding no evidence of dominant triplet superconductivity induced by proximity effects, based on critical current decay measurements.

Contribution

The paper provides experimental evidence showing the absence of dominant proximity-induced triplet superconductivity in $YBa_2Cu_3O_y$-$SrRuO_3$-$YBa_2Cu_3O_y$ junctions through critical current decay analysis.

Findings

Critical current densities of 7.5 and 3.5 MA/cm$^2$ in high-quality junctions.

Exponential decay of critical current with ferromagnetic barrier thickness.

Decay lengths much shorter than the coherence lengths, indicating no dominant triplet superconductivity.

Abstract

Transport measurements in ramp-type junctions of $YBa_2Cu_3O_y-SrRuO_3-YBa_2Cu_3O_y$ 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 $SrRuO_3$. We thus conclude that there is no dominant proximity induced triplet superconductivity in the ferromagnet in our junctions.