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

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 or60-70 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 ofthe critical current versus thickness of the ferromagnetic barrier at 4.2 Kshow exponential decays with decay lengths of 1.1 nm for the 90 K phase and 1.4nm for the 60 K phase, which are much shorter than the relevant coherencelengths $\xi_F\sim 5-6$ nm or $\xi_N\sim$16 nm of $SrRuO_3$. We thus concludethat there is no dominant proximity induced triplet superconductivity in theferromagnet in our junctions.