Equal-Spin local and nonlocal Andreev reflection in altermagnet/superconductor/altermagnet junction

Abstract

We investigated the equal-spin Andreev reflection phenomenon in an altermagnet/super\-conductor/altermagnet (AM/SC/AM) junction, focusing on the roles of the crystal orientation angle and the Néel vector. The crystal orientation angle in the AM effectively determines the spin-dependent transport channels for both electrons and holes, leading to orientation-dependent local and crossed Andreev reflection in the AM/SC/AM junction. We studied how and under what conditions this equal-spin Andreev reflection occurs. Rotating the Néel vector in the AM substantially increases spin-flip channels for both electrons and holes, giving rise to equal-spin Andreev reflection. When the Néel vector $θ=π/2$, the spin-dependent transmission channels for crystal orientations $α=0$ and $α=π/2$ are completely the same, the Andreev reflection coefficients remain different, reflecting the distinct roles of the Néel vector in spin space and the crystal orientation in real space. By tuning the crystal orientation angle and the Néel vector, orientation-dependent conventional and equal-spin Andreev reflection can be realized. This study reveals that Néel vector rotation is the direct cause of equal-spin Andreev reflection in AM/SC/AM junctions and provides a viable pathway for realizing spin-dependent superconducting transport phenomena in AM heterojunctions.