Anisotropic equal-spin Andreev reflection and spin-triplet pairing correlations in antiferromagnet/antiferromagnet/superconductor junctions

We theoretically study Andreev reflection (AR) -induced conductance at antiferromagnet/antiferromagnet/ superconductor (AF/AF/S) junctions. The AF can become spin-polarized when the parity-time symmetry is broken. Equal-spin AR occurs due to spin-flip scattering when the N\'eel vectors of the AFs are noncollinear. We investigate how the staggered sublattice potential and the electrostatic potential affect the AR-induced conductance, and we demonstrate that a pure equal-spin AR is achievable. The signature of the equal-spin AR can be confirmed by studying the conductance spectra. When the left AF is fully spin-polarized, the pairing correlations involving spin-down quasiparticles decrease rapidly, but the equal-spin triplet pairing correlation (↑↑) becomes long-range. This results in a conversion from spin-singlet to spin-triplet pairings, providing further evidence for the existence of equal-spin AR. Specifically, the study focuses on the AR-induced magnetoanisotropic conductance. The conductance exhibits relatively weak magnetoanisotropy due to the competing contributions of conventional and equal-spin ARs. In contrast, when only equal-spin AR is present, significant anisotropic magnetoresistance is observed, which can serve as a distinctive signature of equal-spin AR. The findings suggest that AF/S junctions are ideal platforms for future superconducting spintronics applications.