Long-range supercurrents induced by the interference effect of opposite-spin triplet state in clean superconductor-ferromagnet structures

摘要

By now it is known that in an s-wavesuperconductor-ferromagnet-superconductor ($SFS$) structure the supercurrentinduced by spin singlet pairs can only transmit a short distance of the orderof magnetic coherence length. The long-range supercurrent, taking place on thelength scale of the normal metal coherence length, will be maintained byequal-spin triplet pairs, which can be generated by magnetic inhomogeneities inthe system. In this paper, we show an unusual long-range supercurrent, whichcan take place in clean $SF_1F_2S$ junction with non-parallel orientation ofmagnetic moments. The mechanism behind the enhancement of Josephson current isprovided by the interference of the opposite-spin triplet states derived from$S/F_1$ and $F_2/S$ interfaces when both ferromagnetic layers have the samevalues of the length and exchange field. This finds can provide a naturalexplanation for recent experiment [Robinson et al., Phys. Rev. Lett. 104,207001 (2010)].