Spin-triplet superconductivity induced by PdNi alloy in Co-based Josephson junctions

The conventional proximity effect in superconducting/ferromagnetic (S/F) hybrid systems decays over a short length scale in the ferromagnet, as the two electrons from the spin-singlet Cooper pair enter different spin bands and rapidly lose phase coherence. Spin-triplet Cooper pairs are not subject to this constraint, hence a spin-triplet proximity effect should extend much further into the ferromagnet [1,2]. We report observation of a spin-triplet supercurrent in S/F/S Josephson junctions containing Co(d)/Ru(0.6 nm)/Co(d) trilayers as thick as 2d = 28 nm. The spin-triplet pair correlations are induced by thin layers of Pd$_{0.88}$Ni$_{0.12}$ alloy placed between the central Co and outer Nb layers. The spin-triplet critical supercurrent in our junctions exhibits no discernable decay with increasing Co thickness, whereas the supercurrent decays exponentially with a decay length of 2.4 nm in similarly-prepared junctions without PdNi [3]. When 2d = 20 nm, junctions containing PdNi exhibit a supercurrent more than 100 times greater than that of junctions without PdNi.