Long-range spin-triplet supercurrents in antiferromagnetic Josephson junctions

Abstract

We theoretically study the supercurrent in antiferromagnet/superconductor (AF/S) Josephson junctions. The AF can become spin-polarized when the parity-time symmetry is broken. In S/AF1/AF2/S junctions, the supercurrent, carried by spin-singlet Cooper pairs, is highly sensitive to the electrostatic potential U2 in the AF2 layer. At high U2, the supercurrent undergoes a 0−π transition, similar to the behavior seen in S/F/S junctions. In contrast, at low U2, the supercurrent in the thick fully spin-polarized AF2 layer vanishes, suggesting that a third AF layer (AF3) is required to sustain long-range spin-triplet supercurrents. In AF trilayer junctions, the orientations of the Néel vectors in the AF1 and AF3 layers are crucial for determining the supercurrent behavior. Noncollinear configurations of the Néel vectors promote the emergence of long-range spin-triplet supercurrents. At low U2, the current-phase relation (CPR) follows a sinusoidal form, with the 0−π transition modulated by the Néel vector orientations. Notably, anomalous Josephson current arises when the Néel vectors in the AF1 and AF3 layers lie in the x−y plane. At higher U2, the second harmonic dominates the CPR, leading to a more complex CPR. Furthermore, we propose a simplified physical mechanism to explain the propagation of Cooper pairs, which helps clarify the observed supercurrent behavior.

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