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

摘要

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 types of junctions but without a barrier ("shorts"), the supercurrent densities at 4.2 K reached 7.5 and 3.5 MA/cm2, 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 ζ_F ~ 5-6 nm or ζ_N ~ 16 nm of SrRuO_3. We thus conclude that there is no dominant proximity induced triplet superconductivity in the ferromagnet in our junctions.