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

TL;DR

This paper demonstrates a novel long-range supercurrent in clean superconductor-ferromagnet structures caused by interference of opposite-spin triplet states, explaining recent experimental observations.

Contribution

It reveals a new mechanism for long-range supercurrents via interference of opposite-spin triplet states in clean SF1F2S junctions with non-parallel magnetic moments.

Findings

Long-range supercurrent observed in clean SF1F2S junctions.

Interference of opposite-spin triplet states enhances Josephson current.

Provides explanation for recent experimental results.

Abstract

By now it is known that in an s-wave superconductor-ferromagnet-superconductor ($SFS$) structure the supercurrent induced by spin singlet pairs can only transmit a short distance of the order of magnetic coherence length. The long-range supercurrent, taking place on the length scale of the normal metal coherence length, will be maintained by equal-spin triplet pairs, which can be generated by magnetic inhomogeneities in the system. In this paper, we show an unusual long-range supercurrent, which can take place in clean $SF_1F_2S$ junction with non-parallel orientation of magnetic moments. The mechanism behind the enhancement of Josephson current is provided 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 same values of the length and exchange field. This finds can provide a natural explanation for recent experiment [Robinson et al., Phys. Rev. Lett. 104, 207001 (2010)].